Electric Utility Solutions: Voltage Regulation

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Voltage Regulation
Bill Kersting
What is to be presented
• ANSI Voltage Standards
• Methods of Voltage Regulation
• Example of Regulator Settings
• Example of Placement of Regulators
The ANSI Voltage Standards
• Range A
– Nominal Utilization Voltage =115 volts
– Maximum Utilization Voltage =126 volts
– Minimum Service Voltage =114 volts
– Minimum Utilization Voltage =110 volts
• Range B
– Nominal Utilization Voltage =115 volts
– Maximum Utilization Voltage =127 volts
– Minimum Service Voltage =110 volts
– Minimum Utilization Voltage =107 volts
Tools for Voltage Regulation
• Shunt Capacitors
• Step-Voltage Regulators
• Substation Load Tap Changing
Transformers
Distribution Line Voltage Drop
R jX
Load
+
-
V
S
+
V
L
-
I
I
RI
V
S
V
L
jXI
ZI
0
Im(ZI)
Real(ZI)
( ) ( )
Real Real
drop S r
drop L L L
V V V
V Z I R I jX I
= −
≈ ⋅ = ⋅ + ⋅
• Impedance (Z) and current (I) must be computed
as accurately as possible.
• Impedance best computed using Carson’s
Equations
• Current is a function of “load.”
• If Z and I are not computed accurately, all bets
are off on the calculated system voltages.
V
drop
= Real(ZI
L
)
Capacitor Voltage Rise
R X
Load
+
_
S
V
+
_
L
V
L
I
L
RI
L
jXI
( ) Real
L
ZI
( ) Im
L
ZI
L
V
L
ZI
S
V
δ
θ
C
I C
RI
C
jXI
'
S
V
C
I
L C
I I +
( ) ( )
'
Real Real
rise S S
rise C C C
V V V
V Z I R I jX I
= −
≈ ⋅ = ⋅ + ⋅
ANSI Range A Critical Voltages
Last
Customer
First
Customer
Reg
Output
126
124
122
120
118
116
114
Sub Reg
128
Laterals
Voltage Drop Assumptions
• 1 Volt drop on the service drop
• 2 Volt drop on the secondary
• 3 Volt drop through the transformer
• Minimum Voltage at the Transformer
Primary Terminals will be 120 volts.
Voltage Profiles
Last
Customer
First
Customer
Reg
Output
126
124
122
120
118
116
114
Point
Reg.
Last
Xfm
Min Load
Max Load
Sub Reg
128
Laterals
Step Voltage Regulator
Type B Step Voltage Regulator

R
L

Series
Winding
Reversing
Switch
PT
Control
Control
CT
+
-
SL
-
+
Shunt
Winding
S
L
2
N
Preventive
Autotransformer
1
N
S
V
L
V
S
I
L
I
The Step Voltage Regulator Model
2
1
1
where: 1
L S
R
L R S
R
V V
a
I a I
N
a
N
= ⋅
= ⋅
= 
1 0.00625 Tap
R
a = ⋅ 
One tap change =0.75 V change on 120 V base
Three Phase Voltage Regulator Model
| |
L
abc
I
| |
S
abc
I
| |
S
abc
V
| |
L
abc
V
| | | |
| | | |
| | | |
S R L
abc abc
S R L
abc abc
L R S
abc abc
V a V
I d I
V A V
= ⋅
= ⋅
= ⋅
Voltage Regulator Model Matrix
| |
| | | | | |
_
_
_
1
0 0
0 0
0 0
R a
R R b
R c
R R R
a
a a
a
d A a

(
(
=
(
(
(
¸ ¸
= =
Compensator Circuit
+
-
+
-
line line
R X j +
Reg. Point
drop
V
reg
V PT
N :1
1:1
p s
CT CT −
R
V
Voltage
Relay
c
I
c c
R +jX
line
I
+ -
hi low
kVLL kVLL −
rating
MVA
Control Panel
Control Circuit
LineDrop
Compensator Relay
Voltage Time
Delay
Motor
Operating
Circuit
Control Current Transformer
LineCurrent
Control Potential Transformer
Regulator Control Settings
• Voltage Level – voltage to hold at the regulation
point
• R and X setting (volts) – Equivalent impedance
from the regulator to the regulation point
• Time Delay – time after a tap change required
before the tap is changed
• Bandwidth – allowed deviation from the set
voltage level
Equivalent Line Impedance
For , ,
_

where: =actual line-to-neutral voltage output of regulator
_ =actual line-to-neutral voltage at the regulation point

i i
i
i
i a b c
Vreg Vreg pt
Zline
Ireg
Vreg
Vreg pt
Ireg
=

= Ω
=actual line current leaving the regulator
Compensator Impedance
Volts
where: equivalent line impedance in Ohms
CT =current transformer primary rating
N potential transformer ratio =
120
pt
rated
pt
CT
Zcomp Zline
N
Zline
VLN
= ⋅
=
=
Bandwidth
Bandwidth =2 V
123
122
121
V
o
l
t
a
g
e

L
e
v
e
l
T ∆
Modified IEEE 13 Node Test Feeder
1
13
2
3
5
6 7
8
9
14
10
12 11
4
Modifications
• Line 4-12 changed to phases B-C
• Transformer 6-7 changed to Ungrounded Wye – Delta
• Load at Node 7 converted to Delta-PQ
• Load at Node 8 converted to Delta-PQ
• Load at Node 14 changed to phase B with constant Z
load
• Load added at Node 5 phase c: 300 + j145.3 kVA
• Interchange phase a and c distributed loads on line 3-4
Step 1
• Select regulation point to be Node 4.
• Turn off regulator in Analysis Manager.
• Run power-flow with source set to 126
volts (IEEE 13 Node Test Feeder Start.wm).
• Display Voltage Profile.
• Compute compensator impedance.
Step 1 Voltage Profile
1 2 3 4 5
110
112.5
115
117.5
120
122.5
125
127.5
130
132.5
135
N
o
d
e

V
o
l
t
a
g
e
135
110
V
.a
V
.b
V
.c
5 1 Node
Voltages and Currents from Power-Flow Run

eg.
V
2
2521.87 e
j 0 ⋅

2521.87 e
j − 120 ⋅ deg ⋅

2521.87 e
j 120 ⋅ deg ⋅

|




\
|
|
|
|
|
.
:= V
4
2310 e
j − 3.5 ⋅ deg ⋅

2377.5 e
j − 124.6 ⋅ deg ⋅

2284.2 e
j 116.1 ⋅ deg ⋅

|




\
|
|
|
|
|
.
:=
I
reg
590.8 e
j − 34.4 ⋅ deg ⋅

632.5 e
j − 150.5 ⋅ deg ⋅

651.9 e
j 81.4 ⋅ deg ⋅

|




\
|
|
|
|
|
.
:=
Compensator R and X Setting
CT
p
700 = N
pt
20 =
Zline
i
V
2
i
V
4
i

I
reg
i
:= Zline
0.1671 0.4037j +
0.0541 0.3817j +
0.1426 0.4188j +
|



\
|
|
|
|
.
=
Z
avg
mean Zline ( ) := Z
avg
0.1212 0.4014j + =
Z
set
Z
avg
CT
p
N
pt
⋅ := Z
set
4.2 14j + =
volts
IEEE 13 with Regulator Set
• Set source voltage to 120 V.
• Set regulator control.
– R and X =4.2 +j14
– Set voltage output (level) to 121.
• Analysis Manager
– Set regulator to step.
• Run voltage drop.
– Show results
– Show profile
IEEE 13 with Regulator Set
Full Load with Regs, no Caps
1 2 3 4 5
115
117
119
121
123
125
127
129
131
133
135
N
o
d
e

V
o
l
t
a
g
e
135
115
V
.a
V
.b
V
.c
5 1 Node
Use WindMil “ Set Regulation”
• Select Voltage Drop.
– Analysis Manager
• Set regulators to infinite.
• Set source to 126 volts.
• Select Set Regulation.
– Analysis Manager
• Select substation regulator.
• Select Node 4 as load center.
• Most desirable voltage = 121
• Tolerance 2%
• Unbalanced study
Set Voltage Regulation
WindMil R and X settings
WindMil with R 4.8, X = 14.4 and no feeder caps
• Set source voltages to 120.
• Set voltage level (output voltage) to 121 V.
• Run Voltage Drop.
WindMil R and X setting with no feeder capacitors
WindMil with regs, no caps
1 2 3 4 5
115
117
119
121
123
125
127
129
131
133
135
N
o
d
e

V
o
l
t
a
g
e
V
a
V
b
V
c
Node
WindMil Voltage Profile
Observations
• Regulator taps
– Phase a: 12
– Phase b: 13
– Phase c: 15
• Concern that Phase c is near maximum tap
• Concern about high voltage at Node 2
• Need to add shunt capacitors
Shunt Capacitors
• Source reactive power
– Phase A: 834 kVAr
– Phase B: 805 kVAr
– Phase C: 1040 kVAr
• Install shunt capacitors
– Node 3: 100 kVAr per phases a,b,c
– Node 4: 300 kVAr per phases a,b,c
– Node 4: Switched 300 kVAr per phases a,b,c
WindMil R and X settings with capacitors
Full Load with Regs and Caps
Observations
• Regulator taps
– Phase a: 6
– Phase b: 6
– Phase c: 8
• Concern for voltage unbalance at Node 4
Node 4 Voltage Unbalance
V
4
119.8
124
121.4
|


\
|
|
|
.
:= V
avg
mean V
4
( )
:= V
avg
121.7333 =
Dev
i
V
4
i
V
avg
− := Dev
1.9333
2.2667
0.3333
|


\
|
|
|
.
=
V
unbalance
max Dev ( )
V
avg
100 ⋅ := V
unbalance
1.862 = %
Minimum load of 50%
• Analysis manager
– Set load growth to -50%
• Run voltage drop
– Observe power factor at source
– Switch 900 kVAr at Node 4
50% load reduction with all capacitors
50% load with all Capacitors
50% load with 900 kVAr at Node 4 switched off
1 2 3 4 5
115
117
119
121
123
125
127
129
131
133
135
N
o
d
e

V
o
l
t
a
g
e
V
a
V
b
V
c
Node
10% Growth with Original Capacitors
10% Load Growth
• Analysis Manager
– Set load growth to 10%.
• Run voltage drop
– Voltage profile
– Check kVAr supplied by sub.
– Install new shunt capacitors if necessary.
10% load growth with original capacitors
50% load reduction, switch off 900 kVAr at Node 4
10% Load Growth with original caps
10% Growth with 300 kVAr added at Node 10
10% Load Growth
100 kVAr per phase added at Node 10
IEEE 34 Node Test Feeder
• Will be used to:
– Determine location of downstream step
voltage regulators
– Voltage level
– R and X settings
•My method
•WindMil method
Modified IEEE 34 Node Test Feeder
http://ewh.ieee.org/soc/pes/dsacom/testfeeders.html
9
30
1
8
21
22
23
24
14
33
11 12 25
19 20
26
15
27
28
29
16 17
18
31
Sub
32
5
10
13
2 3 4 6 7
To Start
• System is very unbalanced.
• System is very long (35 miles).
• Voltage level is 24.9 kV.
• Set substation output voltage to 126 volts.
• Run power flow for the IEEE 34 node system
with no regulators or shunt capacitors (IEEE 34
Node Bare Bones).
IEEE 34 with no regulators and no capacitors
IEEE 34 with no regulators or capacitors
Install substation regulators
• Install 3 Step Voltage Regulators connected in grounded
Y in the substation to start the regulation process.
• Potential transformer ratio = 14,400/120
• Current transformer ratio = 100/0.1
• Voltage level = 126 volts
• Bandwidth = 2 volts
• R and X = 0
• Run power flow.
Modified IEEE 34 Node Test Feeder
http://ewh.ieee.org/soc/pes/dsacom/testfeeders.html
30
32
21
22
23
24
14
33
13
10 11 12 25
19 20
26
15
27
28
29
16 17
18
31
Sub
1
2 3 4 5 6 7
8
9
IEEE 34 with Y connected sub regulators,
Voltage Output (level) = 126, R and X = 0
Voltage Profiles with Substation Regulators with Voltage Level = 126
Observations and next step
• Node 5 is the first node downstream where the voltage
drops below 120.
• Select Node 5 as the regulation point for the substation
regulator.
• Set regulators to infinite.
• Run Set Regulator to compute R and X settings.
• Set R and X on the sub regulator control.
• Set voltage level on regulator to 120 volts.
• Run power flow with regulators set as step.
Sub Regulator set with R = 14.4 and X = 9.6
Voltage Output (level) = 120
Install Regulators at Node 5
• Set voltage level = 126
• Regulator set to infinite
• R and X = 0
IEEE 34 Node Test Feeder
http://ewh.ieee.org/soc/pes/dsacom/testfeeders.html
30
32
21
22
23
24
14
33
13
10 11 12 25
19 20
26
15
27
28
29
16 17
18
31
Sub
1
2 3 4 5 6 7
8
9
Substation Regulators Set
Regulators Installed at Node 5 Voltage Level = 126
Observations
• All voltages at Node 5 are between 119 and 121 volts.
• The first downstream node where all of the voltages drop
below 120 V is Node 11.
• Set regulators to Infinite.
• Run Regulation Set to compute R and X from Node 5 to
Node 11.
• Set regulators to step.
• Run power flow.
Sub and Node 5 (R=16.8, X = 7.2) Regulators Set
Observations
• Install a regulator at Node 11.
• Set voltage level to 126.
• Set regulators to step.
• Run Voltage Drop.
Regulator Installed at Node 5
30
32
21
22
23
24
14
33
13
10 12 25
19 20
26
15
27
28
29
16 17
18
31
Sub
1
2 3 4 5 6 7
8
9
11
Reg at Node 11 Set to 126 Volts, R and X = 0
Regulator at Node 5 set with V = 126
No R and X
• With the regulator set at 126 volts, all of
the downstream voltages in the main
feeder are greater/equal to 120 volts.
• No need to set R and X for this regulator
• The only problems occur on the 4.16 kV
line from 19 to 20.
Profile including the 4.16 kV line
Install regulator at secondary terminals of the transformer
• Potential Transformer Ratio = 2400/120
• Primary CT Rating = 100 amps
• Calculate R and X.
• Set regulators to Infinite.
• Load center is Node 20.
• Run Set Regulation.
System does not converge
4.16 Reg set with V = 122, R = 12, X = 7.2
• Use Set Regulation to compute R and X
for Reg 11 and Reg 20 with voltage output
= 122.
Node 5: R = 9.6, X = 4.8; Voltage Output = 122
Node 20: R = 12, X = 9.6; Voltage Output = 122
Set source voltage to 120
• Run with no capacitors.
• Add capacitors.
Source set to 120, no capacitors
Correct feeder power factor to near 1
• Display P and Q on 4.16 kV line.
– Install a three phase capacitor bank to supply most of
the 4.16 kV kVAr load.
– 75 kVAr/phase at Node 20
• Need to add 200 kVAr/phase
– Node 16, 100 kVAr/phase
– Node 822: 100 kVAr/phase A
– Node 848: 100 kVAr/phase
Final with capacitors
Final Regulator Tap Positions
• Sub Regulator: 9, 8, 7
• Node 812: 10, 6, 7
• Node 830: 5, 6, 7
• Node 888: 12, 12, 12
Final kVAr supplied by source
• Source power factor:
– Phase a: 43 (PF = 99.8 %)
– Phase b: 71 (PF = 99.5 %)
– Phase c: 16 (PF = 99.9 %)
To be continued by you
• Minimum load
– Which capacitors to switch
• Load growth
– Where and how big new capacitor banks

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