TRANSFORMER TRANSFORMER PROTECTION PROTECTION -An Over view.-An Over view.

PRESENTED BY,SANGITA SETHISANGITA SETHI

7TH SEM ELECTRICALRED NO_0901106059

COLLEGE OF ENGINEERING AND TECHNOLOGY

CONTENTCONTENT

WHY PROTECTION IS NEEDED for TRFansformer

TYPES OF FAULT. CLASSIFICATION OF PROTECTION

FUNCTION. TEMPERATURE MONITERING

SYSTEM. CONCLUSION.

Why protection is needed in transformer

1.1. To minimize damage and interruption To minimize damage and interruption to the servicesto the services

2.2. Prevents the Electric FailurePrevents the Electric Failure33.Loss of revenue due to outage.Loss of revenue due to outage44.Inconvenience to the consumers.Inconvenience to the consumers55.Down time for repair or replacement is .Down time for repair or replacement is

very highvery high

Types of Faults/Abnormalities in transformer

Core failure due to shorted lamination

On-load tap changer failure due to mechanical disturbance

Terminal failure due to short circuit

Winding failure due to poor insulation

View of the overheated secondary winding lead

Fire in the Transformer

Classification of Protection Functions 1. Protection against Internal Faults

Unit Protection (against Internal Faults)/ Primary Protection Differential Protection. REF Protection.2.Protection against Abnormal Conditions Over Load protection Over Fluxing Protection Switching surge/ lightning

3. Protective Devices (Non-electrical) Buchholz (Main Tank / OLTC) Oil / Winding Temperature Indicators / Relays Pressure Release Valve Air cell protector

Differential Protection Basic Principle :- Works on the principle of Current Comparison from Secondary sides of the associated CTs and as per the abnormality in the current flow due to internal faults in the transformer, the operating coil actuates and issues the tripping command for tripping of the transformer.

PERCENTAGE DIFFERENTIAL RELAY:PERCENTAGE DIFFERENTIAL RELAY:

Restricted Earth Fault Protection ( REF ) Basic Principle :- Works on the principle of Current

Comparison from Secondary side residual current and Neutral current of the associated CTs and as per the abnormality in the current flow due to internal faults in the transformer, the operating coil actuates and issues the tripping command for tripping of the transformer.

Protection for Abnormal Protection for Abnormal ConditionConditionOver Flux Over Flux ProtectionProtection

Principle:-Principle:-Comparison of voltage in the system to Comparison of voltage in the system to the frequency available, decides the nature of flux in the frequency available, decides the nature of flux in the core and accordingly the over flux setting is the core and accordingly the over flux setting is decided and causes the tripping for the value above decided and causes the tripping for the value above the setting adoptedthe setting adopted.

iE = 4.44fNA Bmax

OVERFLUUXING RELAYS IN CONTROL OVERFLUUXING RELAYS IN CONTROL ROOM :ROOM :

V/F RELAY FROM SIEMENS

V/F RELAY FROM SIEMENS

V/F RELAY FROM JVS TECHNOLOGY

Switching surge and lightning Switching surge and lightning ProtectionProtection

Working Principle:- This relay being filled with oil, displaces the oil for the case of gas collection due to internal fault and issues alarm contact and as per the severity of gas collection, tripping results.

Non-Electrical Protection Non-Electrical Protection DeviceDeviceGas monitoring by Buchholtz Gas monitoring by Buchholtz RelayRelay

Positioning of Buchholtz RelayPositioning of Buchholtz Relay

EXTERNAL AND INTERNAL VIEWS OF EXTERNAL AND INTERNAL VIEWS OF BUCHHOLZ RELAY :BUCHHOLZ RELAY :

External view Internal view Internal View

BUCHHOLZ RELAY BUCHHOLZ RELAY CONSTRUCTION :CONSTRUCTION :

There are two floats in the relay :

Upper float - Detects accumulation of gas and generates alarm only. lower float - Detects surge in oil and trips in less than 100ms.

OPERATION :OPERATION :1. In case of incipient faults within the transformers, the heat due to fault causes the decomposition of some transformer oil in the main tank. The product of decomposition contains more than 75% of Hydrogen gas. The Hydrogen gas being light tries to go into the conservative and in the process gets entrapped in the upper part of relay chamber. When a predetermined amount of gas gets accumulated, it exerts sufficient pressure on the float to cause it to tilt and close contacts of Mercury

switch attached to it. This completes the alarm circuits to sound an alarm.

2. If serious faults occur in the transformer, an enormous amount of gas is generated in the main tank. The oil in the main tank rushes towards the conservator via the Buchholz relay and in doing so tilts to close the contacts of Mercury switch. This completes the trip circuit to open the circuit breaker controlling the transformer.

Pressure monitoring System Pressure monitoring System

Working Principle:- For the case of Serious faults inside the transformer, pressure rises beyond the certain limit. Hence a pressure relief device provided on top of the transformer opens to allow discharge of gas and extends the tripping command. This device automatically closes as soon as the internal pressure falls below the critical level.

Air Cell protectorThe inflated ballooning bag The inflated ballooning bag inside the conservator is floated inside the conservator is floated in the oil. For the rise of oil in the oil. For the rise of oil pressure due to temperature, pressure due to temperature, the air from the cell comes out the air from the cell comes out through breather and vice through breather and vice versa.versa.

OIL TEMPERATURE OIL TEMPERATURE INDICATORINDICATOR OTI is a dial type, self powered

instument . Weather proof unit designed for outdoor

application. It basically consist of 3 parts, assembled

together to one complete instrument_ a glass case where the indication dial and

switches are housed together with mechanics that drives the indication &switching operation

A sensing bulb, the actual measuring part A capillary that connect the sensing bulb

to case The temp. sensing bulb is put in oil filled

pocket and is mounted at the top of the transformer

The sensing bulb is filled a gas or liquid with large coefficient of thermal expansion .

It is connected through capillary tube to spiral wound Bourdon tube in the measuring device .

The Bourdon tube will unwind when the gas expand in response to increase in temp. & torque generated is transmitted to a pointer moving in front of a calibrated scale

WINDING TEMPERATURE WINDING TEMPERATURE INDICATIORINDICATIOR WTI is used to measure the winding

hottest spot temp. rise. WTI has the arrangement &working

principle as that of OTI except it has an heater element fitted in the oil well to simulate winding temp.

In some variation, the heater element is located directly in the measuring instrument.

WTIWTI

Conclusion:- Transformer is the most important device for electrical system and needs to be protected from the abnormality change of

electrical and mechanical parameters.