Induction Motor on Furnace

Induction Motor on Furnace

The induction furnace with a power supply frequency in the range of 150-10000 Hz used in the intermediate frequency induction furnace is called an intermediate frequency induction furnace, and its main frequency is in the range of 150-2500 Hz. The power frequency of the domestic small-frequency induction furnace is 150, 1000, and 2500 Hz.

The complete equipment of medium frequency induction furnace includes four parts:

1. Furnace body

The furnace body of the power frequency induction furnace for smelting cast iron is composed of induction furnaces (two sets, one for smelting and the other for standby), furnace cover, furnace frame, tilting furnace oil cylinder, furnace covers the mobile opening and closing device, etc.

2. Electrical parts

The electrical part is composed of a power transformer, main contactor, balance reactor, balance capacitor, compensation capacitor, induction motor of the furnace, electrical console, etc.

3. Cooling system

The cooling water system includes capacitor cooling, inductor cooling, and flexible cable cooling, etc. The cooling water system is composed of water pumps, circulating pools or cooling towers, and pipeline valves.

4. Hydraulic system

The hydraulic system includes oil tanks, oil pumps, oil pump motors, hydraulic system pipes and valves, and hydraulic consoles.

Induction Motor on Furnace

The induction motor uses the principle of electromagnetic induction to generate a rotating magnetic field through the three-phase current of the stator and interacts with the induced current in the rotor winding to generate electromagnetic torque for energy conversion. Under normal circumstances, the rotor speed of the induction motor is always slightly lower or slightly higher than the speed of the rotating magnetic field (synchronous speed), so the induction motor is also called an "asynchronous motor".

When the load of the induction motor changes, the speed, and slip of the rotor will change accordingly so that the electromotive force, current and electromagnetic torque in the rotor conductor will change accordingly to meet the needs of the load. According to the positive and negative of the slip and the size, the induction motor has three operating states of the motor, generator, and electromagnetic brake.

When the rotor speed is lower than the speed of the rotating magnetic field (ns>n>0), the slip is 0

If the motor is driven by a prime mover so that the rotor speed is higher than the rotating magnetic field speed (n>ns), then the slip s<0. At this time, the induced electromotive force in the rotor conductor and the active component of the current will be opposite to those of the motor, so the direction of the electromagnetic torque will be opposite to the rotating magnetic field and the rotor steering, as shown in Figure 5-5b, that is, the electromagnetic torque is Torque of a braking nature. In order to make the rotor continuously rotate at a speed higher than that of the rotating magnetic field, the drive torque of the prime mover must overcome the electromagnetic torque of the brake; at this time, the rotor inputs mechanical power from the prime mover and outputs electric power through electromagnetic induction, and the motor is in Generator status.

If the rotor is rotated against the direction of the rotating magnetic field by mechanical or other external factors (n<0), then the slip s>1. At this time, the relative speed direction of the rotor conductor "cutting" the air gap magnetic field is the same as that of the motor state, so the induced electromotive force in the rotor conductor and the active component of the current are in the same direction as that of the motor state, and the direction of the electromagnetic torque is also the same as that in Figure 5-5a same. But because the rotor turns to change, so for the rotor, this electromagnetic torque appears as a braking torque. At this time, the motor is in the state of electromagnetic braking. On the one hand, it inputs mechanical power from the outside, and at the same time absorbs electric power from the grid, both of which become losses inside the motor.