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    Home»Protection»OVERVIEW OF TRANSFORMER PROTECTION
    Protection

    OVERVIEW OF TRANSFORMER PROTECTION

    madhusmitaBy madhusmitaNovember 20, 2022Updated:December 19, 2022No Comments3 Mins Read
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    There are different kinds of transformers such as distribution transformers, power transformers, autotransformers, regulating transformers, isolation transformers, and rectifier transformers, etc.

    The transformer protection scheme varies based on the type of transformer. Transformer protection depends upon their importance, winding connections, earthing methods and mode of operation etc.

    A transformer has its marshaling kiosk in the yard and a protection panel in the control room.

    Need of  Protection

    • The continuity of transformer operation is very important to maintain the reliability of a power network.
    • Any unscheduled repair work, especially the replacement of a faulty transformer is very expensive and time-consuming.
    • Major damage following a fault may require extensive repair.

    TYPES OF FAULT IN TRANSFORMERS

    EXTERNAL FAULT

    • In case of an external fault condition, the transformer must be disconnected if other protective meant to operate for such faults, fail to operate in a predetermined time.
    • Time graded over current relays is used as backup protection.
    • Thermal relays are used for overload as the transformer should not operate for a long duration

    INTERNAL FAULT

    Short circuit in the transformer winding & connections —

    • Cause immediate damage
    • Detectable at winding by unbalance in voltage or current.
    • Include line-gnd, line-line fault

    Incipient faults –

    • Minor in nature but slowly develop into major faults.
    • Due to poor electrical connections, core faults, failure of the coolant, regulator fault & bad load sharing between transformers.
    SL NOPROTECTION SCHEMEPRINCIPLEPROTECTION ZONE
    1DIFFERENTIAL(87T)Works on the principle of current differential and operation depend on the difference and restraint of currentTransformer winding
    2OVER CURRENT(51,67)It acts on the principle of over-current in the system and behaves as backup protection.Transformer winding
    3EARTH FAULTIt acts on the principle of residual current, an unbalanced current in the system. For the earth fault in the winding, the differential /REF relay actuates,if fails then this relay operates as the backup.Transformer winding
    4RESTRICTED EARTH FAULTThis relay is connected across the residual current in the system and neutral current with the necessary arrangement of stabilizing resistor and other auxiliaries Transformer Winding & Insulation
    5OVER FLUXINGOver fluxing conditions in a transformer can occur during system over-voltage and/or under frequency conditions(v/f). The relay works from the voltage supply and frequency available to the transformer. Transformer Insulation
    6BUCHHOLZ RELAYGas operated relayProtects transformer from an aggravated fault condition
    7PRESSURE RELIEF DEVICEworks on the principle of activation of bellow due to pressureProtects transformer from an aggravated fault condition
    8OIL TEMP INDICATORchange in temperatureProtects transformer from the abnormal rise in temperature
    9WINDING TEMP INDICATORchange in temperatureProtects transformer from the abnormal rise in temperature
    10OIL SURGE RELAYgas operated relayProtects OLTC from an aggravated fault condition
    11AIR CELL PROTECTION——To monitor Oil and Aircell in the conservator
    12ONLINE DGA SET——Monitors the status of Oil
    Transformer Protection Functions

    SUMMARY

    Though there are various types of protection schemes and a variety of relays to sense the fault in a transformer, all these schemes come into play after a fault occurred inside the transformer.

    So the first and most important things are successful installation, maintenance & care of a transformer by which fault can be minimized to a greater extent.

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