Arc Flash Monitoring
1S20 Arc Flash Monitor – 3 point sensors / 2 zones
Compact, economic design
Simple panel mounting for retrofit applications
Two or three arc sensor inputs
Two high speed tripping duty arc sense output contacts
Push button reset
Continuous arc sensor supervision
Integrated self supervision
Fail alarm contact
Medium voltage switchgear is a key element in the power supply chain. Existing protection systems operate effectively under most circumstances, but they are too slow to handle arcing short circuits.
Arcing faults can occur as a result of insulation breakdown due to equipment age & / or poor maintenance.
The degree of damage caused by arcing depends principally on the duration of the arc. If an arc lasts only 100ms, the switchgear needs to be checked & the insulation resistance measured before power can be re-established. With a 200ms arc, the power supply will be interrupted; the switchgear must be checked; power is re-established only after minor repairs. In the event of a 500ms arc the supply is interrupted, metal parts of the switchgear are destroyed & poisonous gases are emitted. A 1s arc destroys most of the switchgear & may cause a fire, injury to personnel & damage to property.
The over-current caused by an arc is, due to its resistance, lower than the overcurrent caused by a “metallic” short circuit. The over-current caused by the arc may also be lower than the protection start current when energising circuits or starting large motors. The consequence of these conditions is that a protection system based solely on over-current detection cannot effectively discriminate between normal system currents & an arc fault condition:
- For moderate arc fault currents the trip time of the over-current IDMT stage will be too slow;
- For very low arc fault currents the instantaneous trip stage of a standard over-current relay cannot be set low enough.