DISTRIBUTION OPERATIONS AND MAINTENANCE

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1 EB-00-0 Tab Schedule Page of 0 DISTRIBUTION OPERATIONS AND MAINTENANCE 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, extent and severity 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 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 most cost effective maintenance tasks that ensure reliability, safety and environmental requirements. For example, sampling transformer oil for the presence of gases associated with insulation breakdown is technically feasible, however, it is generally only cost effective 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 the THESL 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 or will occur in the near future. Performing predictive tasks allows the discovery of evidence that assets are approaching failure and provides an opportunity to take action to

2 EB-00-0 Tab Schedule Page of prevent them from failing 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 the THESL Plant Maintenance Manual. 0 Station Assets Predictive maintenance tasks for stations assets focus on power transformers and batteries (station operations and 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 advanced indication of likely failures. The maintenance of station buildings and properties allows THESL to secure energized equipment from acts of vandalism or hazards to the public, perform visual inspections of major equipment condition, and address any animal contacts. 0 Station power transformers are critical links in the power distribution system, each of which supplies power to large number of customers (approximately,000). 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 insulating and cooling oil of the transformer. This analysis of the dissolved gases along with standard oil tests is performed periodically to detect incipient insulation faults or water contamination. 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. 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

3 EB-00-0 Tab Schedule Page of 0 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 the incoming breaker in switchgear or even a high voltage supply ( kv) breaker in the transmission network. 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 preempting 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, electrical failures may also 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 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

4 EB-00-0 Tab Schedule Page of the maintenance crews and may eliminate a secondary outage caused by a switch failure or for switch maintenance. 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 that 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. 0 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. The inspection and 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. kv cables as these cables have sufficient fault energy to cause extensive damage within the cable chamber. In addition, it may also cause the chamber lid to become dislodged during a low-impedance fault condition creating a public hazard. As described in Exhibit C, Tab, Schedule, THESL is extending infrared scan of cable chambers in the downtown core in 0 as a pilot project with the anticipation of full implementation soon after the pilot project results are evaluated.

5 EB-00-0 Tab Schedule Page of THESL uses a ten-year inspection cycle for testing and treatment of its,000 wood poles. The inspection program looks for decay and treats discovered decay in order to reduce the risk of pole failure and extend the life of poles, thereby enhancing the reliability of the system and public and worker safety. 0 Electrical plant installed in the field is constantly exposed to elements. It endures wide seasonal temperature variations as well as dirt, contamination and moisture ingress. Over time, physical connections and joints may be fatigued to a point that they break from the original bonding and cause live conductors to make contact with metal or concrete housing saturated with water and salt resulting in contact voltage when touched by pedestrians or animals. A typical example of such failure is exposed street lighting wire in a sidewalk handwell or inside a street lighting pole that causes the sidewalk or pole to be energized at a voltage up to 0V. These incidents are referred to as contact voltage and are an emerging issue experienced by some electrical distribution companies as assets age. 0 THESL has elected to employ mobile contact voltage scanning technology. Power Survey Company, which owns the rights to the technology, has been selected to perform scans of the distribution system in Toronto. With mobile scanning, an electric field sensor is fitted to the back of a truck, which is then driven through the areas being surveyed. When a high field is detected, an alarm is sounded and an operator is directed to the source to document the incident and initiate the repair process. Mobile scanning allows for the entire system to be scanned in a shorter period of the time in contrast to a crew to visiting all locations and manually testing for the presence of contact voltage. This method of contact voltage detection has been certified to detect voltages as low as.v on any infrastructure within nine metres of the sensor.

6 EB-00-0 Tab Schedule Page of Mobile detection technology has been used by many utilities, in particular, Consolidated Edison ( ConEd ) in New York City since 00. Feedback received from ConEd and other utilities using this technology, is positive. Due to the condition of aging streetlight assets, it is prudent to maintain a regular scanning program to detect the presence of contact voltage across city streets. Once contact voltage is detected, the source of the contact voltage can be investigated, isolated, repaired and eliminated. The Contact Voltage Scan program will allow THESL to scan the 0 square kilometres of the City for contact voltage four times a year. 0 COSTS The predictive maintenance program value is derived by focussing on those assets having the greatest impact on the reliability of the THESL 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 maintenance alternative, as determined through the RCM process. 0 Table summarizes the total predictive maintenance costs for the 0 Test year, as well as the historical actual and bridge years:

7 EB-00-0 Tab Schedule Page of Table : Predictive Maintenance Costs ($ millions) Predictive Maintenance 00 Historical 00Historical 00Bridge 0Test OH/UG Distribution Assets Stations Assets External Contracts 0. (0.0).. Total Predictive Predictive maintenance costs increases by $ 0. million in the 0 test year. This increase includes a forecasted increase from $ million to $. million for the Contact Voltage Scan program under external contracts. The success of contact voltage scan program in detecting potential electrical hazards on Toronto roads in 00 and 00 drove the decision to increase the coverage area in the 0 test year. Another $ 0. million of the increase in external contracts is attributable to the reassignment of costs for the wood pole inspection program from the preventive maintenance budget in the 00 to the predictive maintenance budget in the 0 test year.