TR ANSFORMER PROTECTION -An Over view. PRESENTED BY, SANGITA SETHI 7TH SEM ELECTRICAL RED NO_0901106059COLLEGE OF ENGINEERING AND TECHNOLOGY
CONTENT WHY PROTECTION IS NEEDED fOR TRfaNSfORmER TYPES Of faULT. CLaSSIfICaTION Of PROTECTION fUNCTION. TEmPERaTURE mONITERING SYSTEm. CONCLUSION.
Why protection is needed in transformer1. To minimize damage and interruption to the services2. Prevents the Electric Failure3.Loss of revenue due to outage4.Inconvenience to the consumers5.Down time for repair or replacement is very high
Types of Faults/Abnormalities in transformer EXTERNAL INTERNAL INCIPIENT FAULTS FAULTS FAULTS SHORT PHASE TO SHORT CIRCUIT IN CIRCUITS EARTH LAMINATIONS HIGH PHASE TO CORE BOLT VOLTAGE, PHASE INSULATION HIGH INTER TURN FAILURE FREQUNCY PROBLEM IN LOCAL HEATING DISTURBANCE TAP CHANGER DUE TO CLOGGING EARTH FAULTS OF OIL OVER LOAD COOLENT FAILURE CONDITION EXCESS INGRESS OF OVER AIR IN OIL SYSTEM EXCITATION
Winding failure due to Core failure due to poor insulation shorted laminationOn-load tap changer failure Terminal failure due todue to mechanical short circuitdisturbance
Classification of Protection Functions1. 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/ lightning3. Protective Devices (Non-electrical) Buchholz (Main Tank / OLTC) Oil / Winding Temperature Indicators / Relays Pressure Release Valve Air cell protector
Differential ProtectionBasic Principle :- Works on the principle of Current Comparisonfrom Secondary sides of the associated CTs and as per theabnormality in the current flow due to internal faults in thetransformer, the operating coil actuates and issues the trippingcommand for tripping of the transformer.
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 ConditionOver Flux Protection Principle:-Comparison of voltage in the system to the frequency available, decides the nature of flux in the core and accordingly the over flux setting is decided and causes the tripping for the value above the setting adopted. Ei = 4.44fNA Bmax
OVERfLUUXING RELaYS IN CONTROL ROOm : V/F RELAY FROM V/F RELAY FROM SIEMENS V/F RELAY FROM JVS SIEMENS TECHNOLOGY
Non-Electrical ProtectionDeviceGas monitoring by BuchholtzRelayWorking Principle:- This relay being filled with oil,displaces the oil for the case of gas collection due tointernal fault and issues alarm contact and as per theseverity of gas collection, tripping results.
EXTERNaL aND INTERNaL VIEWS Of BUCHHOLZ RELaY :External view Internal view Internal View
BUCHHOLZ RELaYCONSTRUCTION : 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 :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 SystemWorking Principle:- For the case of Serious faultsinside the transformer, pressure rises beyond the certainlimit. Hence a pressure relief device provided on top of thetransformer opens to allow discharge of gas and extendsthe tripping command. This device automatically closes assoon as the internal pressure falls below the critical level.
Air Cell protectorThe inflated ballooning baginside the conservator is floatedin the oil. For the rise of oilpressure due to temperature,the air from the cell comes outthrough breather and viceversa.
OIL TEMPERATUREINDICATOR 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 TEMPERATUREINDICATIOR 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.