GE Multilin 850

CHAPTER 4: SETPOINTS PROTECTION
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL 4–221
Admittance
Neutral Admittance
(21YN)
In a medium voltage (MV) network, the compensating reactor is used to compensate the
capacitive fault current ideally to zero at the fault point. However, detection of low earth-
fault current in such networks is challenging when using the conventional current-based
ground fault detection methods. This element uses neutral admittance based criteria to
successfully detect the earth fault in the compensated or isolated MV networks. Measured
or calculated values of neutral current (I
0
) and neutral voltage (V
0
) are used to calculate the
shunt neutral admittance (Y
0
), conductance (G
0
) and susceptance (B
0
). The element uses
one of the three modes (Y
0
, G
0
, B
0
) to operate or block the output operands.
Path: Setpoints > Protection > Group 1(6) > Admittance > Neutral Admittance 1(X)
FUNCTION
Range: Disabled, Trip, Alarm, Latched Alarm, Configurable
Default: Disabled
This setting enables the Neutral Admittance functionality.
CURRENT INPUT
Range: J1 I0, J1 Ig
Default: J1 I0
Current input can be programmed to be either the zero-sequence current, J1 I0 and K1
I0, calculated from the phase currents or measured ground current, J1 Ig and K1 Ig,
supplied externally at ground CT input. The setting range provides flexibility of selecting
the current source bank; currents J1 I0 and J1 Ig correspond to Bank 1 – Slot J1, while
currents K1 I0 and K1 Ig correspond to Bank 2 – Slot K1.
FAST PATH:
Selection of K1 I0 and K1 Ig, is only available with the Slot K bank order code. Otherwise,
the neutral admittance is calculated from the Slot J options only.
VOLTAGE INPUT
Range: J2 V0, J2 Vaux
Default: J2 V0
Voltage input can be programmed to be either the zero-sequence voltage, J2 V0,
calculated from the phase voltages or measured voltage, J2 Vaux, supplied externally at
the auxiliary VT input. The setting range provides flexibility of selecting the voltage
source bank; voltages J2 V0 and J2 Vaux correspond to Bank 1 – Slot J2.
FAST PATH:
When Voltage Input is set as J2 Vaux, it is required that the setpoint Aux VT Connection
(under
Setpoints > System > Voltage Sensing) must be selected as “VN” for this element,
otherwise the element operation will be blocked by the relay.
When Voltage Input is set as “J2 V0”, phase voltages must be wye-connected, and
setpoint Phase VT Connection (under
Setpoints > System > Voltage Sensing) must be
selected as “Wye.”
The neutral admittance is calculated from Slot J options only.