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Protection of power capacitors
Mar 12, 2019

1.capacitor Banks should use appropriate protection measures, such as the balancing differential relay protection or using instantaneous over-current relay protection, for more than 3.15 kV capacitor, a separate device must be on each capacitor fuse, fuse rated current should be according to the characteristics of fuse and plug flow to selected, when the general is 1.5 times the rated current of the capacitor is appropriate, in order to prevent the capacitor tank explosion.

2. In addition to the above mentioned forms of protection, the following types of protection may be provided when necessary:
(1)If the voltage rise is often and for a long time, it is necessary to take measures to make the voltage rise is not more than 1.1 times the rated voltage.
(2) with the appropriate current automatic switch for protection, so that the current increase does not exceed 1.3 times the rated current.
(3) if the capacitor is connected with the overhead line, the appropriate arrester can be used for atmospheric overvoltage protection.
(4) in the high voltage network, short circuit current more than 20A, and the short circuit current protection device or fuse can not reliably protect the ground short circuit, it should be used single-phase short circuit protection device.

3. The correct protection method of capacitor bank is the key to ensure the safe and reliable operation of capacitor. However, no matter which protection method is adopted, it should meet the following requirements:
(1) the protection device should be enough sensitivity, whether the capacitor bank in a single capacitor internal failure, or part of the element damage, the protection device can be reliable action.
(2) can selectively cut out the fault capacitor, or in the capacitor bank power supply all disconnected, easy to check out the damaged capacitor.
(3) in the process of capacitor stop power transmission and power system grounding or other faults, the protection device can not be wrong action.
(4) the protection device should be easy to install, adjust, test and operation maintenance.
(5) less power consumption, running costs should be low.

4. The capacitor is not allowed to be equipped with automatic reclosing device, instead, it should be equipped with automatic tripping device without pressure release. Is mainly due to the need of capacitor discharge time, when the switch of capacitor group trip, if reclosing immediately, is too late to discharge the capacitor, the capacitor may in some feelings and reclosing voltage polarity opposite electric charge, it will make the closing moment produces huge impact current, resulting in capacitor shell expansion, fuel injection, and even explode.

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