Question on switchgear interlocking. Do you need to be able to operate it while doing maintenance?

[electrical429]

So, the main principles of interlocking are:

1. You can't operate disconnector unless associated circuit breaker is open;
2. You can't close earth switch unless associated disconnector is open;
3. You can't Close the disconnector while the associated earth switch is closed to earth;

This can be achieved in the number of ways via castell keys or electrical interlocks depending on if the switchgear is motorised or not.

My question is - do earth switches and disconnectors also require maintenance? I assume the answer is yes. So do you need to be able to operate disconnectors and earth switches when you are maintaining them? Like test its operation? If yes then how is this achieved in case of disconnector for example if it is interlocked with the earth switch? Do you take the interlock keys back and forth between earth switches and disconnectors each time you need to operate the disconnector under maintenance?

 

[crshears]

Key interlocks: yes.

Electrical/logic interlocks: no, these can usually be defeated by selecting control circuitry into maintenance mode.

As an aside, but worth noting:

Some utilities [like mine] incorporate a switchgear interlock system bypass feature at specific sites; this can be invoked by the system operator from the [remote] control centre, and is intended to facilitate the prompt removal of failed equipment [most commonly a stuck breaker] from service. In this instance, the operator will confirm at least one closed loop exists around the switchgear to the stuck breaker, then invoke the SIS bypass; it times out after 30 seconds, but this is more than enough time to open the motorized disconnects on both sides of the stuck breaker.

Using SIS bypass can avert, and has averted, major impacts on our grid's nuclear generation.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[sushilksk]

Yes
Yes
Discoonector can be operated when CB and ES is open, and ES can be operated with disconnector open. Mostly interlock bypass is not required for checking operation.
Yes, if interlocked with keys, Keys needs to be moved between ES and disconnector. Bypassing interlocks is also sometimes required, which can be done after taking all precautions.

 

[electrical429]

Thank you!