9424200996 84-37
BE1-11m Settings Calculation Examples
= 1.7
(
125% + 2%
)
1
= 1.7
(
1.25 + 0.02
)
755
1
60
= 27.17
Equation 84-26. 50-1 Pickup
Set for three-phase mode so that any phase exceeding the setting will pick up the element. Set the
Pickup setting to 27.17 Secondary A. Typically, CT circuit 1 is used because it is on the feed side of the
motor. See Figure 84-46.
Figure 84-46. Protection, Current, Instantaneous Overcurrent (50-1) Screen
Instantaneous Overcurrent (50-2) - Ground Fault Protection
The system is solidly grounded so that a ground fault draws current in the magnitude of a three-phase
fault per IEEE C37.96-2000, IEEE Guide for AC Motor Protection. To determine the three-phase fault
current, consider that the motor subtransient reactance of 0.368 is the limiting impedance. The pickup
setting is calculated using Equation 84-27. A pickup setting of 1/3 of the instantaneous three-phase fault
current is recommended per IEEE C37.96-2000, IEEE Guide for AC Motor Protection. During starting, CT
saturation can produce false residual currents, so we use the running mode current FLA. The circuit CT
ratio (CTR) is 60.
=
1
"
1
3
=
1
0.368
205
60
1
3
= 3.09
Equation 84-27. 50-2 Pickup
Select 3I0 (residual) mode and set the Pickup setting to 3.09 Secondary A as shown in Figure 84-47.
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