Minnesota Power Systems Conference
November 22-4, 1999
Shunt Capacitor Bank
Switching Transients:
A Tutorial and Case Study
G. Gopakumar,
Gopakumar, H. Yan,
Yan, B. Mork
Michigan Technological University
and
K. K. Mustaphi
Northern States Power Company
Capacitor Bank Switching
• Overview of recent installations at NSP
• Observations and trends
• Study work that must be done
• Tutorial on capacitor bank switching
• Brief overview of 115115-kV case study
• Comments
Page 1
MMTU Phase I
(Increased Power Transmission)
Station
Voltage MVAR Configuration
Red Rock
115 kV
240
3 x 80
Kohlman
Lake
115 kV
240
3 x 80
MMTU Phase II
(Increased Power Transmission)
Station
Voltage MVAR Configuration
Forbes
500 kV
600
2 x 300
400 MVAR Thyristor Switched
Page 2
MMTU Phase III
(Increased Power Transmission)
Station
Voltage MVAR
Configuration
Prairie
115 kV
480
12 x 40 MVAR
Little Fork
230 kV
240
6 x 40 MVAR
Sheyenne
115 kV
200
5 x 40 MVAR
Roseau
230 kV
80
2 x 40 MVAR
Others
(Voltage/VAR Support)
Station
Voltage MVAR
Configuration
Eau Claire
Parkers Lake
Aldrich
161 kV
115 kV
115 kV
320
240
240
4 x 80 MVAR
3 x 80 MVAR
2 x 120 MVAR
Elm Creek
115 kV
120
1 x 120 MVAR
Elliot Park
115 kV
80
1 x 80 MVAR
Rogers Lake
115 kV
240
3 x 80 MVAR
Page 3
Others, Cont’d
(Voltage/VAR Support)
Station
Voltage MVAR Configuration
Koch Refinery
Split Rock
Cherry Creek
161 kV
115 kV
115 kV
80
160
40
1 x 80 MVAR
2 x 80 MVAR
1 x 40 MVAR
Lk Yankton
115 kV
40
1 x 40 MVAR
Buffalo Ridge
34.5 kV
80
Total Dist.
69 kV
14
1 x 14 MVAR
Traverse
Trends
• At least 4 GVAR installed in NSP system in
recent years.
• Most installed at 115115-kV and above
• LOTS of stored energy in cap banks
• Higher X/R ratio means less damping than is
observed at lower voltage levels.
• More concern about switching transients
Page 4
Types of Studies Needed
• Inrush/Outrush
Inrush/Outrush Current
• Transient Overvoltage (TRV)
• Voltage Magnification (Interaction with
capacitors on nearby distribution system)
• Existing Equipment Ratings
– Breakers
– Surge Arresters
• New Equipment Ratings
– Breakers
– Surge Arresters
– Inrush/Outrush
Inrush/Outrush CurrentCurrent-Limiting Reactors
• Current Transformer High Secondary Voltage
Getting Started Useful Reference Information
• A. Greenwood, Electrical Transients in Power Systems
• IEEE Std. C37.012C37.012-1979
• IEEE Standards Collection on Power Capacitors
• IEEE Tutorial - Application of Power Circuit Breakers
• IEEE Special Publication - Modeling and Analysis of
System Transients using Digital Programs
• Other misc.
misc. papers
Page 5
Learning the Basic Concepts of
Capacitor Bank Switching
34.534.5-kV PerPer-Phase System
1 - Energization Inrush
CB1 and CB4 Closed, Close Switch S1.
Page 6
Energization Inrush - First Bank C1
i(t ) =
V (0)
sinω0t
Z0
L
C1
Z0 =
ω0 =
1
LC1
S i n g l e B a n k E n e r g i z a t i o n - In r u s h C u r r e n t ( A ) vs . t i m e ( m s )
3500
2625
1750
875
0
-8 7 5
-1 7 5 0
-2 6 2 5
*10
-3 5 0 0
0
10
( fi l e S K _ C 1 . p l 4 ; x - va r t )
20
30
c : S E Q U IV - B U S
40
50
60
70
-3
80
Peak Current = 3041 Amps, Natural Frequency = 500 Hz
Energization Inrush - First Bank C1
i(t ) =
6
V (0)
sinω0t
Z0
Z0 =
L
C1
1
LC1
ω0 =
S i n g l e B a n k E n e r g i z a t i o n - B u s V o l t a g e ( V ) vs . t i m e ( m s )
*10
4
4
2
0
-2
-4
*10
-6
0
10
( fi l e S K _ C 1 . p l 4 ; x - va r t )
20
v: B U S
30
40
50
60
70
Bus Voltage: Peak Voltage = 1.87 per unit
Page 7
-3
80
2 - Back-to-Back Energization
CB1, CB4, S1 Closed. Close Switch S2.
Back-to-Back Energization
i (t ) =
1
V (0 )
LB ω =
sin ω 01t Z 01 =
01
LB C EQ
C EQ
Z 01
1500
C EQ =
C1C2
C1 + C2
B a c k - t o - B a c k In r u s h - C u r r e n t i n t o C 2 ( A ) vs . t i m e ( m s )
1000
500
0
-5 0 0
-1 0 0 0
-1 5 0 0
1 6 .5
( fi l e S K . p l 4 ; x - va r t )
*1 0
1 7 .0
c :S W 1
1 7 .5
1 8.0
1 8 .5
-3
1 9.0
-S W 2
Peak Current = 1400 Amps, Natural Frequency = 9.4 KHz
Page 8
Back-to-Back Energization
i (t ) =
4
1
V (0 )
LB ω =
sin ω 01t Z 01 =
01
LB C EQ
C EQ
Z 01
C EQ =
C1C2
C1 + C2
B u s V o l t a g e D u r i n g B a c k - t o - B a c k In r u s h - B u s V o l t a g e ( V ) vs . t i m e ( m s )
*10
4
3
2
1
0
-1
-2
-3
*10
-4
0
10
( fi l e S K . p l 4 ; x - va r t ) v: B U S
20
30
40
50
-3
60
Peak Bus Voltage = 1400 Amps
3 - Outrush Transient
i(t ) =
V (0 )
sin ω 02t
Z 02
Z 02 =
LF
C1
ω 02 =
1
LF C1
CB1, CB3, CB4, S1 Closed. Fault on Feeder or Bus.
Page 9
4 - Voltage Magnification
CB1, CB2, CB4 Closed. Close Switch S1 or S2.
Voltage Magnification
ω0 =
1 .5
1
=
L2C LV
1
L1C1
V o l t a g e M a g n i fi c a t i o n - D i s t r i b u t i o n B u s V o l t a g e ( V ) vs . t i m e ( m s )
*1 0
4
1 .0
0 .5
0 .0
-0 . 5
-1 . 0
*10
-1 . 5
0
10
( fi l e S K . p l 4 ; x - va r t )
20
v: X F S E C
30
40
50
60
70
Peak Distribution Bus Voltage = 1.76 per unit.
Page 10
-3
80
5 - Transient Recovery Voltage
CB1 Closed, Fault on Bus. Open CB1 to Clear Fault.
Transient Recovery Voltage
Oscillation between Circuit Breaker Bushing
Capacitance and Source Inductance.
4 .5
R e c o ve r y V o l t a g e - V o l t a g e o n S o u r c e S i d e o f C B 1 ( V ) vs . t i m e ( m s )
*1 0
4
3 .0
1 .5
0 .0
-1 . 5
-3 . 0
*10
-4 . 5
30
32
( fi l e S K . p l 4 ; x - va r t )
34
v: S E Q U IV
36
38
40
42
-3
44
Peak Bus Voltage = 1.4 per unit, Frequency = 5 KHz.
KHz.
Page 11
Split Rock - A Case Study
2 - 80 MVAR 115-kV Banks
The Study Zone
• MultiMulti-Port 6060-Hz Thevenin Equivalent
to model surrounding system
• Transformers - coupled RR-L with core
saturation and bushing capacitances
• Transmission Lines: distributed parameter for
long lines. CoupledCoupled-Pi for very short sections
• Capacitors with parallel dissipation resistors
• RLC CoupledCoupled-Pi for Buswork
Page 12
Single Bank Energization
Inrush Reactor Sizing
4400
Inrush
4350
Ipeak, Amps
4300
4250
4200
4150
4100
4050
0
0.1
0.2
0.3
0.4
0.5
Reactor Size, mH
Page 13
0.6
0.7
0.8
0.9
Back-to-Back Energization
Capacitor Outrush Current
Page 14
Outrush Reactor Sizing
1.8e+08
Outrush with Bank#1 in Service
Outrush with Bank#1,2 in SErvice
Definite Purpose Circuit Breaker
General Purpose Circuit Breaker
Ipeak * Frequency, Amps*Hz
1.6e+08
1.4e+08
1.2e+08
1e+08
8e+07
6e+07
4e+07
2e+07
0
0
0.1
0.2
0.3
0.4
0.5
0.6
Reactor Size, mH
0.7
0.8
0.9
Voltage Magnification Summary:
Peak Distribution Bus Voltages
Peak Voltage
on Bus#1/2
Single-Bank Energization
Back-to-Back Switching
21
20
19
18
17
16
1
3
2
2
Cap Bank on Bus#1
3
1
4
Page 15
0
Cap Bank on Bus#2
Other Concerns
• Statistical studies of peak currents and
voltages in synchronous closing schemes
• Failure of synchronous closing scheme
• Time delay required to discharge banks in
cases where reclosing is applied. Nonlinear
voltage ringdown in cases when discharged
through voltage transformers.
• Unintentional rere-energization of bank before it
has discharged. Worst case: energize when
source voltage is opposite the polarity of the
trapped charge.
• Changes in frequency response of system
due to addition of capacitor banks.
CLOSING COMMENTS
• Studies performed over last 10 years and
equipment specified seem to be correct.
• Ferroresonance involving the banks and
regulator transformers has been observed for
short periods of time. Nonlinearity of
transformer makes it hard to predict. Some
work in this area may be in order.
• Simulation results are only as good as the
model. Transmission line and transformer
models must be continually improved.
• Gathering equipment parameters can be most
timetime-consuming part of simulation. Ask for
complete equipment parameters when writing
new equipment specifications.
Page 16
COMMENTS?
QUESTIONS?
Page 17