3-8
BE1-46N Functional Description
FURTHER CONSIDERATIONS (FOR 1 AMP CT)
To determine the negative sequence current pickup setting, calculate the sensitivity required to insure relay
operation at the expected minimum load condition with one pole of the generator breaker open. Assume
the value of negative sequence current under this condition is 0.14 A (secondary) or 0.18 per unit. then for
our example, the relay must be at least this sensitive. This value must be considered as the upper limit for
the pickup setting. A lower setting is recommended. For this example, a value of 12 percent (0.12 per unit)
will be used. Set the PICKUP thumbwheel to this value.
To set the value for the ALARM level of negative sequence current, it is only necessary to determine the
level that will give an operator sufficient time to attempt to correct the condition. A value of 08 may be set
on the thumbwheel.
The K value for this example has been provided by the generator manufacturer. Set this value (25) on the
K SET thumbwheel.
The MAX TIME thumbwheel establishes the maximum time allowed for the negative sequence current
tripping condition (defined by the PICKUP setting) to persist. If it is determined that this value is 500
seconds, set the thumbwheel at 50.
Since (I
2
)
2
t = K establishes the limit of operation, t = 25 divided by 0.12
2
= 1736 seconds.
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