ABB RED615 Technical Manual page 172

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Protection functions

in transformer and LV-side busbar faults. The high-set stage PH3HPTOC operates

instantaneously, making use of current selectivity only in the transformer HV-side

faults. If there is a possibility that the fault current can also be fed from the LV-side

up to the HV-side, the transformer must also be equipped with an LV-side

overcurrent protection. Inrush current detectors are used in startup situations to

multiply the current start value setting in each particular IED where the inrush

current can occur. The overcurrent- and contact-based circuit breaker failure

protection CCBRBRF is used to confirm the protection scheme in case of circuit

breaker malfunction.

GUID-46F45186-75AC-4487-886A-AA8369F6EF9F V1 EN

Example of traditional time-selective transformer overcurrent

The operating times of the main and backup overcurrent protection of the above

scheme become quite long. This applies especially in the busbar faults and also in

the transformer LV-terminal faults. To improve the performance of the above

scheme, a multiple-stage overcurrent protection with a reverse blocking is

shows this arrangement.

Transformer and busbar overcurrent protection with reverse blocking

By implementing a full set of overcurrent protection stages and blocking channels

between the protection stages of the incoming feeders, bus-tie and outgoing

feeders, it is possible to accelerate the operation of the overcurrent protection in the

busbar and transformer LV-side faults without impairing the selectivity. Also, the

security degree of the busbar protection is increased, because there is now a

dedicated, selective and fast busbar protection functionality which is based on the

blockable overcurrent protection principle. The additional time-selective stages on

1YHT530004D05 D

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