Switchgear&Protection
TRANSLAY SCHEME FOR FEEDER PROTECTION
This system is similar to voltage balance system except that here balance or opposition is between the voltages induced in the secondary windings wound on the relay magnet and not between the secondary voltages of the line current transformers. This permits to use current transformers of normal design and eliminates one of the most serious limitations of original voltage balance system, namely its limitation to the system operating at voltages not exceeding 33 kV. In a 3-phase system one relay is placed at each end of each phase of the 3- phase line. It can be simplified by combining currents derived from all the phases in a single relay at each end, using the principles of summation transformer in fig 8. A summation transformer is a device that reproduces the poly phase line currents read more
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MERZ-PRICE VOLTAGE BALANCE SYSTEM FOR FEEDER PROTECTION
Figure shows the single line diagram of Merz Price voltage balance system for the protection of 3-phse line. Identical current transformers are placed in each phase at both ends of the line. The pair of CTs in each line is connected in series with a relay in such a way that under normal conditions, their secondary voltages are equal and in opposition i.e. they balance each other Under healthy conditions, current entering the line at one-end is equal to that leaving it at the other end. Therefore equal and opposite voltages are induced in the secondaries of the CTs at the two ends of the line. The result is that no current flows through the relays. When a fault occurs at point F on the line as shown in Fig 6. It will cause a greater current to flow through CT1 than through CT2. read more
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