Sunday, July 20, 2014

Surge Arresters; Surge arrester works principle; Surge Suppersors

We have discussed about Lightning arrester now lets discuss about surge arrester.
Although they both have same principle of working. In this article we will discuss about brief details about arresters. First you must know about what arrester is ??
Answer to this question is that The arrester provides a low-impedance path to earth from transient voltage or a lightning strike and after that restores to an ordinary operating conditions.

For simplicity you may consider a surge arrester similar to your relief valve on hot water heater or a boiler. High pressure will be released by it until there is a standard operating state achieved. The safety valve is prepared for another operation, when the pressure is returned to standard.

Whenever there exist a high voltage (greater than the standard line voltage) on the line, the arrester drains off the extra voltage and promptly furnishes a route to ground and therefore limits. The arrester then prevent any additional flow of current as clear from the name surge arrester used to address high voltage spikes. Surge arresters are used for in electronic circuits to isolate the electronic circuit from power circuit.

The arrester has two functions;
1.       It must provide a point in the circuit at which an over-voltage pulse can pass to ground and
2.       Second, to prevent any follow-up current from flowing to ground.

There are three types of surge arresters.
They are:
1. Expulsion type
2. Valve type arrester
3. Gapless metal-oxide type

Different types of protective devices are:
1.       Earthing screen
2.       Overhead ground wires
3.       Lightning arresters

1.       The Earthing Screen:-

Substation & the power station can be shielded against direct lightning blows by supplying earthing screens. On incidence of direct stroke earthing screen supplies a low resistance path where lightning spikes are conducted to ground.

2.       Overhead Ground wire:
It's the best way of providing protection to transmission lines. It provides damping effect on any noise as the lines acts as a short circuited secondary traveling along it. You might have seen HT lines along with overhead ground wire.

Limitations of Overhead Ground wire
(i)      It needs added price.
(ii)     There exists a chance falling across the line conductors, thus causing a short circuit error and of its breakage.
(iii)    Ground wires and the earthing display neglect to provide protection.


Type 1 Surge Protectors

Type 1 surge protectors are made to be installed where there is a direct lightning strike hazard high, particularly when the building has outside lightning protection system (LPS or lightning rod).

In this scenario IEC 61643-11 standards need the Course I test to be used to surge protectors: the injection of 10/350 microsec nerve impulse current in order characterizes this evaluation to model the immediate lightning strike impact. So these Type 1 surge protectors must be particularly strong to run this high energy pulsation current.

Type 2 surge protectors

These are used at the beginning of installation. i.e. either in main switch board or close to sensitive terminals. These guards are examined following the Class II evaluation from IEC61643- 11 based on 8/20 microsec pulsation current injection.

Type 3 surge protectors

In the event of remote gear or really sensitive, secondary phase is needed: these low energy SPDs could be Type 3 or Type 2. Type 3 SPDs are analyzed with a mixture waveform (1,2/50 microsec - 8/20 microsec) .

Types of Surge Arresters according to Class

1. Substation Class
Substation class arresters are commonly used in substations or electrical power stations and other high voltage constructions and places.
These arresters shield against overvoltages and both lightning, than it was created to manage when the electrical device has current.
These arresters are made to shield gear above the 20 MVA range.

2. Intermediate Class

Like substation group arresters, intermediate type arresters shield against spikes from overvoltages and lightning, but were created to be applied in moderate voltage gear places, including transformers, electric utility stations, substations or other substation equipment.
These arresters are designed to be used on gear in the range 1-20 MVA.

3. Distribution Class

Distribution group arresters are mostly discovered both dry-type and liquid-filled.
These arresters are less or discovered on gear.
These arresters are occasionally discovered on open paths that have direct connections to machines that were rotating.
These used in range of 100 KVA

4.       Secondary Class

These arresters cause overages that are high voltage to earth, though they don't short all the over voltage from a spike. Secondary category arresters offer the least number of protection and generally don't protect anything with a microprocessor, or solid state technology.