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POWER SYSTEM COMMISSIONING AND MAINTENANCE PRACTICE DET310

POWER SYSTEM COMMISSIONING AND MAINTENANCE PRACTICE DET310 CHAPTER 2:. MAINTENANCE AND FAULT INVESTIGATIONS. 2.0 INTRODUCTION

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POWER SYSTEM COMMISSIONING AND MAINTENANCE PRACTICE DET310

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  1. POWER SYSTEM COMMISSIONING AND MAINTENANCE PRACTICE DET310 CHAPTER 2: MAINTENANCE AND FAULT INVESTIGATIONS

  2. 2.0 INTRODUCTION The deterioration of electrical equipment is normal, and its process is begins as soon as electrical equipment is installed. If deterioration is not checked, it can cause electrical failures and malfunctions. With a correct and proper maintenance and testing program, potential hazards that can cause failure of equipment or interruption of electrical services can be discovered and corrected.

  3. 2.1 MAINTENANCE 2.1.1 Maintenance Strategies The prime objective of maintenance is to keep equipment in good working order, thus maximise lifetime productivity. Maintenance strategies can be categorised as follows: a) Preventive maintenance:Maintenance which is carried out at pre-determined intervals to reduce the likelihood of an item of equipment failing in service. b) Corrective maintenance:Maintenance which is carried out to restore an item of equipment which has failed.

  4. 2.1.1 Maintenance Categories (continue)- c) Opportunity Maintenance:Maintenance which is carried out when higher priority item or equipment is out of service. For example, generator circuit breaker maintenance is carried out when the generator is out of service. d) Statutory Maintenance- Maintenance which is carried out to facilitate timescales and requirements usually associated with health safety.

  5. 2.1.2 Maintenance Policy Consideration Task – Deciding the extent and periodicity of maintenance against realistic and required standards of equipment performance. In Financial terms – cost of maintenance compared with the cost benefit of carrying out the maintenance.

  6. 2.1.2 Maintenance Activities Type of equipment in power system tends to be static and quiescent (accept for alternator and motors). Thus, replacement of worn parts due to mechanical movement is not a major maintenance activity. In general, power system maintenance consists of the following activities: i) Periodic exercising of equipment ii) Visual inspection iii) Cleaning, dusting and painting

  7. 2.1.2 Maintenance Activities (cont-) iv) Lubrication and periodic replacements of parts v) Monitoring and examination of interrupting and insulating mediums vi) Equipment performance tests v) Removal of foliage to maintain clearances.

  8. 2.1.3 Maintenance periodicity In practice, maintenance periodicity tends to follow one of the following patterns: a) Regular intervals during the life of the equipment based on manufacturer’s recommendation and experience b) In conjunction with a), increased maintenance of older equipment where this can be shown to increase asset life, or to obviate health and safety concerns; c) Statutory maintenance requirements;

  9. 2.1.3 Maintenance periodicity(cont-) d) Opportunity maintenance; e) Targeted sampling of a population of equipment such that the target sample is considered representative of the general population.

  10. 2.1.4 POST FAULT MAINTENANCE It has been the practice in former years, in some utilities, to carry out post fault maintenance of circuit breakers which have interrupted or closed onto fault current. In more recent years such maintenance has only been carried out taking into account the magnitude of fault current, and hence the estimated degree of wear and tear on the circuit breaker.

  11. 2.1.5 Maintenance Specification • All maintenance should be carried out in accordance with a maintenance specification. This should consist of concise: • step by step instructions of the work to be carried out. • The necessary instruments, tools and equipment required to carry out the maintenance should also be listed. • Each stage of the instrument instruction should be accompanied by a short summary of what that stage seeks to achieve. • A formal tick list and results sheet should be provided and these should be neatly filed as a record of the work carried out.

  12. 2.1.6 Maintenance records An essential feature of maintenance is the retention of records. Typical maintenance records comprise: i) Date of maintenance ii) Extend of maintenance iii) What was found iv) What extra was carried out v) Who carried out the maintenance vi) Any specific requirements to be carried out in future v) Planned date of next maintenance.

  13. 2.2 INVESTIGATIONS 2.2.1 Investigation Technique The terms” investigations” refers to the analysis to the system incident, usually associated with a system fault. Examples of such activities range from a false operation of protection relay, to a damage transformer, or to a pole of slipping incidents resulting in loss of generation.

  14. 2.2.1 Investigation Technique (cont-) There are effectively up to five stages to an investigations: i) Data collection. ii) Data analysis iii) Damage investigations iv) Diagnostic tests v) Conclusion.

  15. 2.2.2 Data Collection • When collecting data the following should be contemplated. • First intimation of a system will often be by telephone. It is requested that the provider to start at the beginning and reveals the fact slowly. The key point is noted and be repeated. • b) Consider all possible sources of information; example, fault recorders, data loggers, recording instruments , manned control points and personnel observation. • c) Take a wide view of the problem. Consider the situation at the remote end of the circuit. Determine the load conditions. Find out whether there were any simultaneously incidents on the system.

  16. 2.2.3 DATA ANALYSIS a) Collate the info in chronological order and wherever possible in a diagrammatic form. b) Consider whether the incidents has any precedents. c) Be clear that the circuitry involved and whether it deviates from standard circuitry and equipment. d) If the conclusion is not clear cut, list and contemplate possible sources of failure, e.g equipment designs, limitations, faulty components, incorrect commissioning, wrong setting. e) Consider whether power supplies may have been lost temporarily.

  17. 2.2.4 Damage Investigations • This usually related to damage to high voltage equipment • Creep up on the problem, do not disturb anything unless the situation have been fully thought out • b) Take photographs, or procedure drawings and notes at each stage • c) Compare the situation with healthy equipment

  18. 2.2.4 Diagnostic Test • In the first instant repeat the commissioning test and compare the results with the original commissioning results. • b) Write down a brief schedule of any further investigational tests. Note the results at each stage. Note any temporary connections which may require removal when the test are complete. • c) Where it is considered appropriate, repeat the same test a number of times; some faults are transients and will not show up on the first test. • d) Carry out test which, as far as possible, repeat the incident conditions.

  19. 2.2.5 Conclusions • Produce a clear concise statement of • The incident • The investigation carried out • The conclusions and recommendation. • 2.2.6 Post Investigation • Ensure that the recommendations are acted on. The momentum of implementing one set of recommendations are often slows when a subsequent incident occurs.

  20. 1.8 SAFETY RULES 1.8.1 Objectives of Safety Rules To Govern the working and control of electricity supply throughout TNB installation and to ensure the safety all whom may work on TNB installation. The rules applied on TNB employees, Consumers, Contractors and others.

  21. 1.8.2 Personal Safety Equipment. Safety equipment such as safety helmets, belts and harnesses, ropes, gloves, boots which has been provided by TNB for the protection and use of persons required to work on TNB electrical system, must be properly used on all appropriate occasions. Each item of safety equipment must be examined

  22. 1.8.3 Objections When any person receives instruction regarding work on the operation of on HV or LV equipment, he shall report any objections he may have to the carrying out of such instruction to the person issuing them, who will then have the matter investigated and if necessary, refer to higher authority

  23. 1.8.4 Definitions 1.8.4.1 HV apparatus – Any apparatus, equipment and conductors, which are normally operated at a voltage exceeding 600 V phase to earth or 1000 volts phase to phase. 1.8.4.2 LV Apparatus – Any apparatus, equipment or conductors which are normally operated at a voltage not exceeding 600 V phase to earth or 1000 V phase to phase.

  24. 1.8.4.3 Dead At or about zero voltage and disconnected from any live system 1.8.4.4 Earth, Earth or Earthing Connecting to or connected to the general mass of earth in such a manner as will ensure at all times that the body being earthed discharges immediately any electrical energy stored in it and furthermore is maintained at a safe potential with respect to the general mass of earth. When applied to conductors: all phases short circuited and effectively connected to earth either through switchgear with adequately rated EARTHING capacity or by APPROVED portable EARTHING leads or by any other APPROVED devices.

  25. 1.8.4.5 Circuit Main Earth An earth applied by an AUTHORISED ELECTRICAL PERSON prior to issue of an ELECTRICAL PERMIT-TO-WORK or SANCTION-FOR-TEST. When portable EARTHING leads are used for this purpose, an APPROVED label shall be attached 1.8.4.6 High Voltage Switching The operation of HV switchgear, isolators, fuses or other methods of making or breaking a circuit can be energised or de-energised by means of LV equipment, such energising or de-energizing shall be regarded as High Voltage Switching.

  26. 1.8.4.7 High Voltage Zone • A person is considered to be in HV zone if he has: • Entered an outdoor or indoor enclosure containing accessible HV apparatus or • Climbed a pole which supports HV circuits. • passed above the anti-climbing device on a steel tower structure of pole supporting HV circuits. • 1.8.4.8 SAFETY DISTANCE • The distance from the nearest LIVE HIGH VOLTAGE exposed conductor or from an insulator supporting a HIGH VOLTAGE conductor which shall be maintained to avoid DANGER.

  27. 1.8.4.9 Permit to Work Certificate (P.T.W) A form of declaration signed and issued by an AUTHORISED ELECTRICAL PERSON to a COMPETENT ELECTRICAL PERSON in charge of work to be carried out on any APPARATUS, for the purpose of making known to such person exactly what HIGH VOLTAGE APPARATUS is DEAD, ISOLATED from all LIVE conductors, has been discharged, connected to EARTH and on which it is safe to work. (see Appendix B).

  28. 1.8.4.10 Competent Person A person who has sufficient technical knowledge or experience to avoid DANGER and has been appointed by the CFDH-E to receive and complete ELECTRICAL ISOLATION/DE-ISOLATION CERTIFICATES and receive ELECTRICAL PERMITS-TO-WORK and LIMITATIONS-OF-ACCESS. 1.8.4.11 Authorised Electrical Person (PDO Staff) A COMPETENT ELECTRICAL SWITCHING PERSON who has been appointed in writing by the CFDH-E to carry out HV and LV SWITCHING. The appointment may also include the additional authority (for the issue and cancellation of ELECTRICAL PERMITS-TO-WORK and LIMITATIONS-OF-ACCESS, and to receive SANCTIONS-FOR-TEST.

  29. SANCTION-FOR-TEST A form of declaration signed and issued by a SENIOR AUTHORISED ELECTRICAL PERSON to an AUTHORISED ELECTRICAL PERSON (with additional authority) in charge of testing HIGH VOLTAGE APPARATUS for the purpose of making known to such person exactly what APPARATUS is to be tested and the condition under which testing is to be performed. (see Appendix C).

  30. WORK PERMIT A form of declaration signed and issued by the custodian of equipment or plant to the person in charge (Permit Holder) of a working party, giving clearance to work on the specified equipment or plant, detailing restrictions and precautions required to carry out the specified work safely. The permit shall state which other certificates or permits are required prior to starting work (eg. , ELECTRICAL PERMIT-TO-WORK).

  31. Procedures for Initiation of Work 5.1 ACCESS 5.1.1 Access To High Voltage Enclosures And Apparatus Barriers (including plates on access ladders) restricting access to enclosures or cubicles containing LIVE HV conductors shall normally be kept locked. No person except an AEP or a person acting under his direct supervion shall have access to any such enclosure or cubicle in which a LIVE conductor is exposed.All spout or busbar shutters shall be locked shut.

  32. Climbing of Towers and Gantries Gates and devices to prevent climbing of towers and gantries supporting HV conductors shall always be kept locked except when opened by an AEP under an ELECTRICAL PERMIT-TO-WORK, SANCTION-FOR-TEST or LIMITATION-OF-ACCESS. Climbing on Wood Poles Before any pole is climbed, it shall be sounded. No pole badly impaired by decay or damage shall be climbed until the person in charge is satisfied that it has been made safe. No person shall work upon any pole or tower without making proper use of his APPROVED safety harness, which he shall examine to see that it is in good order, on each occasion before use.

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