| 8.1 |
Voltage Transformers |
| 8.1.1 |
Role of Tuning Reactor |
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Assuming, the transformer to be ideal, the Thevenin's equivalent circuit of CCVT is shown in fig 8.3. |
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It is now obvious that Zth due to the capacitance divider, affects the voltage received by the relay. To achieve high level of accuracy, it is therefore necessary to compensate for this voltage drop by connecting a tuning inductor. The tuning inductor‘s value is so chosen that it compensates for the ‘net C' at power frequency (50Hz in India). The phasor diagram across resistive load, is as shown in fig 8.4(a). (See fig 8.4).
From the corresponding equivalent circuit, it is apparent that, if  , then voltage drop across C is neutralized and the relay sees the actual voltage to be measured. (See fig 8.5).
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