What are the starting methods of explosion-proof motors?

Explosion-proof motor starting method: inverter starting

When the explosion-proof motor is started with a frequency converter, it can be started at a lower frequency. At this time, the speed is low and the starting current is small, no impact torque is generated, the start is smooth, and the impact on the motor winding is small, which can effectively extend the service life of the explosion-proof motor.

Frequency converter is a high-tech product in the field of motor control in recent years with good control function. It can adjust the rated speed and torque of explosion-proof motors by changing the frequency of the power grid. Because it involves power electronics technology and microcomputer technology, it is expensive and has high requirements for maintenance technicians. It is mainly used in fields that require speed regulation and high speed control requirements.

Let's take a look at the starting process of the inverter. During the starting process of the motor, the frequency and voltage output by the inverter gradually increase.

The frequency gradually increases from the lowest frequency (such as 0HZ) according to the preset acceleration time. If the starting frequency is set to 3HZ, taking a 4-pole motor as an example, its synchronous speed at the beginning is only: n1=60f/P=60*3/2=90 (r/min). The relative speed between the rotor winding and the rotating magnetic field is only 6% of that at the industrial frequency starting; and the voltage supplied to the motor also gradually increases from the lowest voltage. Therefore, the impact current at the moment of starting is very small. Since the frequency and voltage are gradually increased to the rated value, the speed of the motor rises slowly during the starting process. The starting current Iq will also be limited to a certain range. As shown in Figure (C), Ic is the rated current of the motor. Using variable frequency starting can also reduce the dynamic torque during the starting process. The smooth starting reduces the impact on the transmission machinery.

Triangular step-down starting method for explosion-proof motors

Since the starting current of explosion-proof motors is very large, in order to reduce the system load and prevent overload, we can generally choose reduced voltage starting, and triangular reduced voltage starting is one of them. The characteristics of triangular reduced voltage starting are simplicity and economy. The starting current is about 1/3 lower than that of full-voltage starting. It is suitable for use in places where the load is not large. The principle is to use Y-type connection when starting the motor. At this time, the motor loading voltage is 220V. When the explosion-proof motor is started, it is changed to triangle connection. In this way, the explosion-proof motor receives a voltage of 380V and operates normally. This can effectively protect the explosion-proof motor and circuit system.

There are several ways to start explosion-proof motors in triangle voltage reduction:

1. Manual control

2. Automatic switching control using transistor delay circuit

3. Use intermediate and time relays to delay the conversion start control