3.52
SEL-351A Relay
Instruction Manual
Date Code 20080213
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Frequency Elements
With these settings:
81D1P
≥
NFREQ
the overfrequency part of frequency element 1 logic is enabled. 81D1 and
81D1T operate as overfrequency elements. 81D1 is used in
testing only
.
Underfrequency Element
For example, make settings:
NFREQ =
60 Hz
(nominal system frequency is 60 Hz)
E81
≥
2
(enable frequency element 2)
81D2P =
59.65 Hz
(frequency element 2 pickup)
With these settings:
81D2P
<
NFREQ
the underfrequency part of frequency element 2 logic is enabled. 81D2 and
81D2T operate as underfrequency elements. 81D2 is used in
testing only
.
Frequency Element
Operation
.
Overfrequency Element Operation
With the previous overfrequency element example settings, if system
frequency is
less than or equal to
61.25 Hz (81D1P = 61.25 Hz), frequency
element 1 outputs:
81D1 = logical 0 (instantaneous element)
81D1T = logical 0 (time delayed element)
If system frequency is
greater than
61.25 Hz (81D1P = 61.25 Hz), frequency
element 1 outputs:
81D1 = logical 1 (instantaneous element)
81D1T = logical 1 (time delayed element)
Relay Word bit 81D1T asserts to logical 1 only after time delay 81D1D.
Underfrequency Element Operation
With the previous underfrequency element example settings, if system
frequency is
less than or equal to
59.65 Hz (81D2P = 59.65 Hz), frequency
element 2 outputs:
81D2 = logical 1 (instantaneous element)
81D2T = logical 1 (time delayed element)
Relay Word bit 81D2T asserts to logical 1 only after time delay 81D2D.
If system frequency is
greater than
59.65 Hz (81D2P = 59.65 Hz), frequency
element 2 outputs:
81D2 = logical 0 (instantaneous element)
81D2T = logical 0 (time delayed element)
Summary of Contents for SEL-351A
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