Innovative transformer protection relays

by R Billiet, NTSA

Published in: Transformers and Substations Handbook: 2014

Chapter 2: Design and installation of a substation - page 38

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Read the full article on Innovative transformer protection relays in PDF format.


TRIM Relay
TRIM Relay


When a transformer fails, users are frequently faced with long replacement time intervals and massive replacement bills. There are a few important factors that need to be taken into account to avoid transformer failure:



o Transport cost to the transformer repair factory (often the fault occurs in an unmanned or remote location)
o Repair or rewinding of the transformer
o Transport cost to the original position
o Reconnection
o Commissioning of the repaired transformer

AZT Relay
AZT Relay

When a transformer fails, the factory or the residence has to find alternative energy from other sources, such as generators. This translates into high and unforeseen expenses that are not always covered by insurance. Sometimes, there are no other options and the electricity cannot be restored. It is thus very important to maintain the transformers properly and one must, therefore, be aware of some intrinsic facts about transformers and in particular, the need for transformer protection devices to extend their useful life cycle.

This article considers two transformer protection relays that will extend the life of a transformer:

The first is the Transformer Inrush Limiter Relay (TRIM) which extends the life of transformers by protecting them from transients emanating from frequent switching effects, under conditions such as load shedding

The second is the AZT relay for ‘unmanned’ or remote transformers where maintenance is challenging because of under-qualified staff or the effects of copper theft


Take note

  • Transformers are critical to the operation of industrial plants and residential complexes.
  • When a transformer fails, users are faced with long replacement time intervals and hefty replacement bills.
  • The relays described are useful devices for protecting transformers from damage caused by inrush and the effects of transformer burn-out.