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MV Fused Disconnect

MV Fused Disconnect

MV Fused Disconnect

(OP)
If we don't want to use breaker on incoming 4160V feeder, is it possible to use "remote" operated fused disconnect? (same as we do for low voltage).

RE: MV Fused Disconnect

Yes. Look for the term "Motorized Fused Load Interrupter Switch". All of the usual suspects offer that option. Assuming because of the 4160V reference you are in North America and will want ANSI gear, they are typically Metal Enclosed Switchgear as opposed to Metal Clad.

"Will work for (the memory of) salami"

RE: MV Fused Disconnect

Depending on the size of the load, a 5 kV fused contactor similar to a motor starter is a cost effective application. A latched contactor acts like a circuit breaker and does not drop out on loss of power.

The fuse supplies short circuit protection, the contactor does the on/off control. A protective relay or other overcurrent device is needed to trip the contacotr for overload protection.

Large loads can create fuse sizing issues relative to the contactor interrupting rating. A fuse large enough to carry the load may not protect the contactor during short circuit. Worst case is a ground fault that starts tripping the ccntactor but escalates into a phase-phase fault before the contacts open.

RE: MV Fused Disconnect

(OP)
So in the case of the combination of MV non-fused-disconnector, fuse, contactor, and relay: the relay can send signal to DCS which can then trip the contactor and contactor can trip the disconnector. If we have a combination of fused-disconnector, contactor, and relay: then how will the fused-disconnector trip?

As it is a non-motor load, so will it be ok to not used contactor and relay at all (and use only fused-disconnector)?

RE: MV Fused Disconnect

In that concept, the disconnect doe NOT "trip", it is an isolator. The down side to that is that if you use a vacuum contactor, many people do not consider them as safe for true isolation by themselves, so the isolation switch is necessary. If nobody is there to operate it locally, you need the motorized version anyway. If you have no need of the contactor then, it becomes superfluous.

"Will work for (the memory of) salami"

RE: MV Fused Disconnect

Powercon makes a load-break disconnect which can be armed by putting the manual operating lever to the open position without the load-break switch openning. The arming process,charges the operating spring but a slotted mechanical blocking rod prevents the switch operating arm from moving over center, as most quick make quick break mechanism uses an over center operating mechanism.

The arming process also latches the manual operating lever in the openning position.

Tripping / openning of the load- break switch is achieved by energizing a shunt trip coil, which rotates the blocking rod to enable the switch main arm to go through the slotted rod achieving a quick break operation.

Closing is done manually.

As indicated already ,motorized operator can be fitted for remote openning and closing.

Only one of the devices can be fitted at any one time.

RE: MV Fused Disconnect

(OP)
If closing is manual, then Powercon switch does not seem to be good option because there would be danger of arc flash at the time of manual closing.

RE: MV Fused Disconnect

Load break switch are design with a closing closing unto fault duty. Any fault on the system will be interrupted and cleared by the fuse.

Most arc flash are mainly attributed to human error. I would have no reservation in operating the manual handle with or without a bomb suit. The gear are designed to be operated manually ... But not for everyone it seems.

perhaps the industry have taken the arc flash issue to far ... Even though we had a recent fatality lately due to human error working on improperly isolated gear ... And it was called an arc flash incident.

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