84-20 9424200996
Settings Calculation Examples BE1-11m
Figure 84-25. Protection, Voltage, Undervoltage (27P-2) Screen
Protection - Frequency
Two frequency protection elements monitor for underfrequency and overfrequency conditions. According
to the NEMA MG-1 standard, motors are expected to operate successfully under running conditions at
rated load with a variation of ±10 percent of rated voltage, ±5 percent of rated frequency, or a combination
of the two, provided the sum of the absolute values of the deviations does not exceed 10 percent and the
frequency variation does not exceed ±5 percent.
Underfrequency (81-1)
The 81-1 protection element alarms when the source frequency is 5 percent below nominal. A time delay
of 100 ms is used to avoid nuisance alarms. The pickup setting is calculated in Equation 84-19.
=
(
100 5%
)
= 0.95 60 = 57
Equation 84-19. 81-1 Pickup
Select Under mode, set the Pickup setting to 57 Hz, and set the Time Delay to 100 ms as shown in
Figure 84-26.
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