Buchholz relay is used for protecting transformer against incipient or internal faults. Buchholz relay is a gas-actuated relay installed in oil immersed transformers for protection against all kinds of faults.
When voltage changes occur in rapid succession, with magnitudes large enough to cause lighting level variations. The human eye-brain response is most sensitive to periodic r.m.s. voltage changes that occur at around 8 - 10 cycles per second.
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