This document discusses transformer protection. It explains that protection is needed to minimize damage, prevent electric failure, reduce outages and costs. The document categorizes different types of transformer faults and classifications of protection functions. It describes differential protection, restricted earth fault protection, overflux protection and other monitoring systems like Buchholz relays, oil temperature indicators, pressure releases and air cell protectors. The document emphasizes the importance of protecting transformers from internal faults and abnormal operating conditions.

1. TR ANSFORMER
PROTECTION
-An Over view.
PRESENTED BY,
SANGITA SETHI
7TH SEM ELECTRICAL
RED NO_0901106059
COLLEGE OF ENGINEERING AND
TECHNOLOGY

2. CONTENT
 WHY PROTECTION IS NEEDED fOR
TRfaNSfORmER
 TYPES Of faULT.
 CLaSSIfICaTION Of PROTECTION
fUNCTION.
 TEmPERaTURE mONITERING SYSTEm.
 CONCLUSION.

3. Why protection is needed in transformer
1. To minimize damage and interruption
to the services
2. Prevents the Electric Failure
3.Loss of revenue due to outage
4.Inconvenience to the consumers
5.Down time for repair or replacement is
very high

4. 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


5. Winding failure due to Core failure due to
poor insulation shorted lamination
On-load tap changer failure Terminal failure due to
due to mechanical short circuit
disturbance

6. View of the overheated secondary
winding lead

7. Fire in the Transformer

8. 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

9. 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.

11. PERCENTaGE DIffERENTIaL RELaY:

13. 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.

14. Protection for Abnormal Condition
Over 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

15. OVERfLUUXING RELaYS IN CONTROL ROOm :
V/F RELAY FROM V/F RELAY FROM SIEMENS V/F RELAY FROM JVS
SIEMENS TECHNOLOGY

16. Switching surge and lightning
Protection

17. Non-Electrical Protection
Device
Gas monitoring by Buchholtz
Relay
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.

18. Positioning of Buchholtz Relay

19. EXTERNaL aND INTERNaL VIEWS Of BUCHHOLZ
RELaY :
External view Internal view Internal View

20. BUCHHOLZ RELaY
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.

21. 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.

22. 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.

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

24. OIL TEMPERATURE
INDICATOR
 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

25.  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

26.  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

27. WINDING TEMPERATURE
INDICATIOR
 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.

28. WTI

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