3.59
Date Code 20060320 Instruction Manual SEL-311C Relay
Distance, Out-of-Step, Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Frequency Elements
Other Uses for Undervoltage Element 27B81
If voltage pickup setting 27B81P is applicable to other control schemes, Relay
Word bit 27B81 can be used in other logic at the same time it is used in the
frequency element logic.
If frequency elements are not being used, Relay Word bit 27B81 can still be
used in other logic, with voltage setting 27B81P set as desired. Enable the
frequency elements (setting E81 ≥ 1) and make setting 27B81P. Apply Relay
Word bit 27B81 in a desired logic scheme, using SEL
OGIC control equations.
Even though frequency elements are enabled, the frequency element outputs
(Relay Word bits 81D1T–81D6T) do not have to be used.
Frequency
Element Uses
The instantaneous frequency elements (81D1–81D6) are used in testing only.
The time-delayed frequency elements (81D1T–81D6T) are used for
underfrequency load shedding, frequency restoration, and other schemes.
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