Presentation onInstruments TransformersBy Avdhesh kumar meena B.Tech 4th Year Electrical BranchNIET Alwar Rajasthan avdheshkumarmeena10@gmail.com

What is Transformer ??

A transformer is a static device which is use to convert high alternatic voltage to a low alternatic voltage and vice versa, keeping the frequency same

Principle Of OperationTransformer works on the principle of mutual induction of two coils. When current in the primary coil is changed the flux linked to the secondary coil also changes. Consequently an EMF is induced in the secondary coil.

What is Induction law ?? Faraday’s law states that:

Vs=Ns.dΦ/dt where Vs is the instantaneous secondry winding voltage. Ns is the number of turns in the secondary coil.

Construction of TransformerMainly Transformers have two types of construction….

CORE type constructionSHELL type construction

Core type TransformerIn the Core type the primary and secondary windings are placed on each side of the core. The core type has two limbs

Shell type TransformerIn Shell type transformers the LV & HV windings are sandwiched between each other.

The shell type has three limbs.

Types of TransformerStep UP Transformer : A transformer in which Ns>Np is called a step up transformer. A step up transformer is a transformer which converts low alternatic voltage to high alternatic voltage. Step DOWN Transformer : A transformer in which Np>Ns is called a step down transformer. A step down transformer is a transformer which converts high alternatic voltage to low alternatic voltage.

A wide variety of transformer designs are used for different applications. Auto-transformer Poly-phase transormer Leakage transformer Resonant transformer Instrument transformer

AUTO-TRANSFORMERSAutotransformer is a one winding transformer in which a part of the winding is common to both HV & LV sides

POLY-PHASE TRANSFORMERThree separate single phase transformers are suitably connected for 3 phase operation.A single three phase transformer in which the cores and windings for all the three phases are combined in a single structure.

INSTRUMENT TRANSFORMERSInstrument transformers are necessary for Isolating the protection, control &

measurement equipment from the high voltages of a power system

Supplying the equipment with the appropriate values of current and voltage

Types of Instrument TransformersTwo Types of Instrument X-formers Current Transformer (CT) Potential Transformer (PT)

Current Transformer Construction

Layer 2 Lay

er 1

Core

Point to note about CT Primary current depends on load, but not

on the burden Current coil of Wattmeter or Ammeter is

connected across the terminal of the secondary or Relay

Secondary operates near short circuit conditions

One of the terminal of CT secondary winding is earthed

Types of CT

Care, while operating with CT

Connections of CT and PT

Potential Transformer Potential transformer normally

known as PT. That is a type of step down

transformer. Step down transformer ,step down

the voltage and rise the current. The voltage is step down in the

known ratio called voltage ratio.

Principle of operation PT It is always connected in parallel to the

transmission line. It’s secondary winding is very low with respect to

the primary. The secondary winding is designed so that a

voltage of 100 to 150 v is delivered to the instrument load.

Line voltage =voltmeter reading/Ratio Ratio=no. of turn in secondary/no.of turn in primary

construction of potential transformer Core size is large and made of by

steel. Primary side large no. of turn. Secondary side only few no. of

turn. Secondary and primary winding

are insulated to each other and oil immersed.

Conclusion Current Transformer Measuring current

Monitoring the operation of the power grid

Potential TransformerMeasuring Voltage Provides isolation from high voltages

Thank you