This shouldbe designed to protect the capacitor bank against overloads current. With the modern low loss capacitor, the risk of thermal breakdown, the risk of thermal breakdown is minimal and any failure more usually results from dilectric breakdown. This occurs as a result of over voltage which, in many cases, is caused by excessive harmonic current. Protection can be achieved by means of peak value voltage sensitive relays or current relays having characteristics designed to prevent over voltage.
Where capacitors are connected to a network fitted with fast reclosing breakers, they must be fitted with undervoltage protection to ensure disconnection at voltage drop-out. They must not be reconnected until the residual voltage has fallen below 10 % of the rated value.
External Fuse protection
External fuse can be used to provide protection for individual capacitor units and the smaller capacitor bank. The selected fuse rating must take account of overvoltages overcurrents and switching transients such that spurious operation is avoided.
The purpose of unbalance a faulty bank before overvoltages greater than 10% appear on remaining healthy units. To achieve this, the capacitor units are arranges in single star or double star connections. In case of single star protective relay can be operated by sensing voltage unbalance across by RVT whereas in case of double star protective relay can be operated by sensing fault current of CT connected between neutral of two stars.
When switching a capacitor bank, high current transients appear. These can be particularly high if the bank is connected in parrel with another bank which is already energised.
It may, therefore, be necessary to limit this inrush current by connecting a reactor in series with the capacitor bank.
A complete range of enclosures can be offered to suit all the applications, selected from:
* Ingress Protection ratings up to IP55 for indoor or outdoor use.
* Cubicles, tanks o open racks, floor mounted.
All the following equipments can be offered :
* Controlling switchgear for manual or automatic control.
* Voltage and current transformers.
* Current limiting reactors, Detuning and filter reactors-iron and air-cored.
* Out-of-balance protection systems and Lightning Arrestors.
Information required with enauiry
* Requirements is new or for replacement
* Dimensions of existing units in case of replacement
* Highest system voltage and frequency.
* Temperature category.
* Rated output required in KVAr.
* Single phase / Three Phase.
* Connectiom : Star / Double Star / Delta
* Basic Insulation level
* Location : Indoor / Outdoor
* Fuses : Internal / External Fuse.
* Type of load.
* Single line diagram of the electrical system
* harmonic details if available
* Protection required
* Associated equipmets required.