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how to deal with 10 tons of electric hoist lift motor contactor pull instability?

A 10-ton electric hoist lift motor is 20KW motor due to the power supply line is too long to lift the motor running up to reduce the voltage drop so that the AC contactor voltage drop too large contactor (CJX2-5011) suction is not strong. Frequent jump lead to frequent damage contactors, this failure can not change the power supply situation. 20KW motor with a load directly start the starting current do not know how many A? Is the contactor small?

I would like to use a wide input voltage switching power supply into DC, the use of DC control contactors, do not know if this method works?

These are the solutions:

1, the breaker chooses the rated current 3 times is correct! Because starts the electric current is the moment!

2, star angle operation and start current ratio is, the angle is 1.73 times the star!

Three-phase motor direct start-up current is rated current (motor nameplate above indicate) 4-7 times (depending on the load light and heavy may be.) With star three decompression starting current is full voltage start (direct start) current 1 / 3.

Calculation of motor starting current

The starting current of the motor is 7 times the rated current.

The fuse current is 2.5 times the rated motor current.

Star delta starting current is 2.4 times the rated current

The motor starting current is not a fixed value, in the motor starting process, the current from large to small changes,

Is a reciprocal function of time (i = I + I / (a-t)). No specific formula.

Power is just turned on, the motor is basically no sense of resistance, only the impedance, which is the coil DC resistance, this value is very small,

So the instantaneous current is very large, will be rated several times the current, but the duration is very short, usually only 0.0 seconds. As the motor starts to rotate, the current drops sharply,

If you do not start with the load in 1 second will drop to about 10 times the rated current, with the speed increase, after 2 seconds can be reduced to 2-3 times, then continue to decline until equal to the rated current, which When the motor rotation

Speed ​​also rose to the rated speed.

Therefore, the motor starting current is an average. Due to the different motors, different loads, different

Start mode, start the time required is not the same, the average current there is a big difference.



For large motors,

You need to start the process of current time function for a detailed calculation,

To determine the circuit breaker

Protection setting.

General 40KW the following small motor, the start process is not to provide protection, so the choice of circuit breaker

, As long as they can escape the impact of starting current on the line.

As the circuit breaker action is time-limited, so 4-7 times the rated current line, no-load start to select the lower limit, with the load start to select the upper limit.

Star-angle start, start-up current is 1.7 times lower than the direct start, but the duration to be longer, switch to the angle, the current change is not.

Motor rated power * 2 = Motor operating current

The starting current of the motor is 5 – 7 times of the running current

If so, your contactor is too small. In addition, you can improve the control circuit, but still pay attention to the field measured voltage value to see

3,In fact, it is important regulator. The feeling is because the contactor often moves, and carry the AC motor is inductive load, resulting in surge current is too large.

In fact, the most fundamental reason is the contactor coil voltage fluctuations at both ends of the contactor to reach the minimum voltage, so it leads to contactor disconnected. DC control for the contactor, depends on the DC coil pull-in voltage range, to see your company’s supply voltage fluctuation range to meet the requirements. This can only try.

Essentially the transformer capacity of the factory or not enough. So add a soft start or more reliable frequency converter

4,20KW lifting motor, usually heavy and frequent start. 5011 contactor, in theory, is enough, but the actual use, I will at least with the 9511.. Pull is not strong, add a transformer with 36V voltage level of the coil, the voltage fluctuation does not exceed 100V coil suction is no problem. Plus switching power supply with a DC control, the price of a DC contactor AC contactor 4-5 times

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