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Techno-Economic Evaluation of Power Factor

Improvement Scheme for 11kV, 40kA, 72MW

Main Bulk Intake Substation

Yadavalli Venkata Sridhar and Fakher Al Zalzalah Kuwait Oil Company, Ahmadi, Kuwait

Email: {ysridhar, fzalzala }@kockw.com

Abstract—Techno – Economic Evaluation of power factor

improvement scheme for 11kV, 40kA, 72 MW main bulk

intake substation related electrical network that feeds

various far flung located facility substations consisting of

drive motors that operate in VFD mode & bypass mode.

Evaluation takes into consideration, load profile assessment

for maximum & minimum variation of electrical loads due

to through put capacity variation of facilities and facility

shutdowns for turnarounds. Evaluation covers ETAP

modeling, measurement of harmonic pollution at facility

substations and makes a selection of technology based on

market survey, and addresses the possible alternatives

pertaining to the location of PF improvement equipment in

the network and concludes with cost effectiveness of the

recommended solution. Advantages and disadvantages of

various models discussed.

Index Terms—power factor, Variable Speed Drive (VSD),

harmonics, cost

I. INTRODUCTION

Main Bulk in Take (MBIT) substation is rated for 72MW and feeds to Unit-1, Unit-2, Unit-3, Unit-4, Unit-5, Unit-6, Office complex and Workshop Facilities. If all these facilities operate at their full load capacity the power flow from Main Bulk Intake substation is expected to be in the range of 33MW.

The above stated existing facilities are expected to be further expanded in the various projects to the extent of approximately 10 MW. Further, 25MW is allocated for ongoing project Nos. 13 and 60.

Refer to the Figure. 1 for existing single line diagram

of MBIT substation.

Figure 1.

Manuscript received November 1, 2012; revised December 29,

2012.

A. Power Factor at 0.95 or Above at Main Bulk Intake

Substation

Power Factor is required to be maintained 0.95 or

above at the main bulk in take substation to meet the local

legislation requirements irrespective of type & nature of

load, variations in the load due to less through put &

shutdown activity of the facilities, harmonics presence

and expansion of facilities.

B. Type and Nature of the Connected Load

All units have non liner loads (Variable Speed Drives-

VSDs) that may operate in VSD mode or by pass mode.

The rating of the VSD drive motors is in the range of

1MW and 2.9 MW.

The loads of project nos. 13 & 60 will also be installed

with three (3) Variable Speed Drives each of size 7.1MW.

The other load composition consists of induction

motors of various sizes connected to 3.3kV and 440 volt

level along with associated transformers. Lighting loads

and small nonlinear loads such as battery chargers, UPS

systems, Computers and Switch Mode Power Supplies

(SMPS) are connected at the 440 volts level.

C. Presence of Harmonics and Harmonic Related

Information

As the nonlinear loads operate at all the voltage levels

of existing electrical network, the following assumptions

are made:

The main contribution of harmonics is expected to be

from Variable speed drives of Process Unit drivers.

Hence the physical harmonic measurements carried out at

the 11kV buses of units.

The capacity of UPS systems & Battery Charger(s) is

much less than 15% of the corresponding transformer

capacity at the 440 voltage level; hence the harmonic

presence is ignored.

Refer to Table 1 for existing Harmonics measurements

carried out at the 11KV level of each facility where such

Variable Speed Drivers are operating.

D. Maximum and Minimum Variations of Load and

Load Profile of MBIT Substation

An assessment is carried out for the load variation and

load profile of the MBIT substation. The following

loading conditions are identified:

International Journal of Electrical Energy, Vol.1, No.1, March 2013

37©2013 Engineering and Technology Publishing doi: 10.12720/ijoee.1.1.37-42

For maximum loading conditions, Unit 1, Unit-2,

Unit-3, Unit-4, Unit-5 and Unit-6 are operated

simultaneously to meet the production needs.

For minimum loading conditions, facilities Unit

-1, Unit-2, Unit-3,Unit-4, Unit-5 and Unit-6 are

operated in any of the following combinations:

may operate at reduced percentages of

their full capacities

may be under shutdown

operation of VSDs in the bypass mode

operating standby facilities such as

existing gas engine/turbine facilities in

lieu of electrical drives.

Power requirement of Workshop and Office

Complex may vary during the week days and

weekends as the activity levels keeps on varying.

Ambient temperature imposed load variations

(Summer and Winter variations in HVAC loads

and operating loads)

In all the above conditions the power drawn from

MBIT substation will vary consequently the power factor

also will vary in wide range. Moreover, abnormal

operating conditions of process facilities (such as process

trips both partially and totally) will also impose variations

in the power drawn from MBIT substation.

TABLE I.

Unit Maximum voltage

distortion

Maximum current

distortion

Before

VSD

operatio

n %TH

D

After VSD

operation

%THD

Before

VSD

operation

%THD

After VSD

operation%

THD

Unit 1 1.22% 2.81% 1.62% 2.49%

Unit 2 0.0% 1.1% 1.03% 1.98%

Unit 3 1.27% 1.39% 1.22% 2.53%

Unit 4 1.9% Not

Available

6.3% Not

Available

Unit 5 0.0% 2.96% 0.0% 2.02%

For the purpose of power factor study of MBIT

substation the following Maximum/ Minimum operating

conditions are considered:

Maximum Power condition:

Maximum power when all existing facilities are

operating : 33MW

Maximum power inclusive of future load

additions at the existing facilities: 40 MW

All existing VSD’s operate in VSD mode and

these VSD’ operate at high power factor.

(above 0.95 power factor)

Minimum Power condition:

Two of the VSD’s of existing Units might

operate in the BYPASS mode.

Any two facilities are under shutdown and all

other facilities are operating.

The future load of 25 MW (approximate) pertaining to

the projects 13 and 19, have VSD’s and these will be

operating at a very high power factor. Approximately less

than 3 MW auxiliary loads at the low voltage level

(including lighting) may operate depending on the

process needs.

E. Analysis of Data:

All VSD’s operate at very high power factor.

Operation of VSD’s at facilities will

improve the power factor at MBIT

substation.

The long cables between MBIT substation

and Operating Facilities contribute for

improved power factor due to capacitance

of cables. This also has the impact of high

voltage drop and high heat loss.

At MBIT substation, which is Point of

Common Coupling with Utility, in general

the power factor is in the range of 0.92 or

above, depending on the load factor of the

MBIT substation. If Gas turbines/ Gas

engines (stand by equipment for VSD’s) are

utilized the power factor is expected to go

very low (to the level of 0.83).

F. Assessment of Technologies and Applicability of

Technology

Broadly three methods of power factor improvement

methods are identified:

Capacitor banks (Conventional method of

compensating the power factor improvement)

Active filters [1] (New technology for harmonic

filtering and reactive power compensation)

Hybrid systems (Combined systems of Active

filter plus capacitor banks)

The use of Synchronous Condenser is not considered

in the evaluation due to the reasons, that the existing

electrical network does not use synchronous motors.

Based on the initial assessment of reactive power that

is required to be provided at MBIT substation and range

of harmonic presence, a preliminary conclusion was

arrived, that Capacitor banks (passive technology) will

suffice to carry out the required power factor

improvement.


38©2013 Engineering and Technology Publishing

Review of various industry experiences in connection

with use of capacitor banks is consistent with the above

assumption.

Capacitor banks method of power factor improvement

is well proven technology and it has cost advantage over

other latest technologies. This method has few

disadvantages like inrush current, possibility of switching

failures etc. However taking into the consideration the

technology versus costs involved the power factor

improvement with capacitor banks is preferred [2].

The Manufacturers (ABB, Siemens, Schneider, Eaton

etc.) were assessed for the product range and their

capabilities.

Although the cost of passive capacitors is low in

comparison to other options (Active & Hybrid systems)

at this juncture, as the technology progresses further, the

relative cost between passive capacitors & other systems

is likely to become narrow in near future.

It is technically possible to compensate VAR at

132KV level of MBIT however practically this is not a

suitable solution as one giant capacitor bank needs to be

installed and the step sizes would be extremely large and

would not follow the load profile of the system very well

and cost of such a system is very expensive as the

associated 132KV switchgear is also required.

G. Possible Methods for Power Factor Improvement

Power factor improvement can be carried out in many

ways, such as central compensation, group compensation

and individual load compensation etc.

In the present application individual compensation is

not a good solution due to the multiplicity of drives and

implications of installation of many low voltage level

capacitors. Installation of load end capacitors is not

possible due to hazardous area classification requirements.

Group compensation for two or three facilities put

together is also ruled out due to the reasons of shutdown

schedules of the facilities are not concurrent and do not

match.

VAR compensation at High voltage and/or low voltage

levels of the facilities and compensation at MBIT is

studied in depth for their technical and economic

feasibility in the evaluation.

H. Defining Objectives of VAR Compensation

It is essential to define the objectives of the VAR

compensation very clearly to arrive at a solution. VAR

Compensation objective could be one of the below or

combination:

For compliance to Utility undertaking stipulation

for maintaining the power factor

For improvement of voltage profile & improve

voltage regulation

To relieve the system capacity to meet the

additional load demand

To reduce system losses

To have the combined benefits of all above

Based on the objective, approach and method for VAR

compensation will vary. In the subject evaluation,

compliance to Utility undertaking stipulation to maintain

0.95 at the point of common coupling along with

shutdown requirements of the operating facilities and

transfer of more power on the existing long distance

cables is defined as the objective.

II. SOLUTION AND ETAP SYSTEM STUDIES

Keeping the above objective in focus, selection of

capacitor banks as the equipment for VAR compensation

of MBIT network, the optimum placement of capacitor

banks is carried out the with support of ETAP software.

All the below mentioned three (3) models were studied in

the ETAP software in the steady state mode. Multiple

ETAP runs were carried out in the load flow studies

mode to vary size and location of the capacitor banks for

obtaining near optimum solutions.

A. Identifying the Models

With a view to identify best possible solution (s) for

Power Factor Improvement, Three (3) number models

were developed and studied for technical and financial

comparison purposes [5].

Model No.1: Determine the size and install the Power

Factor improvement at MBIT substation 11 kV bus bar.

(This is in line with objective i. mentioned above)


Factor Improvement at 11kV buses of Unit-1, Unit -2,

Unit-3, Unit-4, Unit-5 and also at MBIT substation (This

is also in line with objectives i. and ii. along with load

variations due to shutdown schedules).


Factor Improvement systems at 3.3kV levels & 440 volts

levels of Unit-1, Unit-2, Unit-3, Unit-4, Unit-5, Unit-6,

Office Complex and Workshop. (This is in line with all

the combined objectives stated above)

B. Evaluation of Model No:1

In this model two capacitor banks (2 X 5,200KVAR)

are required to be installed at 11kV bus of MBIT

substation.

This model meets the Utility stipulation of maintaining

the power factor improvement at 0.95 for load of 40MW

(ie. existing load plus future load on MBIT substation).

This scheme of power factor improvement is of low cost,

approximately $1,050,000/- and cheapest of three models

and easy to install at MBIT substation 11kV bus due to

the following:

Two spare breakers need to be allotted for

feeding the Capacitor bank that are readily

available in the panel line up.

Existing Floor space can be used for installing

the Capacitor bank panels

Shut down of the facilities is not required.

Requires least time for implementation.

Makes available additional KVA at MBIT

substation for future use (4,181KVA)

However this model has following disadvantages:

Number of steps of switching will be wide and

broad. Because of wide step size there is a

possibility a load bank may not be able to follow



load variations. In order to follow the load

variations, if the number of steps is increased,

this might increase the foot print of the overall

equipment.

Load variations that would happen due to the

shutdown of units cannot be totally addressed by

the model.

Reassessment of existing HVAC capacity of the

substation is required. Additional air

conditioning equipment will be required.

In this method of power factor improvement scheme,

all downstream equipment and cables will be subjected to

reactive loading and heat losses will continue to be as

earlier. However there is no impact on the electrical

efficiency of the network and power factor will not be

maintained at 0.95 at the unit substations fed by MBIT.

A preliminary steady state short circuit analysis

indicates that existing 11KV switchboard rating of 40KA

board is sufficient. Further, critical transient analysis

study is needed for analyzing the out rush current into the

faulted bus conditions to assess the impact of peak

making current rating of the board with the installation of

capacitor bank.

C. Evaluation of Model No:2

Total of 6 capacitor banks rated for 11kV are

considered in this model. One (5000KVAR) capacitor

bank at MBIT substation and one capacitor bank each at

Unit-1, Unit-2, Unit-3, Unit-4 and Unit-5 (1250KVAR

each) are required to be installed. Total capacitors will

deliver into the network 11,250 KVAR.

This Model No: 2 meets the Utility stipulation of

maintaining the power factor at 0.95 for load of 40MW at

MBIT Substation and also at each of 11KV bus of Unit

substations. In this Model No.2 existing lengthy cables to

each unit will be relieved of reactive current thereby

reducing the voltage drop & heat losses enabling transfer

of more power (over and above the existing power

transfer) on the existing cables within the stipulated

voltage drop of Company standard in order to meet the

future load additions at each of the Units. This model

releases the capacity at MBIT substation and makes

available additional 3968 KVA approximately at MBIT

substation level. In some cases such as Unit-2, the voltage

will be improved in this model due to installation of

power factor improvement equipment at 11KV bus of

Unit-2.

This Model No: 2 require one feeder breaker at each of

the unit 11KV bus and require space at each unit

substation for installation of 11KV capacitor banks. The

cost of this Model No: 2 is expected to be in the range of

$ 1,680,000/- . The advantages of Model No: 2 are as

follows:

The 11KV buses at Unit’s also will be

maintained to close 0.95 power factor for a load

of 6 to 6.5MW approximately.

On the existing cables (linking MBIT & Unit

substations) more power can be transferred

maintaining the percentage voltage drop within

the relevant standards.


substation for future use (3,968KVA)

As the VAR compensation is done at the unit

substation, this gives better power factor control

at MBIT to maintain 0.95.

The disadvantages of Model No: 2 are as follows:

Total Six (6) capacitor banks are required

Space requirement is more and floor space has

to be created.

Method 2 costs more in comparison to that of

Model no1 and 3.

Shutdown is required at each of the panel.

D. Model No.3 Evaluation Results

In this Model No: 3 capacitor banks at 3.3KV

(600KVAR, 1 no.) bus and 440 volt (300KVAR, 2 nos.)

bus are considered in at Unit-1, Unit-2, Unit-3, Unit-4,

Unit-5. Further capacitor banks are considered at 440 volt

buses of Unit-6 (200KVAR,1no.), Workshop and Office

Complex at 440V level (250KVAR,1no.) and one

capacitor bank at MBIT substation(3000KVAR) for any

major change in load profile and non-availability of

capacitor banks at downstream substation due to

capacitor failures. Total capacitors will deliver into the

network 11,750 KVAR.

This Model No: 3 meets the Utility stipulation of

maintaining the power factor at 0.95 for 40MW load. In

total, 22 capacitor banks are required in this model. This

scheme releases 5052 KVA at MBIT substation and

releases the capacity of 3.3 KV & 440 volts transformers,

cables etc. at each of installed location, thereby reducing

the heat losses leading to energy efficient network. As

such, availability of additional capacity from transformer

(s) is not useful as there are technical limitations at the

11KV network level.

This Model no: 3 requires feeder breaker at each

voltage bus of the Unit (3.3KV bus and 440 volts buses)

and requires space for capacitor bank installation at each

of the unit for installation and existing floor space. The

cost of this Model no: 3 is expected to be in the range of

$ 1,395,000/-.

The advantages of Model 3 are as follows:

This model complies with the basic principle of

VAR compensation which shall be carried to

closer to the load.

3.3KV & 440 volts buses at Units also will be

improved and maintained at 0.95 power factor.

On the existing cables more power can be

transferred maintaining the percentage voltage

drop with in the relevant standards.

Because of distributed capacitor banks at all

voltage levels, system overall heat dissipation

losses reduce leading to the energy efficient

network.


substation for future use (5052 KVA)

Cost is less in comparison to Model No.2

The disadvantages of Model No: 3 are as follows:

Twenty two (22) capacitor banks are required in

comparison to Model no.1 and Model.no2.

Shutdown is required at each of the switchboard.



Additional capacity released from 3.3KV and

440 volts transformers is not useful as this

capacity is not sufficient to power up expansion

facilities due to limitation of feeders and

limitations of expansion of 3.3KV and 440 volts

switchboards. Furthermore Units are expanded

by taking 11KV input to a new a localized

distribution substation for the purpose of facility

expansion.

E. Verification of Above Information Through

Internationally Reputed Manufacturers

A request for budgetary quote was forwarded to

internationally reputed North American and European

manufactures with all the relevant & complete data along

with defined objective. The approach adopted by the

reputed manufacturers also matched with the above

analysis. The budgetary quotes prices vary from each

other in a very wide range. The cost figures mentioned

above is based on budgetary costs taking other associated

costs.

Table 2 is brief cost comparison chart for the three

models in terms US dollars ($):

TABLE II.

S.No.

Description of Item

Model No.1

Model No.2

Model No.3

1 Capacitor

cost 517,500/-

1,084,173/-

690,000/-

2 Cabling works

22,500/- 29,400/- 30,000/-

3 Additional

feeder panels 150,000/- 150,000/- 255,000/-

4 Civil&HVAC

Works 300,000/- 300,000/- 150,000/-

5 Installation

cost 60,000/- 116,427/- 270,000/-

6 Total Cost 1,050,000/

- 1,680,000/

- 1,395,000/

-

F. Impact of Harmonics Present in the Existing

Network of MBIT Substation on the Proposed

Capacitor Banks:

The Budgetary quotes have taken into consideration

the harmonics present in the network and accordingly

each of the capacitor banks is provided with detuned

reactors. The detuned reactor in the capacitor bank circuit

ensures that resonance conditions are avoided,

consequently the harmonic currents will not flow through

the Capacitor Banks. The detuned capacitors also ensure

to limit the inrush currents to help improve the switching

transients. 7% detuning reactors will be part of capacitor

banks. The 7 % detuning reactor detunes the bank at

189Hz (below 4th

harmonic and above the 3rd

harmonic).

As the Capacitor banks with detuned reactors are meant

for power factor improvement only and do not perform

any harmonic filtering function. Hence with the capacitor

bank installation the harmonic pollution levels will not

change [3] and [6].

G. Capacitor Switching and Related Aspects

The capacitor switching operation (energizing, de-

energizing, fault clearing and reclosing etc.) is associated

with the following technical issues [2]:

Restrike due to excessive voltage across the

circuit breaker blades

Energize capacitor bank when another capacitor

bank is charged (known as back to back

switching)

Voltage magnification in low voltage capacitor

banks, under certain conditions when the HV

Capacitors are switched on

Prestrike arcing in the electro mechanical

switching devices even before the circuit breaker

is closed

Outrush currents that flow during the bus fault

condition

Over voltages may occur if the system is sharply

tuned at one dominant harmonic produced by the

inrush current.

When capacitor bank is taken into service the inrush

currents that flow through the network can cause

protection problems also. The capacitor bank switching

takes place in the electrical network very often if the load

variation is frequent. Every time the switching action

takes place for power factor correction, the travelling

waves will be generated in the network that could (may)

damage high/ low voltage networks of existing Variable

Speed Drives, UPS systems and other existing electrical

equipment [4].

Capacitor switching can be implemented either

through the static switching method or electro mechanical

switching method:

Static switching method of capacitor banks: This

method eliminates the switching transient related

problems and switching can be done in 10ms.

This type of switching systems is quite costly.

For example 5500 kVAR automatic Reactive

power compensation consisting thyristor

switched Capacitor banks IP 23 indoor

application along with its associated transformer

might cost in the range of $837,660/- excluding

the costs associated for cabling, feeder panels,

HVAC and installation.

Electro- mechanical switching: Conventional

electro- mechanical switching breakers with

improved characteristics that suit to capacitor

banks switching are employed in this method. In

comparison to Static switching this switching

method is cheaper and the transient issues are

dealt with separately.

After a detailed interaction with the manufacturers it

has been established that electro-mechanical switching of



capacitor banks will not pose any threat to the operation

of the Variable Speed Drives and related control

networks. Based on this clarification electro mechanical

switching is considered and recommended in the subject

study.

The specification for Circuit breakers for capacitor

switching can be specified with particular attention to

Transient Overvoltage, Transient Recovery Voltage and

Surge Arrester in accordance with IEC standards.

III. RECOMMENDATION

It is recommended to run all the VSD’s at their full

load, as the power factor at MBIT can be maintained

above 0.91 without any VAR compensation. As the

variations of the loads cannot be controlled due to

shutdowns, planned or unplanned, it is recommended to

improve the power factor at 11kV buses of unit

substations and MBIT.

Based on the above evaluation, Model Number No. 2

is preferred and recommended. This Model number No. 2

is useful for implementation of power factor

improvement scheme for substations where the following

situations are encountered:

Type and nature of the load varies and the

details of load are not available at the time of

PF scheme implementation.

Staggered project schedules will impose a

situation that centralized compensation may

not be feasible.

Selection of centralized capacitor bank with unknown

load and network parameters is generally not

recommended.

Model no.2 recommendation is based on a compromise

or tradeoff between cost and performance based on the

objective defined.

Utility undertaking did not identify the penalty that

will be levied in the event of noncompliance to stipulated

power factor. It is understood and assumed that the

payback period may vary in the range of 3 to 5 years

based on the quantum of penalty that will be levied by

Utility undertaking.

ACKNOWLEDGMENT

The authors wish to thank Ms. Ameena Rajab Team

Leader (Design) and Mr. Jasim Al-Quraini (Team Leader

Power Management) for their support.

REFERENCES

[1] B. Singh, K. A. Haddad, and A. Chandra, “A review of active filter for power quality improvement,” IEEE Transactions on

Industrial Electronics, vol. 46, no. 5, October 1999.

[2] R. Natarajan, “Power system capacitors”.

[3] M. Mcgranaghan, S. Peele, and D. Murray, “Solving Harmonic

resonance problems on the medium voltage system,” in Proc.

CIRED- 19TH International Conference on Electricity Distribution. [4] S. J. Kulas, “Capacitor switching techniques,” in Proc.

International Conference on Renewable Energies and Power

Quality ICREPQ, Spain 15th 17th April 2009.

[5] K. Ellithy, A. Al-Hinai, and A. Moosa, “Optimal shunt capacitors

allocation in distribution networks using generic algorithm – Practical case study,” International Journal of Innovations in

Energy Systems and Power, vol. 3, no.1, April 2008. [6] M. Hamoudi and H. Labar, “Compensation capacitors effect on

harmonics distribution in electrical networks,” European Journal

of Scientific Research ISSN 1450-216X, vol. 27, no. 3, pp 392-399, 2009.

Yadavalli Venkata Sridhar is a Specialist Electrical Engineer

associated with Hydro-Carbon Industry for the past 34 years. He is a

post graduate engineer with specialization in Electrical Machines and Industrial drives.

Fakher Al Zalzalah is a Specialist Electrical Engineer associated with

Hydro Carbon Industry for the past 25 years and serving Kuwait Oil

Company in the capacity of Specialist In-charge for Electrical and Instrumentation Systems.



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