Transformer Basics, Operation and Protection.pptx

Transformer Details

1. TRANSFORMERS FUNDAMENTALS, OPERATIONS & PROTECTION 1

2. Contents Introduction of Generation, Transmission and Distribution. Working Principle of Transformer. Transformer Drawing and Parts. Why We Use Transformer in Transmission and Distribution. Cause of Transformer Failure and Faults. Transformer Protection and Measures. Bucholz Relay Protection in Oil Type Transformer. Silica Gel Protection for Moisture in transformer oil. Preventive Maintenance and safety Precautions .

3. 3 Introduction- Generation, Transmission & Distribution

4. 4 Introduction Transformer is a static device(No Rotating Parts). It is used to transform (Step up/Step down)the electrical energy from one alternating current circuit to another. Frequency remain same. Transformer is a vital link in a power transmission system and distribution .

5. Working Principle • Works on the principle of electromagnetic induction • Primary winding creates magnetic flux when AC flows • Magnetic flux induces voltage in the secondary winding • Voltage transformation depends on turns ratio.

6. 6 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

7. 7 Basic Types of Transformer 1. Based on Function: Step-Up Transformer – Increases voltage,decreases current (used in power transmission). Step-Down Transformer – Decreases voltage, increases current (used in distribution). 2. Based on Construction: Core-Type Transformer – Windings surround the core limbs. Shell-Type Transformer – Core surrounds the windings. 3. Based on Cooling : Oil Type Transformer- Oil used for insulation and Cooling. Dry-Type Transformer – Air-cooled, no oil used. 4. Based on Number of Phases Single-Phase Transformer – For single-phase loads. Three-Phase Transformer – For three-phase power systems .

8. 8 Power Transformer Term power transformer is used to refer to those transformers used in the generator and the distribution circuits, and these are usually rated at 500 KVA and above. Power systems typically consist of many generation locations, distribution points, and interconnections within the system or with nearby systems, such as a neighboring utility. The complexity of the system leads to a variety of transmission and distribution voltages. Power transformers must be used at each of these points where there is a transition between voltage levels.

9. 9 Transformer Diagram

10. 10 Why use transformer ??? To reduce of transmission losses. For increasing the low voltage level to high voltage level. The voltage level of a power is increased; the current of the power is reduced which causes reduction in ohm or I2R losses in the system. Low level power must be stepped up for efficient electrical power transmission.

11. 11 Transformer Protection-Why ??? To Protect the Transformer from severe damages. Time required to rectify the Transformer in case of damages is more. Operation of a power network when the power transformer is out of service is always difficult.

12. 12 What cause transformer failure ? Insulation Breakdown Over heating due to over excitation Oil contamination and leakage Cooling system failure Phase to phase and Phase to Ground Fault Turn to Turn Fault Transformer Overload

13. 13 What cause transformer failure? Winding failures 51% Tap changer failures 19% Bushing's failures 9% Terminal board failures 6% Core failures 2% Miscellaneous failures 13%

14. 14 What cause transformer failure? Insulation deterioration come from: Moisture Vibration Overheating Voltage surge Winding Bushing Bushings deterioration come from: General aging Contamination Cracking Internal moisture

15. 15 What cause transformer failure? Core insulation failure Shorted lamination Core overheating Core problem Miscellaneous CT problem Oil leakage Oil contamination Metal particle Moisture

16. 16 Transformer Faults Internal faults 1. Winding Failure 2. Winding inter-turn faults 3. Core insulation failure, shorted laminations 4. Over fluxing. External faults 1. Overloads 2. Overvoltage 3. Over heating 4. External system short circuits.

17. 17 Transformer Protection 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 .

18. 18 Transformer Protection Scheme Mechanical Buchholz relay Sudden pressure Pressure relief Temperature protection Electrical Differential Protection Over Fluxing Over Voltage Under Voltage Neutral Unbalance Restricted Earth Fault Back up O/C & E/F

19. 19 Buchholz Relay Protection The Buchholz relay is placed between the main tank and the conservator. Such type of relay is used in the transformer having the rating higher than 500KVA. It is not used in small transformer because of economic consideration .

20. 20 Buchloz Relay Protection The Buchholz relay protects the transformer from internal faults. It is the gas actuated relay .

21. 21 Bucholz Relay Protection

22. 22 Buchhloz Relay Protection When the fault occurs inside the transformer, the temperature of the oil increases. The oil evaporates in the form of the gas. The generation of the gas depends on the magnitude of the fault occurs inside the transformer. The internal failure occurs in the transformer either because of the insulation breakdown between the winding or the winding have the weak initial contact .

23. 23 Buchholz Relay Protection The relay has two elements 1st stage and 2nd stage. The 1st stage for alarm and the 2nd stage for trip. During faults and continuous operation due to increase in I2R and Gas level increased , the Bucholz relay alarm switch activated and give command to the primary circuit VCB to trip the HT supply. The setting of 1st stage is done at collected gas volume of 300 to 500ml .

24. 24 Sudden Pressure Relay Protection This relay is designed to detect a sudden pressure increase caused by arcing or internal faults.

25. 25 Pressure Relief Protection This is used to evacuate any over pressure inside the transformer to avoid explosion of the transformer tank. The pressure relief device limits the tank overpressure and reduces the risk of tank rupture and uncontrolled oil spill, which might also cause a fire.

26. 26 Pressure Relief Protection

27. 27 Silica Gel Breather Silica gel breathers is used on the conservator of oil filled transformers. The purpose of these silica gel breathers is to absorb the moisture in the air. During the breathing process, the incoming air may consist of moisture and dirt which should be removed to prevent any damage. Air is made to pass through the silica gel breather, which will absorb the moisture in the air and ensures that only dry air enters the transformer. Silica gel in the breather will be blue when installed and they turn to pink color when they absorb moisture which indicates the crystals should be replaced.

28. 28 Silica Gel Breather

29. 29 Oil Level Gauge When oil level is low from fixed minimum oil level then minimum oil level alarm is ringing. When oil level is high from fixed maximum oil level then maximum oil level alarm is ringing.

30. 30 Oil Level Gauge

31. 31 Oil Level Gauge

32. 32 WTI Relay Protection WTI – Winding Temperature Indicator Purpose : Monitors hot-spot winding temperature . More accurate protection than OTI for winding overheating. Construction & Working: Like OTI + heater coil inside indicator. CT secondary current feeds heater → simulates winding heating. Pointer shows equivalent winding temperature . Protection Functions: Alarm: at ~95°C (adjustable). Trip: at ~105°C (adjustable). Can trigger fan based on winding temp. Importance: Protects transformer insulation & extends life. Detects abnormal loading or cooling failure early.

33. 33 OTI Relay Protection OTI – Oil Temperature Indicator Purpose: Monitors top oil temperature of transformer. Provides alarm, trip & cooling control . Construction & Working: Bulb sensor placed in top oil pocket. Temperature rise → fluid expands → pointer moves on dial. Alarm & trip contacts operate at preset temperatures. Protection Functions: Alarm: at ~85°C (adjustable). Trip: at ~95°C (adjustable). Can start cooling fans/pumps automatically .

34. 34 Differential Relay Protection This scheme is employed for the protection of transformers against internal short circuits. It provides the best overall protection for internal faults. It compares the current entering the transformer with the current leaving the element. If they are equal there is no fault inside the zone of protection

35. 35 Restricted Earth Faults Relay Protection Differential protection has excellent operation in most fault cases, but in the situations that a single phase to ground fault that current increases slightly and causes differential protection not to detect the fault. Restricted earth fault (REF) relay can be used as a complementary of differential protection.

36. 36 Over fluxing Protection A transformer is designed to operate at or below a maximum magnetic flux density in the transformer core. The flux in the core increases with either increasing voltage or decreasing frequency. Flux density can be formulated : B = V/F

37. Preventive Maintenance Visual Inspection – Check for oil leaks, physical damage, and signs of overheating. Oil Level & Quality – Inspect oil level in conservator tank and test oil for BDV (Breakdown Voltage). Silica Gel Breather – Check silica gel color; replace when it turns pink (moisture saturated). Bushing Inspection – Clean bushings, check for cracks, tracking marks, or leakage current. Temperature Monitoring – Verify proper operation of temperature gauges and alarms.

38. Preventive Maintenance Cooling System – Check radiator fins, fans, and pumps for proper operation. Connections & Terminals – Tighten all loose connections and inspect for corrosion. Earthing System – Test earthing resistance periodically to ensure effective grounding. Load Monitoring – Record load current and voltage regularly to avoid overloading. Relay & Protection Testing – Test Buchholz relay, pressure relief device, and protective relays. Insulation Resistance (IR) Test – Perform megger test periodically to assess winding health. Noise & Vibration Check – Listen for abnormal sounds or vibration indicating internal faults. Record Keeping – Maintain logbook for all inspections, tests, and maintenance activities.

39. Safety Precautions Safety Precautions While Operating a Transformer Proper Earthing – Ensure transformer tank, neutral, and body are properly earthed. Check Oil Level & Temperature – Maintain correct oil level and monitor temperature rise regularly. Avoid Overloading – Never exceed the rated load capacity. Inspect Connections – Check all terminals and bushings for tightness and any signs of overheating. Monitor Noise & Vibration – Unusual humming or vibration can indicate internal faults. Follow Switching Procedure – Operate isolators and circuit breakers as per standard operating sequence.

40. Safety Precautions Handle Tap Changer Carefully – Change taps only when transformer is de-energized (for off-load tap changers). Fire Safety Measures – Keep fire extinguishers (preferably CO₂ type) near transformer. Keep Area Clean & Dry – Ensure no water, oil spill, or vegetation near transformer. Personal Protective Equipment (PPE) – Always wear insulated gloves, safety shoes, and helmet during operation. Follow Lockout-Tagout (LOTO) – Before maintenance or inspection, isolate and tag-out power supply. Regular Testing – Periodically test insulation resistance, oil BDV, and protective relays.

41. Thank You