Buchholz relay is a gas- actuated relay installed in oil-immersed transformers for protection against all kind of faults. It is used to gives an alarm in case of slow developing faults or incipient faults in the transformer and to disconnect the transformer from the supply in the event of severe internal faults. It is installed in the pipe between the conservator and main tank as shown in fig11 below. This relay is used in oil-immersed transformers of rating above 750 kVA. CONSTRUCTION Fig 12 shows the constructional details of buchholz relay. It consists of a domed vesselplaced in the pipe between the conservator and main tank of the transformer. The device has two elements. The upper element consists of a mercury type switch attached to a float. The lower element contains a mercury read more

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SELF BALANCE SYSTEM The self balance system discussed in the category ‘ protection of generators’ can also be used without any modification for transformers; but the same type of equipments should be used for both primary and secondary windings. OVER CURRENT AND EARTH FAULT PROTECTION The over current protection is needed to protect the transformer from sustained overloads and short circuits. Induction type over current relays are used which in addition to providing overload protection acts as back up relays for protection of transformer winding fault. Fig 10 shows the combined over current and earth fault protection. The earth fault protection is used to provide protection against any earth fault in the windings of the transformer. It works on the principle that when the read more

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The differential protection used for transformers is based on the principle of current circulation. This type of protection is mostly used for transformers as this responds not only to inter turn fault but also provides protection against phase-to-phase faults. Following are the complicated features in transformers and there remedial measures: 1.In a power transformer, the currents in primary and secondary are to be compared. As these two currents are usually different, therefore the use of identical tr4ansformers will give differential current and operate the relay even under no load conditions. The difference in magnitude of currents in primary and secondary of power transformers is compensated by different turns ratios of C.T.s. If T is the turn’s ratio of power transformer, then read more

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