Busbar sub sectionalizing

[mbrooke]

What benefit is there to having midpoint busbar sectionalizing switches? My calculations show nothing is gained because they can actually reduce the availability of a busbar- however upon looking at manufacture literature and actual substations commissioned in Europe and Asia- half the time its common to have them.

 

[Julius Right]

In my time, in a fossil power station, a low voltage duplex transformer switchgear worked open coupling breaker and each transformer rated power was approximate 70% of the total required power. The coupling was closed only for a short-time if one of transformers was in trouble. Each equipment supplied as pumps, compressors and other was doubled and each equipment was able to support 70% of the total [calculated] burden. If this policy of redundant equipment changed in order to minimize the initial cost and consider the non-supplied power less important then no need of the coupling breaker indeed.:weeping:

 

[Sahib]

Well, if the two transformers cannot be paralleled but both are required, then........

 

[Tony S]

You have to take in to account the total fault current of two transformers in parallel. You also have to look at the knock on effect upstream.

I’ve paralleled transformers to take one out for maintenance, it took less time than it took to write this sentence.

Paralleling transformers at our intake substation was tricky to say the least, the DNO (PoCo) had to be involved. Without their help we would be paralleling parts of the area 132kV system.

I don’t know about US systems but UK DNO transformers are rated for 125% O/L in summer and 150% O/L in the winter. This is where Julius’s post comes in to the equation, if the transformers are normally 70% loaded you can swing the entire load on to one.

 

[mbrooke]

But here is the thing- in many of these applications everything is paralleled. One could skip sensationalizing the busbar in that you already have another busbar should the other need to be removed from service. The thing is why further add isolaters?

 

[Tony S]

OK you run two transformers in parallel and a fault occurs on one of the outputs, what happens on the rest of the system?

 

[mbrooke]

OK you run two transformers in parallel and a fault occurs on one of the outputs, what happens on the rest of the system?

The system sees voltage dip, increase in reactive power and the circuit breaker trips within 5-6 cycles.

 

[Sahib]

The system sees voltage dip, increase in reactive power and the circuit breaker trips within 5-6 cycles.

Tony's question is for radial circuit configuration where fault takes out all equipment downstream. But if you have much costlier but more reliable primary loop and secondary loop configuration, it does not happen.

 

[mbrooke]

Tony's question is for radial circuit configuration where fault takes out all equipment downstream. But if you have much costlier but more reliable primary loop and secondary loop configuration, it does not happen.

But what does that have to do with busbar sensationalizing?

 

[mbrooke]

You have to take in to account the total fault current of two transformers in parallel. You also have to look at the knock on effect upstream.

I’ve paralleled transformers to take one out for maintenance, it took less time than it took to write this sentence.

Paralleling transformers at our intake substation was tricky to say the least, the DNO (PoCo) had to be involved. Without their help we would be paralleling parts of the area 132kV system.

I don’t know about US systems but UK DNO transformers are rated for 125% O/L in summer and 150% O/L in the winter. This is where Julius’s post comes in to the equation, if the transformers are normally 70% loaded you can swing the entire load on to one.

Paralleling the 132kv system is beneficial if your equipment can tolerate the short circuit forces. For one during a fault you just get a 6-30 cycle dip instead of a complete outage and then transferring over. Second an interconnected system usually has a higher critical clearing time due to its "elasticity"


Anyway, for the bus coupler you have at least two options:

 

[mbrooke]

From an engineering guide, the full spectrum of options:



https://electrical-engineering-portal.com/circuit-configurations-hv-mv-switchgear-installations