Precautions before starting the DC motor

DC motor as the starting device of the equipment plays a key role like the "heart". The user must follow the instructions to ensure the normal operation of the DC motor. Start control is a very important step for DC motors. For the normal operation of the equipment, we should pay attention to the following points when starting up:

1. DC motor wiring

The power plant generally adopts a parallel DC motor. The armature terminals are H1 and H2 and the terminals of the excitation winding are B1 and B2. The wiring is H1 and B1 is connected to the positive pole of the DC power supply. After H2 is connected to B2, Connect the negative pole of the DC power supply.

2. Reduce the starting current of the DC motor

Generally, except for DC motors of less than 4 kW, which can be started directly, all DC motors should start at less than 2 times the rated current of the motor. To reduce the starting current, it is generally necessary to limit the starting current in the armature circuit during the starting of the motor to limit the starting current or to reduce the starting current of the motor when the motor starts. Since the starting resistor is connected in the armature circuit, the equipment is simple, economical and reliable, so it is widely used.

For DC motors of 220V and 11KW: rated current of DC motor: Ie=11000/220=50(A), it is estimated that the internal resistance drop of rated operation is about 8% of rated voltage, then the internal resistance of DC motor: Rs =0.08x220/50=0.352(Ω) Motor direct starting current: IQ=220/Rs=220/0.352=625(A) The direct starting current is more than twice the rated current of the motor, which is enough to damage the armature winding.

When starting with a 3Ω resistor in series, the starting current of the motor: IQ1=220/(Rs+0.352)=220/(3+0.352)=65(A) The starting current can reach the starting requirement and reach The purpose of reducing the current.

3. DC contactor coil problem

For DC contactors for operation, the contactor coils should be long-term. For the CZ0 series contactors, they all run for a short time. Therefore, when the contactor is operated for a long time, the coil must not be burnt. Therefore, after the start of the start, the running contactor should be connected to a coil of about 150W, 1000Ω. The resistance prevents the coil from burning out.

4. Measurement of DC current

For the measurement of DC current, the shunt type is generally adopted. In the main circuit, a 100A, 75mv shunt is connected, and the positive and negative poles of the shunt are connected to a 75mv 0∽100A ammeter.

After the DC motor is started, check the normal running current of the motor. If it is stable, listen to it as long as the motor has no abnormal noise.