Three phase asynchronous motors are widely used in enterprise production due to their excellent advantages. To ensure the good operation of asynchronous motors, relevant personnel need to be familiar with the structural parameters and operating knowledge of the motor equipment, master the common faults and handling methods of the motor, and timely discover and solve the hidden dangers of motor accidents. The rated value of three-phase asynchronous motors is engraved on the nameplate of each motor. Here, Xinte Motor editor will give a brief introduction to the structure and nameplate parameters of three-phase asynchronous motors, generally including the following:
1. Model: In order to meet the needs of different purposes and working environments, electric motors are made into different series, each series is represented by various models. For example, Y 132 M-4:
Y → Three phase asynchronous motor, among which the product name code for three-phase asynchronous motor is: YR for wound asynchronous motor; YB is an explosion-proof asynchronous motor; YQ is a high starting torque asynchronous motor.
132 → Center height of machine base (mm);
M → Machine base length code;
4 → Number of magnetic poles;
2. Connection method: This is the connection method for the specified three-phase winding. There are six lead wires labeled U1, V1, W1, U2, V2, and W2 in the junction box of a typical squirrel cage motor. Among them, U1 U2 are the two ends of the first phase winding; V1 and V2 are the two ends of the second phase winding; W1 and W2 are the two ends of the third phase winding.
If U1, V1, and W1 are the starting ends (heads) of the three-phase winding, then U2, V2, and W2 are the corresponding ending ends (tails). These six lead out terminals need to be correctly connected to each other before connecting to the power supply. There are two connection methods: star (Y) connection and triangle connection. Usually, three-phase asynchronous motors with a power of less than 3kW are connected in a star shape; Connect those above 4kW to form a triangle.
3. Rated power PN: refers to the mechanical power at the output end of an electric motor when operating at the rated conditions specified by the manufacturer, generally measured in kilowatts (kW). For three-phase asynchronous motors, their rated power is PN=UNIN η NcosN, where η N and cosN are the efficiency and power factor under rated conditions, respectively.
3. Rated power PN: refers to the mechanical power at the output end of an electric motor when operating at the rated conditions specified by the manufacturer, generally measured in kilowatts (kW). For three-phase asynchronous motors, their rated power is PN=UNIN η NcosN, where η N and cosN are the efficiency and power factor under rated conditions, respectively.4. Rated voltage UN: refers to the line voltage applied to the stator winding during the rated operation of the motor, measured in volts (V).
It is generally stipulated that the working voltage of an electric motor should not be higher or lower than 5% of the rated value. When the working voltage is higher than the rated value, the magnetic flux will increase, which will greatly increase the excitation current. If the current is greater than the rated current, the winding will heat up. Meanwhile, due to the increase in magnetic flux, the iron loss (proportional to the square of the magnetic flux) also increases, causing the stator core to overheat; When the working voltage is lower than the rated value, it causes a decrease in output torque, a decrease in speed, an increase in current, and overheating of the winding, which is also detrimental to the operation of the motor.
The Y series small and medium-sized asynchronous motors produced in our country have a rated power of over 3kW, a rated voltage of 380V, and winding connections in a triangular shape. For rated power of 3 kW and below, the rated voltage is 380/220V, and the winding is Y/connected (i.e. when the power line voltage is 380 V, the motor winding is star connected); When the power line voltage is 220 V, the motor winding is connected in a triangular shape.
5. Rated current IN: refers to the line current of the stator winding of an electric motor at rated voltage and rated output power, measured in amperes (A).
When the motor is unloaded, the rotor speed approaches the synchronous speed of the rotating magnetic field, and the relative speed between the two is very small, so the rotor current is approximately zero. At this time, the stator current is almost entirely the excitation current that establishes the rotating magnetic field. When the output power increases, both the rotor current and stator current increase accordingly.
6. Rated frequency fN: The frequency of China's power grid is 50 Hertz (Hz), so except for exported products, the rated frequency of asynchronous motors used domestically is 50 Hertz.
7. Rated speed nN: refers to the speed of the rotor of an electric motor at rated voltage and rated frequency, with rated power output at the output terminal, measured in revolutions per minute (r/min). Due to different requirements for speed in production machinery, asynchronous motors with different numbers of magnetic poles need to be produced, resulting in different speed levels. The commonly used is a four pole asynchronous motor (n0=l500 r/min).
8. Rated efficiency η N: refers to the efficiency of an electric motor operating at rated conditions, which is the ratio of rated output power to rated input power. Namely, η N=× 100%=× 100%.
9. Rated power factor cosN: Because the motor is an inductive load, the stator phase current lags behind the phase voltage by one angle, cos is the power factor of the asynchronous motor.
The power factor of three-phase asynchronous motors is relatively low, about 0 at rated load 7～0. Between 9, it is even lower under light and empty loads, with only 0 2～0. 3. Therefore, it is necessary to correctly select the capacity of the electric motor, prevent the large horse from pulling the small car, and strive to shorten the idle time.
10. Insulation level: It is classified according to the maximum allowable temperature of the insulation material used in the motor winding during use. The so-called maximum temperature refers to the maximum allowable temperature of the hottest points in the insulation structure of the electric motor.
11. Working mode: Reflecting the operation of asynchronous motors, it can be divided into three basic modes: continuous operation, short-term operation, and intermittent operation.
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