9424200994 Rev N 63
Negative-Sequence Voltage (47)
Protection
Negative-sequence voltage protection is included as a mode of the 27X (Auxiliary Undervoltage) and 59X
(Auxiliary Overvoltage) elements. Refer to the Auxiliary Undervoltage (27X) Protection and Auxiliary
Overvoltage (59X) Protection chapters for information on how to set up and program the V2 (negative-
sequence voltage) mode of the 27X and 59X elements.
Negative-sequence voltage protection is used to sense power-system imbalance. This situation occurs
when a large single-phase load is switched onto the system, or when transformer-input fuses blow in only
one or two phases. Negative-sequence voltage protection is good for detecting improper phasing when
an oncoming generator is paralleled to the power system. All motor loads should be protected from the
heating caused by unbalanced voltage (either on the bus or on each motor feeder). Industry standards
state that the existence of unbalanced voltage feed results in 4 to 10 times the current imbalance. For a
motor feeder, the negative-sequence voltage unbalances should not exceed 5 percent to avoid
overheating and damage.
BE1-11g Negative-Sequence Voltage (47) Protection
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