Failure Analysis of Medium Voltage Capacitor Banks: The Egyptian Experience

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1 Failure Analysis of Medium Voltage Capacitor Banks: The Egyptian Experience Mohamed A. EL-HADIDY Dalal H. HELMI Tech. Consultant Studies and Research Dept. Egyptian Electricity Transmission company Egypt

2 CONTENT GENERAL APPROACH OBJECTIVES FAILURE MODES EXAMPLES OF FAILURE MECHANISMS UTILITY MAINTENANCE PRACTISES RESULTS AND RECOMMENDATION

3 - GENERAL- System reliability depends on components reliability Power capacitor banks reliability evaluation through their failure modes, rates and mechanisms have been investigated at about 190 substations in TN, in which 2450 MVAR capacitor banks are installed The study includes 9 vendors for whom the Capacitor Banks are installed during the period of early installation in 1985 till 2008.

4 - APPROACH - - Analyzing the available Capacitor Failure data of all vendors, over the banks lifetime. - Classify different types of failures - Conducting deep analysis and comparisons between different vendors OBJECTIVES Assess the failure modes, rates and mechanisms of MV capacitor banks installed in the Egyptian Network, and sum up utility experience in this field

5 Typical two step capacitor bank installation 1.8 MVAR 3.6 MVAR, or 5.4 MVAR

6 - FAILURE MODES-

7 CAPACITOR BANKS FAILURE RATES The following analysis of the failures covers only 5/9 of these vendors. The other 4 have smaller number of installations, and hence capacity, and exist in only one or two of the Egyptian Network 6 zones.

8 Table 1: Failure Rates of Capacitor Banks Main Components % of the total Failure: Capacitors = 48% Contactors = 18% Controllers = 37%

9 Table 2: Some subcomponent failure statistics in one of the zones

10 EXAMPLES OF FAILURE MECHANISMS In 2008, EETC noticed two types of problems in the newly delivered MV caps from X vendor. Observation of oil leakage from some capacitor bushing Decline in capacitance values which leads to tripping of the bank by the unbalance protection. An investigation task force was formed from vendor company & utility personnel

11 1. OIL LEAKAGE FROM THE BUSHING Problem traced down to the quality of adhesive material used to seal the bushing with the tank.

12 2 CAPACITANCE VALUE DECLINE Scanning Electron Microscope investigation of faulty capacitor element Contamination of capacitor metal film by materials used for soldering Cap units to connection leads

13 UTILITY MAINTENANCE PRACTISES Failed components replaced from the existing spare parts stock under the responsibility of utility maintenance crew the technical staff of the vendor Sometimes spare parts, such as fuses, contactor coils, auxiliary relays, timers etc, are obtained from the local market.

14 Utility perform detailed harmonics measurements at locations: of failed capacitor where caps are intended to be installed. Also, conducts many tests at the factory, commissioning tests and periodic tests (+ harmonic measurement).

15 RESULTS AND RECOMMENDATION Capacitor bank failure modes and failure rates analysis is important to reveal the reliability and goodness of all stages starting from: putting specifications, designing, testing, installing, operating, and maintaining. This helps also in selection of good manufacturers of: capacitors, contactors, fuses, controllers, bushings etc (Vendor 3 discarded).

16 Failure analysis requires a follow up investigation and root cause analysis. (capacitor failures were viewed more as routine annoyances that had to be accepted). The trend today is to approach each capacitor failure as the potential result of a design, operation or maintenance defect.

17 An in-depth investigation should be conducted by an expert and before any potential evidence is disturbed. Once the root cause of the failure is determined, the info can then passed on to the responsible department(s). Appropriate changes can then be made where applicable.

18 The two problems identified in this paper illustrate that there are many potential sources can lead to or cause capacitor failures.

Determination of Fault Location in Shunt Capacitor Bank through Compensated Neutral Current

Determination of Fault Location in Shunt Capacitor Bank through Compensated Neutral Current International Journal of Advances in Scientific Research and Engineering (ijasre) E-ISSN : 2454-8006 DOI: http://dx.doi.org/10.7324/ijasre.2018.32630 Volume 4, Issue 3 March - 2018 Determination of Fault