Date Code 990430 Overcurrent, Voltage, Synchronism Check, and Frequency Elements 3-49
SEL-351P Manual Técnico
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)
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
Refer to
Figure SECTION 3: .28.
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.
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