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STANI MEMORIAŁ COLLEGE OF ENGINEERING & TECHNOLOGY

POWER SYSTEM DESIGN LAB EXPERIMENT NO. 6

Aim: - Instrument Transformers: Design considerations of CTs & PTs for measurement and protection.

Apparatus Rcqiiirenients: - Current Trans for mer, Potential Transformer, AC supply. Watt Meters. Patch Cords.

Theory:-

Instrument transformers are high accuracy class electricaldevices used to isolate or transform voltage or current levels. The mast common usage of instrument transformers is to operate instrumenLs or metering from high voitage or high current circuits. safely Lsolating secondary contro! circuitry from the high vo!tages or currents. The primary winding of tlie transfonner is connected to tlłe high voltage or high current circuit. and the meter or relay Ls connected to the secondary circuit.

Current Traasformer:-

A current transformer (CT) Ls ased for measurement of electric currents. Current transformers, together with voltage traasformers (VT) (potential traasformers (PT)), are known as iastrument traasformers. When current in a circuit Ls too high to directly apply to measuring instruments. a current transformer produces a reduced current accurately proportional to the current in tlłe circuit. which can be conveniently connected to measuring and recording iastruments. A current traasformer also isolates the measuring iastruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power indastry.

Current traasformers (CT) are a series connected type of instrument transformer. They are designed to present negligible load to the supply being measured and have an accurate current ratio and phase relatioashiptoenable accurate secondary connected metering.