CIRCUIT BREAKER POLE MERLIN AND GERRIN MAKE AT TATA POWER COMPANY

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1 CASE STUDY OF RECTIFICATION OF 132 Kv SF 6 CIRCUIT BREAKER POLE MERLIN AND GERRIN MAKE AT TATA POWER COMPANY AUTHOR Gerrin France. After around three years of service one pole developed SF 6 gas leakage. With only a sketchy manual available and with specially fabricated jigs and tool, the author successfully undertook repairs to this pole. This paper details the repair activities. Mr. A. V. Prasanna 214 Veena Vihar 17-A Jai Shankar Yagnik Marg, Sion, Mumbai alpha.prasanna@gmail.com EXECUTIVE SUMMARY OEM seldom get into the root cause of failures of their equipment. Their do not care attitude results in equipments with minor defects being declared as scrap. This case study involves a leaking SF 6 gas from a pole of 132 Kv circuit breaker of Merlin Gerrin make. Efforts to send this pole for rectification proved futile as the OEM refused to undertake repairs, they were interested in selling a spare pole at enormous cost. To tide over the troublesome gas leakage and to provide a permanent solution the author with the concurrence of the management successfully under took repairs of the pole. INTRODUCTION This study involves the failure, rectification, carried out on a leaking pole of 132 Kv SF 6 circuit breaker at Trombay Thermal Plant of Tata Power Company. During Air blast circuit breakers were replaced by state of art SF 6 circuit breaker imported from Merlin Fig. 1: 79

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3 Fig. 3: OCCURRENCE IN BRIEF PREPARATION FOR REPAIRS During November 1988, one pole of SF6 circuit breaker at location DT6 Transformer started developing gas leakage( point C in fig 2). Initially the gas filling which started as once a month drifted to once in 3 days. Many gas cylinders were used to keep the bay in service. 1. The leaky pole was disconnected from electrical and hydraulic connection (as the operating mechanism was oil) and shifted to the Transformer repair shed. This shed had a gantry crane to facilitate ease of dismantling and assembly. 81

4 2. The pole was mounted on a pedestal and a special dust proof enclosure was created by using scaffolding materials and Plastic sheets. 3. Vacuum pump, connecting hose, 3 way valve, spare SF 6 gas cylinder, were arranged from Carnac Receiving station as it had 220 Kv GIS of M&G make. Special connecting fixture were fabricated in the workshop. ANALYSIS & RECTIFICATION i. By using suitable lifting tackles top fixed contact assembly was dismantled. ( item a in fig 2), Next top porcelain interrupter chamber was dismantled (item b in fig 1) ii. On the mating surfaces O rings provided had cracked due to atmospheric variations and hence the gas started leaking from these joints. iii. New O rings were replaced and liberal quantity of RTVM (Room Temperature Vulcanizing Media) compound were smeared on all the mating surfaces and the top porcelain chamber and fixed contact were assembled back in place. iv. Using a vacuum pump, 3 way control valve, and SF 6 gas cylinder the interrupter chamber was evacuated ref fig 4. Then gas was filled to 2 bars. After checking through soap solution, and gas detector for absence of gas leak, this gas was purged out. The process was repeated 3 times. Finally the pole was filled with SF 6 gas at 6.2 bars (with temperature correction factor). v. Routine electrical test including AC Hipot was conducted on this pole and the results were satisfactory. vi. The pole was shifted to its location and taken in service. There has been no leakage of gas further. CONCLUSION Fig. 4: After executing the repairs, which was first by any standards within the system and outside, it was felt that with right tools and a bit of technical knowhow any rectification work can be carried out. The total repair activity was completed in 3 days time. Support from the management is equally important. With this repair, the author was able to save replacement cost of the pole and also set up a procedure for future repairs. 82

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