As per Shri SKB Valli sir strong message regarding Maintenance activities and awareness to enhance safety and Qualitative production

 As per Shri SKB Valli sir strong message regarding Maintenance activities and awareness to enhance safety and Qualitative production.

[4/19, 11:58] Dr Amar Nath Giri: EHS (Environment, Health, and Safety) questions and answers regarding the induced duty test for a 33 kV/18 MVA Transformer, utilizing 4 kg/9 kg DCP fire extinguishers, sand buckets, and a Nitrogen Injection Fire Protection System (NIFPS).

I. Safety Preparation for Induced Duty Test (HV & MV)

1. What is the main purpose of an induced duty test?

It tests the dielectric strength of the insulation between turns, windings, and ground by inducing a voltage (usually 2x or more) at a higher frequency (100–200 Hz) to avoid core saturation. 

2. What is the required PPE for this test?

Insulated gloves (Class 0/1), safety shoes, helmet, safety goggles, and arc-rated clothing. 

3. How to ensure safe isolation before testing?

Ensure the transformer is disconnected from the 33kV and 11kV busbars, LOTO (Lockout/Tagout) is applied, and the windings are grounded. 

4. What is the safe clearance for a 33 kV system?

The minimum clearance in air is typically 320 mm for phase-to-ground and 400 mm for phase-to-phase. 

5. Why is a high-frequency supply (e.g., 100 Hz or 200 Hz) used?

To avoid saturation of the magnetic core, allowing the required voltage test level to be induced without exceeding magnetic flux density limits. 

II. DCP Extinguishers and Sand Buckets (4kg/9kg)

6. What are the classes of fire on a transformer?

Class B (oil) and Class C (electrical). 

7. How should a 4 kg or 9 kg DCP extinguisher be operated?

Using the P.A.S.S. method: Pull the pin, Aim at the base of the fire, Squeeze the handle, Sweep side-to-side. 

8. How often should the DCP extinguishers be weighed?

Extinguishers should be weighed at least once every 2 years (or per local regulation). If weight drops by more than 5%, it needs to be recharged. 

9. How to use sand buckets in a transformer emergency?

Sand should be thrown at the base of the oil fire to extinguish it through smoldering (smothering). 

10. What is the discharge time for a 9 kg DCP extinguisher?

It is typically 13 seconds or more, providing a 2–6 meter discharge throw. 

III. NIFPS (Nitrogen Injection Fire Protection System)

11. What is the fundamental operating principle of NIFPS?

It operates on the principle of DRAIN AND STIR, reducing internal pressure and temperature below the oil’s flash point. 

12. When should NIFPS automatically activate?

Upon detection of an internal fault by the Buchholz relay, pressure relief device (PRD), or differential relay, combined with a sudden pressure drop. 

13. What is the role of nitrogen in NIFPS?

It is injected from the bottom of the tank at high pressure to stir the oil and lower its temperature. 

14. What does the NIFPS check before activating?

It ensures the transformer is electrically isolated, preventing the system from operating while energized. 

15. What are the main components of NIFPS?

Fire detectors, nitrogen cylinder, PLC/Control Panel, inlet valve, and drain valve. 

IV. Emergency and Operational EHS

16. What must be done if oil temperature exceeds 40°C during tests?

Tests should be delayed, as high oil temperature can lead to inaccurate results or potential thermal runaway. 

17. What should be done to check for leakage before the test?

Visually inspect the transformer for leaks (valves, bushings, top cover) and verify positive nitrogen pressure if equipped. 

18. What should the operator do if an abnormal noise occurs?

Stop the test immediately, isolate the test supply, and inspect the transformer for internal faults. 

19. How long should you wait for capacitance to discharge?

It is advisable to wait at least 5-10 minutes for large, high-voltage transformers after de-energizing. 

20. What is the final action before finishing the testing?

The transformer must be thoroughly discharged to the ground using discharge rods to eliminate residual charge.