Sel 411L - Frequency Estimation; Polarizing Quantity for Distance Element Calculations; Table 3.53 VMEMC Relay Setting

P.3.119
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Polarizing Quantity for Distance Element Calculations
Polarizing Quantity for Distance Element Calculations
The relay uses positive-sequence memory voltage as the polarizing quantity
for distance element calculations. Memory polarization ensures proper
operation during zero-voltage three-phase faults and provides expansion of the
mho characteristic back to the source impedance, improving fault-resistance
coverage. However, longer memory may impair distance element security
when a power system disturbance causes a fast frequency excursion.
The polarization memory is adaptive. The relay normally uses positive-
sequence voltage with short or medium length memory. This short or medium
length memory works satisfactorily for all faults other than zero-voltage three-
phase faults. When the relay measures positive-sequence voltage magnitude
lower than a threshold, it automatically switches to a long memory polarizing
quantity.
The VMEMC setting allows you to choose between short or medium length
memory voltage for the normal polarizing quantity. To closely follow the
power system frequency, set VMEMC = 0. When VMEMC is deasserted
(logical 0), the relay normally uses a short memory time constant that closely
follows the positive-sequence voltage, yet automatically switches to the long
memory when necessary. This setting provides less expansion of the distance
element characteristics, while still providing security for zero-voltage three-
phase faults. SEL recommends that you use this setting.
If your application requires more expansion of the distance element
characteristics, set VMEMC = 1. When VMEMC is asserted, the relay
normally uses medium length memory and automatically switches to the long
memory when necessary. This setting provides the same element operation as
provided in firmware R105 and earlier, including greater expansion of the
distance element characteristics and the same security for zero-voltage
three-phase faults.
The short memory is not available for series compensated lines
(ESERCMP = Y). When ESERCMP = Y, the relay uses the medium length
memory and automatically switches to the long memory polarizing quantity
when the relay detects voltage inversion or positive-sequence voltage
magnitude lower than a threshold.
Frequency Estimation
The relay uses filtered analog values related to the system frequency to
calculate internal quantities such as phasor magnitudes and phase angles.
When the system frequency changes, the relay measures these frequency
changes and adapts the processing rate of the protection functions accordingly.
Adapting the processing rate is called frequency tracking.
Table 3.53 VMEMC Relay Setting
Name Description Range Default Setting
VMEMC
a
a
If the Advanced Settings are not enabled (setting EADVS :=N), the relay hides the setting. If
the Series Compensation Line Logic Setting is enabled (setting ESERCMP := Y), the relay
hides the setting.
Memory Voltage Control (SELOGIC Equation) SV 0
b
b
Setting VMEMC is forced to 1 if the Series Compensation Line Logic Setting is enabled
(setting ESERCMP := Y).