Differential protection used on large high-voltage motors?_Wolong Nanyang Explosion-proof Motor, China Motor Manufacturer

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Differential protection used on large high-voltage motors?

source：未知 time：2024-07-15 10:12nbsp; click：

Compared with small and medium-sized motors, high-voltage motors are expensive and are used in critical and special applications. Whether it is the disposal of the motor body after a failure or other problems derived from the failure, it may be much more serious than we can imagine. For this reason, some high-voltage motors used in special occasions will use differential protection devices, the purpose of which is to detect problems in a timely and effective manner and prevent them from further deteriorating.

Motor differential protection is mainly used for medium and large motors in high-voltage power grids. It reflects the quality of the motor's internal operation. Generally, the operating current values at the beginning and end of the motor winding are calculated. When the specified threshold is reached, the protection action is automatically triggered!

Differential protection is a very effective protection measure for the safe operation of electrical equipment. It uses the characteristics of the input current and output current vector difference of electrical equipment to trigger the protection action, making it a very classic application for any two-port electrical network, generator, motor, transformer and other electrical equipment.

Differential protection is relatively widely used on large high-voltage motors. For example, high-voltage motors used in mine main power and main ventilation equipment must be equipped with differential protection devices to ensure the safe and reliable operation of the system and avoid major economic losses and safety accidents caused by unexpected shutdowns.

The stator windings of large high-voltage motors usually adopt star connection, with three output terminals by default. When differential protection is introduced, the motor must have 6 output terminals. The differential protection device applied to the motor works as follows: detect the starting and ending currents of the motor, and compare the phase and amplitude difference between the starting and ending currents. Under normal circumstances, the difference in amplitude and phase between the starting and ending currents is zero, that is, the current flowing into the motor is equal to the current flowing out of the motor; when a short circuit fault such as phase-to-phase, turn-to-turn or to ground occurs inside the motor, a differential current is generated between the two and when it reaches a certain value, the protection function is activated.

The motor differential protection device is constantly being improved and perfected according to actual needs, and can provide multiple protection functions such as current quick-break, thermal overload inverse time overcurrent, two-stage time-limited negative sequence, zero sequence current, rotor stagnation, long start time, frequent start, etc.

For large-capacity motors, the differential protection device should be designed according to the three-phase longitudinal differential. In this way, it can not only serve as the main protection for the short circuit between the motor stator winding and the lead wire, but also as the main protection for single-phase grounding fault, acting on instantaneous tripping, and realizing the dual protection of input and output states.

The currents with the same direction and equal magnitude flowing through the two ends of the motor are called through currents, while the currents with opposite directions are called non-through currents. As the main protection, the motor ratio braking differential protection uses the non-through current as the action amount and the through current as the braking amount, and monitors and measures these specific parameters in real time to distinguish the normal state, fault state and abnormal operating state of the protected components.

Parameter characteristics under different states

Under normal operation, the through current is the load current, and the non-through current is theoretically zero; when the motor is in a phase-to-phase short circuit state, the non-through current will increase sharply; when the motor has an external fault, the through current will increase sharply.

The protection device can sensitively respond to the internal phase-to-phase short circuit state action output, thereby achieving the purpose of protecting the component, and it will reliably not act in normal operation and out-of-zone faults.

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