Maintenance in INSTALLATION AND MAINTENANCE OF ELECTRICAL EQUIPMENT

Maintenance in INSTALLATION AND MAINTENANCE OF ELECTRICAL EQUIPMENT

1. Maintenance Unit-5

2. Introduction Maintenance is the process for maintaining any equipment or machinery in a proper and efficient condition. Maintenance can be defined as those activities required to keep the equipment in operating condition so that it continues to meet specifications. It ensures that the production plant or equipment is available for use at minimum cost, for scheduled hours. Maintenance increases the availability of equipment by reducing down time. It assures the equipment availability for instant operation

3. Classification of Maintenance Corrective or breakdown maintenance - Carried out when an equipment fails or does not work satisfactory. Preventive maintenance- Carried out to reduce the failure of equipment to minimum. Contracted maintenance- Contract terms are agreed upon by the supplier of equipment and user, and may include both preventive an corrective maintenance.

4. Preventive Maintenance It means proper maintenance. It consists of adoption of measures to know before breakdown and prevent them before they occur than allowing breakdowns to happen and the take action. Functions are: Periodic visual inspection of various equipment to locate condition leading to breakdown. Upkeep of equipment and plant and repair defects at their initial stage. To attend major breakdown and repairs .

5. Well planned preventive maintenance programmes will have following aspects. Inspection - What to inspect and how? Frequencies - How often to inspect? Schedules - When to inspect? Organisation - Who to inspect? Records - What to record and how?

6. Advantages of Preventive Maintenance It prevents unscheduled interruption to various machines and equipment and premature failures. It makes an affective use of systematic maintenance and inspection to determine the need for minor and major repairs. It reduced breakdown to a minimum and increases the efficiency of equipment and machinery. Satisfactory maintenance of machines and other equipment at low cost. It helps to plan flexibility in operation due to accurate knowledge of machinery conditions. Lowers wear and tear of machine and other equipment. Makes working condition better. Increases life of machine. Provide greater safety and protection to workers. Cost of repairing is reduced.

7. Classification of Preventive Maintenance Routine maintenance- Should be carried out daily. Visual inspections, minor repair to remain equipment in operation, cleaning of tank cover, bushings, fixed and moving contact of starters, replacement of burnt contact. Periodic maintenance- Carried out weekly, fortnightly, monthly, quarterly, or half yearly depending upon requirements and condition of machine. Inspection of loose parts, ventilation, change of oil, replacement of worn parts, insulation checking. Overhaul - Carried out half-yearly or yearly. Replacement or renewal of main units, assemblies and parts of electrical equipment. (Rewinding of motor stator and rotor, replacement of busing of H.V C.B, partial or complete dismantling of equipment) Maintenance on fault- Carried out immediately as and when a fault occurs. E.g. blowing of fuse, short circuit or overloading etc.

8. Breakdown Maintenance When industrial plants or electrical machines are running, and stop incidentally, it is known as breakdown. Causes: Faulty design construction Incorrect installation or use Overload Negligence Wear and tear Accident

9. Breakdown maintenance is carried out as and when necessary. The following are the main recommendations for implementation to breakdown maintenance. Engineering records -Proper entry of all detected faults into repair card of electrical equipment is of special importance. Inspection - It must be carried out by senior and competent person. Two groups: External (vibration, abnormal sound, wear and slackness, lubrication) and internal inspection (carried out during pre-planned shut down-monthly / quarterly / half-yearly). Servicing - Cleaning, adjustment, lubrication and maintenance functions without dismantling equipment. Testing - Performance of devices such as relays etc depend upon testing and proper setting. Done by responsible person who has thorough knowledge of use and proper handling of testing equipment.

10. 5. Engineering analysis- Few equipment require more frequent repairs. Reasons: defective design, faulty material, unhealthy operating conditions, misuse of equipment, poor maintenance, low quality material used in equipment. 6. Tool and tackles- Proper tools reduce amount of manual labour required for handling heavy equipment. Heavy and time consuming manual work can be reduced. 7. Inventory control of stores and spares- To make inventory of all spares required and should be made readily available for use whenever required.

11. Maintenance of transformers It is essential to have periodic maintenance of power transformers by trained persons, and with maintenance facilities. Transformer needs regular maintenance for satisfactory service. It includes: Routine daily inspection (DI) Routine monthly inspection (MI) Annual inspection (AI) Routine weekly inspection (WI) Quarterly inspection (QI) Un-scheduled maintenance (US)

12. Daily checks Check tank and radiators for unusual noise, oil and water leaks. Check oil level in conservator. Check relief vents whether normal or open. Check whether cooling water is flowing, whether oil circulation pump is operating when necessary, whether fans start when necessary. Check relay panel temperature indicators and confirm normal condition. Check position of tap-changer. See that all control/alarm/switches are closed and fuses in circuit are well placed.

13. Monthly checks Check oil level in main tank. If oil level has fallen down below specified level for given temperature, the cause of leakage should be determined. Check and record oil temperature. Check bushing surface for signs of chipping, dirt, oil etc. Check presence of nets, shrubs etc in neighbourhood of transformers. Check terminal connections, earthing connections for tightness. Other checks mentioned in daily checks.

14. Annual Inspection Check foundation for cracking and settling. A slight shift of transformers may break bushings or connection oil and water pipes. Clean dirt and oil from radiating surfaces. Repaint as necessary. Stop excessive vibration of radiator tubes, tighten or loose the vibrating parts. See that relief diaphragm is in operating condition and close tightly. Check chemicals in breather and replace if depleted. Check oil level indicators and relays for proper operation. Replenish oil if below normal. Drain out and replace bushing oil if dirty or discoloured. Check external supply and drain piping for leaks. Test coils for leaks by applying air pressure to coils.

15. Check calibration of temperature indicators and relays, check and clean relay contacts and operating mechanism. Clean porcelain with water, chloroethylene or other suitable cleaner. Repair chipped spots by painting with lacquer such as red glyptal . Tighten all bus and ground connections. Check motor, gear shafts and lubrication of OLTC. Check condition of contacts and refinish if burned or corroded. Check IR between each winding and between each winding and ground. Check dielectric strength of insulating oil in main and auxiliary tanks. The acidity of insulating oil in main tank should be checked at intervals of not more than 5 years.

16. Unscheduled maintenance If the transformer has been properly maintained and not overheated and barring internal failure, it should not require untanking within normal life. If sludge has been allowed to form due to overheating and oxidation of oil, transformer should be untanked and the core, coils oil passages, tank and water cooling coils are washed down with clean oil under pressure to remove sludge and other accumulations which prevent proper circulation of oil. Inflammable liquids should not be used in cleaning the core, coils, or inside of tank. While untanked , check for loose laminations, core bolts, insulating blocks etc. The necessity for filtering and/or reclaiming the insulating oil will depend on the results obtained from the oil dielectric and oil acidity tests. It may be more economical to replace the oil in small transformers rather than filter and reclaim it.

17. Maintenance schedule of synchronous motor Maintenance of synchronous machine may be alternator or motor is “must” and can be termed as an insurance for trouble free performance of equipment. Following are the main points required for maintenance schedule of synchronous machine. General - The machines should be stopped and isolated from all supplies before any maintenance work is done. The frequency of maintenance required depends to a large extent upon the site conditions. Cleaning - The unit should be periodically cleaned internally by blowing out with a jet of dry air and by wiping away and deposits of grease and carbon dust with a clean dry cloth. Brushes - Brushes should be examined initially after every 100 hours running. Care must be taken to see that brush holders are not allowed to touch the surface of slip rings. The brushes should be replaced when they wear down to within 3 mm of their support arms.

18. Slip rings- During normal running the slip rings should have a dark burnished appearance free from grooving and uneven wear. If it is essential to resurface “process known as skimming” the slip ring, the brushes must be readjusted or repositioned. Bearings - The bearings are charged with grease at works, and the bearings should be recharged after every 3000 hours of running. Do not mix different grades or grease or over fill the bearings. Periodically clean and recharge the bearings. Oil leakage- For lubrication, it should be neither be excessive oiling or insufficient lubrication. The lubrication should be appropriate and periodic. Special care must be taken that there should not be any type of leakage of oil on stator. This results into breakdown of stator winding insulation. Temperature- The insulation temperature and body temperature must be recorded frequently. It should ne within permissible limits so that machine can run smoothly.

19. Trouble shooting in DC motors Sr. No. Trouble Causes Remedial measures 1. Fail to start Circuit open Brushes are not making contact with commutator Bearing is seized Current is not available Repair the broken leads or faulty switch. Adjust springs, and if brushes are worn out, replace them. Replace/Repair the bearing. Check starter 2. On starting, it starts then changes the direction of its rotation Reverse polarity of D.C supply Check generator for reason of changing polarity. 3. Motor does not pick up rated speed Over load Voltage low Starting resistance has not been completely cut out Armature winding bars short circuited Inspect bearings to ensure they are okay. Check load and ensure it is within capacity of motor. Check voltage Starter needs thorough checking In case winding coils found burnt, commutator bars are found black, motor should be repaired.

20. Sr. No. Trouble Causes Remedial measures 4. Motor runs high speed Voltage available is more than rated voltage. Load is too less Shunt field coil is shorted Ensure rated voltage Increase the load or put fixed resistance in armature circuit Replace it by new coil 5. Motor runs very slow Low voltage Over loaded Check for correct voltage Check bearings, check for excessive load 6. Motor runs very hot It is overloaded and drawing more current Ventilation is defective Shorted coils Reduce load Check ventilation Repair windings 7. Brushes are sparking Poor soldering connections Shorted commutating pole turns Open circuited coils Resolder them properly Repair the coils Repair the coils 8. Brushes are getting worn out very fast Brushes too soft Commutator is found to be rough Moisture Replace brushes with grade of brushes recommended by manufacturer Grind its face Protect motor from moisture or replace it by enclosed motor

21. Sr. No. Trouble Causes Remedial measures 9. Unusual vibration which may indicate unbalance Misalignment Bent shaft Foundation incorrect Re-align Either straighten the shaft or replace it Level the foundation 10. Giving unusual noise Mounting is loose Laminations of armature are loose Armature is running the pole face Mechanical vibration including noisy bearing Tighten foundation bolts Replace them Re-align the rotor Find causes and take remedial measures. Regarding bearing refer to maintenance of bearings

22. Patrolling of Power lines Power lines are required to be inspected visually by the responsible crew of the undertaking for detection of defects which may later on develop into fault and disturb the entire power system. Patrolling of the power lines can be classified as under: (a) Patrolling by Supervisory Staff : The engineer in charge of the line may patrol the line as frequently as possible but specially before the start of rainy season and snow season and t ake necessary steps to rectify the faults thus detected, so that the line may remain reliable during extreme weather when the supply is needed most. After rainy and snow seasons, detailed patrolling should again be carried out and defects removed so that lines may be more dependable. (b) Regular Patrolling : Regular patrolling schedule be chalked out and meticulously followed. Detailed patrolling should be done by linemen in case of important lines regularly at the interval of 30 days. In case of other lines patrolling be done at the interval of 45 days.

23. (c) Emergency Patrolling: In case of forced outage patrolling should be ordered forthwith. The basic purpose of such patrolling is to locate the fault as early as possible and to restore the supply of power. While ordering the emergency patrolling a permit to work should be obtained. Line should be always considered "ALIVE" unless it has been positively made dead. When the fault has been located, the engineer in charge should be informed and necessary action be taken to repair the lines. During repair of the line, the engineer and lineman should remain in contact on telephone. Patrol Report Patrol report books duly numbered and each report having four copies be issued to the in charge of lines, evaluation of the reports will help Electricity supply companies in taking remedial measures in t ime.

24. Maintenance of the Overhead Lines Transmission and distribution lines are conductors bound to internal stresses, strains, and environmental conditions that are constantly acting, tending either, instantly or gradually to weaken one part or an other of the line. Every insulator, Jumper, conductor and each support is responsible for the conveyance of the power. It is therefore necessary that periodic inspection is carried out to check the line to detect the defects which may put the whole system out of gear. The failure of one pin insulator or one insulator string will put the entire system out of operation , as such, periodic, frequent patrolling, inspection of the line, removal of faults after observing routine precautions is but necessary.

25. The person on patrol must also be on a close look out for damaged conductors, insulators, and structures. A pair of field glasses and binoculars is usually necessary If a storm comes up while patrollers are out on a time, they should call the dispatcher as soon as possible, telling where they can be reached. Tree gangs have sole duty to remove bushes, trim, the trees and remove harmful timber from sight-of-way. Emergency crews are stationed at locations always available by telephone or radio so that every important section of transmission system can be reached by a crew with in a reasonable short time. A light truck, provided with two way radio and with the necessary tools and materials for making immediate repairs; may be used. Small store houses containing spare parts, such as insulators, lengths of cables and clamps should be available at every time. Such store houses should be kept locked. A routine inspection and stock checking of materials in such store houses is helpful.

26. The maintenance of line is in following steps. Routine patrolling and inspection. Clearing insulators periodically where necessary. Tightening of clamps and fixtures periodically. Replacement of cracked insulators. Clearing of trees, bushes etc. Inspection of earthing. Check tower for corrosion of galvanized steel tower members and take remedial actions.

27. Maintenance of Underground Cable Practically no maintenance is required on underground cables after making an annual inspection. Following are some special points to be checked for proper maintenance of underground cables. (a) Terminal boxes should be carefully inspected if there is any sign of leakage of the impregnating oil. (b) On all types of cables periodic inspection and insulation resistance test should be made regularly (c) Check of excessive cable temperature. (d) Overheating of cable will cause discoloration. (e) Check, if any accumulation of water in cable ducts. ( f ) Check any dripping of water, oil, other liquid on to cables.

28. (g) Check for any indication of insulation swelling, brittleness, corrosion of lead sheath. (h) A check should be made for any excessive mechanical stress, which may be caused during laying of cable. ( i ) Insulation resistance test: The cable is tested with Meggar. Both the ends of the cable should be disconnected from supply and equipment terminals. The test is made between one conductor and earth one by one. Overall insulation resistance There is no set standard for minimum acceptable insulation resistance for the cable in use. A longer cable will have more leakage path man the shorter cable as insulation resistance of a cable depend on its length and operating temperature  

29. Maintenance of Substation The maintenance work should be carried in systematic way so that there is not any interruption in supply. The maintenance schedule are divided into two categories . Firstly the maintenance of substation is done in case of emergency i.e. in case of failure. Secondly the repair of the substation is carried out during operation . The team for the maintenance work should be skilled personnel. For the maintenance of different equipment lying in substation should be carried out by expert. The maintenance includes: Daily, weekly, monthly, half yearly maintenance. Yearly Maintenance Maintenance once in two years. Maintenance once in five years

30. H. H. H. H. H.

31. Maintenance of switchgear  Inspection, servicing, examin in g and overhauling depends upon: 1. The environmental conditions like chemical fumes, dust, humidity/moisture and changing of ambient temperature etc. 2. Rated current, operating duty and frequency of operations. 3. Repeated operations i.e. switching duty: Only general guide lines are obtained from the manufacturer. It is difficult to get the exact maintenance schedule meeting local requirement of each site. So the maintenance schedule is framed after initial periodic inspection at site. It is necessary to keep the distinction between the maintenance of fixed devices like bus-bars, insul a tors, enclosures etc. and switching devices like circuit breaker contactors, isolators and earthing switch etc. having moving parts.

32. A regular inspection and servicing is required for removing dust, damp and corrosion etc. from the fixed parts. A regular inspection and periodic replacement of worn out parts needed for moving parts . Care is taken for the functional readiness the switching devices. Mainly, the maintenance of switching devices connected with the wearing out of contacts, mechanism components and destroying of quenching medium. It has been observed that contact looses some material and the quenching medium gets decomposed during every breaking operation . The composed products are deposited on the internal insulating parts of circuit breakers. The destroying of contacts and the internal insulation proportional to square of current, where I is the breaking current in KA.

33. Inspection and Maintenance of HT oil Circuit Breaker The high voltage oil C.Bs are used in large industries for power distribution at transformer substations for load switching and also connecting, disconnecting and protecting entire installation . During operation heavy current flows through its current carrying parts and the contacts are heated to high temperatures by the arc between them at the time of closing or opening the circuit. Thus the arcs can burn the contacts and the oil . Frequent circuit opening and closing leads to rapid wear of the contacts and moving parts of high voltage oil C.Bs and their operating mechanism. High voltage C.B causes serious trouble due to inadequate maintenance and adverse surrounding conditions. The preventive maintenance is essential for high voltage oil breaker.  

34. (i) Cleaning of bushing as and when necessary. (ii) Checking the oil level in the circuit breaker monthly. Add more oil if level is low. (iii) Taking sample of oil for testing from the tank of circuit breaker quarterly or after every six tripping. (iv) Check the contacts as per the manufacturer instruction. (v) Replacement of the oil of the tank of C.B when test result is not satisfactory. (vi) Operating Mechanism: Tightening of all nut and bolts if found loose, lubrication of parts subject to friction and correct operation of spring.    

35. Inspection and maintenance of l.t c.B To prevent L.T C.B from excessive wear and tear and breakdown following inspection and maintenance is required. General cleaning Checking of oil level Visual inspection of moving and fixed contacts. Enclosures: Check it for its condition Cleanliness Damage to internal parts Contactor Proper contact pressure, breakage of contact springs Loose connections Oil: Condition of oil. Conduct dielectric test if oil is carbonized and contains other foreign materials. Relays : Testing and setting for correct operation of thermal, over current and no volt coils at set values.

36. Special inspections