GE D60 Instruction Manual page 456

GROUPED ELEMENTS
The compensated overvoltage function provides protection against an overvoltage due to the opening of the remote
terminal of a transmission line—the so called the Ferranti effect. This can be achieved using a transfer-tripping scheme.
However, with high voltage, more corona can exist on the line and inhibit the proper reception of a carrier-transfer-trip
signal. Also, the presence of a line with an open terminal in weak systems can raise the voltage level of the local bus.
Detecting and tripping a line with an open terminal can prevent tripping at the local bus in this case.
5
The function approximates the voltage rise at the far end of the transmission line according to the following relationship:
where
V_1 is the positive-sequence voltage (phasor quantity) in secondary volts measured at the local terminal
I_1 is the positive-sequence current (phasor quantity) in secondary amps measured at the local terminal
V is the phase VT secondary setting in the case of wye VTs and the phase VT secondary setting divided by
nominal
case of delta VTs
Z and Z
C_mag C_ang
V_1 is the calculated positive-sequence voltage magnitude at the remote terminal
C
If the magnitude of Z
approximately equal to the positive-sequence voltage at the remote end of the line. A more accurate setting of Z
made if the positive-sequence charging current and the voltages at the local and remote line ends resulting from an open
breaker are known. In this case, the required reach setting is:
The following settings are available.
COMPENSATED OV Zc MAG
positive-sequence series impedance of the line. Alternately, if the positive-sequence charging currents and local and
remote voltages are known, then this value can be calculated from equation above.
COMPENSATED OV Zc ANG
COMPENSATED OV I_1max
remote overvoltage is anticipated.
5-278
Figure 5-159: Transmission line with remote terminal open
Figure 5-160: Phasor diagram
represent an impedance between the local and remote terminals
is set to one-half the series impedance of the line (R + jX
C
— This setting specifies the magnitude of the impedance Z
— This setting specifies the angle of the impedance Z
— This setting specifies the maximum expected positive-sequence line current for which a
), the compensated voltage is
L
in secondary ohms. Set it to half the
C
in degrees.
C
D60 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS
Eq. 5-25
in the
can be
C
Eq. 5-26