Basler Electric BE1-11m - Manual (Page 564)

552 9424200996 Rev L
Instantaneous Overcurrent (50-3) - Unbalance Protection Trip
The NEMA MG-1 standard states that the existence of unbalanced voltage feed results in four to 10 times
the current unbalance in a synchronous motor stator. Small voltage unbalance causes a large current
unbalance, so current is used to measure the unbalance. The unbalanced voltage feed to the motor
should not exceed 5 percent. The BE1-11m must monitor and react quickly for a current unbalance
condition. Because the BE1-11m uses negative-sequence current in the 49TC thermal model, additional
unbalance (and single-phasing) protection can be added using the Average mode.
Low current levels must be scaled to prevent nuisance pickups. This scaling is in reference to motor Full
Load Amperes. This element has a block output when the average current is less than 25 percent of rated
FLA.
The Average unbalance calculation has two states. When the average current, I
Average
, is greater than the
motor FLA, the BE1-11m uses Equation 65.
𝑈𝑛𝑏𝑎𝑙𝑎𝑛𝑐𝑒(%) =
𝐼
𝑀𝑎𝑥𝑖𝑚𝑢𝑚
𝐼
𝐴𝑣𝑒𝑟𝑎𝑔𝑒
Equation 65. Unbalance Calculation, State 1
When the average current is less than motor FLA, then the BE1-11m uses Equation 66.
𝑈𝑛𝑏𝑎𝑙𝑎𝑛𝑐𝑒(%) =
𝐼
𝑀𝑎𝑥𝑖𝑚𝑢𝑚
𝐹𝐿𝐴
Equation 66. Unbalance Calculation, State 2
Refer to the Instantaneous Overcurrent (50) Protection chapter for more information on unbalance
calculations.
The pickup setting calculation is shown in Equation 67.
𝑃𝑖𝑐𝑘𝑢𝑝 = 𝑁𝑒𝑚𝑎 𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 (5%) ∙ 𝐴𝑝𝑝𝑟𝑜𝑝𝑟𝑖𝑎𝑡𝑒𝑃𝑟𝑜𝑡𝑒𝑐𝑡𝑖𝑜𝑛 (4)
= 5% ∙ 4 = 20%
Equation 67. 50-3 Pickup
Select Unbalanced mode, set the Pickup setting to 20%, and set the Time Delay to 5 seconds as shown
in Figure 385.
Figure 385. Protection, Current, Instantaneous Overcurrent (50-3) Screen
Instantaneous Overcurrent (50-4) - Unbalanced Protection Alarm
If there is an increasing voltage unbalance in the power system (incorrect phase connections, stator turn-
to-turn faults, or motor winding connections corroding or loose, for example), the BE1-11m can alarm so
that you can take action before tripping the motor on unbalance current. Use the 50-4 element to alert
operations and maintenance personnel to take corrective action.
The pickup setting calculation is shown in Equation 68.
Settings Calculation Examples BE1-11m