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Talking about threeMotor protectorWhen they are undersized or underconfigured, two possible scenarios can occur. In some cases, they will trip continuously, taking up valuable time from your maintenance crews, and in some cases, they may not even trip on minor undervoltages or overloads, which are not always obvious and can shorten the life of the motor.

To avoid some common mistakes when configuring motor protection, here are steps to keep in mind.

1) Undervoltage protection is set too high – A motor that runs below rated voltage may overheat and have a shorter life. Make sure the undervoltage protection is set too high, it can and probably will disconnect the motor when it is not needed.

For example, a three-phase motor is rated at 230V, which means the acceptable operating voltage according to NEMA is 207V (230V x 90%). However, if the adjustable undervoltage relay is set to 220V, a 5% drop in voltage is enough to disconnect the motor.

2) The thermal overload setting is incorrect, the basic requirement for the overload protection setting is 125% of its full load current; however, it makes sure you read the overload relay instructions.

If the 125% value is not built into the relay, it must be set to motor current + 25%.

For example, suppose you want to protect a motor with a full load current of 60A, and you have an overload relay that can be set from 50A to 100A. If the device already takes 125% into account, it must be set to 60A. If not, the correct setting is 75A (60A + 25%).

If the overload protection is set too low, the motor can trip even during normal operation. For example, if the dial of the above protection device is set to 50A and it is left for a 60A motor, it may not trip immediately if the motor is only lightly loaded, giving the impression that it is operating normally. However, a higher motor load that causes the current to exceed 50A will trip the device.

certainly,Motor protectorThe overload protection should also not be set too high, as the motor will not receive adequate overload protection. For example, if you add 25% to an overload relay that already has a built-in 125% value, the actual overload protection value will be 156%, which is not in compliance with the NEC.

3)磁保护设置不正确——在故障情况等情况下，磁保护必须立即断开电机，但必须允许浪涌电流不断开。应该记住的另一件事是，如果磁保护是固定的，请确保其跳闸曲线允许浪涌电流，浪涌电流只能达到额定电流的 800%。然而，如果磁保护是可调的，则设置一个值，使其不会因浪涌电流而跳闸。如果电机有降压启动器、固态启动器或变频驱动器，请确保浪涌电流较低。