insights winter 15 16
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insightsinsightsWinter 2015-16
A DRESSER-RAND BUSINESS PUBLICATION
NEW HGM ENGINE
HITS THE MARKET
COMBINED RESOURCES
EXPAND OPPORTUNITIES
FOR LNG PROJECTS
TWO BECOME ONE
dresser-rand.com/insights
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CONTENTS
06
insightsWINTER 2015-16
This document contains
statements related to
our future business and
financial performance
and future events or
developments involving
Siemens that may
constitute forward-
looking statements.
These statements may
be identified by words
such as “expect,” “look
forward to,” “anticipate,”
“intend,” “plan,” “believe,”
“seek,” “estimate,” “will,”
“project” or words ofsimilar meaning. We may
also make forward-looking
statements in other
reports, in presentations,
in material delivered to
shareholders and in press
releases. In addition,
our representatives may
from time to time make
oral forward-looking
statements. Such
statements are based on
the current expectations
and certain assumptions
of Siemens’ management,
of which many are beyond
Siemens’ control. Theseare subject to a number
of risks, uncertainties and
factors, including, but not
limited to those described
in disclosures, in particular
in the chapter Risks in the
Annual Report. Should
one or more of these
risks or uncertainties
materialize, or should
underlying expectations
not occur or assumptions
prove incorrect, actual
results, performance or
achievements of Siemens
may (negatively or
positively) vary materiallyfrom those described
explicitly or implicitly in the
relevant forward-looking
statement. Siemens
neither intends, nor
assumes any obligation,
to update or revise
these forward-looking
statements in light of
developments which differ
from those anticipated.
engineer’s notebook
VSDs Motor Inverter Design Concept for
Compressor Trains Avoiding Interharmonics
in Operating Speed Range and Verification
Ultimately, a close collaboration between the manufacturer of
the driver and compressor is of vital importance when designing
a variable speed drive system-driven turbo compressor train.
15
02
people power
The Power of Giving Back
Dresser-Rand KG2 turbines provide on-site electrical power for
one of Russia’s largest oil producers.12
The latest HGM engine model offer
a balanced relationship between
efficiency, reliability and price.
14New HGM Engine
Hits the Market
Welcome to Komi
See how the passionate efforts of our employees help make their
communities a better place to live and work.
10
Berenice touts the right tools, good communication skills and
flexibility as keys to success in her key client manager role.
08
Expanded portfolio of compressors
and drivers available for LNG
applications.
Combined Resources
Expand Opportunitie
for LNG Projects
Bruce Bailie, integration program
manager, reinforces importance of
communication and positive spirit.
candid visions
Two Become OneThe First 40 Years Are the Hardest
At 85, Dave Morse is still moving and shaking in the compressor
business.
04
profile
Making Best Use of the Tools at Hand
Dresser-Rand offers a wide variety of product training programs
for 2016.
33 Product Training Programs
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Janet Straub Ofano,
external/internal
communications
specialist & editor,
insights magazine
Collaboration, Communicationand (the right) CombinationIn reviewing this edition, these three concepts cropped up throughout.
While we face a challenging business climate due to low oil prices, both inside and outside
the workplace our employees collaborate, communicate and combine their resources, efforts
and knowledge to achieve personal and professional success. They continue to accomplish
amazing things within the communities where they live and work as highlighted in the
People Power feature.
In an interview with Bruce Bailie, the integration program manager for the Dresser-Rand
business, we learned that a successful integration requires all three attributes. As you’ll see
in the Candid Visions feature, Bruce shared with us some of the highlights and challenges during
the Siemens / Dresser-Rand integration, pre- and post-close.
Our profile feature gives us a glimpse into the life of key client manager, Berenice Flores.
Strong communication skills and a delicate balancing act help ensure a win-win between herclient and Dresser-Rand.
One of my favorite articles, “The First 40 Years are the Hardest,” is a delightful read about the
talented, amicable and highly regarded Dave Morse. Six impressive decades in the business
and his enthusiasm and commitment remain.
We listened to our clients’ demands for a 1 MW power output “sweet spot” and created
the HGM 420 Guascor® gas engine. This efficient, reliable, cost effective engine achieves
approximately 91 percent thermal efficiency.
A Russian oil producer selected Dresser-Rand KG2 turbine generator sets to upgrade its power
generation facilities. The decision was based on a combination of factors: the KG2 turbine
accepts a wide variety of fuels; it boasts a simple, low-maintenance design; it’s highly reliable;
and the turbines operate with a heat recovery system, so they not only produce electric powerbut provide heat energy as well – an important attribute in the frigid Komi climate.
With the combined resources of Siemens, the value proposition for LNG clients from the new
Dresser-Rand business within Siemens Power and Gas division expanded. The addition of
Siemens’ SGT-750 gas turbine driver and Industrial Trent® 60 aero-derivative gas turbine to the
portfolio increases our capabilities for offshore and onshore liquefied natural gas (LNG) projects.
And finally, even the Engineer’s Notebook feature embraces the importance of collaboration
between manufacturers of compressors and drivers to design a suitable variable speed drive
system-driven turbo compressor train.
As you peruse this issue, I’m confident you’ll see these three important themes that underscore
the importance of the human element as we persevere during this downturn in the oil business.It is these practices that will continue to smooth the way for our continued success.
Enjoy – and Happy New Year!.
Janet Straub Ofano
editor, insights magazine
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c a
n d i d
v i s
i o n s
Bruce Bailie
program manager
integration
2 insights
BB: Before the deal closed the effort was all
about strategy and planning. This phase was quite
challenging in an environment where we could not
freely share information because Dresser-Rand
and Siemens were still competitors. Once the deal
closed there was tremendous urgency and the foc
immediately centered on execution. We changed
the structure of the integration team to reflect
the project deployment phase. The integration
managers moved on to the executive staff of thenew business. One of the integration managers,
Chris Rossi, became CEO of the Dresser-Rand
business. The integration project leadership was
transferred to Christian Gerbaulet and me.
insights: What is your role, as program manager,
following closing?
BB: To best serve our clients, we must avoid
disrupting ongoing business and quickly move to
Editor’s Note: Mid-2015, Siemens acquired Dresser-Rand and formed the new Dresser-Rand business, wherein
Dresser-Rand’s business, together with Siemens’ compressor unit and the related service business, formed a new
business within Siemens Power and Gas Division.
We recently interviewed Bruce Bailie, the program manager for the integration of the new Dresser-Rand business.
Two Become One
Iinsights: What were the integration managers’
initial roles?
BB: The integration managers comprised senior
leaders from both companies with the knowledge,
insight and experience to mentor and guide a
team to architect the new business. They defined
a compelling vision of the business that Siemens
wanted to form and then developed a detailed
and robust master plan to achieve that vision.
They assembled an integration team consistingof top functional and business leaders from both
companies. The team developed the integration
master plan to ensure the resultant business was
founded on the “best-of-the-best” from either
company.
insights: What were the differences for the
integration team before and after the deal closed?
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c a n d i d
v i s i on s
our new business model. The program manager is a
bit like a conductor for the integration process and
teams and ensures that all 26 work streams
(or project teams) are coordinated in their activities
and schedules. Managing risk and rapidly identifying
and escalating issues is critical to success. Good
communication is essential, as is ensuring constant,
reliable communication at all levels. It’s also
important to understand how any changes inbusiness decisions, such as consolidating legal
entities, might impact the overall integration
master plan.
insights: How long does an integration team
typically remain in place post-close with an
acquisition of this magnitude?
BB: It really depends on the type of acquisition and
the strategy for the new business. Our integration
work is expected to run two years post-close, but a
number of work streams will complete their work
within the first year. Some functions take longerbecause of the integration complexity, such as
information technology and finance. The bottom
line is to maintain top-notch service to our clients
so as to not interrupt their businesses during the
integration.
That’s one of the primary reasons our executive
vice president of Services Worldwide for the
Dresser-Rand business, Luciano Mozzato, formed
a Client Experience Council. This worldwide team
of carefully selected, cross-functional Dresser-Rand
business personnel provides recommendations anda strategic roadmap that deliver on our vision to
earn client loyalty for life.
insights: What, in your opinion, is the most
important aspect of integration success?
BB: Good communications. We must share what
needs to be done, and why it needs to be done.
Then the teams figure out how to accomplish their
tasks. Understanding the rationale for the plan
helps keep everyone aligned.
insights: What do you feel was the biggest
challenge so far? And what went particularly well?
BB: Prior to final closing, we were not able to share
the level of detailed information needed to make
decisions for the path forward. Dresser-Rand and
Siemens were still competitors and neither of us
could share anything that could give either company
a competitive advantage. Once the transaction
closed, we had to quickly confirm assumptions
made and validate the related decisions.
As far as what went well, we held welcome events
at facilities all over the world that were especially
well received. Employees of the combined business
had the opportunity to meet one another, hear
our leaders’ visions for the new business and ask
questions.
Also, the work stream structure mostly worked to
perfection. Each of the 26 work streams had their
own sub-projects, which allowed them to focus on
their own areas of business. And having smaller
sub-projects enabled the projects to run efficiently.
insights: Have you seen any synergies between the
two organizations?
BB: Realized synergies thus far have exceeded our
expectations.
For example, a Louisiana pipeline company
requested an overhaul of its legacy Siemens
compressor and needed spare parts inspected and
refurbished. Dresser-Rand had an existing masterservice agreement with the client and an excellent
working relationship and rapidly responded. This
relationship, coupled with Siemens’ strong technical
background on the equipment, translated into the
overhaul of four legacy compressors.
In another example, a pulp and paper plant in
Indonesia damaged the inlet valve body of its
Siemens legacy steam turbine. Siemens experts
offered to balance the rotor to prevent potential
issues during start-up; however, the client could
not afford the approximately $1 million inproduction losses if the unit had to be shipped
elsewhere for repair. Dresser-Rand’s Indonesian
repair center field service team in Cilegon
developed a comprehensive service plan and was
able to perform the work on site.
Earlier last year, Siemens signed an 18-year long-
term service agreement with a firm in the United
Arab Emirates. Under the agreement, the new
business will now provide service and maintenance
for nine Trent 60 aero-derivative gas turbines and
nine Dresser-Rand centrifugal compressors.
insights: Are there any last words of wisdom about
the integration to-date?
BB: We all need to have open minds and work
together with a positive spirit to build our future
around the mainstay of our business – earning our
clients’ loyalty for life. •
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T
are the Hardest
Those who know Dave Morse might imagine his
office as an archive of compression history. It’s true.
Dave’s office is full of old technical manuals, text
books, price books, early compressor photographs,
and D-R and its competitors’ history and literature.
However, the most complete collection of
compressor industry information in the officeresides within Dave himself.
Perhaps most commendable though is Dave’s
willingness to patiently share his wealth of
knowledge with others. He has a brilliant mind
with an infallible memory and remains selfless
in teaching, nurturing and supporting others – a
characteristic that shone in Dave from an early age.
Dave, along with his brother and two sisters, was
raised in Cedar Rapids, Iowa, where his father was
a credit and office manager for a large department
store and his mother was a housewife. He spenthis high school summers as a YMCA summer camp
counselor for boys.
Dave attended Iowa State University on a Naval
Reserve Officers Training Corp (NROTC) scholarship
and graduated in June 1952 with a BS degree in
General Engineering. He immediately went on
active duty to fulfill his scholarship commitment. He
served one year on the USS Deuel, APA-160 (attack
transport) and two years on the USS LST-1164
(landing ship tank). Dave was the first ship’s officer
to arrive in Pascagoula, Mississippi, where she wasbeing built.
Dave’s Compressor Career BeginsAfter fulfilling his scholarship commitment, Dave
began his career as an application engineer at
Ingersoll-Rand’s New Orleans, Louisiana sales
office in July 1955 and supported the branch
manager and three sales engineers. At that time,
I-R offices handled a variety of products, including
reciprocating and vane-type air compressors,
reciprocating and centrifugal gas compressors,
reciprocating and centrifugal pumps, steam
condensers, and steam turbines.
“The most challenging part of that job was keeping
up with the three sales engineers!” Dave recalls.
One of the things he enjoyed most was learning
about the equipment and how it works.
A little more than two years later, Dave was
promoted to sales engineer and covered most of
Louisiana and Southern Mississippi. After 11 years
in Louisiana, Dave was transferred to I-R’s gas
engine marketing department at I-R headquarters
in New York, N.Y. One year later, I-R de-centralized
and moved its marketing departments to its
supporting factories and Dave relocated to Painted
Post, N.Y., where he was later promoted to gas
engine marketing manager.
In 1971, the gas engine marketing departmentwas consolidated with I-R’s packaging subsidiary,
Southwest Industries (SWI), and moved to the SWI
facility in Houston, Texas. Here, Dave managed
application engineering and sales coordination
for integral gas engine compressors and gas field
separable compressors. Later, he also served as
manufacturing manager and facility operations
manager.
In 1974, Dave transferred to the I-R Compression
Services (I-RCS) Division in Tulsa, Oklahoma, as
engineering manager, later adding the servicedepartment to his responsibilities. The I-RCS
business was growing rapidly; business doubled
in 1974 and grew at a rate of approximately 33
percent for several years thereafter. By 1977 that
growth required I-RCS to de-centralize into district
Dave became district manager in charge of sales,
service and operations of both the 59-01 Tulsa
District and 59-05 New Orleans District.
In 1980, as a result of another re-organization, Dav
returned to the I-R sales team in Tulsa as district
At 85 years old, Dave Morse is still moving and shaking in the
compressor business.
First 40 YearsThe
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manager of field compression sales, and later as
district manager for turbo and reciprocating sales.
He retained this position following the combination
of Dresser Industries and Ingersoll-Rand in 1987 to
form Dresser-Rand.
Dresser-Rand’s compression sales team was created
in September 1988 and Dave returned to his
position as sales coordination manager. He held this
title until his retirement in December 1997. He later
consulted with D-R Compression Services untilSeptember 2000 and then contracted for
Dresser-Rand’s high-speed reciprocating
compressor (HSRC) business unit – and still does
today.
Sixty Years of
Compression KnowledgeThere is no doubt that Dave has seen a lot of
changes in the compression industry over the last
six decades, from the days of integral gas engine
compressors (often packaged) to the introduction
of the high-speed, balance-opposed separable
compressor by D-R / Clark Brothers in 1957 and D-R
/ I-R in 1958, to the growth of the packaged, high-
speed reciprocating compressor industry.
“My greatest challenge has always been to increase
Dresser-Rand’s business and market share,” says
Dave. “There is always room to improve.” He
participated in many new product developments,
including the TVS-TVR-SVS, KVGR, KVSR, KVR, 5HHE,
5RDH, 5.5RDS, HOS™, VIP®, HOSS™, and MOS™
compressors.
“In addition to learning more each day about the
equipment and the industry, getting to know our
clients and how they apply our compressors in their
business is always interesting and challenging,”
notes Dave.
Dave observes, “There is no greater reward than
watching people you have hired and/or helped train
succeed.” Over the years, Dave has shared his wisdom
via “Morse-grams” or other immediate means. Among
those are: “define the question;” and “working withgood people with a “team” spirit seeking win-win
solutions makes it that way.”
“It’s a Wonderful Life”Dave’s family life has been just as rich. In 1958, Dave
married Pat, a Baton Rouge native. They had two
children. Ed, born in 1960, is a professional musician,
and Karen, born in 1965, is a computer specialist at
St. Francis Hospital in Tulsa, Oklahoma. Pat passed
away in 2005, following an 18-year battle with
Parkinson’s disease.
Dave’s commitment to serving others goes back to
the beginning…as a summer camp counselor in high
school, a naval officer who served his country and
then serving his company and colleagues. He
remains well-known and respected in the
compression industry today.
Being 85 years old and able to contribute to one
company for the last six decades is a blessing few can
enjoy, and an accomplishment not many can claim. •
““The first 40
years are thehardest; work
is (even) more
fun when you
don’t have to.”
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SGT-750 Low-weight
Industrial Gas TurbineThe Siemens SGT-750 low-weight industrial gas
turbine was designed and developed to incorporate
size and weight advantages of the aero-derivative
gas turbine while maintaining the robustness,
flexibility and longevity of the traditional heavy-
duty industrial gas turbine. With a power output
of 37 MW for power generation, or of 38.2 MW
for mechanical drive, the SGT-750 turbine was
specifically designed for long operating times
with extended overhaul intervals. It offers high
reliability resulting from extremely low downtimesfor planned overhaul and maintenance work (only
17 days in 17 years), and achieves the highest
availability in its performance class.
The SGT-750 turbine offers easy access to all the
key components. It is assembled as a unit on a
single-lift frame with a divider between the turbine
and the driven equipment. The SGT-750 turbine
is a two-shaft machine optimized for simple cycle.
It has a single, rigid rotor compressor body that is
electron beam-welded to ensure reliable, stable
and uniform run-up in hot or cold conditions. Axial
blade attachment grooves allow blade replacement
without rotor removal.
Industrial Trent 60
Aero-derivative Gas TurbineThe Siemens Industrial Trent 60 aero-derivative
gas turbine (ADGT) delivers up to 66 MW of
electric power in simple cycle service at 42 percent
efficiency. It meets the higher power and variable
speed demands required by LNG operators
and offers fast delivery and installation times.
Renowned for its fuel economy and cost savings,the Industrial Trent 60 ADGT has already been
selected by clients for an LNG onshore project as
well as two floating LNG (FLNG) offshore projects
since Dresser-Rand and Siemens came together.
LNGo ™ Natural Gas
Liquefaction SystemLNG clients can combine these expanded Siemens
products with Dresser-Rand’s DATUM® compresso
and LNGo™ natural gas liquefaction system, the
latest innovation for the LNG market. The LNGo natural gas liquefaction system uses a combination
of Dresser-Rand technologies, including its MOS™
reciprocating compressor, Guascor® gas engine
and Enginuity® control system in a portable, small
footprint package that can be placed on well pads
gas flares and similar sites. The system allows for
small, portable, stand-alone plants and can be
moved to support changing requirements and
needs.
Boil-off Gas Compressors
Siemens is the technology and market leader forcryogenic temperature boil off gas compressors
for LNG production plants. With operating
temperatures as low as -160 degrees Celsius
(-256 degrees Fahrenheit), Siemens single shaft bo
off gas compressors (STC) are designed to withstan
thermal shock and feature heavy duty dry gas seal
protected in a heated seal carrier, variable inlet
guide vanes for easy start up and best turndown,
and an option for direct online start-up which doe
not require static cooling nor gas needed for flarin
With the combined resources of Siemens, the value proposition for LNG clients
from the new Dresser-Rand business within Siemens Power and Gas divisionhave expanded. Dresser-Rand’s innovations in compression technology, rotor
dynamics, head capacity, and efficiency per compression section all serve to
provide incremental production gains that are important to the operator. The
addition of Siemens’ SGT-750 gas turbine driver and Industrial Trent® 60 aero-
derivative gas turbine to the portfolio increase Dresser-Rand’s capabilities for
offshore and onshore liquefied natural gas (LNG) projects.
Combined Resources ExpandOpportunities for LNG Projects
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The STC boil-off gas compressor takes the
evaporated gas at the storage temperature and
pressure and compresses it. The compressed vapor
is then cooled and expanded to re-liquefy it – or it
is cooled and injected directly into a pressurized
liquid stream for sale of gas.
World Class Test FacilitiesThanks to the combined resources, the Dresser-Rand
business comprises four world class test facilities
(Duisburg, Germany; Hengelo, The Netherlands;Olean, NY, United States and LeHavre, France) that
can full load test a main liquefaction train with both
a driver and a compressor.
Magnolia Project in
Lake Charles, LouisianaLast year, four Siemens SGT-750 gas turbine
drivers for the main refrigerant trains were sold to
Magnolia LNG LLC for the initial two LNG trains. This
scope will then be expanded into the full four-train,
eight million tons per annum (mtpa) facility locatedin Lake Charles, Louisiana USA.
The project for LNG Limited features four mixed
refrigerant Siemens STC-SV barrel-type compressors
which will each be driven by a Siemens SGT-750
industrial gas turbine, while four ammonia
refrigerant STC-SV compressors will each be driven
by a Siemens SST-600 steam turbine. Additionally,
the scope of supply includes two motor-driven
feed gas booster compressors. The subsequent
two LNG trains necessary to achieve the full eight
mtpa for Magnolia will bring the total number of
compressors to 20 at the site.
The SGT-750 industrial gas turbine driving the
compressors was one of the main reasons for
selecting Siemens for the project because the
turbine’s power rating is a good match for the
LNG train design. Its power output is more than
enough for the project’s requirements, providing
about an extra three MW compared to its nearest
competitor, thus providing a solution that reduces
project risk. The SGT-750 turbine also has lower
emissions and lower operating expenditures over
the plant’s lifetime, compared with the competition.
Apart from the performance of the gas turbine,
an important factor in Siemens securing the
contract was its ability to provide the entire LNG
compression train. It enabled Magnolia LNG to
bundle the entire LNG compression train through
a single supplier for better support and project
efficiency. This approach simplifies mechanical
design, reduces interfaces for better project
management, streamlines commissioning, andgenerally lowers overall project risks.
Installation of the LNG trains at Magnolia, expected
to begin in late 2016 or early 2017, comes at an
important time, and not just for the United States.
There has been tremendous interest in the SGT-750
gas turbine across the industry and Magnolia will be
an important demonstration of its suitability to such
applications, especially in this mid-range-sized LNG
facility. •
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p r o f i l e
8 insights
P
Perhaps this phrase helps describe the work
mindset of Berenice Flores, a key client manager
for a major oil company. After all, this Hemingway
classic is her favorite novel. “It’s a tale that includes
many virtues, especially courage and endurance,”
she says.
“I see my role as Dresser-Rand’s representative
to the client and as the client’s representative to
Dresser-Rand. It’s somewhat of a balancing act. I
have to ensure that my client’s needs are met, as
well as those of our company.
In a competitive market like this, being able to
discuss how the Dresser-Rand business can match
its services to a client’s needs is what helps position
us ahead of our competitors,” Berenice continues.Among her responsibilities are providing support
in the sales cycle for all opportunities, fulfilling
quotation requests, maintaining the price book,
and solving any issues that arise with order
execution and delivery, to name only a few. It’s
easy to imagine that working in so many facets
of the business could become stressful, but
Berenice manages her workload with the support
of her coworkers and by continually updating her
communications skills.
“I think it’s important that we all seek to improvehow we communicate,” she maintains. Berenice
also enjoys the collaborative nature of her work,
adding “I like learning different topics, interacting
with different people and solving problems. That’s
why I was always attracted to jobs where I get to
interact with people at various organizational levels
and across cultures – where there is always room
for learning.”
With a degree in Business Administration from
the Instituto Tecnologico y de Estudios Superiores
de Monterrey, Berenice has worked with an
assortment of diverse companies, including Alucap
Group, Panasonic, Mattel, and Amazon.com.
She also worked as a contractor when her twin
daughters were smaller, giving her the flexibility to
work from home.
Berenice grew up in the Mexican city of Cuernavac
the capital of Morelos state, located about an hou
south of Mexico City. Known for its great weather
year round, it is celebrated as “The City of the
Eternal Spring.”
“Cuernavaca is a beautiful place to grow up,” says
Berenice. “It is full of history, culture, traditions,art, and great food.” With its gated haciendas and
sprawling estates, the city has attracted foreign
princes, archdukes and other nobles seeking to
enjoy its warmth, clean air, fresh water springs,
and eye-catching architecture. Central among
these structures is the Cuauhanahuac Museum,
also known as Cortes Palace – home of the Spanis
conqueror, Hernan Cortes – which helps preserve
the region’s history.
Another “can’t miss” site, according to Berenice,
is the Cathedral of Franciscan Order, built in
1522. It was the fifth Franciscan construction in
Mexico, established by the first 12 Franciscan friar
who arrived in the country. “There are so many
fascinating sites in my hometown that I enjoyed
with family and friends. Now, I go back as much as
can with my twin daughters. I want them to collec
great memories as I did when growing up.”
Making Best Use
of the Tools At Hand
BERENICE FLORES
Berenice Flores,
key client manager
In Ernest Hemingway’s, The Old Man and the Sea, the aging fisherman,
Santiago, would say to himself, “Now is no time to think of what you do
not have. Think of what you can do with what there is.”
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pr of i l e
Reminiscing about growing up in Cuernavaca,
Berenice reveals that her mother was her biggest
role model. “She was a teacher. She taught with
passion, dedication, love, and joy. I witnessed many
times how grateful her former and current students
were to her and she was highly respected not only
by her pupils, but by parents as well.” Perhaps
that’s why Berenice has always chosen jobs where
she interacts with people at various organizational
levels.
Outside the office, Berenice is passionate about
doing what’s best for her family and maintaining
a strong connection with them. The focus of her
priorities, she says, is making sure her daughters
have a good education. “I want to teach them
to think critically, to be open-minded and
encourage them to keep the appetite they have
for learning.” Among her pastime activities are
teaching her daughters volleyball, visiting parks and
museums, attending classic concerts, and reading
Brain Pickings, an online assortment of eclectic
information.
When asked about lessons learned on the job at
Dresser-Rand, Berenice reveals that “no matter
what industry you work for, you can adapt and fit in
as long as you are willing to learn and work the best
you can. And it’s important to be flexible, creative
and able to work with the tools provided.”
Just like Hemingway’s fisherman, Santiago. •
“Now is no time to
think of what you
do not have. Think of
what you can do
with what there is.” Santiago - The Old Man and the Sea
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p e o p l e p o w e r
10 insights
We recognize that strong communities are advantageous
for growth and prosperity. Worldwide, our employees
look for ways to give back, strengthen community
programs and support worthwhile causes.
The Power of Giving Back
Duisburg’s Turbo Bikers Conquer
Challenging Circuit to Raise Money
for Local CharitiesFor the last eight years, the Turbo Bikers team
at Siemens Duisburg, Germany location has
participated in Europe’s largest non-stop 24-hour
mountain bike race. Held in Duisburg, this annual
event attracts approximately 2,400 cyclists. The
winner is the team that bikes the most rounds;
each round is 5.3 miles, or 8.5 kilometers.
In August, 450 teams (consisting of one to eight
people) competed on the 262 foot (80 meter)
elevation gain Landschaftspark Nord circuit.
The Landschaftspark public park in Duisburgwas designed in the early 1990s as a tribute
to the area’s industrial past as a coal and steel
production plant.
“You really need a mountain bike to conquer the
track because there is no street and part of this
circuit involves going through the old plant,” says
Peter Bongartz, the Turbo Biker’s lead organizer
responsible for Services Sales and Marketing for
the Americas at Siemens. “And because we bike
24 hours non-stop – as many as 373 miles
(600 km) per team – sleep is an elusive luxuryfor a while,” Bongartz added.
About six weeks prior to the race, the Turbo
Bikers begin soliciting colleagues, friends and
family for either a fixed donation or an agreement
to pay a specific amount for each mile (km) biked
– typically between one USD cent, or 0,01 euro
and USD 1.65, or 1.50 euro per mile / km.
See the peoplebehind our
products and services.
Last year, the Turbo Biker teams (two teams of
eight and six teams of four) biked approximately
373 miles (600 km) in a 24-hour time period andraised nearly USD 15,400 (14,000 euros). Proceeds
including race entry fees, were donated to the
Bunter Kreis organization that supports families
with premature infants, disabled children and
children with chronic illness or disabilities and
the VKM organization that provides consultation,
training and school inclusion services to people
with handicaps.
“Since the team’s inception we have raised
approximately USD 93,000 (85,500 euro) to help
local organizations,” says Bongartz. “We are well
aware that help is needed worldwide, but we
choose to donate to organizations close to home
and ensure that 100 percent of the donations go
directly toward helping these children and their
families.”
Further information and photos can be found at:
www.turbo-biker.de. •
Editor’s Note: People Power is about recognizing our employees for their selfless service and dedication to being
a part of something bigger than themselves by giving back to their communities. We are happy to highlight in this
issue three examples of the passionate efforts of our employees and how they’re playing a role in making their
communities a better place to live and work.
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Camp STEMovation Inspires Students
to Pursue Degrees in Science,
Technology, Engineering, and
MathematicsReynaldo Guerra was failing math classes during
his junior year of high school and was kicked offthe basketball team as a result of his poor grades.
Motivated by his desire to continue to play the
game he loved, Guerra began working on his math
skills just as intensely as he practiced basketball.
Before long, Guerra realized he actually enjoyed
math.
Guerra graduated from the University of Houston’s
(UH) Cullen College of Engineering in 2003 with
a BSME degree. During his time there, Guerra
was part of the Mexican American Engineers and
Scientists (MAES) organization that coordinated fun,hands-on projects with K-12 students at Houston-
area schools to inspire them to pursue degrees in
STEM.
Following college graduation, Guerra and some of
his former class mates formed Camp STEMovation,
a nonprofit organization that brings science,
technology, engineering, art, and mathematics
(STEAM) workshops and activities into Houston-area
schools in low-income neighborhoods.
Employees Ride to Raise Money
for National Multiple Sclerosis (MS)
SocietyIt began as a few D-R business employees from
Houston’s Latin America Services team gathering
informally after work to bike together a few times
a month. By April 2015, this small team grew by
word of mouth into an organized cycling team of17 colleagues who signed up for the BP MS 150 in
April 2015.
The BP MS 150 is a two-day fundraising bike ride
organized by the National MS Society South Central
Region. It is the largest of 100 bike events in the
United States with 13,000 cyclists, 3,500 volunteers
and countless spectators. The 180-mile ride begins
in Houston and finishes in Austin, Texas.
In 2015, the first day of the race was cancelled due
to heavy rain the week prior which flooded the
campground at LaGrange where the teams werestaying. Refusing to let the weather stop them, the
D-R team rode to Fayetteville (close to LaGrange)
on Saturday and then car-pooled back to Houston.
Photo: Nathan Powell; Pablo Enrique Alarcon; Graham
Sherlock; Jennie Orellana; Chris Cowden; Erick Scherzer;
Christopher Petrillo; David Sanchez; Bernardo Alvarez;
Jerome Beguerie; Maribel Socorro; Octavio Primo.
Source: University of Houston Cullen College of Engineering
On Sunday, the team car-pooled back to Fayetteville
at 4:00 am to complete day two of the race.
This year, the MS Society raised approximately
$20 million, of which the Dresser-Rand business
team collected more than $12,000. Six D-R business
employees volunteered their time to help make the
event a success. •
In March 2015, Camp STEMovation held a STEAM
Extravaganza event at Rick Schneider Middle School
where the students participated in hands-on, super
hero-themed STEAM workshops. The workshop
Guerra taught began by teaching students basic
engineering principles. He then challenged the
students to build super hero lairs using just stripsof card stock paper and tape. The lairs were then
subjected to three tests: Guerra dropped the lair to
the floor; he then stood on the lair with one foot;
and finally, he simultaneously dropped two large
college-sized textbooks onto the lair.
Students were awarded points based on how well
the lair survived all three tests, the aesthetics of the
lairs and how many materials were used to build it.
The student awarded the most points won science
kits and a trophy.
“You can see thelightbulbs going off in
their heads,” Guerra
said of the students who
partook in the event.
Suddenly they go from
having never even heard
the word ‘engineering’ to
this becoming an option
for them.” •
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The climate is often severe, with long, cold winters
and short, cool summers. Average temperatures in
January hover just above zero degrees Fahrenheit
(-18 degrees Celsius).
Welcome to Komi.
One of the northernmost republics of European
Russia, Komi is located approximately 650 miles
(1,046 km) north of Moscow and less than 400
miles (644 km) south of the Arctic Circle. It’s
among the largest oil and gas producing regions in
European Russia and one of the country’s top 10
producers.
One of the area’s oldest fields, Lekkerskoje (Lekker),
is situated near the city of Usinks, founded in 1966
as an oil and gas production center settlement.
Since the Lekker deposit is in a remote location,
there are no external electric power networks.
Because of this, it’s critical to maintain an
uninterrupted power supply.
Initially, diesel power stations were used to provid
power to the local infrastructure. Russia’s second
largest oil producer, Lukoil-Komi (a branch ofLukoil), decided to upgrade its power generation
facilities at Lekker. After careful consideration of t
proposals, company managers opted to purchase
and install four 1.8 MW Dresser-Rand KG2 turbine
generator sets and auxiliary equipment. Zvezda-
Energetika, a key player in the Russian power
generation industry, was selected as the local
packager for the four skid-mounted KG2 turbine
generator sets.
Dresser-Rand KG2 turbines provide on-site electrical power
for one of Russia’s largest oil producers.
Welcome to
Komi
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Sustainable Power StationsDesigned to meet demanding emissions regulations,
the KG2 gas turbine is ideally suited for continuous
power generation on- and offshore, emergency and
stand-by power supply, and as an indirectly-fired
option for CO2-neutral biomass plants. Because of
its simple, low-maintenance design, high reliability,
and operational experience, the KG2 turbine
generator package is a preferred solution for these
types of applications. The wide fuel range also
enables operation on extremely low heating value
fuels, landfill gas and associated gas from crude oil
production.
One of Lukoil-Komi’s key variables in choosing the
KG2 is that it can accept a wide variety of fuels,
ranging from pipeline quality natural gas to low
heating value gas. According to Russian Federationlaw, flaring of gas is subject to heavy fines. The
Dresser-Rand power station solved this problem
by producing electricity on-site from available
resources, which prevented flaring. These types of
power stations are specifically engineered for fuel
flexibility and sustainability, so that the gas can be
used as an energy resource instead of being wasted
through venting or flaring. It’s not only efficient, but
better for the environment, too.
A History of Reliable OperationThe KG2 has proven itself in a variety of
installations, with more than 1,200 units clocking
more than 25 million operating hours with 99
percent availability. Some engines have been
running more than 245,000 continuous hours and
have achieved a lifetime of more than 30 years of
run time.
The unit requires minimal maintenance, important
in a region with limited accessibility. In addition, the
package is suited to the harsh northern conditions
because the container is constructed in such a
way that all maintenance can be performed from
the inside. Some of the competing units have
tight containers and maintenance is possible only
through open doors or hatches.
Cogeneration – an Added BenefitAnother advantage of the versatile KG2 turbine is its
combined heat and power (CHP), or cogeneration
capability. CHP systems facilitate electricity
production and provide useful heat at a very high
efficiency. The turbines at Lekker operate with a
heat recovery system, so they not only produce
electric power but provide heat energy as well. •
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TThe Guascor HGM 420 model provides 1 MWe of
power and extends the Guascor HGM family of low
emissions, lean burn, spark-ignited gas engines that
employ Miller Cycle technology. The 42-liter, V12
engine (bore 160 x stroke 175 mm) is rated 1,040
kW mechanical and 1,010 kW electrical at 1,500
rpm. The engine achieves greater than 42 percent
mechanical efficiency and its electrical efficiencyexceeds 41 percent.
The Guascor HGM 420 gas engine is normally
connected to an external grid and is suitable for
projects that require approximately 1 MWe of
power. With high thermal demand and continuous
operation, these engines can be supplied as stand-
alone power units, as part of a cogeneration system
on a skid, packaged as a gen-set, or containerized.
In addition to its electrical efficiency, the Guascor
HGM 420 gas engine is able to recover heat from
Clients with high energy efficiency requirements can now take advantage of
the Dresser-Rand business’ new Guascor® HGM 420 gas engine. The newest
model in the Guascor HGM engine family, it offers a balanced relationship
between efficiency, reliability and price.
main and auxiliary water circuits, as well as heat
from exhaust. It achieves approximately 91 percen
thermal efficiency and can run more than 8,000
hours per year with the balance of the year set
aside for routine maintenance.
The Guascor HGM 420 model is also available
at 1,800 rpm, with 1,040 kW mechanical and1,006 kW electrical. The engine achieves greater
than 40 percent mechanical and 39 percent
electrical efficiencies, respectively, as well as
90 percent of total heat efficiency.
The overall power range of the Guascor HGM fam
is 520 to 1,240 kW at rated speeds from 1,500 to
1,800 rpm. These engines can burn a wide variety
of fuels including natural gas, biogas from anaerob
digestion of organic matter, methane from landfill
sites and sewage plants, and most any type of gas
derived from bio digestion processes.
•
Hits the MarketNew HGM Engine
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VSDS Motor Inverter DesignConcept for Compressor Trains Avoiding Interharmonics in
Operating Speed Range and Verification
Volker Hütten
Head of Numerical Design Department
Siemens Energy Sector
Duisburg, Germany
Tim Krause
Mechanical Design Engineer
Siemens Energy Sector
Duisburg, Germany
Vijay Anantham Ganesan
Medium Voltage Drive System Consultant
Siemens Industry Sector
Nuremberg, German
Christian Beer
Senior E-Drive Expert
Siemens Energy Sector
Erlangen, Germany
Sven Demmig
Medium Voltage Drive System Consultant
Siemens Industry Sector
Nuremberg, Germany
Editor’s Note: Reproduced with permission of the Turbomachinery Laboratory (http://turbolab.tamu.edu). From
Proceedings of the Forty-Second Turbomachinery Symposium, Turbomachinery Laboratory, Texas A&M University,
College Station, Texas, Copyright 2013.
Volker Hütten has been the head of the
Numerical Design department of Siemens Oil
& Gas Division, in Duisburg, Germany since
2010. During his more than 21 years in this
company he is responsible for the machinery
dynamics of compressors and compressor
trains of order related tasks. He has been
active in correlating analytical results with
field data in numerous troubleshooting and problem
diagnosis situations. Volker Hütten received his Diplomadegree from the University of applied sciences in Krefeld
in 1990.
Christian Beer is a senior e-drive expert at
Siemens Oil & Gas Division in Erlangen,
Germany. Since 1989 he has specialized
in electrical drive systems and has been
responsible for LNG e-drive solutions.
Tim Krause is a mechanical engineer
at Siemens Oil & Gas Division in
Duisburg, Germany, where he is
responsible for engineering and
troubleshooting of compressor trains
in the field of machinery dynamics. He
received his diploma degree from the
University of applied sciences in
Dortmund in 2005.
Vijay Anantham Ganesan is medium
voltage drive system consultant
at Siemens Industry Sector in
Nuremberg, Germany. He received
his M.Sc. degree in electrical power
engineering from RWTH Aachen
University, Germany in 2005. From
2005 to 2010, he was a research
assistant at Leibniz University Hannover, Germany.
Sven Demmig is a medium voltage drive
system consultant at Siemens Industry
Sector in Nuremberg, Germany. After
achieving his PhD in the field of electrical
drive systems, he has been working for
Siemens since 2008.
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A
ABSTRACT
During operation of compressor trains by a variable speed drive system (VSDS),
integer and non-integer harmonic currents are generated in the inverter. Via the
electrical system of the inverter and the motor, an excitation torque is transferred
across the motor air gap into the main mass of the motor rotor. The frequency
of this excitation may cause torsional resonances. Due to the rapid increase in
excitation frequency of integer harmonics, intersections with relevant torsionalnatural frequencies (TNFs) can in general be avoided within the operating speed
range. In contrast, the intersections of the noninteger harmonic excitation
frequencies, also called interharmonics, with TNFs within the operating speed
range may have an essential impact on the vibration behaviour of the rotating
equipment. This aspect has to differentiate between two train configurations. The
first are direct driven trains and the second, trains including an intermediate gear.
For direct driven trains, only fatigue problems have to be considered. In trains with
an intermediate gear, on top of that, interaction of torsional and lateral movement
may have a negative effect on the lateral vibration behaviour of the gear rotors.The main focus of this publication is on a simple but effective method for turbo
compressor applications that allows avoiding main resonances within the operating
speed range caused by intersections of interharmonic excitations with relevant
TNFs. This method is based on detailed knowledge of the inverter behaviour
and possible design options of the motor itself. This in-depth understanding was
developed by correlating numerical and experimental results based on dynamic
torque measurements of real turbo compressor trains. During this investigation the
mechanically relevant torsional excitations were identified. Therefore, the different
types of inverters and their corresponding characteristics had to be analyzed and
understood in detail. This knowledge, in combination with possible motor designs,
with regard to the number of pole pairs and the most common train configurations
(direct driven and/or trains including intermediate gears), is incorporated in this
report.
IntroductionAdvantages of VSDS Driven Trains
Rotating equipment in the turbomachinery industry
traditionally uses mechanical drivers as primemovers. Process and mechanical engineers have
confidence in their equipment and might have
reservations about not yet installed electrical
equipment. Ongoing discussions about energy
efficiency, equipment availability, operability and
avoidance of green house gas emissions (GHG)
has lead to a steadily increasing use of electric
motors, either as fixed speed or as variable speed
drivers. The industry has reacted with an array of
electrical drive systems that can beneficially replac
gas turbines and gas engines as prime movers of
compressors and pumps. In smaller power ratings
the electric motor is unchallenged in all industrial
fields, including the oil & gas industry. Its simplicitrobustness and performance is unmatched by any
other drive in most all applications. In megawatt
power ratings, however, electric motors are
challenged by gas turbines. Detailed driver selectio
studies are the rule when it comes to find the
best suited driver for a given application. With the
introduction of electronic variable speed drives in
the late ‘70s to the industry the benefits of fixed
speed electric motor drives have been significantly
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enhanced and these additional features are most
often the reason for their selection:
• Soft start and fully torque controlled operation
over a wide speed range
• Dynamic and accurate speed control via
electronic variable speed controllers
• Ability to ride through brief power busdisturbances
• Energy efficiency above 95 percent also in part-
load mode and related speed range
• Shaft speeds in excess of the customary 3,000
or 3,600 rpm dictated by the power system
frequency, eliminating step-up gears in many
cases
• Insensitivity to frequent start/stop cycles and
ability to (re)start fully loaded compressors
• Instantaneous starting capability providesprocess flexibility
• Lower GHG and noise emissions
Suppliers of such motors and many engineering
contractors have the experience, know-how and
tools to select and recommend the optimum
variable speed drive system for a given application.
History
After the technology’s potential to realize variable
speed operating envelopes in combination with
high efficient electric drives was discovered, it wasinstalled more frequently. However, it turned out
that the ecologic and economic advantages of all-
electric compression with VSDS driven trains come
along with a technical issue to solve.
For many years occasionally high lateral vibration
in intermediate gears as well as coupling or shaft
end damage occurred and was reported to the
industry (Corcoran, et al., 2010), (Kita, et al.,
2008), (Kocur and Corcoran, 2008), (Naldi, et al.,
2008), (de la Roche and Howes, 2005), (Feese and
Maxfield, 2008). Measurements revealed high
torque oscillation amplitudes, initially caused by
torque oscillations generated in the inverter. These
travelled across the motor air gap towards the
rotating equipment and excited the fundamental
TNF of the entire train.
Variable speed drive systems rectify alternating line
current (AC) of 50 Hz and/or 60 Hz, to direct current
(DC), and invert the DC to a variable frequency AC
current in order to operate the motor at variable
speeds. As illustrated in Figure 1 the electrical
conversion from line side to the motor side, quite
small harmonic distortion of the inverter output
current causes forced torsional vibration. Due to
small amplitudes, this is outside the resonances of
a well endurable load for the train components.
Unfortunately, the vibration is amplified when the
excitation frequency of torque ripples match a TNF
with a suitable mode shape to excite the train.These can then be high enough to either transfer
the torsional vibration energy into lateral pinion
vibration through the gear, or even exceed the
component’s fatigue lifetime capacity.
Figure 1. Electro-mechanical interaction.
The turbocompressor manufacturers historically
dealt mainly with torsionally easy to handle gas
and steam turbine drives and fixed-speed electric
motors. They now had to close the ranks with the
electric drive equipment manufacturers to gainground in bringing the two disciplines, electrical and
mechanical engineering, together.
Technical Impact of Torsional Resonances
Excited by VSDS
In principle, generated harmonic torque oscillations
may have an essential impact on the torsional
vibration behavior of the entire train. Consequently,
the train-responsible party, mostly the compressor
manufacturer, must carry out detailed analyses to
examine the operational condition of the rotating
equipment in order to do a proper engineeringdesign. Therefore, close collaboration of driver
and compressor manufacturer in designing and
engineering of such a VSDS-driven train is essential,
as also stated by Hudson (1992).
First of all, it is an essential task to avoid fatigue
in the torque-transmitting elements. Torsional
excitation may cause fatigue which could eventually
lead to a catastrophic failure of torque transmitting
elements. During the engineering phase of
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any project the occurring peak torque and the
corresponding torque capability of each individual
train component has to be evaluated. Furthermore,
in systems including intermediate gears, elevated
lateral vibration of the pinion and bull-gear rotors
could also occur. Due to the fact that torsional and
lateral vibrations are coupled via the gear mesh,
excitations have to be examined to avoid higher
lateral amplitudes and/or to avoid clattering ingears in addition to fatigue problems.
Based on the authors’ experience, excessive
high lateral vibrations caused by a torsional
excitation were observed in some cases. It is due
to the coupled movement in lateral and torsional
direction, a more or less plausible behaviour.
Nevertheless, the authors have, in some cases, also
observed high torsional vibration amplitudes and,
simultaneously, only few microns of relative shaft
vibration corresponding to the torsional excitation
frequency.
A case of white noise excitation in contrast to the
widely known single frequency excitation has not
yet been encountered by the authors. However,
two cases of VFD compressor trains in the LNG
industry showing such phenomenon were recently
published (Kocur and Muench, 2011).
Ultimately, only a dynamic torque measurement
during string testing and/or during commissioning
would be able to identify the potential risk of a
failure. The alternative is to have a reliable strategy
for the engineering. One specific will be presentedas the main topic of this paper, but also other
options will be discussed which positively influence
the aspects.
Generation of Torque Ripples in VSDSPrinciple of Generation of Torque Ripples
The motor air gap torque is generated by the rotor
flux in combination with the stator current. For a
perfect sinusoidal stator current waveform and
a perfect air gap field, the motor torque would
be constant. Using a VFD, the motor currentwaveform is not perfectly sinusoidal. The AC-DC-AC
conversion adds torsional excitation frequencies to
the system. Integer harmonics and interharmonics
excitation generated in the converter cause torque
oscillations in the motor air-gap. This effect cannot
be disregarded due to the fact that interharmonic
excitations can be of such frequency that they can
generate torsional resonances in the operating
speed range.
The air gap torque ripple generated by the VFD
characteristic can be split in two categories
(Figure 2):
• Integer harmonic torque excitation
• Interharmonic torque excitation
The excitation frequencies are written for the
integer harmonic torque harmonics as f exc-h = C1*f dand for the interharmonics as f exc-i = |(C2*f do-C3*f l)|
The integer harmonics are directly proportional to
the motor stator current frequency and therefore
the motor speed. The characteristics depend on
the converter topology e.g. VSI or LCI and the puls
number of the motor side rectifier. The amplitudeof the air gap torque ripple depends, just to
mention the main factors, on:
• Switching device characteristic
• Motor impedance
• Motor voltage
• Motor cable characteristic
• PWM characteristic for VSI drives
The non-integer harmonics are caused by the not
perfect DC current (LCI drives) or DC-voltage (VSIdrives). This means the characteristic of the line si
inverter is modulated on the motor currents by th
motor side rectifier. Because of this modulation, th
frequency of the interharmonics depends on the
line frequency, the motor frequency and the pulse
number of the motor and the line side rectifier. Th
amplitude is influenced by the same parameters a
the integer harmonics plus additional parameters
Figure 2. Typical VFD Campbell diagram.
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the DC-link and the line side:
• DC-link capacitance / inductance
• Line side characteristic (harmonic pre-load,
frequency-dependant impedance, etc.)
• Transformer impedance
The resulting torque ripple frequency of the
interharmonic air gap torque varies within therange of operation depending on the parameters
explained before. Nevertheless, this may result
in an interaction with the TNF of the mechanical
string even if the amplitude is much lower than the
amplitude of the integer harmonics.
Because of the large number of parameters
influencing the amplitude of the air gap torque
ripple, the prediction of specific amplitude is
complicated and only possible with tolerances. But
knowing the drive and motor type the torque ripple
frequencies over the complete speed range can bepredicted easily even without any simulation.
It has to be pointed out that this kind of behaviour
is inherent to all state-of-the-art inverters in
the entire market. It varies only with regard
to interharmonic frequencies and excitation
magnitude for each particular configuration.
Typical Motor Design and Number of Pole Pairs
Electrical motors can be built in 2, 4, 6, … pole
design (equivalent to number of pole pairs (NPP) of
1, 2, 3, …) and this leads to synchronous speed of:
nsyn = (f l / NPP) *60 (1)
As can be seen in Figure 3, a motor with a number
of pole pairs of 1 runs with supply frequency.
Whereas a motor with a number of pole pairs of 2
at half and with a number of pole pairs of 3 at one-
third of the supply frequency accordingly. This is an
essential fact in order to find resonance-free train
design solutions within this new design concept.
Overview of Relevant Frequency Converter Types
In the turbomachinery industry two frequency
converter types are typically used:
• Voltage source inverter (VSI)
• Load commutated inverter (LCI)
Both types have specific advantages and
disadvantages and the selection is based on power
and voltage range, complexity and the referencesituation. In general, VSI are used for the lower
power ratings up to 25 MW and the LCI is the
preferred solution for the highest power ratings
up to 120 MW. In the range of 15 to 25 MW both
topologies can be used. The VSI can be used with
all motor types and topologies with different pulse
numbers. The VSI will generate motor voltage in
block form. The resulting motor current depends
on the stator inductance, the cable parameter,
the pulse number, and the control characteristic.
Nevertheless, the current total harmonic distortion
(THD) of VSI drives is lower than the current THD ofLCI drives. As explained before, this leads to a lower
torque ripple which may be advantageous for the
overall compressor string design.
The LCI instead can be used for synchronous
motors only. Also for the LCI topologies, different
pulse numbers are available. The motor current is
generated in a block form, results finally in higher
current THD.
Experience With and Consequences
of Interharmonic ExcitationSeveral case studies of vibration issues related to
torque excitation caused by inverter fed motors
have already been published. Here, two of our
own typical examples of case studies are presented
which were used in order to get an in-depth
understanding of the operating behaviour of the
individual inverter types. This information is needed
to realize the new train design concept that is lastly
the main focus of this publication.
Excitation Pattern of a VSI
In the first case, a 1.5 MW 12-pulse VSI inverterfeeds the induction motor of a single-shaft radial
compressor train with intermediate gear. During
run-up with constant acceleration the dynamic
torque measurement at low speed coupling
recorded amplitudes as shown in Figure 4. As the
inverter speed control actively accelerates the train,
the harmonic and interharmonic excitation lead to
Figure 3. Effect of number of pole pairs (N pp ) on
motor speed.
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dynamic torque peaks at speeds where torsional
resonance occurs. The blue line is the torque
measurement and the green line shows the motor
speed, both versus time. Some torque peaks can
be observed: one single major amplitude at about
2,700 rpm and some peaks quite close together
especially in the low speed range.
It is practical to plot these together with the TNFs
and excitation frequencies in a Campbell diagram.
Figure 5 represents this diagram with the first two
TNFs (dashed lines) and torque ripple excitation
frequencies (solid blue lines) versus motor
operating speed. At motor speeds where the first
TNF and excitation frequency intersect, a resonance
is present. The red circles indicate the relevant
resonances.
The diagram reveals that the by far dominating
torque peak at 2,700 rpm is caused by the |3*f do-
6*f l| interharmonic excitation frequency exciting
the first TNF. This excitation should therefore, as
major resonance, not fall within the operating
speed range. Apart from this, secondary amplitude
at about 10 percent peak-to-peak the motor rated
torque are observed. The first natural frequency
is stimulated by the |9*f do-6*f l| interharmonic
excitation frequency and 1*f do at about 900 rpm.
Due to its mode shape, the first natural frequency
for this train configuration commonly leads to
the highest torque amplification for excitation at
the motor air gap. Torque amplitudes at otherspeeds, due to their limited amount, are considere
not relevant for the train design. These results
leveraged the confidence to use the numerically
derived excitation frequencies for this inverter typ
for the later described train design concept.
Excitation Pattern of a LCI
The following example is related to a 16 MW
12-pulse LCI-driven synchronous motor train,
connected to a 50 Hz grid, including intermediate
gear and a single shaft radial compressor. The
train has been designed to operate in a speed
range of 1,260 rpm to 1,890 rpm. In order to get
the required information with regard to relevant
interharmonic excitation the train was equipped
temporarily with strain gauges at the low-speed
coupling for a dynamic torque measurement.
During the measurement program the train was
ramped-up slowly with an acceleration rate of 0.2
up to 0.5 rpm per second. The measured dynamic
torque (blue line) and the motor speed (green
line) are shown versus time in Figure 6. Four main
torsional resonances could be observed. These
resonances correlate with the fundamental TNF an
the expected interharmonic torque excitation of th
6- and 12-order. Based on that result, it means tha
higher orders of interharmonic excitations are not
relevant regarding torsional excitation within this
system.
Figure 4. Trend of motor speed and dynamic torque at
low speed coupling.
Figure 5. Campbell diagram with relevant resonances.
Figure 6. Ramp-up of 16 MW LCI-driven train.
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In the next step it is essential to know what
happens to the torque amplitude by running
in resonance conditions. In order to get an
understanding of the behaviour of the vibration
system, each individually observed resonance was
entered for a period of time. For one example
of these tests see Figure 7. The observed torque
amplitude was generally higher during continuous
operation in contrast to crossing the resonance.However, the maximum torque amplitude achieved
stationary conditions. This information is of
paramount importance with regard to a worst case
operating scenario of the fatigue design of the
train components running in resonance condition
permanently.
For this particular case, the measured torque
amplitudes at torsional resonance condition were
above the expected, based on the state-of-the-art
electro-mechanical simulation. Nevertheless, theapplied service factors considering the simulation
uncertainties ensure that the mechanical train
components are capable of withstanding the
observed dynamic torque amplitudes permanently.
Therefore, the train can be operated without any
operational restrictions.
Comparison of Simulated and Measured Results
Several VSDS driven trains were investigated on
a numerical basis. For some of them, measured
results of dynamic torques are available for
correlation. The analytical investigation is generally
able to identify the relevant interharmonic
excitations. The TNF and the corresponding motor
speed can be determined with satisfactory accuracy.
But nevertheless, based on the authors experience
of correlating results of various simulated and
observed torsional turbomachinery systems, the
peak torque amplitude in the state of resonance
condition cannot be predicted with sufficient
accuracy in order to carry out a fatigue analysis on a
numerical basis only. Therefore, it can be concluded
that further uncertainties exist in the electrical
and also in the mechanical model. To compensate
for these uncertainties the service factors are
conservatively selected. This guarantees safe design
while accepting the drawback of over-engineering.
For an accurate prediction of the occurring dynamic
torque in the train elements, the magnitude of
torque excitations including realistic tolerances areessential. Further investigations and improvements
of the electro-mechanical simulation model are of
course an ongoing task.
Experience with Interaction of Torsional
and Lateral Vibrations
For trains including an intermediate gear and/or for
trains with an integrally geared type compressor,
the torsional and lateral vibration system are
coupled in movement via the gear mesh. In such
a case, the lateral vibration spectrum may also
present frequency components of the torsional
excitation frequency.
Higher lateral vibrations were observed in the field
with trains featuring gears. This kind of observation
is not only reflected by the authors’ experience, but
is also published in other literature sources (Kita, et
al., 2008), (Naldi, et al., 2008).
At a first glance it seems to be plausible that
high torque fluctuation also produces high lateral
vibrations. This is the reason why only concerns
regarding high dynamic torques are raised, when
high lateral gear shaft vibrations are also evident.
In contrast, cases could also be observed where
high torque fluctuations were measured, although
only insignificant lateral vibrations of the gear
pinion and/or the bull gear could be seen. Having
the physical relationships in mind, this issue boils
down to the influence of the dynamic oil film
stiffness of the gear bearings.
Generalized, one can only conclude that if
TNFs can be measured in the lateral vibration
spectrum, dynamic torque oscillation will, with highprobability, be present in the train. However, low
levels of radial vibrations do not necessarily mean
low levels of dynamic torque fluctuation in the train
components.
White noise excitation
Harmonic, inter-harmonic and control loop torque
disturbances form the group of single frequency
excitation mechanisms. These are widely considered
the main issue related to VFDs, but recently two
Figure 7. Stationary operation in resonance of 16 MW
LCI-driven train.
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cases of VFD compressor train torsional vibration
were published, which were connected with white
noise excitation (Kocur and Muench, 2011). This
made it necessary for the involved parties to
rethink the strategy for torsional analysis, including
the system response to banded Gaussian white
noise into the scope. The authors cannot give a
recommendation in this matter, since they have
never experienced a case of torsional vibration
related to white noise, simulated or practical, with
their equipment so far.
Conventional Strategies of Dealing
With Interharmonic ExcitationIf a resonance with an interharmonic excitation is
detected and countermeasures are found to be
necessary, one can today choose from a wide range
of proven alternatives. These can be sorted into one
of the following categories:
• Damping increase
• Excitation reduction
• Torque transmitting component fatiguecapability increase
• Resonance avoidance
What follows, they are presented and discussed
with their inherent advantages and disadvantages
to give an overview.
Inverter Control Setup
Although the basic root cause was not exactly thesame in all of the case study papers mentioned in
the introduction, for all of these cases modifications
of the setup of the inverter control or inverter
control type change finally reduced the excitation
torque amplitudes sufficiently. De la Roche and
Howes (2005) describe the case of a motor-
driven reciprocating compressor with motor shaft
failure on one of two trains. For the first train,
inverter software parameter change was able to
increase, as well as satisfyingly decrease the torque
oscillations. They and Corcoran and Kocur (2008)
as well, mention the speed feedback into theinverter control to be a contributing factor to the
overall vibration. It is considered able to amplify
the oscillation, when the speed control counteracts
the speed fluctuation initiated by the torsional
vibration.
When torsional vibration is present, it is
adequate to first exhaust the remaining room
for improvement in the inverter control for
optimization.
Designing Components Robust Enough to
Withstand Torque Ripples
According to the applicable paragraphs of API617
7th edition, if excitation mechanisms are known
to act in a compressor train, the train responsible
party shall conduct a stress analysis. This shall show
permissible amplitudes compared to high cycle
fatigue capabilities of the train components. Itwould be therefore satisfying to design the relevan
train components in such a way that they can
withstand the occurring dynamic torsional load ov
the train’s lifetime. The benefit for the operator
is that the train can be operated with the whole
speed range specified, although resonances are
present only at certain speeds.
Necessarily, the dynamic torque amplitude must
be known from torque measurement records, or
it must be sufficiently and accurately predicted
by torsional analysis. Independently, whether the
simulation model is a harmonic forced response
simulation or a coupled electrical/mechanical
simulation, both deliver the dynamic torque
response within the train elements of interest at th
detected resonant conditions. These results vitally
depend on the damping assumption made in the
analysis and the accuracy of the expected dynamic
air gap torque excitation magnitude. If uncertainti
regarding the above aspects are present, service
factors need to be conservatively defined. From th
authors’ point of view, there is still some need for
refinement of simulation models. It promises for tfuture service factors to be reduced to appropriate
figures, thus preventing over engineering.
Individual Exclusion Speed Ranges at
Resonance Condition
The torsional resonances described before can
also be avoided by using individual exclusion
ranges. It is practicable to determine resonances
of relevance, i.e. with a dynamic torque amplitude
probable to exceed a component’s high cycle
fatigue capability, by torque measurement at
the manufacturers test bed facilities or duringcommissioning. The countermeasure is then to
implement the identified resonant motor speeds
into the inverter speed control. These speeds,
plus a separation margin including tolerances and
uncertainties, are blocked. It is by this, of course,
not possible to exclude resonances from the speed
range, but it limits the time of operation within to
a minimum. In a variable speed performance map,
blocked speed ranges can be illustrated as the are
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shown in Figure 8. It must be clear that for the plant
operator, a blocked speed range, even if it is small,
always is a limitation of production flexibility.
Using individual exclusion ranges seems to be a
simple and effective solution. However, a lot ofparameters and uncertainties have to be born in
mind by setting the real problem solving exclusion
speed ranges.
For one single train installed, these include the
accuracy of the dynamic torque measurement itself,
changing of material properties over life cycle and/
or due to temperature and local grid frequency
variation, just to name few. The last parameter
can, especially in countries with high grid frequency
fluctuation, become the decisive parameter for the
blocked speed range. It would necessarily increase,unless the grid frequency was considered in a speed
control algorithm as an additional parameter, which
is possible.
In case of multiple identical trains installed, efforts
increase. If a torsional measurement is going to
be done for one train only, it should be critically
discussed, how material property uncertainties
between the train components are reflected in the
determination of the blocked speed range(s).
Damping in Control Loop
Active damping of the load or the process using
the VFD is standard in some industries. Also for
compressor strings there are approaches to use
the VFD for active damping (Naldi, et al., 2008).
The challenge for the compressor trains is the low
frequency of the switching devices and the limits
of the specific topologies. Another challenge is the
identification of the train characteristic. The control
loop needs as input parameter the actual status of
the train. Therefore, additional sensors are most
likely needed.
The conventional multi parameter control system
of an inverter is extended by an additional damping
control loop. This feature should be considered
in detail during engineering and also during the
commissioning process in order to achieve a reliable
operation. As long as additional sensors need tobe installed and are crucial for the functionality,
redundancy is essential.
Damper Coupling using Elastomeric Elements
Occurring torque response in resonance condition
is mainly determined by the magnitude of the
torque excitation and the mechanical amplification.
Therefore, torsional damping is a significant
influence parameter for the overall system.
Couplings consisting of a steel structure combined
with integrated elastomeric elements are used
as common dampening device. The main task ofthese elastomeric elements is to absorb torsional
vibration energy by compressed deformation of
the elements in contrast to solid steel couplings.
It is of utmost importance that this coupling be
located close to the node of the mode shape of the
fundamental TNF to be most effective in increasing
system damping. As a consequence of the material
properties, the rubber elements degrade over time
due to heating up and environmental factors. The
main disadvantage of this kind of coupling is usually
increased maintenance for reliable operation,
in contrast to solid steel couplings. Due to thisfact, elastomeric couplings are principally not
allowed per specification of the operators for some
applications.
The authors are convinced that using such kind of
coupling may help to limit the torque amplitude
during crossing resonances for a short period
of time. However, for VSDS-driven trains it may
happen that the train is running in condition
of a torsional resonance for a longer period.
If amplitudes are excessively high, running in
resonance condition for a longer period mayoverload the elastomeric elements. Coupling
failure in a VSDS-driven train are, in most cases,
not necessarily caused by a poor coupling capability,
but are quite often caused by the train behaviour
itself (Corcoran and Kocur, 2008).
Figure 8. Blocked speed ranges in a performance map.
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New Train Design Concept to
Avoid Interharmonics in Operating
Speed RangeBasis of the New Train Design Concept
In principle, the basis of the new train design
concept to avoid interharmonics within the
operating speed range is an in-depth understanding
of inverter behavior, motor design and finally,the various compressor train configurations and
their corresponding torsional behavior. First of
all, it is essential to work out the details of the
mechanically relevant torsional excitations caused
by the individual inverter types. This task has
been done on a numerical basis by simulating the
electrical and mechanical system. Due to the fact
that the occurring torque amplitude in a state of
resonance condition is connected with tolerances,
although using state-of-the-art coupled electrical
and mechanical simulation models, correlation
with dynamic torque measurements are of vital
importance. This is to separate the relevant
exc