Causes of overcurrent of electrical engineering inverters and overcurrent protection!

1, over current protection function

In the inverter, the object of overcurrent protection mainly refers to the case where the peak value of the current exceeds the allowable value of the inverter with abrupt nature. Because the overload capability of the inverter device is poor, the overcurrent protection of the inverter is crucial. An important part has been developed so far.

(1) Causes of overcurrent

1. Overcurrent in the work, that is, the drag system has an overcurrent during the working process. The reason is mainly from the following aspects:

1 The motor encounters an impact load, or the transmission mechanism is out, causing a sudden increase in the motor current.

2 The output side of the inverter is short-circuited, such as the short-circuit between the output terminals and the motor, or a short circuit inside the motor.

3 The inverter itself is not working properly. For example, two inverter devices of the same bridge arm in the inverter bridge are abnormal during the alternate work.

For example, due to the high ambient temperature or the aging of the inverter device itself, the parameters of the inverter device are changed, resulting in one device being turned on during the alternation process, and the other device is still turned off in the future, causing the same The "straight through" of the upper and lower devices of a bridge arm causes the short-circuit state between the positive and negative terminals of the DC voltage.

2. Over-current when the speed is increased When the inertia of the load is large, and the speed-up time is set too short, it means that during the speed-up process, the working efficiency of the inverter rises too fast, and the synchronous speed of the motor rises rapidly. However, the rotational speed of the motor rotor cannot be kept up due to the large inertia of the load, and as a result, the rising current is too large.

3. Overcurrent in the deceleration When the inertia of the load is large and the deceleration time is set too short, it will cause overcurrent. Because the speed reduction time is too short, the synchronous speed decreases rapidly, and the rotor of the motor maintains a high speed due to the inertia of the load. At this time, the speed at which the rotor winding cuts the magnetic line is too large to generate an overcurrent.

(2) Processing method

1. At the start of the start, it will trip at a rising speed. This is a phenomenon in which the overcurrent is very serious.

1 The working machine has no card,

2 Is there a short circuit on the load side, check if there is a short circuit to the ground with a megger

3 Is the inverter power module damaged?

4 The starting torque of the motor is too small, the drag system can't turn

2. Do not trip immediately when starting, but trip during operation, main inspection

1 The speed setting time is too short and the acceleration time is lengthened.

2 Deceleration time setting is too short, lengthening deceleration time

3 Torque compensation (U/F ratio) setting is too large, causing excessive no-load current at low frequencies

4 The electronic thermal relay is improperly set, and the operating current is set too small, causing the inverter to malfunction.

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