Basler Electric BE1-11m - Manual (Page 539)

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Figure 352. 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 0.15 is the limiting impedance. The pickup
setting is calculated using Equation 44. 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.
𝑃𝑖𝑐𝑘𝑢𝑝 = �
1
𝑋"𝑑
∙
𝐹𝐿𝐴
𝐶𝑇 𝑅𝑎𝑡𝑖𝑜
� ∙
1
3
= �
1
0.15
∙
363
80
� ∙
1
3
= 10.08 𝐴 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦
Equation 44. 50-2 Pickup
Select 3I0 (residual) mode and set the Pickup setting to 10.08 A as shown in Figure 353.
Figure 353. Protection, Current, Instantaneous Overcurrent (50-2) Screen
Instantaneous Overcurrent (50-3) - Unbalance Protection
The NEMA MG-1 standard states that the existence of unbalanced voltage feed results in four to 10 times
the current imbalance. The negative-sequence voltage unbalances should not exceed 5 percent. This
application uses negative-sequence current as the input to an overcurrent element to sense unbalance
conditions. For conservative protection, choose 4
• 5%, which is 20 percent imbalance. A 10 second
delay is appropriate because the heating is slow (motor mass is large). The pickup setting calculation is
shown in Equation 45.
𝑃𝑖𝑐𝑘𝑢𝑝 = 𝑁𝑒𝑚𝑎 𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 (5%) ∙ 𝐶𝑜𝑛𝑠𝑒𝑟𝑣𝑎𝑡𝑖𝑣𝑒 𝑃𝑟𝑜𝑡𝑒𝑐𝑡𝑖𝑜𝑛 (4) ∙ 𝐹𝐿𝐴
𝑆𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦
= 0.05 ∙ 4 ∙ 4.54 = 0.908 𝐴 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦
Equation 45. 50-3 Pickup
Select I2 mode, set the Pickup setting to 0.908 A, and set the Time Delay to 10 seconds as shown in
Figure 354.
BE1-11m Settings Calculation Examples