Electric Induction Motor

Product Description

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 ({\displaystyle n_{s}}); 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)%.

Synchronous speed[edit]

An AC motor's synchronous speed, {\displaystyle f_{s}}, is the rotation rate of the stator's magnetic field,

{\displaystyle f_{s}={2f \over p}},

where {\displaystyle f} is the frequency of the power supply, {\displaystyle p} is the number of magnetic poles, and {\displaystyle f_{s}} is the synchronous speed of the machine. For {\displaystyle f} in hertz and {\displaystyle n_{s}} synchronous speed in RPM, the formula becomes:

{\displaystyle n_{s}={2f \over p}\cdot \left({\frac {60\ \mathrm {seconds} }{\mathrm {minute} }}\right)={120f \over {p}}\cdot \left({\frac {\mathrm {seconds} }{\mathrm {minute} }}\right)}.^[32][33]

For example, for a four-pole, three-phase motor, {\displaystyle p} = 4 and {\displaystyle n_{s}={120f \over 4}} = 1,500 RPM (for {\displaystyle f} = 50 Hz) and 1,800 RPM (for {\displaystyle f} = 60 Hz) synchronous speed.

The number of magnetic poles, {\displaystyle p}, 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.

 

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

Note:
(1) GW - means medium frequency induction furnace, - 1 - means induction furnace capacity of 1 ton, - 500 - means furnace rated power of 500 KW, / 1 - means furnace operating frequency of 1000 Hz, / 0.5 - means melting furnace frequency of 500 Hz, - J - means hydraulic tilting furnace (furnace shell is steel shell), - JJ - means mechanical tilting furnace. (the shell of the furnace is aluminum alloy).

(2) The above quoted price is for routine configuration. Other configurations can be added, such as leak alarm, water temperature alarm, furnace switch, cover mechanism, lining ejector and transformer, cooling device (open and close cooling tower, closed cooling tower, plate heat exchanger)

3) If necessary, send technicians to carry out the commissioning: the domestic section is free; the overseas section travel expenses, accommodation and food are borne by the user and each person is subsidized 150 US dollars per day.

4) I quote EX-W at a price including simple packing, including shipping charges to Shanghai port area and all inland charges in China.

V) The above electric furnace voltage levels are 380V, 690V and 950/1000V, and the frequency is 50HZ. If the user equipment requirements are different from the above voltage levels and frequencies, each item needs to be increased by 15000USD.