Level detector
The residual voltage can be selected from the Vg or V0 setting. The options are "Measured
VG" and "Calculated V0". If "Measured VG" is selected, the voltage ratio for VG-channel
is given in the global setting Configuration/Analog inputs/Voltage (VG,VT). If
"Calculated V0" is selected, the voltage ratio is obtained from phase-voltage channels
given in the global setting Configuration/Analog inputs/Voltage (3V,VT).
Example 1: VG is measured from open-delta connected VTs (20/sqrt(3) kV : 100/sqrt(3)
V : 100/3 V). In this case, "Measured VG" is selected. The nominal values for residual
voltage is obtained from VT ratios entered in Residual voltage VG: Configuration/
Analog inputs/Voltage (VG,VT): 11.547 kV :100 V. The residual voltage start value of
1.0 × Vn corresponds to 1.0 × 11.547 kV = 11.547 kV in the primary.
Example 2: V0 is calculated from phase quantities. The phase VT-ratio is 20/sqrt(3) kV :
100/sqrt(3) V. In this case, "Calculated V0" is selected. The nominal values for residual
current and residual voltage are obtained from VT ratios entered in Residual voltage V0:
Configuration/Analog inputs/Voltage (3V,VT): 20.000 kV : 100 V. The residual
voltage start value of 1.0 × Vn corresponds to 1.0 × 20.000 kV = 20.000 kV in the primary.
If "Calculated V0" is selected, the residual voltage nominal value is
always phase-to-phase voltage. Thus, the valid maximum setting for
residual voltage pickup value is 0.577 × Vn. Calculated V0 requires that
all three phase-to-ground voltages are connected to the protection relay.
V0 cannot be calculated from the phase-to-phase voltages.
Transient detector
The Transient detector module is used for detecting transients in the residual current and
residual voltage signals.
The transient detection is supervised with a settable current threshold. With a special
filtering technique, the setting Min trip current is based on the fundamental frequency
current. This setting should be set based on the value of the parallel resistor of the coil, with
security margin. For example, if the resistive current of the parallel resistor is 10 A, then
a value of 0.7×10 A = 7 A could be used. The same setting is also applicable in case the
coil is disconnected and the network becomes ungrounded. Generally, a smaller value
should be used and it must never exceed the value of the parallel resistor in order to allow
operation of the faulted feeder.
Fault indication logic
Depending on the set Operation mode, 67NIEF has two independent modes for detecting
ground faults. The "Transient EF" mode is intended to detect all kinds of ground faults.
The "Intermittent EF" mode is dedicated for detecting intermittent ground faults in cable
networks.
Section 4 1MAC059074-MB A
Protection functions
362 615 series ANSI
Technical Manual
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