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The Tata Power Company Ltd EQA Group
Title : OCCURRENCE ANALYSIS REPORT
Form No: EQA-PS-01-FM-01 Page no. 1 of 7
Rev. No.: 00 Rev. Date: 01-11-2002
From: AGM (ETA) Date: 10th June ’09 Ref: E/PS /OAR/161 To : Sr. Mgr ( Chembur, Vikroli, Mankhurd) Cc: GM (Engg, Proc & TS), DGM (T & D) Sub : 22 kV REL Fdr # 5 tripping due to Failure of A-phase floor bushing at Chembur R/S on 29th April 2009 1. Occurrence in brief:
On 29th April 2009, at 13:00 hrs, 22 kV REL -5 feeder tripped due to failure of A-phase floor bushing at Chembur R/S.
2. Observations: The floor bushing was found damaged partially (ref. exhibit -1) and a void was noticed between the conductor and resin insulation of the bushing. The resin was found melted and its deposits were found on the surface of bushing. The hole formed on the bushing exposed the conductor surface and carbon deposits were noticed on the damaged portion of the bushing (exhibit-2), Relay targets: A B Phase, E/F – Inst. 3. Investigations & Analysis:
Damaged A-phase bushing was brought to ET&A Lab for Investigation. Following steps were followed
3.1) Insulation Resistance test
a) Conductor to body ground point >100 m ohm at 1 kV
3.2) Hi pot test
Hi pot test was done on the bushing by slowly increasing the voltage (exhibit-3).
An arc was observed at 7KV and subsequent increase in voltage, the arc turned into fire at the damaged point. The test was abandoned to minimise further damage.
The Tata Power Company Ltd EQA Group
Title : OCCURRENCE ANALYSIS REPORT
Form No: EQA-PS-01-FM-01 Page no. 2 of 7
Rev. No.: 00 Rev. Date: 01-11-2002
4) Insulation was exposed for further investigation by cracking the surface of damaged portion of the bushing (exhibit-4). A Clear void was noticed at the top portion of bushing (exhibit-5). A copper mesh was noticed between two layers of resin insulation (exhibit-6), which is probably used for balancing the voltage gradient (exhibit-7). Insulation Resistance test carried out on the copper mesh and the ground point indicated continuity. The mesh connection is brought to a separate point for grounding purpose. The failure was noticed at the junction between conductor and the mesh and the resin was found totally charred (exhibit-8)
3. Conclusion: The above observations indicate that the bushing failure is on account of partial discharge phenomenon between the conductor & the copper mesh over a period of time. 4. Recommendations: To conduct PD detection test using Ultra Sonic PD detector on remaining bushings of the switchgear for further analysis.
Encl. Exhibits 1 to 8
Engineer (Yasmeena.S)
SH (T.Murali Krishna)
AGM (M.V.Kini)
The Tata Power Company Ltd EQA Group
Title : OCCURRENCE ANALYSIS REPORT
Form No: EQA-PS-01-FM-01 Page no. 3 of 7
Rev. No.: 00 Rev. Date: 01-11-2002
Exhibit – 1: A phase damaged bushing.
Exhibit – 2: Damaged part of Bushing
The Tata Power Company Ltd EQA Group
Title : OCCURRENCE ANALYSIS REPORT
Form No: EQA-PS-01-FM-01 Page no. 4 of 7
Rev. No.: 00 Rev. Date: 01-11-2002
Exhibit – 3: Hipot test set up
The Tata Power Company Ltd EQA Group
Title : OCCURRENCE ANALYSIS REPORT
Form No: EQA-PS-01-FM-01 Page no. 5 of 7
Rev. No.: 00 Rev. Date: 01-11-2002
Exhibit – 4: After removing the insulation
Exhibit – 5: Void
The Tata Power Company Ltd EQA Group
Title : OCCURRENCE ANALYSIS REPORT
Form No: EQA-PS-01-FM-01 Page no. 6 of 7
Rev. No.: 00 Rev. Date: 01-11-2002
Exhibit - 6: Copper mesh
Exhibit -7: Copper mesh in between resin Layers
The Tata Power Company Ltd EQA Group
Title : OCCURRENCE ANALYSIS REPORT
Form No: EQA-PS-01-FM-01 Page no. 7 of 7
Rev. No.: 00 Rev. Date: 01-11-2002
Exhibit -8: Discharge path