Power Transmission and Distribution

PTD 01/2005 1

Power Transmission and Distribution

PTD 01/2005 2

Protection in Series Capacitor EnvironmentProtection in Series Capacitor Environment

X1=0.8*(XL1-Xc) Setting recommendation without Consideration of the subsynchronous frequencies

Power Transmission and Distribution

PTD 01/2005 3

Protection of Series Compensated LinesSubsynchronous Frequencies

R1 X1

R1 X1

Xe

Xe

Re

Re

Xc

Xc

uc(t)

uc(t)linesystem

e(t)

Fig. 2: Single-line diagram of a line-to-line short-circuit with series capacitor and no gap-flashover

R X,LXC,C

uc(t) i(t)e(t)

Fig. 3: Single-line diagram of reduced system for the calculation of the subsynchronous current components

Phase-to-Phase Fault,

no Gap-Flashover

Differential Equations for

Capacitor Voltage:

)(2

2

teudt

duRC

dt

udLC c

cc

Power Transmission and Distribution

PTD 01/2005 4

Protection of Series Compensated LinesSubsynchronous Frequencies

Series-Compensated Lines

Example Fault No. 454 (1)

29 i(t)

i(t)

Phase-to-PhaseFault

14 13

100V i(t)

Reduced system for calculation

29

95.03mH 115.6mH 14

95.03mH 115.6mH 14

421.26mH

Peak Value of Gap-Flashover Voltage for every capacitor 200kV primary and 50V sec.

Peak Value of Gap-Flashover Voltage for the capacitor in the reduced system 100V sec.

All impedances are secondary values!

3.14 29.84 4.35 36.3 21.4

148.8 F

3.14 29.84 4.35 36.3 21.4

148.8 F

14.98 132.28 42.8

74.4 F

Peak value of gap flashover voltagefor the capacitor in the reduced system 100V sec.

All impedances are sec. values

Peak value of gap flashover voltage for every capacitor is here 200kV prim and 50V sec for 400kV system.

74.0

21

1

E

UK

gap

trans

Power Transmission and Distribution

PTD 01/2005 5

Protection of Series Compensated LinesExample of Impedance Measurement