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Arc flash incidents can cause injury and even death to personnel in the vicinity of the event, catastrophic damage to equipment, and severe financial losses due to lost production, repair and replacement costs, increased insurance costs, and possible legal actions.
The overall standard for low voltage switchgear (LVS), IEC 61439-1/2, prescribes mandatory requirements for LVS design verification. It does not, however, address arc flash prevention or mitigation.
Recognizing the growing need to verify new arc flash mitigation technologies, the International Electrotechnical Commission (IEC) first issued IEC TR 61641—Enclosed low-voltage switchgear and controlgear assemblies – Guide for testing under conditions of arcing due to internal fault—as an addendum to IEC 61439. IEC TR 61641 describes methods for testing various passive arc flash systems such as barriers, reinforced panels, arc flaps, arc chimneys, and even full insulation of live parts (arc ignition protected zones).
As it is a “technical report” (TR), IEC TR 61641 is advisory only; compliance is not mandatory. What’s more, it applies to only normal (doors closed) operation, not maintenance (doors open) operations, plus it covers only passive arc flash mitigation systems, and does not specifically relate to active ones. A passive arc flash mitigation system only lessens the damage or directs the arcing from a full-discharge arc event in a dedicated direction. An active arc flash mitigation system is designed to sense an arc at its onset and reduce the energy it releases.
As a further step towards addressing this arc flash verification need, is the IEC launched IEC TS 63107 in May 2020. This new Technical Specification (TS) states requirements for integration and testing an Internal Arc-fault Mitigation System (IAMS) in low-voltage switchgear and controlgear assemblies.
According to IEC, “an IAMS consists of an IACD (Internal Arc-fault Control Device) and an IARD (Internal Arc-fault Reduction Device). An IACD uses the effects of an arc, e.g. light, gas pressure, change of current, and/or voltage to detect an arc inside the switchgear to generate a trigger signal for an associated IARD. An IARD reduces the arc energy below the level which would be released if an IARD was not present and the fault would be interrupted by the conventional short-circuit protective device (SCPD).”
An IARD can be built using a variety of technologies and strategies. These may include using upstream circuit breakers (SCPDs) to interrupt the power source, along with a parallel connection of a low-impedance current path and an arc quenching device (AQD), or using an Internal Arc Limiting Device (IALD) in series.
Eaton’s ARCON 3G IAMS system, for example, has sensors that detect the light emitted by the fault and the rapid current rise in generates. The central processing unit signals the quenching device, which creates a bolted short-circuit on three poles parallel to the location of the fault. The short circuit reduces the voltage required for the arc fault to nearly null, quenching it within 2 ms of its initiation—well before its maximum destructive force can be achieved.
The IEC TS 63107 integration test is designed to prove that a chosen IAMS and the switchgear into which it will be integrated work perfectly together. The specification describes how to perform all the necessary tests. It also offers a series of guidelines to help OEMs properly incorporate an IAMS into an LVS.
In general, the IEC 61439 series includes tests for construction (degree of protection, protection against electric shock, internal connection, etc.) and performance (dielectric properties, verification of temperature rise, short-circuit withstand strength, mechanical operation, and electromagnetic compatibility). IEC TS 63107 requires additional temperature rise and short circuit tests on the IAMS (including its AQDs) installed within in the LVS, plus verification of performance of the IAMS device, including repowering scenarios.
Inside the switchgear, there can be areas that are protected by the IAMS and other areas that are unprotected. The protected areas must be verified for arc fault detection, mitigation and extinguishing. Further functional tests must be performed to show that that IAMS and SCPD do not generate unwarranted tripping of circuit breakers or other unintended operations.
The verification test must simulate defined and documented worst-case conditions for an arc flash event. To determine the worst-case scenario, an analysis must be made, taking into account the characteristics of the IACD and the IARD, the positions of the sensors, and possible arc locations. For the test, an arc should be ignited at the point in the IAMS-protected area where an arc fault is most likely to occur. The ignition points are detailed in chapter 10 of IEC TS 63107.
If circuit breakers are installed as the SCPDs, a test for unintended operation of the IAMS must be carried out using the highest possible let-through energy, that is, with the rated short circuit current and the rated short-time current at the corresponding rated operational voltage.
Recently, Eaton performed a successful TS 63107 verification of its ARCON 3G Arc Fault Protection System integrated with its xEnergy Main low voltage switchgear assembly.
The low voltage assemblies tested were xEnergy Main Fixed XF, Removable Mixed XR, and Withdrawable XW panels configured with IZMX40 and IZMX16 air circuit breakers (ACB), NZM molded case circuit breakers (MCCB), and fuses. The IAMS used was the Eaton ARCON 3G (with secondary sensors) and an Arc Quencher (AQD: fixed, single shot) with ARCON line and NTFS (Nuisance Tripping Free Sensor) sensors. The IARDs used were IZMX16 and IZMX40 ACBs.
All tests were carried out simulating worst case conditions. All configurations successfully passed the tests with currents between 7,5kA at 230V up to 105kA at 415V (75kA at 690V). For more detailed results, consult your local Eaton specialist.
For more useful information about internal arcs, related verification, arc energy calculation, arc risk evaluation, and additional methods to increase the safety of your low voltage switchgear system, be sure to download Eaton's Consulting Application Guide for Low Voltage Systems.
