Check for

Capacitor terminals are shorted together and to the body firmly.

Disconnect the short and test the capacitor on capacitor 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.

Measure capacitance on digital capacitor meter or multimeter if the meter is available. Since these instruments are very delicate, make sure to discharge capacitor fully before making connections.

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

A DC charging supply and its control method should be compatible for connected capacitive load and the desired repetition rate. Constant current charging is preferred over constant voltage charging. RC time constant to charge capacitor should be greater than 1 seconds to avoid heavy inrush currents. The supply should be protected against external short circuit. It should reset automatically on power failure, i.e. if mains power is restored after a brief interval of outage, sudden voltage should not get applied to the capacitor.

If possible, it should have over current protection, high voltage cutout, transient spike suppresser, RF filter and an inductor to limit di/dt.

Discharge circuit and switch, crow barring mechanism (if used) should be capable of handling heavy discharge currents and high coulomb charge transfers in a very short period, considering skin effect at resonance frequencies. Fuses and resistors are not used in discharge circuit. However, in exceptional conditions, low inductance fast acting special type of HRC fuses are also available.

Since the capacitors internal inductance is very low, it is important for the user to exercise care in selection of interconnecting leads in discharge circuit as-coaxial bushings, cables, parallel plate bus bars etc. and protective devices as co-axial switches and fuses. Otherwise the advantages of capacitors with low inductances could be nullified. Our engineers will be happy to review your selection with this in mind.

Wide variety of switches are available to discharge capacitors at a particular instant. Ignitrons are costly; have limited voltage ratings and are not indigenously available. Other alternative is to use trigger gap under high gas pressure, preferably nitrogen. Dry, filtered nitrogen, with adjustable pressure arrangement, has good repeatability and offers longer life and less maintenance of electrodes because of less carbon deposition.

Triggering system can be manual or automatic. External electronic triggering is preferable. Triggering system should be fully isolated with respect to maximum system voltage using blocking capacitor. It is likely to retain electrical charges. It should be handled only in shorted to earth condition.

Earthing switch is recommended to discharge capacitors remotely as and when required. It should discharge capacitors through a suitable discharge resistor within few seconds. Preferably, it should be automatic so that upon power failure or switching off system supply or after opening the door of H.T. zone, capacitors should get discharged automatically.

• When a large block of capacitors is being used in any experiment, protective walls may be erected around the block.

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

• Proper insulating supports should be provided for all live parts.

• Run a double circuit earthing connection to capacitors and tie up the shield if necessary into this. This earthing must be securely tied into the main earthing system at nearest distance. Adequate conductor cross-section must be provided to discharge capacitor to ground.

• Check the connections of the connecting cable or busbars with particular reference to the following.

Adequate size of conductor to handle peak discharge current. Also, if voltages are high, use round pipes (copper) of large diameter to reduce corona effect.

Geometric shape and configuration for cancellation of flux to reduce inductance. Large diameter, short overall length of conducting path, close proximity of incoming and outgoing currents (with insulating material in between, having sufficient mechanical strength to take care of attractive forces during discharge), use of material having high conductivity and low permeability for conductors and high resistivity, low permeability near conductor are the key factors to reduce the inductance.

When not carrying current, use non-magnetic stainless steel bolts.

Avoid corners, sharp bends, sudden change in conductor cross-section, etc. in a discharge circuit. It leads to uneven current densities due to skin effect and also increases inductance.

Proper soldering or crimping of cable socket on the cable strands, cleaning of cable socket and firm bolting of the same on the capacitor assembly terminals and bus bars. When multistrand cables are used, all strands should form a joint with sufficient contact-surface area. The joint and cable should be mechanically strong enough to withstand heavy repulsive forces generated by discharge current.

Check all the connections. Megger up various components to make sure they are open or short as desired.

Great care should be taken to make sure that no loose parts as nuts, washers, spanners, etc. are lying around H.T. zone. These could get energised and travel at dangerous speed in any direction.

Test individual subsystems separately. Keep capacitors disconnected from supply and shorted to ground and test power supply by operating it to full rated voltage. Test spark gap fully for pressure withstands test. Test other subsystems as earthing mechanism, crow-barring, triggering circuit, measurement and control circuits, oscilloscope settings, etc. as far as possible independently.

Connect the complete system together and take 4-5 trials on smaller voltages with sufficient interval between each trial. If possible, connect suitable external resistor or inductor in discharge circuit to limit current during trials.

The hermetically sealed capacitor unit has no moving parts. If used carefully, it can give a fairly long useful service.

During operation, make sure that charging voltage, peak discharge current and ambient temperature are never exceeding the rated limits. There should be sufficient interval between any two discharges of capacitor. Don't keep capacitors charged at high voltages for longer periods.

High charging current indicates poor insulation between live part and body. It may be because of deposition of moisture or dirt or connecting too many capacitors in parallel.

Check whether there are any loose/sparking contacts in the system. Check whether any connections are getting hot. Tighten if necessary.

Check for crackling sound from capacitor during charging or after discharge. It is due to internal partial discharges. Check if any capacitor is bulging.

If the supply voltage doesn't rise but the charging current increases rapidly then one of the capacitor in the bank may be short.

If any capacitor is found bulging, disconnect it and short it through suitable resistance. Don't try to open the container as dangerous pressure may get developed inside the container. Keep it in open space and shoot it by rifle from safe distance depending on the energy of capacitor.

If the capacitor is leaky, cleanup the leaky spot and solder it with the help of a tin-maker, if the leak is in the metal portion of a welded joining.

If the leak is on the joint between the porcelain and the body-Heat up the capacitor under the sun or in a warm cabinet upto 50 degree C/60 ^degree C Desolder and remove the sealing washer on top.

Allow to cool and clean the surface with trichlotoethylene. While the surface is cooling, apply properly mixed `Araldite' Or `Dobecote'. This will be slightly sucked in. Allow the Araldite to set for 24 hours. Solder back the sealing washer on top after topping up proper oil - if too much oil has leaked out. Again heat up the unit to50 degree C/60 ^degree C

.There should be no leakage. The unit can be put back into circuit.