Power System 2002 Conference: Impact of Distributed Generation CLEMSON UNIVERSITY ELECTRIC POWER RESEARCH ASSOCIATION 1 Distribution Capacitor Placement

Power System 2002 Conference: Impact of Distributed GenerationCLEMSON UNIVERSITY ELECTRIC POWER RESEARCH ASSOCIATION

1

Distribution Capacitor Placement With Distributed Generation Concerning

Voltage Drop Reduction

Clemson University

Clemson, SC, USA

March 13, 2002

Thomas M. Haire Dr. Adly A. Girgis


2

Topics

• Background Information

• Procedure and System

• PQ Solution

• PV Solution

• Solution Comparison

• Conclusion


3

Background

• Sizing and placement standard “two-thirds rule.”– A capacitor may be placed two-thirds the length

of the line and may be two-thirds the size of the reactive load.

• Does not hold for economic consideration.– This paper desires to make the voltage profile as

flat as possible.


4

“Two-Thirds Rule”

x

n i

ni

2 1

2 1I

I

nC iS

2

2 1

Where,xi distance from substation to ith capacitor

n number of capacitorsIci capacitor load size (Amps or VARs)

1, to maximize peak power loss reductionIs reactive load (Amps or VARs)


5

Procedure

• Analyze using Newton-Raphson LoadFlow• PQ Solution

– Specify generator real and reactive power.– Allow generator voltage to float.– Design capacitors for constant generator power

factors of 1, 0.9, 0.8.– Capacitors placed and sized according to “Two-

Thirds Rule.”


6

Procedure (cont.)

• PV Solution– Specify generator real power and voltage.– Allow generator reactive power to float

between 0.8 and 1.– Design capacitors for estimated generator

power factors of 1, 0.9, 0.8.– Capacitors placed and sized according to

“Two-Thirds Rule.”


7

System Studied• 300 A circuit

• (From observed conditions)

– Zone 1, 6 mi, 4.374 MW, evenly distributed

– Zone 2, 0.75 mi, 1.458 MW, evenly distributed

– Power factor is 0.9 lagging.

• Wire– 477 ACSR, 18/1 str.

• DG– 2 Natural gas engines

– 1.062 MW each

0-6.0 mi.4.374 MW

6.0-6.75 mi. 1.458 MW

DG DG 7.5 mi.

SS


8

PQ Solution


9


10

Voltage Conclusions• The more reactive power produced by the DG,

the less voltage drop for any given number of capacitors.

• Excluding unity power factor at all loads.

• Voltage Support from both real and reactive power flowing from both directions.

• In practice, design generator settings and capacitor placement for DG producing maximum reactive power.


11

Power Reduction Conclusions

• Real and reactive power consumed by the wires is the least when all loads have capacitors and DG is operated at unity power factor.

• This formation will produce the least current flowing in the wires.


12

PV Solution


13


14

Voltage Conclusions• Best profile is a result of designing the

capacitors as if no DG was present.

• This would be a design for the DG power factor to be 1; however, the DG will not operate at unity power factor.

• In practice, use the “Two-Thirds Rule” as normal and let the DG chase the power factor of the system.


15

Power Reduction Conclusions• The real and reactive power loss decreases

as the number of capacitors increases.• Most graphs show no true trend to the

change in power as a result of design changes related to different DG power factors.

• In designs other than unity power factor, the load flow had difficulties finding a solution without lowering the DG voltage.


16

Solution Comparison

• The PV solution provided the better solution for voltage reduction.

• This results from not forcing any source in the system to supply a specific power.

• In these tests, the DG operated near the low power factor setting as in the PQ solution.


17

Conclusions• The more reactive power produced by the

generator, the flatter the voltage profile.• If the real and reactive power from the

generator are kept constant, design the capacitors for max. reactive power from the generator.

• If the voltage and real power are to be kept constant, design the capacitors as if the DG does not exist. Then allow DG to “chase” the system reactive power.


18

Questions?

Thank You!

Thomas M. Haire

[email protected]

(864) 656-7219

Documents

Power System 2002 Conference: Impact of Distributed Generation CLEMSON UNIVERSITY ELECTRIC POWER RESEARCH ASSOCIATION 1 Distribution Capacitor Placement