Generally speaking, the factory motor is based on a given power-frequency voltage (380V, 50hz) to obtain the rated speed value. If it does not reach 380V under actual working conditions, such as only 300V and 50hz, the voltage is obviously under pressure. Basically, it can't reach the rated speed because, depending on the design of the motor, it must have a voltage of 380V and a frequency of 50hz. To excite, at the rated voltage, the magnetic field strength is not up to, and the magnetic flux is very small, so it will definitely affect the speed, not because of the 60f/p formula to see the speed change. For example, in the case of 380V 40Hz input, according to the formula E=K*F*Q, E remains unchanged and F decreases, then Q flux increases. This is a case of overvoltage. Too much excitation will cause the motor to heat up and possibly burn out over a long period of time. Therefore, the value of magnetic flux should not be too large, which is determined by the bearing capacity of the motor in design. Usually at constant torque speeds (below 50 hz), the magnetic flux at this point is the rated magnetic flux, also known as the full magnetic flux. If the voltage/frequency increases, it will exceed the flux value, causing the motor to heat up.

Constant torque speed control:

In other words, let the flux be constant, v over f is equal to q is constant. Why is it called constant torque speed regulation? In other words, the load torque is a fixed value, and so is the motor output torque. See formula: t = k * I * q, when q is constant, the motor output torque is proportional to the I, because the value of q can through the nameplate V (rated voltage) / 50 hz to calculate, so when the q is constant, the rated current of the coil (regardless of whether there is a load, by determining the largest current, can also determine the maximum torque of the motor output (can also determine how much torque motor to drive the constant load), so the motor over-current capacity reflects the overload capacity (torque).

The following provides a constant torque speed, which only needs to be delivered by the inverter through a motor modulated by a voltage at a certain frequency (magnetic flux, the ratio of predetermined values). The load torque is also a fixed value, so the constant N, T and of course, the input power P are therefore fixed. If F increases and the speed N increases, the power P will increase, because the torque T will not increase due to the increase in speed (this is also known as a constant torque load, such as a conveyor belt. Constant torque characteristics are independent of load torque and speed, where torque remains constant or substantially constant at any speed in general applications, such as conveyor belt, mixer, or extruder type friction load and crane, hoisting potential load, etc.)

Another point is that the rated speed is the value obtained when the motor is idling. For the meaning of this value, when the rated voltage and rated power are reached, the larger the value, the smaller the output torque. This is a characteristic of constant power speed regulation. Formula T=9550*P/N(rated speed). Therefore, in the case of f-type 50Hz(when the output power is the maximum), when n is large, attention should be paid to the fact that T is small to avoid accidents caused by T being too small and smaller than the load torque. In constant power speed regulation, speed regulation is achieved by reducing the magnetic flux to reduce the output torque and thus increase the speed, so it is also known as weak magnetic speed regulation.