Long-Duration Voltage Variations
-
Upload
george-foster -
Category
Documents
-
view
79 -
download
6
description
Transcript of Long-Duration Voltage Variations
![Page 1: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/1.jpg)
1
Long-Duration Voltage Variations
![Page 2: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/2.jpg)
2
LoadV2V1
V2
I
I
RI
jX IV1
At given pf at full load, nominal V2
R X
![Page 3: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/3.jpg)
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
![Page 4: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/4.jpg)
4
V2,NL = V1
At no load, V2 normally rises to equal V1
V2FL
%100V
VV%100
VVV
RegR2
R2NL2
FL2
FL2NL2
Last equality assumes full-load voltage is nominal or rated value for the system
![Page 5: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/5.jpg)
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
![Page 6: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/6.jpg)
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)
![Page 7: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/7.jpg)
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)
![Page 8: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/8.jpg)
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
![Page 9: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/9.jpg)
9
Loads…
Step voltage regulators
RaiseLower
Load side
Source side
![Page 10: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/10.jpg)
10
V sensing and gate control
Source side
…Load side
…Electronic tap-switching voltage regulator
![Page 11: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/11.jpg)
11
Loads…
voltage regulator set at 105% without line-drop compensationV(x)
x120 V
126 V
114 V
voltage profile for light load
voltage profile for heavy load
![Page 12: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/12.jpg)
12
Loads…
voltage regulator set at 100% with line-drop compensationV(x)
x120 V
126 V
114 V
voltage profile for light load
voltage profile for heavy load
![Page 13: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/13.jpg)
13
V(x)
x120 V
126 V
114 V
![Page 14: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/14.jpg)
14
V(x)
x120 V
126 V
114 V
Voltage profile after load rejection
Needs rapid runback controls
![Page 15: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/15.jpg)
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
![Page 16: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/16.jpg)
Example of Flicker
Power system model at Ulleung Island of South Korea.
YDG
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]
SMESPs, 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]
Y
Y
0.378+j0.195 [Ω]
PL, QL
VGPWG Unit
![Page 17: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/17.jpg)
System Responses
Wind speed data.
0 10 20 30 40 50 606
8
10
12
Win
d sp
eed
[m/s
]
Time [sec]
0 10 20 30 40 50 6058
59
60
61
62
0 10 20 30 40 50 600.0
0.5
1.0
1.5
2.0
2.5
Freq
uenc
y [H
z]
Time [sec]
Without Wind generator With Wind generator
Activ
e pow
er [M
W]
Time [sec]
Wind generator Diesel generator 1&2 Hydraulic generator 1&2 Load
Responses of active power and system frequency.
![Page 18: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/18.jpg)
System Responses with SMES
0 10 20 30 40 50 6058
59
60
61
62
0 10 20 30 40 50 600.0
0.5
1.0
1.5
2.0
2.5
Freq
uenc
y [H
z]
Time [sec]
Without SMES With SMES
Act
ive
pow
er [M
W]
Time [sec]
Wind generator Transmission line Diesel generator 1&2 Hydraulic generator 1&2 Load
Responses of active power and system frequency with SMES .
![Page 19: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/19.jpg)
19
Source side Loa
d
Thyristor-controlled reactorOne type of static var compensator
3rd 5th 7th
capacitors configured as harmonic filters
Flicker Mitigation Techniques
-Adding series reactor
![Page 20: Long-Duration Voltage Variations](https://reader036.fdocuments.us/reader036/viewer/2022081506/56813657550346895d9de1c0/html5/thumbnails/20.jpg)
20
Source side Loa
d
Thyristor-switched capacitorAnother type of static var compensator
capacitors are gated fully on in sequence