INSTALLATION OF LT CAPACITORS

A

UPON RECEIVING THE CAPACITORS.

No. of packages

Contents of Packages

Chipped or broken insulators

Oil leakages

Dented Parts

Inform us immediately and put a claim for insurance, if necessary. Shortages or damages claims made after 10 days of receipt of material will not be entertained.

1

Open covers to see that, no live part is accidentally touching the body. The fuses and discharge resistors are firmly in their places. There is no leakage/loss of oil apparent on visual inspection. Iron brackets if used across the bus bars, to prevent damage to HRC fuses in transit are removed.

2

Run an insulation test between the live parts and the body. Sometimes a megger gives poorer values due to polar nature of our oils. Clean all the porcelain parts and measure the insulation resistance. These values must comply with the requirements of Indian Electricity Act. These must preferably be measured with a 500 V stabilised D.C. supply and a micro ammeter or with a 2000 volts, preferably motorised, megger.

B

Storage

While in storage, periodically check for oil leakages & also for open or assessable copper parts, which are likely to be stolen.

C

For selecting the accessories:

Use the following rules :

Thus for 20 KVAR capacitor, current rating will be 20x2.6 = 52 amps. Then nearest switch fuse rating available is 63 amps. Select this. This applies for power contactors also. Then nearest fuse link rating available is 63 amps. The nearest cable aluminium rating available is 52 amps. At 2 amps/Sq. mm select a size of 26 mm in PVC-A1 cable. Nearest available size is 25 Sq. mm. Use this. The ammeter scale should be 0-60 or 0-80 amps. The current transformer ratio should be 80 : 5 or 60 : 5

Quality of accessories :

Switch blades must make and break simultaneously. Use the best grade switches. Poor quality switches keep on blowing fuses of a capacitor. They also damage capacitors.

D

At the time of Installation:

4. Run a double circuit earthing connections to capacitors and switchgear and tie up the shield of the cable, into this. This earthing must be properly tied into the general earthing system.
5. Megger up between the live parts and body and between individual phases. If found satisfactory, the unit is ready for switching on.

E

At the Instant of switching on:

1. Make sure that there is adequate load on the system. The normal current of a 20 KVAR capacitor at 440 volts is 26 amps. Therefore the minimum load current at which the capacitor should be switched ON is 30-35 amps or when an equivalent of 20/25 HP motors are operating at full load and not just idling.
2. If one capacitor unit is already on and a second one is to be added then minimum load current on this bus system must be equal to or more than the combined capacitor current of the two banks by at least a factor of 1.35 to 1.5.
3. After switching off the capacitor - wait for at least one minute before switching it on. Earth all the live terminals only after waiting for one minute before touching these with spanner etc. If precautions 1,2,3 are not observed, this could lead to dangerous situations both for plant and personnel.
4. Observe the current and the line voltage. A 20 KVAR capacitor gives 26 amps line output at 440 volts and 27.82 amps output at 415 volts. The current varies directly as the voltage. The KVAR output varies in the proportion of squares of the voltages.
5. Switch off the capacitors when there is not enough load. This is a MUST.

( If the capacitors are kept ON when there is no load or less load then Power Factor goes to leading side and system voltage increases which may cause damage to the capacitors as well as other electrical equipments and severe disturbations can take place.)

6. If the line voltages are more than the capacitor rated voltage, then do not switch on the capacitors. As the load builds up, the line voltage will fall. Switch on the capacitors then only.

F

For Normal Maintenance of HT Capacitor Bank:

1. Keep a check on the temperature of container. This should not normally rise by more than 15 to 20 Degree C above the ambient. A temperature check by the feel of hand is very misleading. Use a thermometer and put the bulb of thermometer in good contact with the body.

If the temperature rise is too high -

Check whether voltages go too high at night or during the idle times, with/without capacitors. Bring these voltages down with the help of the electric supply authorities.

Check whether there are any loose/sparking contacts in the capacitor system.

Check with an oscilloscope whether the system currents show large portions of harmonics or sparking. Write to us in details-if no definite cause can be attributed. Disconnect the hot units and keep these asides.

2. Check the condition of external discharge resistors and HRC fuses. Replace the HRC fuses, If burnt out. Replace the discharge resistors, if burnt out and blackened or if their leads are broken off. Do not replace fuse with copper wires.

3. If you suspect that the capacitor is dead or is not working properly, check the line currents with an ammeter and line voltages, with a voltmeter. Correlate these. Some times tong testers are not very accurate and give only a rough indication. If this is not possible, disconnect the capacitor discharge it fully, and test on the resistance scale with an ohmmeter of a multimeter used in radio repairs. A healthy capacitor shows short at the beginning but keeps on building resistance reading. A dead capacitor shows a steady short or a steady open.

G

In Case of Leaky Capacitors:

The hermetically sealed capacitor unit has no moving parts. If used under standard conditions of supply and maintained properly, it can give a fairly long useful service.