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The Principle and Application of Current Differential Protection

Posted Feb 28 2014 7:20am

Current differential protection is an electromechanical apparatus, normally with greater than a single coil, designed to calculate operating conditions on an Frequency and Voltage Control and trip circuit breakers when a fault is detected. It needs a set of existing transformers at each and every end of your energy line, or every side of the transformer. The existing protection relay then compares the currents and calculates the difference among the two.

Existing differential protection is significant to note the direction of the currents also as the magnitude, as they may be Tensor quantities. Commonly it offers superior protection for transmission line protection. It has quite a few benefits more than other schemes of protection, for instance centralized busbar protection, directional comparison relay, and so on. The essential advantages over Power Stability Control System involve greater sensitivity for high resistance faults, 100% line protection, and greater efficiency in the single-pole-tripping mode, particularly throughout evolving and cross-country faults. In addition to the well-known specifications of high-speed communication and sampling synchronization, a microprocessor-based differential relay needs ñ as per principle of differential protection ñ that the currents are monitored on all the circuits connected to a protected line including tapped transformers and lines. This may create a problem because the tapped connections are meant to provide a cost-effective alternative to actual substations.

Principle of existing differential protection is one simple conceptual technique. The Phasor Measurement Unit actually compares between primary current and secondary existing of power transformer, if any unbalance found in among primary and secondary currents the relay will actuate and inter trip both the primary and secondary circuit breaker of your transformer. The secondaries of both CTs should be connected to same present coil of differential relay in such a opposite manner that there will be no resultant existing in that coil in normal working condition on the transformer. At maximum through fault existing, the spill output produced by the small percentage unbalance may be substantial. Therefore, differential protection of transformer should be provided with a proportional bias of an amount which exceeds in effect the maximum ratio deviation.

Nowadays, the discusses application problems and solutions permitting the application of current differential protection to tapped transmission lines without measurements at the tap point. Modern current differential protection can provide at least 1 zone of distance protection. This suits the application nicely as no extra cost is generated and the trip time is not increased by the output and input contacts activation times as it would be when using an external relay.

It can be seen that existing differential protection plays an vital role in some fields in accordance with it positive aspects and application. Moveover, with present differential protection develops, many interrelated products are booming with it. Present differential protection manufacturers seize opportunities and meet the challenge.

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