What is a surge arrester
A surge arrester is a device which is used to protect devices from system transient over-voltages which may cause flashover and serious damages to the equipment. When a transient over-voltage appears at the arrester location the arrester will conduct internally and discharges the surge energy to ground. Once the overvoltage is reduced sufficiently, the arrester will stop conducting and the current will return to its normal state.
Where should a surge arrester be located
It should be located at or near the main transformers on both high and low voltage sides. It can also be located at the line entrance or on a bus that may be connected to several lines.
It should be located to give maximum protection to all major sub-station equipment. Location of the arrester on the line side of the fuse will minimize the fuse stress and it also helps to avoid the partial discharge of the fuse link, when the surge arrester responds to a transient over-voltage
It can also be located on the line side of the circuit breaker and thus it could protect the gap in the circuit breaker when in the open position
How to select a surge arrester
- Determine the continuous operating arrester voltage normally the system rated voltage
- Select a rated voltage for arrester according to the standards
- Determine the required long duration discharge capability according to the voltage level
- Determine the maximum prospective fault current and the protection tripping times at the location of the surge arresters and match it with the surge arrester duty
- The surge arrester housing porcelain creepage distance must be selected in accordance with the environmental condition
Types of surge arrester
- Metal oxide type
- Gapped silicon carbide type
- Polymer/porcelain arrester
Metal oxide type
This type of surge arrester will use zinc oxide valve and thus it will provide a better performance, the used zinc oxide valve has greater non-linear volt-current characteristics
The valve is capable of being applied without any gaps in the design which will remove the spark-over characteristics of the arrestor this type of surge arrester usually provides lower discharge voltage
Gapped silicon carbide type
This type of surge arrester has more non-linearity than the zinc oxide, because of this non-linearity it could burn out the arrester. A gap prevents burnout
It is vulnerable to moisture ingress that leads to failure due to a reduction in spark over. Contamination can also affect the voltage distribution which could result in spark over reduction. This gapless design could eliminate the high heat associated with the arcing discharges.
During a reclose operation occurs and if the fault is not cleared then the arrester is subjected to a second fault current and the second operation could lead to arrester explosion because the porcelain had already been weakened by the first fault and it could lead to the equipment damage
The polymer arrester station has the ability to vent out the side, the housing won’t be weakened when it is exposed to fault current so that the polymer arrester can be reclosed several times without the fear of failure.
Classification of surge arrester
The classification of surge arrester is based on the voltage rating, protective characteristics and fault withstand characteristics
Distribution class arrester
These types of arresters are widely used and it has a voltage range of 1-30KV they have the highest discharge voltage for an incoming surge and there is no need for pressure relief
Intermediate class arrestor
These arresters have a voltage range of 3-120KV and it has better protective characteristics than distribution arresters. Pressure relief capabilities are needed.
Station class arrester
They have the lowest discharge voltage so that it can provide better protection, their voltage rating is in the range of 3-684KV and pressure relief capability is needed.