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Why is differential protection used on large high-voltage mo
source：未知 time：2024-09-18 09:10nbsp; 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 internal operation of the motor. Generally, the operating current values at the beginning and end of the motor winding are calculated, and the protection action is automatically triggered when the specified threshold is reached!
Threshold
The threshold is also called the critical value, which refers to the lowest or highest value that an effect can produce! 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 any two-port electrical network, generator, motor, transformer and other electrical equipment have very classic applications. Differential protection is relatively more 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 definite time 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 current with the same direction and equal magnitude flowing through the two ends of the motor is called the through current, while the current with the opposite direction is called the non-through current. As the main protection, the motor ratio brake differential protection uses the non-through current as the action amount and the through current as the brake amount, monitors and measures these specific parameters in real time, and distinguishes the normal state, fault state and abnormal normal operation state of the protected element.
low voltage electric motor, Ex motor, Motor manufacturers in China, three phase induction motor, Wolong Nanyang Explosion Protection 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 definite time 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 current with the same direction and equal magnitude flowing through the two ends of the motor is called the through current, while the current with the opposite direction is called the non-through current. As the main protection, the motor ratio brake differential protection uses the non-through current as the action amount and the through current as the brake amount, monitors and measures these specific parameters in real time, and distinguishes the normal state, fault state and abnormal normal operation state of the protected element.
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 the 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 element, and it is reliable not to act during normal operation and out-of-zone faults.
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