Transformer Protection

A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core.

1. WELCOME

2. Koradi Training Center (KTC),Nagpur Topic - TRANSFORMER PROTECTION Presented by: Pranay Ingale Atish Verma Vedant Thakre Shweta Kohale Pallavi Mathane Aniket Awate Harsh Sonkuwar Akshay Narnavre

3. CONTENT Introduction Types of Transformers Components Construction Main parts of Transformer Transformer Protection

4. A transformer is a static device. The word 'transformer' comes form the word 'transform’. Transformer is not an energy conversion device, but it is device that changes AC electrical power at one voltage level into AC electrical power at another voltage level through the action of magnetic field. Transformer works on Faraday's law of mutual induction Faraday's law of electromagnetic induction states that, when a change takes place in the magnetic flux which is linked with a circuit, an electromotive force current will induce in the circuit. It can be either to step-up or step down. Commonly used transformer type, depending upon voltage they are classified as: -Step-up Transformer -Step down Transformers WHAT IS TRANSFORMER ?

5. TYPE OF TRANSFORMER ON THE BASIS OF OUTPUT VOLTAGE A.STEP UP TRANSFORMER : step up transformer transforms a low voltage high current into a high voltage Low current. In this type of transformer number of turns of secondary is greater than number of turns in primary . In short if the output voltage that is secondary voltage is higher than the primary voltage the transformer is called step up transformer.

6. step down transformer transforms a high voltage low current into a low voltage high current. In this type of transformer number of turns of primary is greater than number of turns in secondary. In short if the output voltage that is primary voltage is higher than the secondary voltage the transformer is called as step down B.STEP DOWN TRANSFORMER

7. COMPONENTS (PARTS OF TRANSFORMER ) Breather Radiators and fans Explosion vent Breather Radiators and fans Explosion vent Tap changers Buchholz relay Temperature Gaug e Core Winding Insulation Tank Core Winding Insulation Tank Terminal and bushings Transformer oil Oil Conservators

8. CONSTRUCTION The transformer mainly consists of the Magnetic circuit, electric circuit, dielectric circuit, tanks, and accessories. The main elements of the transformer are the  primary and secondary windings  and the  steel core . The core of the transformer is made up of silicon steel in order to provide a continuous magnetic path. Usually, the core of the transformer is laminated for minimizing the eddy current loss.

9. MAIN PARTS OF TRANSFORMER TANK Main tank is the robust part of transformer that serves mainly two purposes: It protects core and windings from the external environment and provide housing for them. It is used as a container for transformer oil and provides support for all other external accessories of the transformer. Main tank of the transformer are made up of fabricated rolled steel plates. They are provided with lifting hooks and inbuilt cooling tubes. In order to minimize the weight and stray losses, aluminum sheets are also being used instead of Steel plates.

10. RADIATOR AND FANS Since power losses in the transformer are dissipated in the form of heat. So a cooling arrangement is required for the power transformer. Dry-type transformers are generally natural air-cooled. But when we talk about oil-immersed transformers then several cooling methods are used depending upon kVA rating, power losses, and level of cooling required. Hence to provide proper cooling, radiators and fans are installed on the main tank of the power transformer. Radiators are also called cooling tubes. In a large power transformer, forced cooling is achieved with the help of cooling fans fitted on the radiator.

11. This Photo by Unknown Author is licensed under CC BY The Conservator Tank of a transformer is defined simply as a cylindrical tank mounted on the roof of the transformer main tank. It is used to provide enough space for the oil in the transformer to spread after heating. The main function of the conservator Tank When the transformer is loaded and when the ambient temperature rises, make the volume of oil inside the transformer increase. A conservator tank of the transformer supplies adequate space to this expanded transformer oil. It also is designed as a reservoir for  transformer   insulating oil. CONSERVATOR TANK

12. The function of transformer oil is to provide insulation between windings as well as cooling due to its chemical properties and very good dielectric strength Core balance Current Transformer (CBCT)It dissipates the heat generated by the core and windings of a transformer to the external environment. When the windings of transformer gets heated due to flow of current and losses, the oil cools down the windings by circulating inside the transformer and transfer heat to the external environment through its cooling tubes Hydro-carbon mineral oil is used as transformer oil and acts as coolant. It is composed of aromatics, paraffin, naphthene's, and olefins. TRANSFORMER OIL

13. INSULATION To avoid any electrical activity between any part of insulation is used , An ideal insulating material should posses some property Should have high value of resistance Should have high melting point It should be cheap and flexible Should not consume any power Should not detoriate This Photo by Unknown Author is licensed under CC BY

14. Breather is a cylindrical container filled with silica gel and directly connected with the conservator tank of the transformer. The main function of the breather is to supply moisture-free fresh air to the conservator tank during the expansion and contraction of transformer oil. This is because the transformer oil when reacting with moisture can affect the insulation and cause an internal fault in a transformer. That's why the air entering in conservator tank should be moisture free for better life of transformer oil. BREATHER

15. The main function of the tap changer is to regulate the output voltage of transformer by changing its turns ratio. There are two types of tap changers. 1. On-load tap changer:- in an on-load tap changer, tapping can be changed without isolating the transformer from the supply. Hence it is capable to operate without interrupting the power supply. 2. Off-load tap changer:- in off-load tap changer, the transformer needs to isolate from supply to change its tapping (turns ratio). An automatic tap changer is also available. TAP CHANGER

16. Common Types of Transformer Protection Other Protections

17. Overheating protection Transformers overheat due to the overloads and short circuit conditions. The allowable overload and the corresponding duration are dependent on the type of transformer and class of insulation used for the transformer. Higher loads can be maintained for a very short amount of time if it is for a very long, it can damage the insulation due to  temperature rise above an assumed maximum temperature.   The temperature in the oil-cooled transformer is considered maximum when its 95*C, beyond which the life expectancy of the transformer decreases and it has detrimental effects in the insulation of the wire .

18. Overcurrent protection The overcurrent protection system is one of the earliest developed protection systems out there, the graded overcurrent system was developed to guard against overcurrent conditions. power distributors utilize this method to detect faults with the help of the IDMT relays. that is, the relays having: Inverse characteristic, and Minimum time of operation. The capabilities of the IDMT relay is restricted. These sorts of relays have to be set 150% to 200% of the max rated current, otherwise, the relays will operate for emergency overload conditions.

19. Differential Protection of Transformer The Percentage Biased Current Differential Protection is used to  protect power transformers  and it is one of the most common  transformer protection schemes  that provide the best overall protection. These types of protection are used for transformers of rating exceeding 2 MVA. Earth Fault Protection (Restricted) A very high fault current can flow when a fault occurs at the transformer bushing. In that case, the fault needs to be cleared as soon as possible. So, that is why the relay is named  Restricted  earth fault protection relay. This relay has three phases, if a fault occurs, they will have three components, the  positive sequence components, the negative sequence components, and the zero sequence components .

20. Buchholz (Gas Detection) Relay The  Buchholz relay  is fitted in between the main transformer unit and the conservator tank when a fault occurs within the transformer, it detects the resolved gas with the help of a float switch. The main purpose of Buchholz Relay is to give the protection to a transformer from the different faults happening in the transformer like short circuit, core etc. Over-fluxing protection   transformer is designed to operate at a fixed flux level exceed that flux level and the core gets saturated, the saturation of the core causes heating in the core that quickly follows through the other parts of the transformer that leads to overheating of components, thus over flux protection becomes necessary, as it protects the transformer core. To protect the transformer from over-fluxing, the  over-fluxing relay  is used. The over-fluxing relay measures the ratio of Voltage / Frequency to calculate the flux density in the core.

21. Vv OTHER PROTECTIONS ARE - CIRCUIT BREAKERS What is CIRCUIT BREAKER The circuit breaker is a switching device which also offers protection by tripping & cutting off the supply to load in case of fault. Primarily the circuit breakers are used for switching of different kinds of load in Industries, Buildings, Commercial Complexes, `and Hotels, etc. NEED OF CIRCUIT BREAKER Many kind of abnormal conditions are there which exist in our electrical system that have the potential to damage the circuit & its components. These conditions are defined as ‘ FAULTS’.Further , fault is categorized as mentioned below: Overload Short Circuit Earth

22. TYPES OF CIRCUIT BREAKER VACUUM CIRCUIT BREAKER  (VCB) Vacuum Circuit Breaker or VCB is used for Medium Voltage applications. In VCB the contacts operation & arc quenching takes place inside bottles where Vacuum is present. SF6 CIRCUIT BREAKER SF6 circuit breakers are also used mainly in medium voltage applications. In this breaker SF6 gas is used for arc quenching due to its ability of quenching the arc very efficiently. SF6 Breakers being highly efficient in arc quenching are still not preferred much as SF6 being a poisonous gas, is dangerous to environment & humans .

23. V Oil CIRCUIT BREAKER (OCB) Oil Circuit Breakers were also used on high voltages & Oil was used as the arc quenching medium. AIR CIRCUIT BREAKERS The air circuit breaker is also known as an air blast circuit breaker as they are air-based circuit breakers. In this circuit breaker type, the arc extinguishing medium used is a high-pressure air blast. In case of a faulty current flow, the blast valve opens the contact. The restriking of the arc is prevented by sweeping the ionized particles into the atmosphere, which increases the strength of the dielectric in the medium.

24. ADVANTAGE OF LIGHTNING ARRESTER Lightning arresters help prevent lightning damage to the apparatus because of high voltages. The lightning arrester provides a low-impedance road all the way to the ground for the lightning's current. It then restores to a normal operating condition. The device which is used for the protection of the equipment at the substations against travelling waves, such type of device is called lightning arrester or surge diverter. In other words, lightning arrester diverts the abnormals high voltage to the ground without affecting the continuity of supply. It is connected between the line and earth, i.e., in parallel with the equipment to be protected at the substation. LIGHTNING ARRESTOR

25. GROUNDING TRANSFORMER A grounding transformer or earthing transformer is a type of auxiliary  transformer  used in  three-phase electric power  systems to provide a ground path to either an ungrounded wye or a delta-connected system. Grounding transformers are part of an  earthing system  of the network. They let  three-phase  ( delta connected ) systems accommodate phase-to-neutral loads by providing a return path for current to a neutral. Grounding transformers are typically used to: Provide a relatively low-impedance path to ground, thereby maintaining the system neutral at or near ground potential. Limit the magnitude of transient overvoltages when restriking ground faults occur. Provide a source of ground fault current during line-to-ground faults. Permit the connection of phase-to-neutral loads when desired.

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