9424200996 84-41
BE1-11m Settings Calculation Examples
Figure 84-52. Protection, Current, Instantaneous Overcurrent (50-5) Screen
Instantaneous Overcurrent (50-6) - Jam Protection
The 50-6 element is used for jam protection while the motor is running. It protects the motor when the
load torque exceeds the torque capability of the motor. This condition develops motor current equal to or
approaching locked-rotor current, and reduces terminal voltage depending upon the motor impedance.
The motor can be removed from service faster when using the 50-6 element instead of the 49TC element
for jam protection. This fast tripping for a jammed condition results in less motor heating, allowing the
motor to be returned to service faster after the cause of the stall (jam) has been corrected.
The maximum stall time is listed on the motor name plate per the NEMA MG-1 standard. In this example,
the conservative protection pickup setting is calculated as 70 percent of LRA as shown in Equation 84-34.
= 70%
(
)
1
= 0.7
(
755
)
1
60
= 8.808
Equation 84-34. 50-6 Pickup
Select three-phase mode and set the Pickup setting to 8.808 Secondary A as shown in Figure 84-53.
Figure 84-53. Protection, Current, Instantaneous Overcurrent (50-6) Screen
Current Differential (87)
BE1-11m Motor Protection Systems with a style number of xxxxxxxxPxxxxx are equipped with differential
protection. Differential protection is preferred on all motors, but not all motors are built with access to both
ends of the motor windings. In this case, differential protection cannot be used.
Differential protection is selected over other methods because of its sensitivity, speed, and security. The
BE1-11m provides two types of differential protection. One method, flux balance, is used for small motors.
Flux balance requires one ring or doughnut CT per phase of sufficient diameter to accommodate
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