Page 269 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

The secondary of a current transformer should never be left open under any circumstances.

Potential transformers (Fig 12)

Fig 12

PT are used to measure HV in combination with low voltage voltmeters. They are accurate-ratio step-down
transformers. When divided by voltage transformation ratio, gives the true voltage on the high voltage side.
Shell-type ordinary two-winding transformers discussed. Power rating is extremely small. Upto voltages of 5,000
usually of the dry type 5,000 to 13,800 volts, either dry type or oil immersed type.
Voltages above 13,800 always oil immersed type.Operate instruments or relays or pilot lights, their ratings are
usually of 40 to 100 W. For safety, the secondary should be completely insulated from the high-voltage primary
and grounded. (Fig 13)

Fig 13

Power measurement (Fig 14)

Fig 14

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CITS : Power - Electrician & Wireman - Lesson 41-49