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.

 

[wcaseyharman]

Tripping an upstream breaker faster will reduce the process impact on the rest of the plant and reduce potential equipment damage by removing the fault quicker. I would tend toward fast arc detection relays unless I don’t have access to the upstream device or it’s a fuse.

 

[bacon4life]

Safer dissipation of arc products is unrelated to the IP rating. Here are some videos showing normal versus arc resistant design:
Arc flash that blows the door open directly at the operator:

Arc flash explosion - Eaton videos

The video shows an arc flash explosion in real life

videos.eaton.com

Arc resistant gear where the arc products are vented up and away from the operators:

 

[stevenal]

OP was speaking of transformer enclosures and cable connection boxes. I'm aware of arc-resistant switchgear, but do they make the OP's items arc resistant flavors? Protecting against a random insulation failure might be overkill. Protecting someone opening such an enclosure to perform work live is another story.

 

[slavag]

Arc detection relay send close command to UFES. You need both of them.

 

[bacon4life]

I had assumed the IEEE standards for arc resistant gear covers the whole package we buy from the switchgear vendor to attach a 115 kV/15 kV transformer to the outgoing 15 kV cables. Even if testing standard doesn't quite cover the cable terminations, I assume a vendor could at least employ similar design principals as they use on the rest arc resistant switchgear. Perhaps if the OP really does need explosion proof stuff, the should look into stuff for classified areas (e.g. petroleum vapors).

Regarding arcs inside the transformer, transformers typically include pressure relief as part of the design. I have started seeing substation transformers with pressure relive valves piped specifically to avoid hot oil spraying all over the place. I am unclear whether the additional piping interferes with the capacity of the pressure relief valves.