# Naked Science Forum

## General Science => General Science => Topic started by: NTYNUT on 10/08/2018 12:47:55

Title: How does switch gear work?
Post by: NTYNUT on 10/08/2018 12:47:55
Hello
What is Spring charge in switch gear
Title: Re: How does switch gear work?
Post by: NTYNUT on 10/08/2018 12:50:00
what is healthy circuit in it
Title: Re: How does switch gear work?
Post by: evan_au on 11/08/2018 01:48:10
When you interrupt an electrical circuit, you can get arcing which damages the switch. So you want to disconnect the current as quickly as possible to protect the switch itself (and any people nearby).
- If you get a fault, you get arcing which damages the equipment with the fault. So you want to disconnect the current as quickly as possible to protect the device with the fault (and any people nearby).
See: https://en.wikipedia.org/wiki/Switchgear

To break the circuit very quickly takes energy, which may be in the form of:
- A mechanical spring, which you compress with a lever (or a motor). This is used to mechanically separate the electrical contacts quickly.
- A magnetic field, produced by the fault current flowing through the arc itself. This is used to expand the arc so that its resistance increases. it has more area to radiate energy, it cools down and goes out. Sometimes this is assisted by arc-resistant baffles which further increase the path length of the arc.
- Pressurised gas (air or an inert gas like sulphur hexafluoride), which blows cold air on the arc, putting it out

A nice clip from Jurassic Park here: https://www.quora.com/What-is-spring-charging-of-circuit-breaker
Title: Re: How does switch gear work?
Post by: NTYNUT on 14/08/2018 09:14:06
Hello
How to place or put circuit breaker in Switch gear how it is decided it name plate rating
Title: Re: How does switch gear work?
Post by: chris on 14/08/2018 11:10:47
When you interrupt an electrical circuit, you can get arcing which damages the switch. So you want to disconnect the current as quickly as possible to protect the switch itself (and any people nearby).
- If you get a fault, you get arcing which damages the equipment with the fault. So you want to disconnect the current as quickly as possible to protect the device with the fault (and any people nearby).
See: https://en.wikipedia.org/wiki/Switchgear

To break the circuit very quickly takes energy, which may be in the form of:
- A mechanical spring, which you compress with a lever (or a motor). This is used to mechanically separate the electrical contacts quickly.
- A magnetic field, produced by the fault current flowing through the arc itself. This is used to expand the arc so that its resistance increases. it has more area to radiate energy, it cools down and goes out. Sometimes this is assisted by arc-resistant baffles which further increase the path length of the arc.
- Pressurised gas (air or an inert gas like sulphur hexafluoride), which blows cold air on the arc, putting it out

A nice clip from Jurassic Park here: https://www.quora.com/What-is-spring-charging-of-circuit-breaker

Thanks for this, @evan_au - I'd never thought about this before and it had never occurred to me why the switches on breaker boxes were always so stiff and would "give" suddenly (as the spring drove the connection home).

Now I know!
Title: Re: How does switch gear work?
Post by: NTYNUT on 14/08/2018 11:43:48
How circuit breaker are build
Title: Re: How does switch gear work?
Post by: rami999 on 14/08/2018 22:50:59
Do you mean Car Gear?
Title: Re: How does switch gear work?
Post by: Bored chemist on 14/08/2018 22:55:37
Do you mean Car Gear?
Clearly, no.
Title: Re: How does switch gear work?
Post by: evan_au on 15/08/2018 11:27:14
Quote from: NTYNUT
circuit breaker in Switch gear: how it is decided it name plate rating
Important factors when ordering or installing CIrcuit Breakers are:
- AC or DC? (DC is much harder to break, and DC circuit breakers are polarity-sensitive!)
- Operating voltage
- Normal operating current
- Trigger current & response time (this is a complex relationship)
- Maximum short-circuit current

In electrical networks, the maximum short-circuit current needs to take into account the impedance of the transmission line from the generator, as this is the only thing that will limit the maximum fault current.

Quote
How are circuit breakers built?
See: https://en.wikipedia.org/wiki/Circuit_breaker