High-voltage motor manufacturers reminded that, compared with ordinary motors, high-power high-voltage motors are expensive, and the application site is critical and extraordinary. Whether it is the treatment of the motor body after the interference, or other problems due to the interference, it is probably more than we can imagine Is much more serious.
For this reason, for the high-voltage variable frequency motors used in some extraordinary places, the motor manufacturers will initiate the recovery of the differential shielding device, the goal of which is to find the problem in real time and effectively and prevent the problem from further deterioration.
Motor differential protection is mainly used for medium and large motors in the high-voltage power grid. It echoes the quality of the internal operation of the motor. Generally, the operating current values at the beginning and end of the motor windings are used for calculation, and the protection action is automatically triggered when the specified threshold is reached!
Differential protection is a very effective protection method for the safe operation of electrical equipment. The vector difference between the input current and output current of the operating electrical equipment triggers the characteristics of the protection action, so that any two-way electrical network, high-power motor, high-voltage motor, transformer, etc. Electrical equipment has very classic applications.
Differential shielding is relatively used in large-scale high-voltage variable frequency motors.For example, the main power of the mine and the high-voltage motor for the main ventilation equipment must be equipped with a differential shielding device to ensure the safe and reliable operation of the system, and to prevent the major economic losses and security disturbances that will be caused by unexpected shutdowns.
The stator windings of large-scale high-voltage motors are usually star-connected, and three outlet terminals are defaulted.When the differential shield is introduced, the motor must have 6 outlet terminals.The differential protection device applied to the motor acts like this: it detects the start and end current of the motor, and compares the phase and amplitude difference between the start and end current.Under normal circumstances, the difference between the amplitude and phase of the start current and the end current is zero, that is, the current flowing into the motor is the current flowing out of the motor; when there is a short circuit such as phase-to-phase, turn-to-turn, or to ground in the motor, between the two That is, when the difference flow occurs and reaches a certain value, the screen result is activated.
The differential protection device of the motor is constantly modified and improved according to actual needs. It can provide current quick-break, thermal overload inverse time overcurrent, two-stage negative sequence, zero sequence current by time limit, rotor stagnation, excessive starting time, and frequent Start-up and many other protection results.
For extra-large-capacity motors, the differential shielding device should be designed according to the three-phase longitudinal differential design.In this way, it can not only be used as the main shield for short-circuit between the stator windings and lead wires of the motor, but also as the main shield for single-phase grounding obstacles. It can be used for instantaneous tripping and realize the dual protection of input and output states.
