How Ti and ENERSYS Switchboards Set a New Standard in Arc Fault Safety

The IEC 61439 series of standards contains requirements that apply to the construction, verification, and performance of low-voltage switchgear and controlgear assemblies under normal as well as abnormal conditions. However, it does not address internal arcing faults.

Assemblies validated according to IEC 61439 standards rarely experience internal arc faults. Nonetheless, an internal arc fault cannot entirely be discounted. Electrical arcing is the release of electricity along an ionised path between two conductive bodies maintaining a difference in potential. It arises when there is a breakdown in the dielectric strength of the surrounding medium, like air.

Arcing produces significant electromagnetic interference and poses hazards, including fire, explosion, equipment damage, and potential injury to people in the vicinity. IEC 61641 is a technical report developed by the International Electrotechnical Commission (IEC). It aims to ensure the safety and reliability of electrical enclosures by testing their ability to withstand and contain internal arc faults.

A short circuit is an accidental or intentional conductive path between two or more conductive parts that forces the electric potential differences between them to become equal or nearly equal. An arc is a free-burning short circuit through air that occurs due to a fault between live parts with a significant potential difference.

Short circuit currents provide the initial energy required to establish and sustain an arc. The magnitude of current during internal arcing can vary widely depending on factors such as insulation breakdown and the impedance of the arcing path. Internal arcing with lower current levels compared to short circuits is also possible.

The core temperature of the arc rises to several thousand Kelvins, and the arc roots can melt through the internal metallic enclosure of the switchgear within a few milliseconds, which makes it critical to quench the arc immediately.

IEC standards, including IEC 61641, are recognised and adopted globally. IEC 61641 provides a comprehensive and standardized methodology for conducting internal arc tests. It outlines the test setup, test procedures and criteria for evaluating the performance of electrical equipment during internal arc events. It ensures that electrical enclosures and components can withstand and contain the effects of internal arc events while minimising the risk of injury or damage to personnel and surrounding equipment.

This standard also defines constructional requirements for an arc ignition protected zone and offers suggestions for arc mitigation. The IEC periodically reviews and updates its standards to reflect advancements in technology and safety practices. Manufacturers can stay up to date with the latest testing methodologies and best practices to ensure their products meet current industry standards.

Adhering to IEC 61641 Panels helps manufacturers meet regulatory requirements and demonstrate compliance with safety standards. It provides a benchmark for evaluating the performance of electrical equipment in real-world scenarios.

To ensure that switchboards can handle real-world arc fault conditions, IEC 61641 outlines a structured and rigorous testing protocol. This section walks through the setup and assessment methods used to evaluate switchboard performance under internal arc stress.

●   Test Setup

The switchboards undergo internal arc testing under normal service conditions. The applied voltage is 105 ±5% of the rated operational voltage. The arc is initiated by connecting a bare or plated copper wire between all phases at locations where the resultant arc can impose higher stress on the assembly. The chosen wire diameter depends on the prospective short-circuit current values.

The test duration is normally between 0.1 to 0.5 seconds, depending on the time response of electrical protection devices. The indicators are placed at a distance of 300 mm vertically parallel to all the faces of the assembly. They are arranged in a checkerboard pattern covering 40 to 50% of the test zone. The indicators are made from 100 percent black cotton fabric, specifically cretonne for the restricted access region or interlining lawn for the unrestricted access region, representing personnel clothing.

●   Test Assessment Criteria

Class A - Personnel protection:

• Doors and covers of the assembly do not open, and other parts stay effectively in place.
• Arcing does not create any holes in the enclosure or ignite the indicators.
• The protective circuit for the accessible part of the enclosure remains effective.

Class B - Personnel and panel protection:

• The assembly confines the arc to the defined area where it starts and prevents propagation to other areas within the assembly.

Class C - Protection and limited operation:

• After clearing the fault or isolating or disassembling the affected functional units in the defined area, emergency operation of the remaining assembly remains possible. This is verified by a dielectric test according to IEC 61439-2 with a test voltage of 1.5 times the rated operational voltage for 60 seconds.

Class I - Arc ignition protected zones:

• Assemblies under this class provide maximum protection against internal arcing faults by using arc ignition protected zones. In these zones, all live conductors are insulated separately so that a foreign conductive body cannot touch a live part and initiate an arc.

To mitigate the dangers of internal arc faults, switchboards rely on two major protection approaches: passive and active. These strategies work hand in hand to limit damage, protect equipment and personnel, and ensure continuity of operations when arc incidents occur.

●   Passive Protection

Passive protection makes the panel mechanically capable of withstanding the electric arc. Manufacturers achieve this by reinforcing the mechanical strength of the panel and providing pressure relief flaps and spring door latches to release gases and debris generated during arcing.

Passive solutions also include features that reduce the probability of an arc flash by using insulated busbars, segregation between compartments and creation of arc ignition protected zones.

●   Active Protection

The amount of destruction caused during arcing directly depends on arc duration and arc current. Relays that detect the arc flash light can be installed to send tripping signals to the circuit breaker.

Similarly, a current limiting device, such as a fuse can be used to reduce the arc fault clearing time.

When it comes to the real-world implementation of internal arc protection, Ti and ENERSYS switchboards stand out. Designed with compliance, performance, and personnel safety in mind, these panels incorporate a range of features that go beyond the standard. Here’s a closer look at what makes them a benchmark in low-voltage safety.

1. In terms of arcing protection, the Ti and ENERSYS ranges of low voltage switchboards are certified as Class C. They protect people and restrict the arc to a limited area while enabling minimal operations after a fault.
2. All insulating materials and supports used inside the panel are tested and certified based on IEC 61439 standards.
3. Busbars are insulated using sleeving, which prevents inadvertent contact between two phases.
4. Supports have a higher CTI, greater than 600V, which ensures zero tracking and high dielectric strength.
5. Busbars and link works are designed with clearances higher than specified in the standard to enable faster arc quenching.
6. The enclosure is solidly constructed with appropriate separations, hinges, and camlocks to withstand arcing accidents.
7. Switchboards are installed with pressure-relieving flaps to release the excess pressure build-up during an arcing event.

Internal arc testing according to IEC 61641 offers another level of assurance specific to switchgear and controlgear assembly safety. Whereas LV panels certified according to IEC 61439 focus on overall construction and performance, IEC 61641 addresses, in particular, the critical issue of internal arcing.

This standard entails rigorous testing and classification of the panels to ensure that they are able to withstand and contain internal arc faults, prevent harm to personnel, and minimise damage. Compliance with the IEC 61641 alongside the IEC 61439 certification can assist in providing a full-scale safety framework.