By: Soto, Victoria

Class: Mechatronics

Instructor: Dr. Yacoub Alsaka

Class: ECET 402, DeVry University

Date: Week 6, 6/15/13

My Introduction To

Power Plant Controls

Six weeks ago, I started searching the Internet for “Power Plant Controls”. Using

variations including “electric” and “panel”, I found ICE (Instrument and Controls Engineering).

I looked up the basic theory of conventional and non-nuclear generating plants. (I prefer to

avoid nuclear power because we do not know how to safely dispose of the residue of the

process.) I looked up turbines, generators and transformers, looking for gauges and controls

associated. I looked for the names of manufacturers of dials, gauges and indicators. I looked up

pumps, valves and solenoids. Back to power plants, I searched for images of control panels but

did not see pictures clear enough to identify indicators and controls.

A few weeks later, I was working with the idea of writing about a wind and solar system

for electricity generation, being started for the first time and describing how the control panels

might appear. I visualized the contractor handing me the keys before sunrise. I was planning to

wave to the mechanic near the windmill and have him release the brake when the sun rose and

heated the air to the east, causing our wind to breeze towards that direction. When the wind

turbine generated enough power, the solar panel motors would energize and the panels would

turn to the sun. When they were lined up, they would easily start generating dc voltage and my

inverters would start producing alternating current. Now I could enter the control room. The

light switch would work and illuminate consoles that the employees would station themselves at

while they monitored the gauges and controls displayed on the control panel. My primary

thoughts at this time were, “What dials and gauges are the operators watching? In other words,

what information is important to the running of this type of plant?”

I sent e-mails to a variety of energy producers but received no responses. I went to the

three local libraries (county, college and university) but could not find any books on the controls

involved in electric power generation. There were scarcely any books for advanced electrical

engineering at all. I visited the local utility company’s distant “Energy Education Facility”, but

the mechanical engineer there was only able to tell me about modifying a consumer’s property to

reduce consumption or supplement a home with newer appliances, including new magnetic

induction fluorescent bulbs, modern heating and air conditioning systems, solar panel mounting,

wind vane variants, and how to perform energy audits for households and small industries. He

did show me how the building’s heating and air conditioning was monitored by software and

flappers and dampers sealed off or admitted outside air if the temperature and humidity would be

beneficial if added to the indoors condition. It was interesting, but the electrical engineer who

might have helped was off for the day.

Finally, I realized that there were at least three energy producers in my immediate area;

we have a local wind turbine, a solar plant or two, and a “gasification plant”. I contacted the

windmill folks, but plant security would not let me see the wind mill or controls up close. The

gasification plant was supposed to use coal to generate electricity, but there was no coal

anywhere around. When I pressed the “call” button at the gate, I was told that the plant was

indeed operating but had nobody available to give me a tour. I drove out to the Solar Plant

(SEGS 1) and was given an appointment to visit, Friday at 2 p.m., by another “voice” at a gate.

A locomotive is a simple power plant with minimal controls.

I left work early Friday, hoping to try the gasification plant again. Nobody was available

for tours. With an hour or two to spare, I thought about the trains that stop near my back door

and whistle their way through the towns. A locomotive is a power plant. I did not know anyone

in the depots that would show me a driver’s compartment, so I went to the local railroad

museum. I toured the historical displays with equipment, track parts and dishes and menus from

the Harvey House Girls era. On one counter, I saw an operating instructions booklet for an old

Morrison Knutson 1200G Locomotive. In the first section, under general description, there was

a picture of the engine control panel. There were only five indicator lights, showing the

condition of the prelube pump and system, the fuel valve, a critical engine fault, and a warning of

methane in the driver’s compartment. There were very few switches for the engineer to control;

prelube and engine start, motor cutout and isolation (for truck [wheel assembly] drive motors),

five different lights, and emergency fuel and engine stop.

While I looked around, I was queried about my interest in the shelved books in the gift

shop. I described the paper I was planning to write and was informed that this person asking

questions was an Amtrak engineer, and former electrician, from out of town who would be

pleased to show me around the locomotives on display outside the museum. He was especially

knowledgeable about the model EMD 40-2 and told me to look it up on-line¹. I eagerly

encouraged his discourse. He could not show me the control room, but he described the action

of the locomotive. He described the batteries that ran the electric motors that started the diesel

engine which drove the electrical generators and other electro-mechanical components (as

mentioned in Appendix A). The generator creates electricity for the motors between the axles.

Once they are running, the motors control the traction to the wheels that are resting on the sum

total of a “dime’s worth of surface”, according to my informant. He also described watching a

few ladies in high heels being able to pull a locomotive, once inertia was overcome.

When asked about controls, he indicated that older locomotives had a few operator

controls but newer models are almost completely automated. He showed me the sand box at the

front end of the engine that dribbled sand onto the metal track in case there was any wheel

slippage which is the first item of concern to the train operator. Next, he showed me the 27 pin

connector in the front of the engine, describing one possible difficulty if one of the pins was bad

– of eight positions of control on the speed mechanism, the bad pin in one case was a multiplier

that had kept him from his fastest speeds. One of the other problems that engineers watch for is

overcurrent situations where the generator’s exciter fails; there is no control of the system, units

overheat and the locomotive simply quits. He could have discussed other systems, such as the

air brakes from the air compressor controlled by the diesel engine or the switchgear components

that respond to the controls in the engineer’s compartment, but we had used all the time I had

available before I returned to the solar plant.

This type of solar plant had a complicated control panel with additional GUI monitoring.

Next, I visited SEGS-1 where sunlight produces a maximum of 14 megawatt–hours. This

relatively small farm was built in the mid-1980s and has controls of that era. The manager

introduced me to the technician who monitored a panel of dials and gauges. From one window

he could see the heat exchanger assembly and from another he could watch solar collectors.

When asked the purpose of my visit, I discussed the basic line my term paper was to take (see

Appendix B.) Almost immediately, I was told that this plant does not base the interaction with

the sun on photovoltaic cells.

The nearby defunct (California) Solar-1 had used heliostatic² mirrors to concentrate

sunlight into a tower-top boiler. Cold water rose and was heated, returning to ground level as

steam to run a turbine to generate electricity. Apparently, salts were originally added to interact

with the water’s thermal and pressure properties and the system worked well. Then for some

reason they decided to use salt in a fluid state. Something cooled the system and solidified the

salt, creating a non-removable blockage and shutting down the plant. It had been an early

innovative experiment gone wrong. A few years later, Luz Engineering Corporation built at least

four solar plants in the area and then went bankrupt. One of the workers here near Barstow,

California was handed the keys and managed to keep it operational.

This facility³ uses parabolic mirrored troughs to focus the sun’s energy onto a pipeline of

oil that circulates through the farm and the heat exchanger.

(Draft of a solarpipe. By Benderson2 from McSush. 11/10/2009. Copied from Wikipedia Commons)

There are two very small photovoltaic patches on each trough that measure solar strength

and compare signals with a differential amplifier. The difference value will drive the trough to

focus the sunlight directly on the pipe, plus or minus its radius. The motor does not continuously

drive the mirrors. Instead, they are allowed to focus on one side of the pipe before being

readjusted to the other side of the pipe for the next time period. If I were to stand in the field, I

would hear various sections of mirrors turning every three or four minutes, but most do not travel

simultaneously. The heat exchanging system works on water being preheated by the oil to about

500 degrees, superheated by operator controllable burners, depleted of minerals, oxygen and any

moisture by the addition of a chemical the worker called “Deha”⁴. The superhot clean steam is

pushed into the turbine. As it courses through the turbine, a vacuum at the other end causes an

extra push and the steam exits to a condenser where a difference in elevation is used to create the

pressure differential. The excess heat is released and the water is recaptured entirely. (My

original idea of running my plant’s turbine without water is not impossible, but not common.)

The turbine drives a generator and the electricity passes directly to the grid. I was

also told that my basic theory of starting a plant without electricity does not apply at this

location. They view the sunrise and determine if it will be worth their time, efforts and money to

produce electricity a day at a time. This plant draws electricity from the grid to run all the

motors to turn the mirrors to the east. Then the water is preheated so the temperature difference

is not destructive.

The operator has a control panel with many gauges of critical plant values. The first

gauge most workers stopped to check was the one indicating how many megawatts the plant was

producing. Apparently, this one lets them know whether they will be getting paid or not.

Apparently I had arrived during one of the best days so far this year. The meter read 12 MW.

By the end of the day, it was expected to bottom out at about 3 MW before the sun set. Though

this plant runs year-round, only the four months from June through September generate enough

electricity to “make payroll”. During weekdays in the summer, the plant can make $300 per

hour while weekdays in the winter produce only $30 per hour. Weekends are only good for $10

per hour because industrial customers are the biggest users and most companies don’t work

weekends.

Next on the panel were temperature and pressure gauges for water, steam and oil at

different places in the flow. The generator had several indicators on a separate panel with a

graphic representation of what appeared to be primary and secondary coils. There were meters

reading values for the cooling water, differential current, field loss, overcurrent, and exciter

rectifier failure, to name a few. The back side of the generator panel had blocks of relays. The

primary operator did not explain them, but by this time, I had mentioned that we were learning

PLCs and he called in the instrument specialist.

Some of the sections of panel that I had taken to be modular, vertical, linear gauges

turned out to be PLCs. When the gauge was drawn forward out of the panel, it was seen to have

a row of dip switches for addressing, an EEPROM with controlling instructions, and a selector

for manual, automatic, or cascading mode. In manual, the operator could nudge the set points for

more efficiency. In automatic, the actual readings were compared to the set points and

adjustments were made to control flow as necessary. Cascaded units compared readings of

multiple gauges before corrections were made. The specialist mentioned that the voltage

readings were “1 to 5”, the current readings were “4 to 20” and the pressure readings (for the IP

units) were “3 to 15”.

Among the gauge manufacturers were Shinkawa Electric and Bentley Nevada, both of

which make good products for high vibration areas, such as turbines. The turbine’s lube oil is

critical and the temperature is one of the few values that can automatically shut down the plant.

There are flux probes used for the tachometer and eccentricity measurements, using fiber optic

media for transmission of signals. At 3600 rpm, the turbine frequency passes to a transducer and

produces a voltage for the associated meter.

In the middle of the room, a console held three computer displays and a computer switch

rack. The first computer showed weather condition, field conditions, steam generator pressure

(390 psi), superheat temperature (700 degrees), turbine-generator condition and output, auxiliary

heater, and qualities of the dry steam at the turbine. The operator showed me a chart of the

extreme temperatures that could be obtained by changing the pressure on the steam. The

switching unit came next and it apparently could control individual mirrors or groups of 8 or 16

or entire rows. Each unit was polled and allowed to move in accordance with its condition. The

next section of the console was a computer display that could show the qualities or conditions of

individual or multiple reflectors. The third screen showed the entire field of mirrors with colors

indicating modes (track or maintenance) and approximate attitude (upright or dropped). The

operator could call up one unit or a set on the second display and could change the position or

schedule for the collectors and the third screen would display the response. The operator

mentioned that in the morning, he usually sent the command to turn all the troughs to the east

several times because the controller, the motors or the dishes themselves could hang up.

I had arrived at two p.m. and the operator had plenty of time for my questions, but by

four p.m., he was starting to make adjustments to keep the system at peak production as the sun

started to lower. With the oil temperature cooling in the field, he would need to reduce

temperatures in the heat exchanger to keep differences in safety zones and to keep differential

pressures correct. The object was to maintain maximum power output for as long as possible by

making some adjustments to set points, turning down heaters, changing some valve settings in

order to keep a balance and eke out all the power left in the cogeneration process.

This is a picture from the Luz Engineering Corporation’s brochure. It is not the actual

panel at SEGS 1, but may be the control panel at one of their other 3 or 4 similar facilities in the

Mohave Desert.

A typical system containing gas, water, and steam, with turbine and generator⁵:

Appendix A: (Locomotive Controls - partial)

HOW THE LOCOMOTIVE OPERATES

1. The fuel pump is driven by an electric motor which, for fuel priming, uses current from

the storage battery. Once the engine is started and running, the fuel pump motor uses

current directly from the auxiliary generator. The fuel pump transfers fuel from the fuel

tank under the locomotive to the engine injectors.

2. The diesel engine is started by means of two series connected 32-volt cranking motors

that engage the flywheel ring gear when starting current is applied. The storage battery

supplies electric current to engage the starting pinions and rotate the cranking motors.

3. When the engine is running, it supplies mechanical power through shafts and couplings

to directly drive three electrical generators, the air compressor, motor and generator

blowers, and engine mounted lube oil and cooling water pumps.

4. The auxiliary generator charges the storage battery and supplies low voltage direct

current for the control and lighting circuits. The companion alternating current generator

furnishes power to the static exciter, various transducers, the three radiator cooling fans,

and the inertial separator blower motor. The main traction alternator supplies high

voltage AC to a power rectifier assembly which then delivers high voltage DC to the

traction motors for locomotive pulling power.

5. By means of the cab controls, low voltage circuits are established to actuate the engine

governor and the switchgear in electrical cabinets. This switchgear controls generator

excitation and distribution of power.

6. Six traction motors are located under the locomotive. Each traction motor is directly

geared to an axle and pair of driving wheels. These motors are located in two trucks

which support the locomotive weight and distribute it to the driving wheels.

7. The throttle electrically controls speed and power by actuating a governor mounted on

the engine and by tying the response of the locomotive power control system to throttle

position. The main generator converts the engine's mechanical power to electrical power,

which is then distributed to the traction motors through circuits established by the various

switchgear components in the electrical cabinet.

8. At locomotive start the throttle controls electrical devices that provide rapid power

response at a level consistent with smoothly controlled starting.

9. During heavy-drag low-speed operation, as well as at moderate and high operating

speeds, a load regulator operates to maintain power output at the specific level called for

by throttle position. This prevents the engine from being overloaded or under loaded.

10. The air compressor supplies, to the reservoirs, air under pressure used primarily for

the air brakes. The air brakes are controlled by the operator through suitable equipment in

the cab.

11. Except for manual operation of the cab controls, the locomotive operation is

completely automatic. Various alarms and safety devices will alert the operator should

any operating difficulties occur.

ENGINE CONTROL PANEL

The engine control panel, Fig. 2-3, is located at the upper left hand corner of the electrical

cabinet that forms the rear wall of the cab. This panel contains various switches and

alarm lights, along with a battery charging meter or light. Since all of these items will be

used at one time or another during operation, a brief description of their individual

functions is provided.

Note that an alarm bell accompanies alarm signal light indications. The bell will ring in

all units of a locomotive consist, but the light will come on only in the affected unit.

Fig. 2-3 - Engine Control Panel with Typical Extras

High Voltage Ground/Fault Light

The high voltage ground light indicates an electrical path to ground caused by insulation

failure, the presence of water, or an electrical arc. When the light is on, the locomotive

will not develop power and the engine will remain at idle. The light can be put out by

pressing the H.V. Grd. reset pushbutton. It is not necessary to isolate the unit, nor is it

necessary to have the throttle in idle while pressing the button.

When the high voltage ground light comes on for the third time after resetting, isolate the

affected unit.

CAUTION: Always report ground relay light indications to proper maintenance

personnel.

Excitation Limit Light

An electrical system relates generator excitation to main generator output and acts to hold

power at an acceptable level during various temporary conditions of locomotive

operation. Should this system lose calibration or somehow fail, there would be no

protection against abnormally high generator current.

An excitation limit relay senses high generator field current and acts to modulate it.

When this action occurs, generator current and voltage are held to acceptable values.

The excitation limit condition is normally temporary and no action is required by the

operator; however, if the condition persists, the green excitation limit light comes on, a

timing relay drops generator excitation and locks in the excitation limit circuit.

_____________________________

WHEEL SLIP CORRECTION

Instantaneous reduction of locomotive power together with automatic sanding functions

to correct wheel slip. After adhesion is regained, a timed application of sand continues

while power is smoothly restored. The system functions entirely automatically, and no

action is required by the locomotive operator.

Depending upon the seriousness of slipping, the wheel slip light may or may not flash on

and off as the wheel slip control system functions to correct the slips. However, the

IDAC wheel slip control system reacts so rapidly to correct minor slips that the wheel

slip light seldom comes on to indicate severe slips. The wheel corrective action is often

seen at the load current indicating meter as a steady reduction of load current below that

which is normally expected at full throttle for a given speed. Do not misinterpret this

power reduction as a fault. It is simply the wheel slip control system doing its job and

maintaining power at a level within the adhesion conditions established by track and

grade.

NOTE: Whenever possible, operation on grades should be at full throttle position.

Throttle reduction during wheel slip is recommended only when wheel slip conditions are

such that repeated wheel slip causes severe lurching that may pull a train apart. Such

severe conditions may indicate the need for a helper or the need to take the train up the

hill in two parts.

Appendix B: (Original Start of Term Paper)

The big day has come. The contractor finished the construction of my power plant and handed me the keys last night. Now it is very early the next day, just before sunrise. As the sun peeks over the horizon, I feel the breeze pick up from west to east. I wave to my employee at the wind vane. He disengages the mechanical brake and the blades start to spin lazily as the tail turns from the sun. My team and I look at each other, pleased with this first step. The 120 volt, single phase ac signal from the inverter is transmitted, initially, directly to the solar array. When the voltage is strong enough, motors turn the solar panels to the farthest east position. Once the panels are turned, additional power flows into the control facility I am about to enter.

Before, there was no power for lights. Now, as I open the door and engage the light switches, light fills the room. My three employees assigned to monitor control panels walk to their stations and press power switches. Lights blink on, gauges illuminate, needles bounce up and down and settle (some at center, some at the low end of the dials), and the refrigerator hums. It is a sign that the solar farm is producing 240 volts, 3 phase from the inverters. I press the “on” button for my computer and start a pot of coffee. If things work properly and there is a gentle wind and bright sunlight, as expected on an average day in the Mojave Desert, I will be able to produce 40 MWh which is enough for half the residences in the local community. The railroad has their locomotive power plants and the military bases have some wind and solar electricity generation. I don’t need to provide for local industries.

We do not have water to spare in the desert, so my back-up system is a natural gas generator that uses heated and pressurized air to turn a turbine which turns a generator that feeds the transformer.

The first control panel, “A”, is dedicated to my wind farm. The most important sensors measure wind speed at nacelle level for several towers. Beside and below those are the gauges for vane speed and direction for each unit. A smaller gauge indicates the angle of attack of the vanes. If the vanes do not match the wind direction within a few degrees, the operator can send signals to test the sensor and corrections to yaw (turn horizontally) the nacelle.

There is a temperature sensor in the nacelle to measure the generator’s heat. If too hot, the generator can be stopped or vented with louvers when sand is not flying too high. There is also a filter that can sense grit and prevent the louvers from opening. We don’t have enough water to run standard radiators.

(Then I started reading about angle of attack, tip speed ratio, power efficiency, cut-in and cut-out speeds, and tried to estimate the number of windmills I would need.)

Since I am using 220 volt regulators on site, I need meters to verify that output. I also want to watch the current as wind changes and to be wary of heat issues. Thermometers in the nacelles have sensors routed to the control panel. Current and voltage readings are on the reverse of the primary panel for the maintenance crew’s needs. The front side of the panel shows power only, to confirm that, relative to the wind speed, I hope to get at least 50% efficiency in power output.

Some of the functions that run in automatic, through the PLC, are blade angle adjustment (with stall (flat of blade) and furl (edge of blade) limits, turbine presentation/orientation, and generator speed…

Works Cited:

Internet Sites:

Locomotives:

¹Elwood, George. http://www.rr-fallenflags.org/manual/manual.html. Operator Manuals.

[“Tom Gardner provided me access to his Operator Manual collection…”]

Solar Power:

²BrightSource Energy. http://www.brightsourceenergy.com/how-it-works. How heliostats work. [BrightSource’s system uses … thousands of tracking mirrors, known as heliostats…]

³Global Energy Observatory. http://globalenergyobservatory.org/geoid/5306. SEGS 1

Statistics.

[SEGS I (Daggett) Solar Power Station USA is located at Daggett, California, USA. …with a design capacity of 13.8 MWe. It is operated by Solel. (Correction: SunRay Energy Inc.)]

⁴Bombay Ammonia & Chemical Company. http://www.bomammonia.com/deha.htm. Water

Treatment.

[N,N-DIETHYLHYDROXYLAMINE (DEHA) is used in Water Treatment Chemical Formulations for controlling corrosion in boiler… oxygen scavenging.]

General Power Plant System:

⁵Calpine. http://electricalandelectronics.org/wp-content/uploads/2008/10/gas-power-plant.jpg.2008: Calpine Corporation, Houston, Texas. Gas Turbine Combined Cycle: Power Plant System Schematic. [Calpine is North America's leading geothermal power producer.]

Bibliography (cont.)

Books, e-Books:

Power Plants:

Knowlton, Archer E., ed. Standard Handbook for Electrical Engineers, 7th Edition. 1941:

McGraw-Hill Book Company, New York, NY. [Section 3: Measurements. Section 10: Prime

Movers (Turbines and Generators). Section 12: Power System Electrical Equipment

(Switchgear, Relays, Excitation).] (Personal collection.)

Lindsley, David. Power-Plant Control and Instrumentation: The Control of Boilers and Hrsg

Systems. 2000: Institution of Electrical Engineers, Washington, D.C.

Raja, A. K., et al. http://site.ebrary.com/lib/devry/docDetail.action?docID=10323349. Power

Plant Engineering. 2006: New Age International, Daryaganj, Delhi, India.