3. 3
Voltage Regulation
• Definition: Voltage regulation (at point x)
is the percent voltage rise caused by
unloading a power system (at point x)
– Assumption 1: The original power factor at
point x is given
– Assumption 2: The original voltage is the
nominal value at point x, or a given value if
not nominal; the source voltage is fixed
– Assumption 3: Original system is at full load,
or a given value if not full load
4. 4
V2,NL = V1
At no load, V2 normally rises to equal V1
V2FL
%
100
V
V
V
%
100
V
V
V
Reg
R
2
R
2
NL
2
FL
2
FL
2
NL
2
Last equality assumes full-load voltage is
nominal or rated value for the system
5. 5
• The system inductive reactance usually
causes voltage drops under normal
loading
• If the load pf is leading or if very long
transmission lines at EHV (345 kV and up,
the line charging current may be very
large), then regulation may be negative
6. 6
Root Cause
• Most long-duration voltage variations are
caused by too much impedance (Zth) in the
power delivery system
• The power system is too weak for the load
– voltage drops to a low value under heavy
loads (lagging pf)
– voltage rises to a high value under light loads
(more leading or less lagging pf)
7. 7
Solutions to Improve Voltage
Regulation
• Add shunt capacitors to increase the load power
factor (not leading however) tending to decrease
the load kVA by decreasing the load kVAr
• Add static var compensation or other dynamic
reactive power compensation (same reason as
shunt capacitor addition, but better control)
• Add series capacitors to lines to cancel part of
the jXI voltage drop (long transmission lines and
(rarely) short lines with impact loads)
8. 8
Solutions to Improve Voltage
Regulation
• Add voltage regulators to boost V under heavy
load and buck voltage under light load
• Increase the size of conductors to reduce Z
11. 11
Loads
…
voltage regulator set
at 105% without line-
drop compensation
V(x)
x
120 V
126 V
114 V
voltage profile
for light load
voltage profile
for heavy load
12. 12
Loads
…
voltage regulator set
at 100% with line-
drop compensation
V(x)
x
120 V
126 V
114 V
voltage profile
for light load
voltage profile
for heavy load
15. 15
Flicker
Sources of flicker
-Load change
-Induction motor starting
-Variable power generation
Observable flicker is dependent on the following:
-Size (VA) of potential flicker-producing source
-System impedance (stiffness of utility)
-Frequency of resulting voltage fluctuations
16. Example of Flicker
Power system model at Ulleung Island of South Korea.
Y
DG
4.5[MW]/0.5[MW]
4.5[MVA]/0.5[MVA]
3.3[kV]/6.6[kV]
DG
1.5[MW]
1.5[MVA]
3.3[kV]/6.6[kV]
WG
0.6[MW]
0.6[MVA]
0.48[kV]/6.6[kV]
1.53+j0.790 [Ω]
1.16+j0.600 [Ω]
SMES
Ps, Qs
C 0.305 MVAR
Load 6[MW]/2[MW]
6.0[MVA]/2.0[MVA]
0.23[kV]/6.6[kV]
1.16+j0.599 [Ω]
Y
0.6[MVA]/0.1[MVA]
6.6[kV]/3.3[kV]
HG
HG
0.6[MW]/0.1[MW]
0.1[MW]
D
Y
D
Y
D
D
0.378+j0.195 [Ω]
PL, QL
VG
PWG Unit
D
17. System Responses
Wind speed data.
0 10 20 30 40 50 60
6
8
10
12
Wind
speed
[m/s]
Time [sec]
0 10 20 30 40 50 60
58
59
60
61
62
0 10 20 30 40 50 60
0.0
0.5
1.0
1.5
2.0
2.5
Frequency
[Hz]
Time [sec]
Without Wind generator
With Wind generator
Active
power
[MW]
Time [sec]
Wind generator
Diesel generator 1&2
Hydraulic generator 1&2
Load
Responses of active power and system
frequency.
18. System Responses with SMES
0 10 20 30 40 50 60
58
59
60
61
62
0 10 20 30 40 50 60
0.0
0.5
1.0
1.5
2.0
2.5
Frequency
[Hz]
Time [sec]
Without SMES
With SMES
Active
power
[MW]
Time [sec]
Wind generator
Transmission line
Diesel generator 1&2
Hydraulic generator 1&2
Load
Responses of active power and system frequency with SMES .
