DISTRIBUTION OPERATIONS AND MAINTENANCE

Transcription

1 EB Exhibit F Tab Schedule Filed: 00 Aug Page of DISTRIBUTION OPERATIONS AND MAINTENANCE 0 PREDICTIVE MAINTENANCE Predictive maintenance expenditures fund work that is required to test and audit distribution system assets. Predictive maintenance is intended to anticipate equipment failures and to minimize the number and extent of these failures. It relies on scientific methods of testing or inspection that utilize actual data gathered for the purpose of setting performance standards for the asset and its components. Predictive maintenance entails performing maintenance tasks on distribution assets without power interruption to THESL s customers. Predictive Maintenance is derived from RCM II, which is designed to determine the optimal maintenance tasks for the assets within their operating context. Optimal in this sense means the least costly maintenance tasks that satisfy reliability, safety and environmental requirements. For example sampling transformer oil for the presence of gasses associated with insulation breakdown is technically feasible; however, it is generally only worth doing for larger transformers having a high impact on reliability and resulting in high cost of failure. Predictive Maintenance tasks are identified only where monitoring predictive conditions are technically possible and practical. 0 DISCUSSION Predictive maintenance supports THESL s goal of asset modernization by helping to detect future failures. Many failures are related to factors other than asset age, such as breaker component wear, insulation breakdown in power class transformers, or poor intermediate-voltage connections. By testing specific assets against a base reference of a normal condition THESL can determine whether a failure is in the process of occurring. Performing predictive tasks allows the discovery of evidence that assets are approaching failure and provides an opportunity to take action to prevent them from failing

2 EB Exhibit F Tab Schedule Filed: 00 Aug Page of completely. This evidence may also lead to the pre-emptive replacement of a declining asset, either on an individual basis, or for an entire population if a failure mode becomes common throughout an asset class. The specific asset classes that are included in the predictive maintenance program are itemized and referenced in the latest edition of THESL s Plant Maintenance Manual. These predictive maintenance programs build upon the findings of the ACA performed by Kinectrics Inc., which is contained in Exhibit D, Tab, Schedule. 0 0 Station Assets Predictive maintenance tasks for stations assets focus on power transformers and batteries (emergency power systems) located within the stations, and on the station facilities themselves. By performing predictive inspection and testing on these equipment types THESL obtains an advance indication of likely failures. The maintenance of station buildings and property helps THESL secure energised equipment from acts of vandalism or hazards to the public. Station power transformers are critical links of the power system. Each of them supplies power to anywhere from 00 to,000 customers. Transformer breakdowns are usually associated with chemical decomposition of the insulating materials. Such decomposition is detectable by testing for the presence of latent gases, which become dissolved in the cooling oil of the transformer. This analysis of the dissolved gases in the transformer oil is a very important test that is performed periodically to detect incipient insulation faults. The findings from these tests are documented and used to schedule follow-up repairs. Critical or major deficiencies that may affect safety or system reliability are corrected immediately.

3 EB Exhibit F Tab Schedule Filed: 00 Aug Page of 0 All protective relays and control circuits within distribution sub-stations are powered via batteries, which are charged by station rectifiers (charging systems). This source of control voltage is essential for indication lights, alarms and the actuation of equipment such as circuit breakers, SCADA control system, fire protection, and emergency lighting. Failure to maintain sufficient voltage can render the protective system and the breakers inoperative. This may cause damage to electrical assets and the loss of control capability for the entire station. If this occurs, the protection and coordination of the subordinate distribution plant is escalated to the next upstream protective device, such as a breaker from a transmission substation or even a kv breaker in a Hydro One substation. In this event, any potential outage may affect a much larger customer base and physical area. Predictive testing of batteries and charging systems reduces the probability of premature battery failure going undetected, thereby pre-empting potential associated outages. External Contracts Infrared and ultrasound scans on station switchgear provide advanced warning of incipient electrical faults. These faults are detected by scanning contact points for signs of overheating, surface tracking and corona. 0 Beyond sub-stations, most electrical failures originate from loose connections, tracking due to contamination on the surface of insulators, and corona. Infrared and ultrasound scans can be performed while the equipment is in service. These tests detect failures before the component insulation completely fails. Failure has the potential to cause considerable damage to adjacent equipment, potentially long outages and costly repair work. Load break switches, disconnect switches, and bolted electrical connections are tested before routine maintenance outages so that the problems found during the tests can be

4 EB Exhibit F Tab Schedule Filed: 00 Aug Page of corrected during the routine maintenance outages. Having information about the condition of the equipment in advance of the maintenance outage is a great advantage to the maintenance crews. 0 Infrared inspection of overhead, three-phase line components identifies potential hot spots, allowing for corrective measures to be taken before they have an impact on system reliability. Infrared inspection is conducted on all overhead. kv,. kv and. kv three-phase feeders and three-phase distribution circuits. In addition to the overhead line components, any electrical equipment which exists in proximity to these circuits, is also inspected. These inspections are conducted by external contractors annually, typically during the summer peak loading months of July and August. Pad-mounted switches are installed primarily on feeders (mostly. kv), and some have connections to more than one feeder. Infrared scanning provides a quick audit of the condition of the live (current carrying) parts and components, including connections and terminations of the switch inside the pad-mount enclosure. They also are visually inspected for signs of contamination build up and tracking. Units with excess contamination build up are scheduled for CO cleaning. 0 The inspection/maintenance of cable chambers is typically performed in two stages. The inspection and documenting of deficiencies are usually conducted in the summer months using an infrared inspection of the cable splices and digital photographs of all chamber walls. This program is limited to those areas of Toronto containing. kv cables. These. kv cables have sufficient fault energy to cause extensive damage within the cable chamber and may cause the chamber lid to become dislodged during a lowimpedance fault condition.

5 EB Exhibit F Tab Schedule Filed: 00 Aug Page of THESL uses a ten-year inspection cycle for testing and treatment of its inventory of,000 wood poles. The inspection program looks for decay and treats discovered decay in order to reduce the risk of pole failure, thereby enhancing the reliability of the system and public and worker safety. 0 COSTS The predictive maintenance program value is derived by focussing on those assets having the greatest impact on the reliability of THESL s distribution system in the event of failure. These assets require extraordinary effort to isolate, and during periods of isolation, leave the distribution grid at an elevated risk of outage. The programs represented in Table for Predictive Maintenance on station transformers, station breakers, critical switches and poly-phase line components are both technically feasible and represent the most cost-effective alternative (as determined through the RCM process). Table : Predictive Maintenance Costs ($ Millions) Predictive Maintenance Historical Bridge Test Test 00 Test OH/UG Distribution Assets* N/A N/A N/A N/A N/A Stations Assets External Contracts Total Predictive * Costs are included under External Contracts as all work is performed by contractors. 0 During 00 and previous years the Stations predictive maintenance program included the thermographic inspection of three-phase, overhead primary feeder circuits and padmounted switches. This inclusion was made in order to aggregate similar work and improve efficiency. For 00 and the test years this work has been outsourced in

6 EB Exhibit F Tab Schedule Filed: 00 Aug Page of combination with the thermographic inspection of cable splices on. kv underground feeders. Outsourcing of this program accounts for the reduction in cost of the Stations program, and the corresponding increase in scope of external contracts. During the bridge year and test years the cost of predictive maintenance is affected by minor variations in the volume of work required in each year and the effects of inflationary pressures. The cost for the predictive programs remains relatively flat after adjustments for inflation-driven increases in labour, equipment and contract rates.