Arc protection

Arc protection – Reyrolle 7XG31

Reyrolle 7XG31

Arc fault protection is a relatively new technique employed for the fast clearance of arcing faults on busbars & within metal clad switchgear & associated cable boxes.

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Arc protection Reyrolle 7XG31


The arc is detected using an optical sensor & the signal input to a protection device which also monitors the load current on the system. Conventional current based protection techniques are at times challenged by the nature of arcing faults, and can result in slow protection clearance times. Slow protection clearance times increase the risk to nearby personnel and increase the degree of damage to plant and equipment. By employing an optical detection technique, arc fault protection results in fast clearance of arcing faults.


When an arc fault start current is coincident with a signal from the optical sensor a trip command is output. An arc trip only signal can be achieved within 10ms which can be considerably faster than that provided by a traditional IDMT overcurrent relay. This is because the onset of an arcing fault can occur at relatively low fault currents. Arguably the greatest risk of arc fault damage exists at the CB cable termination & in the CB chamber itself due to the slow clearance times of the IDMT feeder protection.


The ReyArc range of protection devices provide multiple arc fault protection schemes depending on your protection system requirements:


ReyArc Arc Protection range:

  • 7XG3120 Arc Fault Monitor Relay, with 2 or 3 arc point sensor inputs, 2 separate tripping- duty outputs.

  • 7XG3123 ARC Fault Interface Module, with 1 or 2 arc point sensor inputs, high-speed binary output to interface with protection relay binary input.

  • 7XG3124 Arc Fault Monitor, with IEC 61850 and up to 16 arc sensor inputs, 2 tripping-duty outputs.

  • 7XG3127 Arc Fault Monitor, with 4 arc point sensor Inputs and 1 linear sensor input, 2 separate tripping zones with 4 output tripping contact and 1 supervision contact.

  • 7XG3130 High-Speed Arc Sensor, with 1 or 2 optical point sensors per unit.

  • 7XG3140 High-Speed Linear Arc Sensor, with optional sensor length up to 40 metres


The 7XG3130 - RA30 is an optical sensor that responds to the flash of light emitted during the incidence of an arcing fault. Onset of the light flash & detection by the RA30 occurs in a few milli-seconds. When an arc is detected, the resistance presented by the RA30 drops to a level where the current flow increases to approximately 20mA. This increased current flow is instantaneously detected by the 7XG3120 - RA20 and the trip output contacts close. Also, this increased current flow is detected by the 7XG3123 – RA23 module which responds in < 1 ms to close a solid-state contact to activate the arc fault input on the protection relay. The 7XG3127 – RA27 may be configured to suit a wide range of arc flash monitoring applications.