PRESENTATION ON CURRENT TRANSFORMERS

Submitted by – Roopal pancholi

B.Tech (Electrical),

III year, V semester

K13072

Submitted To –

Mr. Kamal Arora

Dean of Electrical Department

CONTENTS1. Introduction2. Instrument Transformers3. Need of Instrument Transformers4. Applications of instrument Transformers5. Current Transformers6. Parts of Current Transformers7. Working of CT’S8. Let’s learn more about CT’s9. Calculation of CT’s10. Applications of Current Transformers11. Safety of CT’S

INTRODUCTION Transformers is a device-1. transfers electric power from one circuit to another2. it does so without change of frequency3. it accomplishes this by electromagnetic induction and4. It is divided into core & shell types of transformers5. for measurement purpose we uses INSTRUMENT

TRANSFORMRS .

INSTRUMENTS TRANSFORMER These are special types of transformers used for the

measurement of voltage , current ,power & energy. As the name suggests , these transformers are used in conjuction with the relevant instruments such a ammeters , voltmeters ,wattmeters & energy meters.

NEED OF INSTRUMENT TRANSFORMERS For the purpose of measurement of large currents and

high voltage in transformer we uses instrument transformer.

It also make it possible to measure it with low range voltmeters and low range ammeters.

For these purpose ,specially constructed accurate ratio instrument transformers are employed in conjunction with many measuring instruments.

They are basically of two types –1. Current Transformers2. Potential Transformers

APPLICATIONS OF INSTRUMENT TRANSFORMER

• It would not be economical to have a ammeter to measure 600amps in a conductor directly , but we can have an ammeter range 0-5amps which corresponds to 0-600amps.

• Similarly , for measuring voltage of 14,400volts directly it would not be economical , so we place 0-120 volts will be corresponds to 0-14,400volts & economical.

The degree to which an instrument transformer produces a current or voltage i. e. proportionate to the one to be monitored is to it’s accuracy.

CURRENT TRANSFORMER They generally used to step

down current in a very predictable fashion with respect to current and phase .

The current (or series) transformer has a primary coil of one or more turns of thick wire connected in series with the line whose current is to be measured.

The secondary consists of a large number of turns of fine wire & is connected across the ammeter terminals.

PARTS OF CURRENT TRANSFORMER Like any transformer, a current transformer has a

primary winding, a core and a secondary winding, although some transformers, including current transformers, use an air core. In principle, the only difference between a current transformer and a voltage transformer (normal type) is that the former is fed with a 'constant' currentwhile the latter is fed with a 'constant' voltage, where 'constant' has the strict circuit theory meaning.

Typically current transformers consist of a silicon steel ring core wound with many turns of copper wire .

WORKING OF CT’S The alternating current in the primary produces an

alternating magnetic field in the core, which then induces an alternating current in the secondary. The primary circuit is largely unaffected by the insertion of the CT.

Accurate current transformers need close coupling between the primary and secondary to ensure that the secondary current is proportional to the primary current over a wide current range.

The current in the secondary is the current in the primary (assuming a single turn primary) divided by the number of turns of the secondary.

The conductor carrying the primary current is then passed through the ring; the CT's primary therefore consists of a single 'turn'. The primary 'winding' may be a permanent part of the current transformer, with a heavy copper bar to carry current through the core.

LET’S LEARN MORE ABOUT CT’S

current transformer windings.mp4

CALCULATION OF CT’S If the current transformer

has primary to secondary current ratio of 100:5,then it steps up the voltage 20 times whereas it steps up the voltage 20 times whereas it steps down the current to 1/20 of its actual value.

Hence , if we know current ratio (I1/I2) of the transformer & the reading of the a.c. ammeter , the line current can be calculated.

For eg; 1. A100:5 transformer is used in conjunction with a 5-amp ammeter . If the latter reads 3.5A,find the line current.

Sol: As we know that I1/I2=100/5 , now primary on line –current =3.5*(100/5)

=70A

APPLICATIONS OF CURRENT TRANSFORMERS Current transformers are used

extensively for measuring current and monitoring the operation of the power grid.

Current transformers can be mounted on the low voltage or high voltage leads of a power transformer; sometimes a section of a bus-bar can be removed to replace a current transformer.

Often, multiple CTs are installed as a "stack" for various uses. For example, protection devices and revenue metering may use separate CTs to provide isolation between metering and protection circuits.

SAFETY OF CURRENT TRANSFORMERS

Regarding safety issues ,it is considered important as the secondary of a current transformer should not be disconnected from its burden while current is in the primary, as the secondary will attempt to continue driving current into an effective infinite impedance up to its insulation break-down voltage and thus compromise operator safety.

Inrush Current Transformer Working principle.mp4

THANK YOU!ANY QUERIES!!