MAINTENANCE OF ELECTRICAL EQUIPMENTS IN HAZARDOUS AREA

Proper maintenance of electrical equipment in hazardous area is an extremely important factor. No matter how much thought and efforts may have gone into classification of hazardous area, proper selection and installation of equipment, but poor or no maintenance can invalidate all this in a second.

We would like to highlight some typical examples, like missing bolts on the covers, open unused entries or use of PVC bushes in place of metallic certified stopper plugs, improper layout of external cables resulting in entry of water into the enclosure, loose fitting of cable glands and insufficient compression of cable in the in the rubber grommets.

Any one of above or any other factor can compromise the enclosure protection and put the whole site at risk.

In view of above, it is extremely important and necessary to keep a close watch on the proper maintenance of electrical equipment in hazardous areas. It is also necessary for the user to keep full record of the location, condition, details of any faults, maintenance and repairs carried out on all the equipments.

RESULTS OF POOR MAINTENANCE

Failure of any electrical equipment can lead to the following hazards.

Explosion in the hazardous area due to electrical sparks and hot surfaces.

Sudden interruption in the operation of plant resulting in loss of production.

Fatal accidents or injuries due to electrical shocks and burn injuries due to sparks or hot surfaces.

REASONS FOR THE FAILURE OF ELECTRICAL EQUIPMENTS

There are several reasons leading to the failure of electrical equipment at the site, some of which are listed below:

Variation in power supply like over voltage, under voltage, unbalanced three phase voltage, surges and frequent failure of the supply.

Overloading of the equipment due to any reason.

Bypassing the operating procedure of the equipment like over riding the protective / interlocking devices.

Inability for undertaking and following shutdown inspection and maintenance schedule.

Handling of equipment by untrained or unskilled personnel lacking sufficient knowledge.

Any adverse change in the environmental conditions at the site which may affect proper functioning of the equipment.

MAINTENANCE

To carry out maintenance work after the equipment has failed is meaningless, as the damage has already been done in terms of partial or total shutdown of the running plant or creating flashovers resulting in damage to the equipment and creating potential source of ignition.

In view of above, it becomes very necessary to follow Preventive Maintenance Schedule which should include inspection of the equipment periodically. This will help the user to a great extent in pinpointing the trouble spots in the equipment well in advance, allowing sufficient time for the maintenance personnel to take remedial measures and thus prevent breakdown of any equipment.

PREVENTIVE MAINTENANCE SCHEDULE

To follow this schedule, it is first of all very necessary to keep and maintain complete data and record of the equipment which should include the following:

List of all Electrical Equipments along with their location.

Test Certificates received from the manufacturer.

Single line diagram indicating incoming and outgoing wiring details.

List of all the parts and components used in the equipment along with their make, quantity, specifications, rating etc.

Layout drawings of incoming and outgoing cables.

Details of other equipments connected to the incoming and outgoing sides of the main equipment.

Serial no. and tag details of the equipment.

Operation and Maintenance manuals received from the manufacturer.

Details of entries, cable glands and blocking plugs used.

Test Records of the equipment should also be maintained as listed below:

Earth resistance of all the equipments.

Insulation Resistance of the equipment with incoming and outgoing cables.

Oil test report of the transformer.

Calibration Tests of the indicating and controlling instruments.

Condition of the batteries with their voltage and rated discharge current.

As part of the preventive maintenance schedule, Visual Inspection of all the equipments should be carried out without opening the equipment, at least once in four months and record should be maintained. This inspection should cover mainly the following points:

Check for any mechanical damage, visible cracks, corrosion, condensate or dust collection.

Check for any loose hardware, tightness of cable glands and compression of cables.

Check tightness of blocking plugs and ensure none of the entries are left open.

Check tightness of cover fixing bolts and ensure that none are missing.

Check tightness of all threaded joints.

Check that all display windows and glass bowls of lighting fittings are clean and wire guards are in place.

Check condition and connections of flexible cables of Hand Lamps, Welding Receptacles etc.

Check that there is no undue vibration of the equipment.

Check levels of oil in oil filled protection enclosures and oil cooled transformers.

Check that the name plate and tag plate data is legible.

Check that the equipment and glass parts are clean and if necessary, clean these with soft and dry cotton cloth.

Touch up the equipment with paint if the same is chipped off or has faded with correct quality and shade.

Check that during operation of the equipment, the surface temperature of any enclosure containing heat generating components does not rise beyond permissible limits.

The other part of Preventive Maintenance Schedule is the Routine Maintenance, which should be carried out at least once in eight to twelve months but when the equipment has been isolated from the electrical supply. Record of the same should be maintained for any future reference. This should mainly cover the following points.

Check the correct performance / operation of all push button actuators, switches, limit switches, MCB’s, ELCB’s, resetting knobs etc. etc.

Check tightness of all cable terminations and earth connections in terminal boxes of the equipments and the condition of connectors / bus bars.

Replace the defective lamps from lighting fittings if required and remove condensate water if any.

Replace blown fuses if any with approved make and correct rating.

Check condition of gaskets and if found deformed or cracked, replace them with correct quality, shape and size.

Remove rust / corrosion if found, clean with brush using CTC, but do not use files or abrasives.

Check the condition of bearings, leakage of oil / grease and replace if necessary.

Never attempt any drilling or tapping in any enclosure or cover and use original size of hardware if required to be replaced.

Check Insulation Resistance of the equipment after any maintenance work to avoid any accidental sparking. Any drastic fall in this value compared to the earlier reading should be investigated and corrected.

Take care that the flame paths of enclosures or the covers are not damaged while removing, handling or inserting covers in the enclosures. Do not use any metallic tool or abrasives on the flame path.

While fixing the cover back, ensure that the flame paths are free from any dirt or foreign particles and after applying a thin layer of suitable grease on the flame paths of enclosures and covers, the cover should be correctly positioned on the enclosure and gently pushed in evenly. Use nylon hammer gently if necessary but do not use metallic hammer as the same may deform or damage the cover. Tighten all the cover bolts properly ensuring presence of lock washers under them.

Ensure that the maintenance work is carried out by persons who understand the implications of not meeting the desired requirements of the equipment.

Written permission of an Authorized Plant Manager should be taken before attempting any maintenance work in hazardous areas.

Surrounding environment with respect to dust, moisture and corrosive gases etc. which affect the properties of Explosion Proof equipments should be regularly monitored.

Preventive Maintenance Schedule, if correctly followed and all records and readings maintained will help the user in finding out and determining any adverse change in the condition and performance of the equipment.

If all the preventive steps as mentioned above are taken, the equipment will give trouble free service for years to come.

REPAIR WORK

Extreme care should be exercised when ever any equipment is taken up for repairs if required, so that after repairs it does not lose any of its FLP and WP properties. Such equipment, first of all should be completely isolated from the electrical supply. Some necessary precautions in this respect are listed below.

Any repair work should be carried out with the consent of the manufacturer or preferably by the manufacturer himself. Any alterations or modifications if carried out without the authorization of the manufacturer will invalidate the test certificate of the equipment.

Any parts or components if required to be replaced should be genuine and identical which should preferably be procured from the OEM.

Ensure that the flame paths of enclosures and covers are not damaged while carrying out repair work and required diametrical clearance is maintained.

Check that the gaskets are not deformed or damaged, if required replace those with original gaskets procured from the OEM. Ensure that the gaskets are fitted in their respective grooves and are compressed sufficiently after tightening of covers with proper torque. All cover bolts should contain lock washers.

Ensure that if at all any cover from the enclosure containing MCCB’s, MCB’s or any other component, is to be removed or put back, in that case all these components should be kept in their OFF position to maintain proper alignment of operating parts fixed on the covers with components fixed in the respective enclosures. Ensure proper functioning of these components after fixing of covers.

If cable glands or any external part like knobs, canopies etc. are to be replaced then these should be of correct size and procured from the OEM only.

If any glass bowl or display window has broken then suitable replacement with glass duly cemented in its metallic part should be procured from the OEM.

After the repair work has been successfully carried out, ensure proper functioning of the equipment, proper earth connection and I.R. value with a suitable Insulation Tester.

Do not ever try any drilling or tapping operation in any FLP enclosure or cover.

Check general cleaning of the equipment after repairs and if necessary clean the same and glass bowls or windows if any, with a soft and dry cotton cloth.