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An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.[1] An induction motor can therefore be made without electrical connections to the rotor.[a] An induction motor's rotor can be either wound type or squirrel-cage type.
Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service, induction motors are increasingly being used with variable-frequency drives (VFD) in variable-speed service. VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable-torque centrifugal fan, pump and compressor load applications. Squirrel-cage induction motors are very widely used in both fixed-speed and variable-frequency drive applications.
In both induction and synchronous motors, the AC power supplied to the motor's stator creates a magnetic field that rotates in synchronism with the AC oscillations. Whereas a synchronous motor's rotor turns at the same rate as the stator field, an induction motor's rotor rotates at a somewhat slower speed than the stator field. The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor. This induces an opposing current in the induction motor's rotor, in effect the motor's secondary winding, when the latter is short-circuited or closed through an external impedance.[28] The rotating magnetic flux induces currents in the windings of the rotor,[29] in a manner similar to currents induced in a transformer's secondary winding(s).
The induced currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. The direction of the magnetic field created will be such as to oppose the change in current through the rotor windings, in agreement with Lenz's Law. The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor-winding currents the rotor will start to rotate in the direction of the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the applied mechanical load on the rotation of the rotor. Since rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slightly slower than synchronous speed. The difference, or "slip," between actual and synchronous speed varies from about 0.5% to 5.0% for standard Design B torque curve induction motors.[30] The induction motor's essential character is that it is created solely by induction instead of being separately excited as in synchronous or DC machines or being self-magnetized as in permanent magnet motors.[28]
For rotor currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating magnetic field (); otherwise the magnetic field would not be moving relative to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio between the rotation rate of the magnetic field induced in the rotor and the rotation rate of the stator's rotating field is called "slip". Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as "asynchronous motors".[31]
An induction motor can be used as an induction generator, or it can be unrolled to form a linear induction motor which can directly generate linear motion. The generating mode for induction motors is complicated by the need to excite the rotor, which begins with only residual magnetization. In some cases, that residual magnetization is enough to self-excite the motor under load. Therefore, it is necessary to either snap the motor and connect it momentarily to a live grid or to add capacitors charged initially by residual magnetism and providing the required reactive power during operation. Similar is the operation of the induction motor in parallel with a synchronous motor serving as a power factor compensator. A feature in the generator mode in parallel to the grid is that the rotor speed is higher than in the driving mode. Then active energy is being given to the grid.[2] Another disadvantage of induction motor generator is that it consumes a significant magnetizing current I0 = (20-35)%.
An AC motor's synchronous speed, , is the rotation rate of the stator's magnetic field,
,where is the frequency of the power supply, is the number of magnetic poles, and is the synchronous speed of the machine. For in hertz and synchronous speed in RPM, the formula becomes:
.[32][33]For example, for a four-pole, three-phase motor, = 4 and = 1,500 RPM (for = 50 Hz) and 1,800 RPM (for = 60 Hz) synchronous speed.
The number of magnetic poles, , is equal to the number of coil groups per phase. To determine the number of coil groups per phase in a 3-phase motor, count the number of coils, divide by the number of phases, which is 3. The coils may span several slots in the stator core, making it tedious to count them. For a 3-phase motor, if you count a total of 12 coil groups, it has 4 magnetic poles. For a 12-pole 3-phase machine, there will be 36 coils. The number of magnetic poles in the rotor is equal to the number of magnetic poles in the stator.
The two figures at right and left above each illustrate a 2-pole 3-phase machine consisting of three pole-pairs with each pole set 60° apart.
Induction furnace is used for smelting or insulating ferrous metals, non-ferrous metals, sponge iron, such as scrap iron, scrap steel, copper, aluminum and so on. Complete working equipment such as continuous casting machine, rolling mill, mainly used for the production of billet, steel bar, angle steel, H-beam, I-beam, etc. Using KGPS, IGBT, single or double power supply technology, PLC (Siemens) can be realized throughout the monitoring.NO. | Electric Furnace Type |
Input power (KW) |
input voltage (V) |
Input current (A) |
Rated power (KW) |
DC current (A) |
DC voltage (V) |
Melting rate (T/H) |
working frequency (HZ) |
working voltage (V) |
cooling water pressure(MPA) |
Rated capacity (T) |
Power consumption (KWH/T) |
|
Power Supply |
Furnace body |
|||||||||||||
1 | GW-0.25-160/1JJ | 180 | 380 (6 Pulse) |
256 | 160 | 320 | 500 | 0.24 | 1000 | 750 | 0.1~0.15 | 0.25~0.3 | 0.25 | 790 |
2 | GW-0.5-250/1JJ | 280 | 380 (6 Pulse) |
400 | 250 | 500 | 500 | 0.4 | 1000 | 1500 | 0.1~0.15 | 0.25~0.3 | 0.5 | 770 |
3 | GW-0.5-250/1J | 280 | 380 (6 Pulse) |
400 | 250 | 500 | 500 | 0.4 | 1000 | 1500 | 0.1~0.15 | 0.25~0.3 | 0.5 | 770 |
4 | GW-0.75-400/1JJ | 400 | 380 (6 Pulse) |
650 | 400 | 800 | 500 | 0.6 | 1000 | 1500 | 0.1~0.15 | 0.25~0.3 | 0.75 | 770 |
5 | GW-0.75-400/1J | 400 | 380 (6 Pulse) |
650 | 400 | 800 | 500 | 0.6 | 1000 | 1500 | 0.1~0.15 | 0.25~0.3 | 0.75 | 770 |
6 | GW-1-500/1JJ | 550 | 380 (6 Pulse) |
800 | 500 | 1000 | 500 | 0.8 | 1000 | 1500 | 0.1~0.15 | 0.25~0.3 | 1 | 750 |
7 | GW-1-750/1JJ | 800 | 380/690 (6 Pulse) |
1200/ 700 |
750 | 1500/ 850 |
500/ 880 |
0.9 | 1000/ 500 |
1500/ 2600 |
0.1~0.15 | 0.25~0.3 | 1 | 720/660 |
8 | GW-1-750/1J | 800 | 380/690 (6 Pulse) |
1200/ 700 |
750 | 1500/ 850 |
500/ 880 |
0.9 | 1000/ 500 |
1500/ 2600 |
0.1~0.15 | 0.25~0.3 | 1 | 720/660 |
9 | GW-1.5-1000/0.5JJ | 1100 | 690 (6 Pulse) |
912 | 1000 | 1140 | 880 | 1.2 | 500 | 2600 | 0.1~0.15 | 0.25~0.3 | 1.5 | 700 |
10 | GW-1.5-1000/0.5J | 1100 | 690 (6 Pulse) |
912 | 1000 | 1140 | 880 | 1.2 | 500 | 2600 | 0.1~0.15 | 0.25~0.3 | 1.5 | 700 |
11 | GW-2-1500/0.5JJ | 1650 | 690 (6 Pulse) |
1360 | 1500 | 1700 | 880 | 1.7 | 500 | 2600 | 0.1~0.15 | 0.25~0.3 | 2 | 675 |
12 | GW-2-1500/0.5J | 1650 | 690 (6 Pulse) |
1360 | 1500 | 1700 | 880 | 1.7 | 500 | 2600 | 0.1~0.15 | 0.25~0.3 | 2 | 675 |
13 | GW-2-2000/0.5JJ | 2200 | 690 (6 Pulse) |
1400 | 2000 | 2275 | 880 | 1.9 | 500 | 2600 | 0.1~0.15 | 0.25~0.3 | 2 | 650 |
14 | GW-3-2500/0.5JJ | 2750 | 690/950 (6 Pulse) |
2275/ 1700 |
2500 | 2840/ 2080 |
880/ 1250 |
2.56 | 500 | 2600/3200 | 0.1~0.15 | 0.25~0.3 | 3 | 610/560 |
15 | GW-3-2500/0.5J | 2750 | 690/950 (6 Pulse) |
2275/ 1700 |
2500 | 2840/ 2080 |
880/ 1250 |
2.56 | 500 | 2600/3200 | 0.1~0.15 | 0.25~0.3 | 3 | 610/560 |
16 | GW-4-3000/0.5J | 3300 | 690/950 (6 Pulse) |
2730/ 2040 |
3000 | 3410/ 2500 |
880/ 1250 |
3.2 | 500 | 2600/3200 | 0.1~0.15 | 0.25~0.3 | 4 | 610/560 |
17 | GW-5-4000/0.5J | 4400 | 950 (6 Pulse) |
2300 | 4000 | 3330 | 1250 | 5 | 500 | 3400 | 0.1~0.15 | 0.25~0.3 | 5 | 600/550 |
18 | GW-6-4000/0.5J | 4400 | 950 (12 Pulse) |
2300 | 4000 | 3330 | 1250 | 5 | 500 | 3400 | 0.1~0.15 | 0.25~0.3 | 6 | 600/550 |
19 | GW-8-5000/0.5J | 5000 | 950 (12 Pulse) |
3400 | 5000 | 4200 | 1250 | 7~8 | 500 | 3400 | 0.1~0.15 | 0.25~0.3 | 8 | 600/550 |
20 | GW-10-6000/0.5J | 6300 | 950 (12 Pulse) |
3750 | 6000 | 4600 | 1250 | 8.5~9 | 500 | 3400 | 0.1~0.15 | 0.25~0.3 | 10 | 600/550 |
21 | GW-12-8000/0.25J | 8000 | 950 (12 Pulse) |
4900 | 8000 | 6000 | 1250 | 9~10.5 | 250 | 3400 | 0.1~0.15 | 0.25~0.3 | 12 | 600-550 |
22 | GW-15-8000/0.25J | 8000 | 950 (12 Pulse) |
4900 | 8000 | 6000 | 1250 | 9~10.5 | 250 | 3400 | 0.1~0.15 | 0.25~0.3 | 15 | 600-550 |
23 | GW-15-10000/0.25J | 10000 | 950 (24 Pulse) |
6500 | 10000 | 8000 | 1250 | 13~15 | 250 | 3400 | 0.1~0.15 | 0.25~0.3 | 15 | 600-550 |
24 | GW-18-12000/0.25J | 12000 | 950 (24 Pulse) |
8160 | 12000 | 10000 | 1200 | 15~17 | 250 | 3400 | 0.1~0.15 | 0.25~0.3 | 18 | 600-550 |
25 | GW-20-12000/0.25J | 12000 | 950 (24 Pulse) |
8160 | 12000 | 10000 | 1200 | 17~19 | 250 | 3400 | 0.1~0.15 | 0.25~0.3 | 20 | 600-550 |
26 | GW-25-14000/0.25J | 14000 | 950 (24 Pulse) |
9460 | 14000 | 11600 | 1200 | 19~21 | 150~200 | 3400 | 0.1~0.15 | 0.25~0.3 | 25 | 600-550 |
27 | GW-30-16000/0.2J | 16000 | 950 (24 Pulse) |
10850 | 16000 | 13300 | 1200 | 21~23 | 150~200 | 3400 | 0.1~0.15 | 0.25~0.3 | 30 | 600-550 |
28 | GW-40-20000/0.2J | 20000 | 950 (24 Pulse) |
13545 | 20000 | 16600 | 1200 | 25~27 | 150~200 | 3400 | 0.1~0.15 | 0.25~0.3 | 40 | 600-550 |
29 | GW-50-22000/0.2J | 22000 | 950 (24 Pulse) |
14932 | 22000 | 18300 | 1200 | 25~28 | 150~200 | 3400 | 0.1~0.15 | 0.25~0.3 | 50 | 600-550 |