Protection Of Distribution Transformer Using Auto Protected System
Distribution transformers are traditionally protected by differential protection schemes that use voltages and
currents to detect abnormalities in the differential zone of protection. For this type of scheme, a short circuit or high
magnitude current must be present to initiate a trip. However, this scheme might not be ideal when transformers need to be
overloaded to mitigate contingency conditions. Using the IEEE Guide for Loading of Oil-Immersed Distribution
Transformers, one can thermally rate transformers beyond their nameplate conditions to a level that is safe for operation.
Using the guide, engineers can establish continuous, emergency and short term emergency transformer ratings. Operators
can use these ratings until the contingency conditions are mitigated. However, once the transformer has surpassed the short
term emergency ratings, the transformer might reach critical temperatures and could possibly sustain damage. Protection
engineers can avoid further transformer damage by using the thermal protection principles of the IEEE standard. This paper
discusses the fundamental thermal principles of distribution transformers, philosophies of operations and the
implementations of thermal protection.
Keywords- Oil Immersed, Thermal Protection.