Arc Flash Mitigation in MV Switchgear: How to Improve Personnel Safety and Reduce Incident Energy

An arc flash in medium-voltage (MV) switchgear can release intense heat, pressure and molten material within a fraction of a second. Consequences include injury, equipment damage and extended outages.

Effective arc flash mitigation switchgear design requires more than choosing an internal-arc-rated enclosure. Engineers must consider fault current, clearing time, configuration and worker exposure.

For EPC contractors, protective systems and operating arrangements should be specified before procurement.

Arc Flash Assessment and Internal Arc Classification Are Different

Internal Arc Classification (IAC) describes tested enclosure performance under specified internal arc conditions. Arc-flash assessment examines worker exposure under actual conditions.

IAC can support containment and the management of hot gases; it does not by itself demonstrate a particular incident energy at a worker's position. Faster clearing does not replace enclosure design.

Leistung Energie's Internal Arc Classification guide explains enclosure accessibility and test ratings in detail. This article focuses instead on reducing the duration of an arcing fault and limiting personnel exposure.

Start With the Arc-Flash Risk Assessment

Assess system configurations, fault currents, settings, breaker times and working distances. A study should examine normal and alternative supply conditions because a lower fault current does not always produce lower incident energy: it may also cause a protective device to operate more slowly.

IEEE 1584-2018 provides incident-energy calculation methods for qualifying three-phase AC equipment within its stated voltage range of 208 V to 15 kV. For systems above that range, including 33 kV, engineers need an appropriately justified assessment method rather than applying those equations automatically.

Identify tasks and locations needing engineering controls.

Faster Fault Clearing Is a Critical Mitigation Measure

Incident energy is strongly influenced by the time an arc persists. Reducing fault duration can materially reduce exposure, although the relationship must be checked using the applicable study method.

Clearing time includes detection, relay logic, trip-circuit operation, breaker opening and arc interruption. A fast relay alone does not guarantee fast isolation if the breaker or trip circuit is slow or defective.

Coordinate Speed With Selectivity

Protection settings must still distinguish between faults on outgoing feeders, busbars and transformer circuits. Overly aggressive instantaneous settings could unnecessarily trip an upstream incomer and disconnect healthy plant areas.

Review the MV switchgear specification checklist alongside fault studies and time-current curves. Where appropriate, busbar differential protection and dedicated fast-tripping schemes may reduce fault duration without sacrificing selectivity.

Arc Detection Relays Can Accelerate Tripping

An arc detection relay uses optical sensors to detect the light associated with an internal arcing event. Depending on the scheme, it may combine light detection with overcurrent supervision to help distinguish an electrical arc from unrelated illumination.

Sensors can be located in busbar, circuit breaker and cable compartments. The protection logic should identify the relevant zone and trip the breakers capable of removing every source supplying that zone.

Specify More Than the Sensor Hardware

For MV switchgear arc flash applications, the EPC specification should define sensor coverage, detection logic, trip outputs, DC supply, supervision, breaker-failure response and alarm interfaces. Where the network can be back-fed, the trip matrix must include alternative supply paths.

Factory tests should demonstrate the complete detection-to-trip chain rather than merely confirm that a sensor sees light. Suppliers must agree on interfaces before manufacture.

Zone-Selective Protection Balances Speed and Continuity

Zone-selective interlocking and other selective schemes can reduce unnecessary upstream delays. In a suitable architecture, a downstream device detecting a fault communicates with an upstream device so that the upstream protection can retain its grading delay. Without an appropriate downstream restraint, the upstream device may clear a fault rapidly within its own zone.

Design depends on relay capabilities and communication reliability; not every panel supports these schemes.

IEC 61850 substation automation may support signalling, subject to verified timing, supervision and failure behaviour.

Remote Switching and Racking Reduce Worker Exposure

Remote switching allows operators to open or close breakers from a controlled location away from the equipment. Remote racking can similarly reduce proximity during a task that may otherwise place personnel directly in front of a switchgear cubicle.

These controls primarily reduce exposure by increasing separation. They do not necessarily reduce the incident energy produced at the source of the arc.

Provide interlocks, clear status and safeguards against unintended operation. Remote operation is not a substitute for isolation, verification of de-energisation or safe access procedures before maintenance.

Some medium voltage switchgear configurations offer motorised racking or operating options, but their availability and suitability should be confirmed for the proposed equipment.

Equipment Layout and Maintenance Conditions Matter

Even advanced arc flash protection cannot compensate for poor equipment arrangement. Engineers should review compartment accessibility, pressure-relief paths, switchroom exits, doors, cable trenches and the positions used for operating or testing equipment.

In E-Houses and compact substations, arc exhaust arrangements must be coordinated with building structure and personnel access. Damaged insulation, contamination and loose connections increase failure risk.

Preventive inspections, thermography where appropriate, cleaning, condition monitoring and breaker maintenance support switchgear safety over the asset life. Work should be planned using suitable isolation and risk-control procedures, with PPE selected from the applicable assessment rather than treated as the primary mitigation method.

What to Specify Before Ordering MV Switchgear

A practical arc flash mitigation package should identify the following requirements before tender evaluation and design freeze.

Specification Area	Requirement to Confirm
System study	Operating scenarios, arcing-current assessment and worker tasks
Fault clearing	Detection, relay and total breaker clearing times
Arc detection	Optical sensor positions, logic and supervision
Protection zones	Selectivity, busbar protection and trip matrix
Remote operation	Switching, racking, controls and interlocks
Switchgear layout	Compartments, accessibility and exhaust coordination
Testing	FAT, SAT, end-to-end trips and failure scenarios
Documentation	Settings, study assumptions, drawings and procedures

Requirements should also establish who is responsible for the arc-flash assessment, relay settings, arc detection integration, SCADA interfaces and commissioning. A clear responsibility matrix reduces gaps between switchgear vendors, protection engineers and the EPC contractor.

Verify Performance During FAT and Commissioning

Factory Acceptance Testing should confirm relay configuration, sensor operation, trip logic, breaker interfaces, alarm indications and relevant simulated failures. Site Acceptance Testing should then verify the installed trip circuits, protection settings and final network configuration.

Review the assessment after source or setting changes; align labels with the as-built system.

Conclusion

Improving arc flash mitigation switchgear performance means combining rapid, selective fault clearance with practical measures that keep personnel away from potential exposure. Arc detection, coordinated relays, remote switching, thoughtful equipment layout and disciplined maintenance all have distinct roles.

The strongest approach is to specify these controls together, based on a project-specific assessment, rather than relying on an IAC rating or one protective device alone.

Planning a Safer MV Switchgear Installation?

Leistung Energie supplies MV switchgear for industrial, mining, utility and renewable energy applications. If your project requires arc detection integration, remote operation or defined protection interfaces, raise these requirements during the switchgear specification stage.

Contact Leistung Energie Australia to discuss your MV switchgear configuration, protection requirements and upcoming project.