Introduction of Electric Motor Parameters

This article will briefly introduce some basic parameters of the electric motor, so that everyone can understand and purchase different electric motors.

Here is the list

Three factors that determine the main power of the electric motor

Rated speed

critical speed of rotor

Three factors determine the main power of the electric motor:

1) electric motor heating and temperature rise are the most important factors in determining electric motor power;

2) Allow short-time overload capability;

3) For asynchronous squirrel-cage electric motors, the starting capability should also be considered.

First, the specific production machinery calculates and selects the load power according to its heat generation, temperature rise and load requirements, and then pre-selects the rated power of the electric motor according to the load power, duty cycle and overload requirements. After pre-selecting the rated power of the electric motor, the heating and overload capacity should be checked, and the starting capacity should be checked if necessary.

If one of them fails, the electric motor must be reselected and checked again until all items pass. Therefore, a working system is also one of the requirements that must be provided. If there is no requirement, it will be processed according to the most conventional S1 working system by default; the electric motor with overload requirement also needs to provide the overload multiple and the corresponding running time; the asynchronous squirrel-cage electric motor drives the fan to rotate greatly. In the case of inertial loads, it is also necessary to provide the load moment of inertia and starting resistance torque curve to check the starting capability.

The above rated power is selected under the premise that the standard ambient temperature is 40℃. If the ambient temperature in which the electric motor works changes, the rated power of the electric motor must be corrected. According to theoretical calculation and practice, when the ambient temperature is different, the electric motor power can be roughly increased or decreased as shown in the table below.

Therefore, ambient temperature needs to be provided in regions with harsh climates, such as India, where ambient temperature needs to be checked as 50°C. In addition, high altitude also affects electric motor power. The higher the altitude, the greater the temperature rise of the electric motor and the lower the output power. electric motors used at high altitudes also need to consider the effects of the corona phenomenon.

Rated speed

The rated speed of the electric motor refers to the speed in the rated working mode.

The electric motor and the working machine it drives have their own rated speed. When selecting the electric motor speed, pay attention to the speed not too low, because the lower the rated speed of the electric motor, the more series, the larger the volume, and the higher the price; at the same time, the electric motor speed should not be too large. High, as this would make the transfer overly complex and difficult to maintain. Furthermore, when the power is constant, the electric motor torque is inversely proportional to the rotational speed. Therefore, those who do not have high requirements for starting and braking can comprehensively compare several different rated speeds from the aspects of initial investment, floor space, and maintenance costs of the equipment, and finally determine the rated speed; although frequent starting, braking and reversing , but if the duration of the transition process has little effect on productivity, in addition to considering the initial investment, the speed ratio and rated speed of the electric motor are also selected mainly according to the actual situation. Minimum amount of loss during transition. For example, the hoisting electric motor needs frequent forward and reverse rotation, and the torque is large, so the speed is very low, the electric motor is large and expensive.

critical speed of rotor

When the electric motor speed is high, the critical speed of the electric motor also needs to be considered. The rotor of the electric motor vibrates during operation, and the amplitude of the rotor increases as the rotational speed increases. When it reaches a certain velocity, the amplitude reaches a maximum value (that is often called resonance). After this speed, the magnitude increases with increasing speed. It gradually decreases and stabilizes within a certain range. The rotational speed at which the rotor amplitude is the largest is called the critical rotational speed of the rotor.

Hangzhou New Hengli Electric Machine MFG. Co., Ltd. With the experience of over 66 years of manufacturing experience in kinds of DC & AC Motors built up the customer-centered product development methodology and do under the special requirements of customers.