34kV Breaker - Local Remote Disables Local Trip

[brad9m]

Can anyone tell me the reasoning behind a 34kV breaker that has a local-remote switch in line with the trip coil for a high voltage breaker? My first instinct is that it is a serious safety concern. If the switch is in Remote and someone needs to trip the breaker locally, they must first take the Local-Remote switch to Local, then press trip. I wanted to pass it off as bad engineering and then I found a website describing a similar implementation.

Besides the obvious safety concern, is there any documentation I could provide the customer to sway the design? I searched the NEC, NESC, and tried to find ANSI, IEEE or other references that state what a bad idea it is to disable protective devices, but I must be using the wrong search terms. Any suggestions?

 

[SG-1]

This is a fairly common feature in control schemes for medium voltage. The Local/Remote usually blocks the control switch close & the control switch trip, never the protective relay trip. If an operator is with the switchgear, the switch can be turned to Local so the control room cannot surprise the operator with an unexpected close or trip. The Local can be used if the Remote circuit fails.

In Remote position no one needs to be at risk while closing or opening the breaker. It is done from the control room.

Nearly every place I have visited the operator was given a set of detailed instructions to follow. They were not allowed to Close or Open any breaker or switch on their own.

If a 38KV meltdown is in progress, I do not suggest trying to manually open the breaker, while standing in front of it.

 

[brad9m]

Thanks

Thanks

This is a fairly common feature in control schemes for medium voltage. The Local/Remote usually blocks the control switch close & the control switch trip, never the protective relay trip. If an operator is with the switchgear, the switch can be turned to Local so the control room cannot surprise the operator with an unexpected close or trip. The Local can be used if the Remote circuit fails.

I've seen plenty of applications that block the close, plenty that block a remote trip, but blocking local trip is new to me. I still don't understand why you would want to block a local trip.

In Remote position no one needs to be at risk while closing or opening the breaker. It is done from the control room.

I agree completely. This should be the norm.

Nearly every place I have visited the operator was given a set of detailed instructions to follow. They were not allowed to Close or Open any breaker or switch on their own.

In my Ops years, we always had something like that.

 

[SG-1]

The operator can still trip locally, you are just objecting to turning the Local/Remote switch to the local mode if it is not already in that position ?

 

[SG-1]

If the button you push to open the breaker is an E-STOP then you would have a good case for not disabling it in remote mode.

How close are the two switches apart ?

 

[beanland]

Training

Training

Most (not all) breakers operating at 30kV or above are owned by electric utilities or power generation plants (e.g. wind or PV). In these cases, NEC does not apply. Utilities and power plants are expected to train operators and have formal switching procedures. If a fault occurs, it is likely that the protective relays will be much faster than the human operator at detecting the event and calling for a trip. However, the use of the Local-Remote switch is a utility-by-utility selection.

 

[djohns6]

I work for a utility company and over the years we have gone through several evolutions on breaker and switch controls . We have some that are true LOCAL / REMOTE devices . Some that have a Supervisory Cut Out configuration where only the remote control is disabled . On newer breakers it's usually just a matter of adding or removing jumpers in the control circuit to achieve your desired scheme . I agree that local trip should never be disabled but it happens .

 

[jdsmith]

Many industrial facilities agree and take the standpoint that any trip function should always be in service to avoid confusion during emergency situations. Local/remote and auto/manual switches that are part of control schemes will centainly supervise closing of the breaker, but usually the local trip at the cubicle and the trip in the station mimic panel will work regardless of the position of other control switches.