Transformer Differential Protection


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    The SIPROTEC 7UT63 and 7UT635 differential protection relays are used for fast and selective fault clearing of short-circuits in transformers of all voltage levels and also in rotating electric machines like motors and generators, for short lines and busbars. The protection relay can be parameterized for use with threephase and single-phase transformers. The specifi c application can be chosen by parameterization. In this way an optimal adaptation of the relay to the protected object can be achieved.

    In addition to the differential function, a backup overcurrent protection for 1 winding/star point is integrated in the relay. Optionally, a low or high-impedance restricted ground-fault protection, a negative-sequence protection and a breaker failure protection can be used. 7UT633 features 4 voltage inputs. With this option an overvoltage and undervoltage protection is available as well as frequency protection, reverse / forward power protection, fuse failure monitor and overexcitation protection. With external temperature monitoring boxes (thermo-boxes) temperatures can be measured and monitored in the relay. Therefore, complete thermal monitoring of a transformer is possible, e.g. hot-spot calculation of the oil temperature.

     7UT63x features full coverage of applications without external relays by the option of multiple protection functions e.g. overcurrent protection is available for each winding or measurement location of a transformer. Other functions are available twice: ground-fault differential protection, breaker failure protection and overload protection. Furthermore, up to 12 user-defi ned (flexible) protection functions may be activated by the customer with the choice of measured voltages, currents, power and frequency as input variables. The relays provide easy-to-use local control and automation functions.

    The integrated programmable logic (CFC) allows the
    users to implement their own functions, e.g. for the automation of switchgear (interlocking). User-defi ned messages can be generated as well. The fl exible communication interfaces are open for modem communication architectures with control system.

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