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MV switchgear testing

Let’s cut the threat of arc flash explosions

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Tom Stefanski Tomasz Stefanski
Director, KEMA Laboratories Chalfont
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Internal arc explosions in medium-voltage (MV) switchgear can kill. Even in the best case scenario where nobody is directly hurt by the explosion, the resulting power outage can cause chaos and hardship for thousands of people and businesses locally. The costs of replacing switchgear and repairing the damage to the grid and surrounding area are high. But they are dwarfed by potential liability claims and economic damage to the reputation of the utility and the manufacturer that supplied the equipment. 

In MV switchgear, internal arcs can reach temperatures up to 35,000 degrees. Around half of that energy is used for heating the air inside the enclosure, generating huge pressure on the switchgear. A robust design with effective pressure-relief venting is vital.  But arc motion within the switchgear enclosure is difficult to predict. So how can you be sure the design of your MV switchgear is really up to the job? 

Physical testing is the only way to be confident of how MV switchgear will behave in the field. It provides verification that your switchgear design really does reduce arc flash exposure and hence reduce the threat of injury. 

Internal arc testing 

Internal arc testing verifies the potential risk to a person standing within a few feet of switchgear during an arc flash. To this end, the test is carried out in a simulated room with indicators that mimic human skin to assess the danger of burns from hot gases escaping. According to the latest standard – IEC 62271-200 (2003) – the position and arrangement of these indicators is determined by who will be able to access the switchgear in use. This replicates the effect of protective clothing that will be worn by authorised personnel but not by the general public. 

Ensuring effective internal arc testing 

At KEMA Laboratories, we have built up extensive experience in testing all kinds of MV switchgear. Using this experience to benefit the whole T&D industry, we have analysed many years of test data to determine exactly what requirements are necessary to ensure the effective internal arc testing of MV switchgear. Key findings of this research include:

  • Testing must be carried out at sufficient voltage, current and power levels to mimic real-world situations
  • Testing at lower voltages does not provide reliable verification of behaviour during an arcing event
  • Arcs in SF6 gas store 3-4 times as much energy as arcs in air

You can find a more complete discussion of our research into effective internal arc testing in our paper: Internal arcing: issues related to testing and standardization. And check out the Downloads section on this page for further papers. 

The benefits of lab-based testing

  • Verification of how switchgear performs under real-world conditions
    • Reduce equipment failures in the field
    • Increase confidence that grid will recover quickly after faults
  • Independent evidence for the quality, reliability and safety of switchgear
    • Streamlined procurement processes for utilities and grid builders
    • More sales opportunities for manufacturers
  • Documents your efforts to improve grid reliability
    • Support in discussions with regulators
    • Evidence against liability if problems do arise
  • Insight into long-term performance and withstand capabilities helps guide maintenance planning

Your trusted partner 

KEMA Laboratories is the leading name in lab-based testing of transmission and distribution (T&D) grid components. At our lab in Chalfont, Pennsylvania – the largest of its kind in the Americas – we offer extensive standards-based physical testing of MV switchgear including circuit breakers, load break switches and metal-enclosed switchgear. Our services help ensure MV switchgear operate to the highest international standards. We combine highly skilled and experienced test engineers with the most advanced test facilities in the world. So you can have complete confidence in the quality of the switchgear we test, and be sure of the most efficient testing procedures.