EVALUATING PROTECTIVE SYSTEM’S RELIABILITY USING CURRENT TRANSFORMER BURDEN RATING

Authors: Obi P.I, *Oputa O, Okeke C, Onwuka I.K, Apkan A.E

DOI Info: N/A

ABSTRACT

Protective systems play vital roles in electricity supply and reliability; therefore, the protective system’s performance/reliability should be evaluated to ensure the safety of the power system. A valuable method of evaluating this system’s reliability is by the use of the burden rating of current transformers (CT) as they are found in almost all protective system as the first contact point between the power system and the protective system. By comparing the performance of four CTs (of different rating) feeding four different burden ratings with the same source/fault current (of 10,000A) with a program developed in MATLAB, the results show that the voltage required for driving the relay is independent of the relay rating but it is directly proportional to the connected burden on the CT. A 1200/5 CT when used with relays with ratings of C100, C200, C300 and C400 each posing an initial burden of 1.09? on the CT all require a driving voltage of 45.42V. As the burden begins to increase, the voltage required to drive the relay increases also to 50.07V, 104.10V, 153.80V and 206.10V for the respective relays. Hence, as the burden is increased, the required voltage to drive the relay also increases until it gets to the point where the current transformer saturates. This increase in the required voltage to drive the relay (that initiates tripping of circuit breakers/alarms and other protective gargets) reduces the sensitivity of the protective system thereby reducing its efficiency and reliability.

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