Arc detection relay Vs UFES (Ultra fast earthing switch) 1

[NickParker]

The transformer specification states that "Transformer enclosures and cable connection boxes shall be designed in such a way that an internal arc will not pose any personnel risk to operators, even in the event of an arc fault."
After consulting with the vendor, they propose using a UFES (Ultra-Fast Earthing Switch) on the transformer enclosure, which can clear faults within 4ms. I am accustomed to using an arc detection relay in MV switchgear, which trips the breaker but takes longer—typically around 50 to 80ms.

I would appreciate your thoughts on using UFES versus an arc detection relay.

 

[davidbeach]

Something has to detect the fault to close the UFES…. I don’t think it’s “or” but rather “and”. The relay for detection and the UFES for quenching.

 

[bacon4life]

The earthing switch does not clear the fault. It instead turns an arcing fault into a solidly grounded fault, while still relying on the upstream breaker to clear. Before adding a device that intentionally creates a bolted fault, I would want to be sure it provides very clear benefits over an arc detection relay.

As to the the transformer specification, it seems impossible to design for zero risk. Vendors respond in weird ways when clients as for impossible things. It may be worth clarifying exactly what level of risk reduction you are attempting to purchase.

The switchgear standards are for arc-resistant gear rather than arc-proof gear. Although fast relaying plays a role in reducing likely energy, the more critical part of arc resistant gear is the physical design of the switchgear. Arc resistant switchgear includes specific venting pathways designed to direct arc fault byproducts away from the operator. Just adding high speed protection to switchgear design that vents directly towards the operator via the panel door blowing off would be a dangerous in the event of relying on the backup protection element.

 

[NickParker]

The earthing switch does not clear the fault. It instead turns an arcing fault into a solidly grounded fault, while still relying on the upstream breaker to clear. Before adding a device that intentionally creates a bolted fault, I would want to be sure it provides very clear benefits over an arc detection relay.

As to the the transformer specification, it seems impossible to design for zero risk. Vendors respond in weird ways when clients as for impossible things. It may be worth clarifying exactly what level of risk reduction you are attempting to purchase.

The switchgear standards are for arc-resistant gear rather than arc-proof gear. Although fast relaying plays a role in reducing likely energy, the more critical part of arc resistant gear is the physical design of the switchgear. Arc resistant switchgear includes specific venting pathways designed to direct arc fault byproducts away from the operator. Just adding high speed protection to switchgear design that vents directly towards the operator via the panel door blowing off would be a dangerous in the event of relying on the backup protection element.

Your reply got me to another question. The vendor's proposed IP rating is IP23, so I need to verify where the openings are since the direction of the gases can't be fully controlled—only certain directions can be blocked. Perhaps I should ask the vendor to provide an IP44 rating instead.