This document discusses transformer protection. Transformers are critical and expensive components that require protection to limit damage from faults. Protection methods include Buchholz relays, which detect gases from arcing; pressure relays, which detect pressure waves from arcing; and thermal relays, which monitor hot spot temperatures. Protection aims to quickly isolate transformers under abnormal conditions like faults, overloads, or overvoltages to prevent failures and simplify repairs.

1. TRANSFORMER PROTECTION
PREPARED BY
JASON
ELECTRICAL AND ELECTRONIC ENGINEERING

2. CONTENTS
• Introduction.
• Transformer Protection Overview.
• Transformer Failures.
• Transformer Protection Review.
• Types of Protection.
• Conclusion.
• References.

3. INTRODUCTION
• Transformers are a critical and expensive component of the power
system. Due to the long lead time for repair of and replacement of
transformers, a major goal of transformer protection is limiting the
damage to a faulted transformer.
• Some protection functions, such as overexcitation protection and
temperature-based protection may aid this goal by identifying
operating conditions that may cause transformer failure.
• The comprehensive transformer protection provided by multiple
function protective relays is appropriate for critical transformers of all
applications.

4. • Induction Law
• The transformer is based on two principles:
• 1. An electric current can produce a magnetic field.
• 2. A changing magnetic field within a coil of wire induces a voltage
across the ends of the coil (electromagnetic induction).

5. TRANSFORMER PROTECTION OVERVIEW
• The type of protection for the transformers varies depending on the
application and the importance of the transformer.
• Transformers are protected primarily against faults and overloads. The
type of protection used should minimize the time of disconnection for
faults within the transformer and to reduce the risk of catastrophic
failure to simplify eventual repair.
• Any extended operation of the transformer under abnormal condition
such as faults or overloads compromises the life of the transformer,
which means adequate protection should be provided for quicker
isolation of the transformer under such conditions

6. TRANSFORMER FAILURES
• winding failures due to short circuits (turn-turn faults, phase-phase
faults, phase-ground, open winding).
• core faults (core insulation failure, shorted laminations).
• terminal failures (open leads, loose connections, short circuits).
• on-load tap changer failures (mechanical, electrical, short circuit,
overheating).
• abnormal operating conditions (overfluxing, overloading, overvoltage).
• external faults.

7. CONDITIONS
Internal.
• Winding Phase-Phase, Phase-
Ground faults.
• Winding inter-turn faults.
• Core insulation failure, shorted
laminations.
• Tank faults.
• Over fluxing.
External
• Overloads .
• Overvoltage .
• Over fluxing .
• External system short circuits.

8. TRANSFORMER PROTECTION REVIEW
• Internal Short Circuit
- Phase Faults
- Ground Faults
• System Short Circuits (Back up Protection)
- Buses and Lines
* Phase Faults
* Ground Faults
• Abnormal Condition
• Open Circuit
• Over Excitation
• Abnormal Frequency
• Abnormal Voltage
• Breaker Failure
• Overload
• Geo-magnetically induced current (GIC)

9. TYPES OF PROTECTION
• Accumulation Gases
Arcing by- production (EX: Buchholz Relay)
• Pressure Relays
Arcing causing pressure wave in oil or gas space (Sudden
Pressure Relay)
• Thermal
Caused by overload, overexcitation, harmonics and Geo-
magnetiocally indued current
Hot spot temperature
Top Oil
LTC Overheating

10. BUCHHOLZRELAY
• It is a gas actuated relay. When a fault develops slowly,it produces
heat, thereby decomposing solid or liquid insulating material in the
transformer.
• The decomposition of the insulating material produces inflammable
gases. The Buchholz relay gives an alarm when a specified amount of
gas is formed.
• The analysis of the gas collected in the relay chamber indicates the
type of the incipient fault.

12. WORKING
• When an incipient fault such as a winding-to-core fault or an inter-turn
fault occurs on the transformer winding, there is severe heating of the
oil.
• This causes gases to be liberated from the oil around 350°C. There is
a build-up of oil pressure causing oil to rush into the conservator.
• A vane is placed in the path of surge of oil between the transformer
and the conservator. Aset of contacts, operated by this vane, is used
as trip contacts of the Buchholz relay This output of Buchholz relay
may be used to trip the transformer.

13. PROTECTION AGAINST FIRE
• Power transformers are subject to fires from many sources. They
often occur because of deterioration of insulation in the transformer.
• This produces arcing which in turn overheats the insulating oil and
causes the tanks to rupture; further arcing then will start a fire.
• Fires are also initiated by lightning and occasionally by dirty insulators
on the outside of the tanks.

15. PROTECTION AGAINST LIGHTNING
• Lightning overvoltage surges originate from atmospheric discharges
and they can reach their peak within a few microseconds and
subsequently decay very rapidly.
• The surge voltage can reach up to 10 times the rated transformer
voltage and they pose the greatest threat to transformers on the
distribution networks.
• The charge from the surge produces both short duration high current
impulse and long duration continuing current impulse which affects the
transformer insulation system.

17. CONCLUSION.
• The protective equipment discussed is engineered to limit the damage
and system disturbance caused by faults which can occur in a
transformer.
• The choice of protective equipment depends on the size and the
connection of a transformer, voltage level, power system grounding
and the protective relays of the power network.
• The power companies also have different opinions about the extent
and choice of pr:otective equipment for a transformer.
• No general recommendations can therefore be made.

18. REFERENCES
• http://sites.ieee.org/fw-pes/files/2013/01/transfguide.pdf
• https://en.wikipedia.org/wiki/Power-system_protection
• https://en.wikipedia.org/wiki/Transformer_protection