INSTALLATION OF HT CAPACITORS

A

UPON RECEIVING THE CAPACITORS.

Check the packages:

Check for

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.

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

If the equipment has to be stored for a while, please ensure the following:

Preferably store the equipment indoors or under cover.

Do not store on top of one another.

Do not store near a heat source.

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:

 

 

1

Series Reactors:

Please check the instructions in our specifications on Series Reactors and make sure that the series reactor has been selected properly and for proper reasons.

2

Discharge Reactors:

Please check against our leaflet on Discharge Reactors similarly as above.

3

Lightning Arrestors:

Distribution type lightning arrestors are designed for light duty as against station type or heavy-duty lightning arrestors. Use the latter since every time the lightning arrestor shorts the system to ground, there is a heavy capacitor current discharge through the same. Each set of lighting arrestor must have its individual and separate earthing plates and an earthing system. This can then be tied into the general earthing system. Lightning arrestors must be used when the HT mains are subjected to heavy impulses such as those due to frequent lightning strikes; those due to switching surges; due to frequent operations of very high HP motors etc or those due to cyclic impulses caused by the firing of high power thyristors and rectifiers on HT mains.

4

Fuses:

The individual or bulk protection fuses must be de-rated by a factor of two. Thus, the normal current of a 84 KVAR-7kV,1 phase capacitor unit is 12 Amps. Use a fuse with a rating of 25 Amps.Two types of fuses are available:

a) Dropout type with replaceable fuse element. Here, keep enough spare fuse elements and see that these are not replaced with copper wires.

b) HRC sealed ceramic type. These are better in performance than (a), above but costly.

 

5

Isolators:

Any isolator which is used on a capacitor bank, must be operated only in the OFF load position or with the CB switched off.

6

Circuit Breakers:

Select a circuit breaker from an established manufacturer and preferably with a proven or certified capacity to operate a capacitor installation.

Vacuum circuit breakers or SF6 Circuit Breakers are the Preferred category.

As far as possible, do not go for existing bulk oil C.B.’s, unless they are de-rated. Avoid minimum oil C.B's, as most of them are not suitable for capacitors. Select On-load isolators with care. Their use at 3.3 kV for small capacitor banks may be justified on grounds of economy.

Selected circuit breakers or contactors must have sufficient breaking capacity in MVA to meet the installation Short Circuit MVA at this point. Some times, a lower MVA H.T. contactor could be used with the backing of sufficient MVA rupturing capacity fuses.

When capacitor banks are operated in parallel, there are heavy inrush currents into a bank which is being put into circuit. This factor must be duly considered at the initial stage while selecting a circuit breaker.

The H.T. OCB contacts and mechanisms are generally not designed for very frequent operations. One particular supplier has limited this to 150 operations per day. These factors must be considered when designing or commissioning a remote operated or automatically operated capacitor installation. If automatic p.f. correction is desired, it is better to select proper HT contactors in place of circuit breakers.

7

Cables:

Cables for capacitor installations must be de-rated by a factor of 2. The cable lugs must be properly fitted and cable ends and cable joints must be securely sealed. Should a cable develop a fault, all capacitors will discharge into this, causing a serious blow up at the fault.

D

At the time of Installation:

All the HT installations, in general, require prior approval by the Electrical Inspector for compliance with the provisions of the Indian Electricity Act.

Following points deserve special mention:

Height of live parts above the ground for open installations:

Here the capacitors will have to be raised on pillars as per our data sheet. Fencing off, of the open installation general earthing, and earthing of lighting arrestors will have to be arranged. Insulation tests, oil test for oil in reactors must be carried. (Capacitors are hermetically sealed and oil cannot be drawn out for test)

For open HT capacitor installations, it is desirable but not compulsory to have a covered roof. When chemical pollution and rainfall are excessive, a covered roof helps and more than pays for itself by averting shutdowns. It also minimises nuisance tripping caused by birds.

The general precautions are as below:

  1. Locate the capacitors in a well-ventilated space. Avoid sites near to heat sources such as boiler rooms, ovens, furnaces etc. If ventilation is inadequate, use a ventilating fan continuously.

  2. Provide a foundation and fix base channels of capacitors on this.

  3. Check the connections of the connecting cable with particular reference to the following:

Adequate size of cable. Proper soldering or crimping of cable socket on to the conductor strands; cleaning of cable socket and firm bolting of the same on the capacitor assembly terminals.

After switching on for a couple of hours, switch off and check whether connections are getting hot. Tighten these if necessary.

  1. Run a double circuit earthing connections to capacitors and switchgear and tie up the shield of the cable, into this. This earthing must be securely tied into the general earthing system.

  2. Before commissioning the bank measure the current output of each unit across 400 volts and keep a record of current and voltage. If the unit is suspected to have developed internal faults, it can always be rechecked against the initial reading.

  3. Reconnect the units into a bank and apply 400 volts, 3 phase. The HT OCB must be in the off position. Measure the total currents and the voltages. If the bank is split in two equal halves, measure the voltage between the two halves. Convert this into a ratio of system volts/400 volts. This should not be more than 4 to 5 volts. If it is more, the two banks are not correctly balanced. Balance the banks by shifting units back and forth and recheck. When this balance is obtained, proceed further.

  4. Meggar up between the live parts and body and between individual phases. If found satisfactory, the unit is ready for switching on.

  5. Check the relays individually with the relay testing kit. Check the operation of the control panel in the off load conditions. Check battery supply voltage and firmness of its connections.

E

At the Instant of switching on:

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

  2. Make sure that there are enough loads on the H.T. mains. Thus, if a 1 MVAR bank is being energised, there should be a steady load of at least 1.5/2 MVA or MWS. Ascertain this by timing the energy meter over a 15 minutes interval. It is risky to switch on a bank with a load which fluctuates practically between zero and the full value, from instant to instant, as in the case of an only arc furnace load in its initial melting stage.

  3. Remove one unit deliberately from the balanced half of the bank. Adjust the neutral unbalanced current/voltage relay at the calculated value where possible or at 1/2 to 1/3 position. Switch on the bank and continue adjusting the relay till it just trips the OCB. Put the setting at slightly below this value. Steps for capacitor with internal fuses are more critical.

  4. Put the disconnected unit back into the half bank, the two halves are now balanced. Switch on the capacitor bank.

  5. If a simple service oscilloscope is available, set this to 50 HZ and connect it across the ammeter terminals of the ammeter on the capacitor system. Adjust properly and study the current wave shape.

    6. If it shows excess of 3rd , 5th or 7th harmonics investigate it. The capacitors will be overloaded due to presence of harmonics and become unduly hot. Trace the wave shape as accurately as possible and send this to us with full details of the load and the system. If the wave shape shows sparking or pulses of high magnitude, switch off and investigate possible sources. Sharp pulses or spikes of any nature destroy a capacitor in no time. These can be and should be diverted. Write to us for advice.

  6. Take a long wooden pole and touch the capacitor body with one end. Hear at other end for any hum or crackling noises. These could come from within a capacitor unit or from outside also. Investigate and eliminate.

  7. Once the bank is energised and switched-off, wait for full five minutes. Then earth the bus system across which you expect to work and keep this earthing while work is being carried on. A standard earthing pole approved by the electrical inspector and with an open trailing copper flexible, which is earthed at one end and tied to the metal probe of the earthing rod, may be used.

Please note the following:

Earthing within less than five minutes of switching off is injurious and dangerous to personal.

If a capacitor system is momentarily earthed and the earthing rod is removed, it can get recharged to a dangerous voltage and can cause accidents. It is best to keep this earthing rod permanently on the bus or live part where work is being carried out. Also remember to remove this when the work is over and the capacitors are to be re-energised.

The above instructions are very important and may be permanently displayed in English and local language prominently near the capacitor installation.

F

For Normal Maintenance of HT Capacitor Bank:

  1. Keep a weekly record of temperature rise for the first six months. If any unit develops more than 20 degree C-temperature rise, investigate and remove the unit. If no spare units are available disconnect one healthier unit from each of the remaining phases and balance the half.

  2. Check the condition of HRC fuses.

  3. Check for leakage/seepage of oil on any equipment. This cannot be accepted. Repair immediately as per details, which are outlined later.

  4. If there is a short or a trip on any phase:

    5. Replace the damaged unit. If no spare is available, remove equal units from other phases and balance.

  5. Before commissioning, check the capacitance values and if possible tan delta on all units in this phase as well as in other phases. These should not have deteriorated.

    If the units are lying unused for more than 3-4 months, Before commissioning, please connect the units across 400 volts and keep them at least for 4 hours on load.

G

In Case of Leaky Capacitors:

Clean up the leaky spot and solder it with the help of a tin-maker, if the leak is in the metal portion of a welded joint.

If the leakage still persists, pack the unit carefully with plenty of paper or cloth around Mark on the packing "Stow away from Food and Drink" and send it back to us. It needs repairs in our plant. Please get our concurrence before sending the unit to us.

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.

 

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