3.51
Date Code 20080213 Instruction Manual SEL-351A Relay
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Frequency Elements
Accuracy
Pickup:
±0.01 Hz
Timer:
±0.25 cycles and ±0.1% of setting
Create Over- and Underfrequency Elements
Refer to Figure 3.32.
Note that pickup settings 81D1P–81D6P are compared to setting NFREQ.
NFREQ is the nominal frequency setting (a global setting), set to 50 or 60 Hz.
Overfrequency Element
For example, make settings:
NFREQ = 60 Hz (nominal system frequency is 60 Hz)
E81 ≥ 1 (enable frequency element 1)
81D1P = 61.25 Hz (frequency element 1 pickup)
Table 3.14 Frequency Elements Settings and Settings Ranges
Setting Definition Range
27B81P undervoltage frequency element block
(responds to V
LN
when Global setting
PTCONN = WYE,
responds to V
LL
when Global setting
PTCONN = DELTA)
25.00–300.00 V secondary
81D1P frequency element 1 pickup 40.10–65.00 Hz
81D1D
a
a
Frequency element time delays are best set no less than 5 cycles. Frequency is determined by
a zero-crossing technique on voltage V
A
. If voltage waveform offset occurs (e.g., due to a
fault), then frequency can be off for a few cycles. A 5-cycle or greater time delay (e.g.,
81D1D = 6.00 cycles) overrides this occurrence.
frequency element 1 time delay 2.00–16000.00 cycles,
in 0.25-cycle steps
81D2P frequency element 2 pickup 40.10–65.00 Hz
81D2D
a
frequency element 2 time delay 2.00–16000.00 cycles,
in 0.25-cycle steps
81D3P frequency element 3 pickup 40.10–65.00 Hz
81D3D
a
frequency element 3 time delay 2.00–16000.00 cycles,
in 0.25-cycle steps
81D4P frequency element 4 pickup 40.10–65.00 Hz
81D4D
a
frequency element 4 time delay 2.00–16000.00 cycles,
in 0.25-cycle steps
81D5P frequency element 5 pickup 40.10–65.00 Hz
81D5D
a
frequency element 5 time delay 2.00–16000.00 cycles,
in 0.25-cycle steps
81D6P frequency element 6 pickup 40.10–65.00 Hz
81D6D
a
frequency element 6 time delay 2.00–16000.00 cycles,
in 0.25-cycle steps
Courtesy of NationalSwitchgear.com
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