Isolator

[Shahid Hafeez]

Hi Everyone

 

I have to ask

 

1-Why the isolator install before the circuit breaker,i know it provide the visible isolation but i want to find

 

out the technically reason

 

2-A signal provided in AVR(Auto voltage regulator) "Out of Step"what is the purpose of this signal.This AVR

 

usally installed in Power transformer and Auto transformer for voltage regulation.

 

 

 

 

[Carl]

Hi Everyone

 

I have to ask

 

1-Why the isolator install before the circuit breaker,i know it provide the visible isolation but i want to find

 

out the technically reason

 

2-A signal provided in AVR(Auto voltage regulator) "Out of Step"what is the purpose of this signal.This AVR

 

usally installed in Power transformer and Auto transformer for voltage regulation.

 

To answer point 1

According to PUWER regulation 19

Quote "Every employer shall ensure that where appropriate work equipment is provided with suitable means to isolate it from all its source of energy” etc

The main aim of the regulation is to allow the machine to be made safe, under certain conditions

Such as when there is maintenance to be carried out when a possible unsafe condition develops.

I can not think of any technical reason why there should be isolation, but in the UK and other ECU countries you will most certainly will be breaking the law if you do not provide isolation and face possible conviction.

Hope this sheds some light on the matter I’ve quoted the PUWER regulations you can have a look at harmonized standards , I’m sure it will be the same ther could be more detail as to where the isolation must be and the way it is marked color etc etc

[jraef]

Re: question #1, I suppose you are speaking of the need for an isolator in front of a VACUUM circuit breaker in a Medium Voltage installation, correct?

 

The reason is, vacuum bottles are very good at switching large high energy circuits in a small space, but they are NOT completely safe in terms of protecting people from dangerous potential voltages. They can "leak", especially after having interrupted a fault, because the vaporized contact material, however minute it is, becomes deposited on the inner surface of the vacuum chamber and can provide a current path. Even if it is a high resistance path, because you are dealing with Medium Voltage levels, the potential energy in it can be lethal. An isolator provides an air gap with sufficient dielectric strength to maintain safety for people working down stream, but is smaller than what an air-break circuit breaker would have had to be because it is not designed to open under load. The Vacuum Breaker interrupts the load or fault, the isolator just makes it safe to work on.