Arc Protection System

An arc protection system is made up of a relay and a sensor. Arc protection systems are important as arc flash accidents occur approximately 8 to 10 times each week in the UK. Unfortunately, many switchgears are left without arc flash protection, despite its common occurrence and destructive potential.

 

What is an arc flash?

An arc flash is one of the most destructive electrical faults possible to have. Not only will it cause tremendous damage to equipment, but could also give life changing and even life-threatening injuries to any personnel within a close proximity.

 

What is the NFPA 70E and where does it apply?

The NFPA 70E addresses employee workplace electrical safety requirements.

It defines work practices that protect workers from electrical hazards, including arc flashes, during the inspection, operation and maintenance of electrical equipment.

The NFPA 70E standard covers most workplace activities related to electrical energy or equipment. The major exceptions are:

  • Vehicles; such as ships, aircraft and railways
  • Communications equipment under the exclusive control of communications utilities.
  • Certain electrical installations under the exclusive control of an electric utility.

How to calculate arc flash rating

As part of NFPA 70E, an arc flash hazard analysis should be done in order to protect personnel from the possibility of being injured by an arc flash.

There are two distinct mathematical methods of calculating the available arc flash energy present at a specific piece of equipment.

 

What is an arc protection system?

8 to 10 arc flashes occur in the UK every week. Without arc protection in place, the consequences can be very serious.
An arc flash protection system is usually made up of a trip relay and a sensor. It detects the arc and sends a trip command to the circuit breaker, which as a result of opening will eliminate the arc.

 

What does an arc protection system look like?

You only need two components to create a reliable arc protection system:

To give the most superior protection, systems can also upgrade to include an AQ1000 arc quenching device.

Arc protection system

 

Video: Arc protection system configuration

This short animation shows a basic configuration setup of an arc protection system. This Arcteq system features an AQ110 and 3 AQ101 relays, along with several point sensors. This comprehensive setup will allow for rapid arc detection (just 2 ms). The quick tripping of the circuit breaker will result in less damage from the arc to both equipment and personnel working nearby because it cannot reach full velocity.

 

It is vital the relay works very quickly because it only takes 300ms for an arc flash to reach maximum velocity.
Here you can see how the severity increases over a short amount of time:

10-30ms (Compression stage). Ignition of current flow through ionised air.
Rapid release of energy.
Maximum pressure.
30-50ms (Expansion stage). Shock/pressure wave (up to 4 bars).
Sound wave.
50-100ms (Emission stage). 20,000°c temperatures.
100-300ms (Thermal or ‘burn through’ stage). Toxic gases.
Steel and copper fire.
Hot shrapnel.