Category: Apparatus Protection in Power System

Transformer Feeder Protection

Transformer Feeder Protection: Transformer Feeder Protection – In order to supply bulk power from a major switching station, the transformer is sometimes connected directly to the feeder without an HV switchgear at the transformer. Although such a scheme provides considerable saving in the cost of switchgear but the problems of providing adequate protection are increased. […]

Gas Actuated Relays

Gas Actuated Relays: Gas Actuated Relays – When a fault occurs inside the transformer tank gas is usually generated, slowly for an incipient fault and violently for heavy faults. Most short circuits developed either by impulse breakdown between adjacent turns at the end turns of the winding or as a very poor initial point contact […]

Restricted Earth Fault Protection

Restricted Earth Fault Protection: This type of Restricted Earth Fault Protection is provided to detect earth-faults within the protected zone of the transformer. A CT is fitted in each connection to the protected winding, and the CT secondary windings are connected in parallel to a relay. Figure (6.8) illustrates the connections of Restricted Earth Fault […]

Star Winding and Delta Winding

Star Winding and Delta Winding: Star Winding and Delta Winding – The magnitude of earth-fault current for a given fault position within a winding depends upon the winding connections and the method of neutral earthing. The two conditions for earth-fault current to flow in the case of a winding fault to earth are: That a […]

Inrush Currents in Transformer

Inrush Currents in Transformer: Magnetizing Inrush Currents in Transformer contain pronounced harmonics but the current during internal fault conditions is sinusoidal. Advantage is taken of this fact in the design of the relay. It was pointed out earlier that for high speed and low primary operating current the harmonic content of the current is filtered […]

Percentage Biased Differential Relay

Percentage Biased Differential Relay: Percentage Biased Differential Relay – In order to avoid undesirable operation on heavy external faults due to CT errors and ratio change as a result of tap changing, a restraining winding is provided which is energized by the through current. In other words the operating winding is biased and operates by […]

Differential Protection of Transformers

Differential Protection of Transformers: Differential Protection of Transformers is the most important type of protection used for internal phase-to-phase and phase-to-earth faults and is generally applied to transformers having ratings of 5 MVA and above. The principle of a differential relay is welt understood and discussed earlier. Any deviation from the normal ratio of the […]

Transformer Protection Types

Transformer Protection Types: Nature of Transformer Faults: Power transformers, being static, totally enclosed and oil immersed develop faults only rarely but the consequences of even a rare fault may be serious, unless the transformer is quickly disconnected from the system. For the purpose of Transformer Protection Types, faults can be divided into three main classes: […]