Protection configuration scheme In addition to the single fuse protection of the capacitor, the protection of the parallel capacitor compensation device is: current fast-break protection, mainly used to protect the fault of the capacitor bank link bus to the ground. Overcurrent protection is a backup for current quick-break protection and doubles as overload protection for shunt capacitance compensation devices. Differential voltage protection is mainly used to protect the capacitor from short-circuit faults at the connection point of the reactor and the winding of the reactor to the ground. Harmonic overcurrent protection, mainly used for harmonic overcurrent tripping. Over-voltage protection, excessive voltage causes the power consumption and heat generation of the capacitor to increase, affecting the service life of the capacitor, and over-voltage protection is required. Low voltage protection, when the busbar connected to the capacitor bank suddenly loses pressure, there may be: (1) once the voltage is restored, the transformer and the capacitor are simultaneously input, causing the overvoltage of the capacitor to be damaged; (2) the accumulated charge of the capacitor after the busbar is out of pressure Before the voltage is released, if the voltage is immediately restored and the capacitor is recharged, overvoltage damage may occur; therefore, low voltage protection must be configured.
Setting calculation principle
Current fast-break protection action current setting calculation principle: The minimum short-circuit current of the short-circuit caused by the capacitor connected to the busbar, and sufficient sensitivity to set. In order to reliably avoid the instantaneous inrush current of the capacitor bank, no delay is added.
Overcurrent protection action current setting principle: (1) The capacitance of the capacitor bank has a deviation of +10%, which makes the load current increase; (2) The capacitor is allowed to work for a long time under 1.3 times of rated current; (3) Under the impact of the inrush current Not mistaken. Generally, it is 1.5 times to 2 times of the rated current, and considering a certain return factor setting. The setting of the action time should consider the above three requirements, and the appropriate setting is generally set to 5s.
The setting of the differential voltage protection operating voltage is based on the principle: (1) determining the number of faulty capacitors when the voltage across the faulty capacitor does not exceed 1.1Un; (2) in the case of the number of faulty capacitors determined in step (1), the normal segment and The differential pressure between the fault segments; (3) The differential pressure calculated in step (2) divided by a certain sensitivity coefficient (generally not lower than 1.3) is the operating voltage of the differential voltage protection. The action time is generally set to 0.5s.
The calculation principle of the setting voltage of the differential voltage protection operating voltage: (1) determining the number of faulty capacitors when the voltage across the faulty capacitor does not exceed 1.1Un; (2) in the case of the number of faulty capacitors determined in step (1), the normal segment and Fault section
The differential pressure; (1) The differential pressure calculated in step (2) is divided by a certain sensitivity coefficient (generally not lower than 1.3), which is the operating voltage of the differential voltage protection. The action time is generally set to 0.5s.
The principle of differential current protection action current setting is: when the capacitor is input, the maximum unbalance current generated by the inrush current is set, that is, Idz=KK△fmaxKYLKtxIn, where KK is the reliability coefficient and Δfmax is the maximum amplitude of the current transformer. Error, KYL is the inrush current multiple, Ktx is the same coefficient of the current transformer on both sides, and In is the rated current. The action time is generally set to 0.5s.
Harmonic overcurrent protection action current setting principle: the equivalent third harmonic current is 1.5 times of the rated current and the continuous operation is not more than 2min.
The principle of setting the operating voltage of over-voltage protection: The original water conservancy and electric power ministry standard stipulates that the power capacitor should be able to operate for a long time under 1.10 times the power-frequency steady-state over-voltage; 1.I5 times the power-frequency steady-state over-voltage, every 24h Running continuously for 30 minutes; 1.20 times and 1.30 times power frequency steady-state overvoltage allows continuous operation
5 min and 1 min. Therefore, the operating voltage of the overvoltage protection can be set to 1.15 times to 1.2 times the busbar rated voltage, and the operating time can be long.
The low-voltage protection operating voltage is generally set to 0.5 times to 0.6 times the busbar rated voltage, and the operating time is generally set to 0.5s.
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