Balancing a 3 phase load

[gerard]

I have a question on balancing a load. We have 3 cabins with the following loads: 10kW, 8kW and 3kW, supplied by a three phase supply. Each cabin will have it's own supply. Is there a simple way of balancing these loads, or is it possible?

 

[nickblake]

Is that total load or can you apply diversity to it

 

[gerard]

Total Load

 

[davesparks]

Anything is possible, but how far you go will depend on how necessary it is.

If this is going to be fed by a DNO supply then your loads will be a drop in the ocean compared to everything else fed from the same Tx

If however you have a small generator supply you will want the total load to be no more than 30% out of balance.

If you need to balance it then you need to look at the nature of the loads/ load profiles aswell as their power ratings.

 

[gerard]

Loads will be supplied by DNO. I can't really change loads so I was just thinking of leaving it as it is - unless someone had another idea?

 

[Darkwood]

Balancing loads from our side of the supply is purely to allow for better scope for future additional circuits especially 3ph ones... of course this cannot always be achieved but do it as best you can.
The problems arise when you have a scenario like a 100amp 3ph supply and you have

L1-85% loaded
L2 60% loaded
L3 15% loaded ----and someone wants to wire a load of say 20% capacity per phase so clearly L1 would overload, thus a better balancing by previous installers would have not made this an expensive addition with either the extra work swapping circuits about or an increased supply application.

In your case I don't have enough info to say you can/can't balance it better even with additional costs, would need a lot of info about the existing supply, balancing, peak KVA demand per phase etc etc... getting this wrong can be costly to the customer in the future, depends whether you act as a proffesional or a sod it and just wire it type... a chat with the customer about the balancing and consequences of taking a possible cheaper option may be needed to give your customer the choice and also to explain a higher quote you may have against another company.


EDIT ... to note balancing of phases with effectively reduce the N current and may in some circumstances like older systems with reduced sizes on N cables need to be factored when making load additions or even modern systems with Harmonic issues that can cause many issues with the Neutrals been overloaded if excessive imbalances occur.

 

[Pete999]

Can't see how you are going to balance these loads, you have 3 cabins each with a SP supply @230v 10A, 8A and 3A respectively, is that correct? if you have any peripheral loads such security lighting etc, which you could take from the phase supplying the cabin with 3 amps.

 

[Darkwood]

Can't see how you are going to balance these loads, you have 3 cabins each with a SP supply @230v 10A, 8A and 3A respectively, is that correct? if you have any peripheral loads such security lighting etc, which you could take from the phase supplying the cabin with 3 amps.

If it was 10A, 8A and 3A I'd be telling the OP to stop been silly and install it and forget.... Think the KW he expresses makes this a worthy query!

 

[benji]

stick 2x3kw heaters in 3rd container

 

[Pete999]

Can't see how you are going to balance these loads, you have 3 cabins each with a SP supply @230v 10A, 8A and 3A respectively, is that correct? if you have any peripheral loads such security lighting etc, which you could take from the phase supplying the cabin with 3 amps.

Correct my mistake, confused KWs with Amps duuuu:6:

 

[Darkwood]

Correct my mistake, confused KWs with Amps duuuu:6:

I gathered it was a Typo but best to let you know straight away

 

[nickblake]

Agree with dave here

 

[davesparks]

If that is the load before diversity I'd say you are probably on a hiding to nothing, once diversity has come in to play you'll probably have naff all load to balance.

Give us the breakdown of the loads for each unit and maybe we can give a better idea.

 

[guest119]

Correct my mistake, confused KWs with Amps duuuu:6:

Time for another 5 weeks at the skill centre for you Pete ...

Boydy

 

[gerard]

I have found out that the phases are not balanced throughout the building. All I can do is wire new loads to the phases with smallest loads

 

[Pete999]

Time for another 5 weeks at the skill centre for you Pete ...

Boydy

Probably right there mate. or could be the OAP club down the community centre

 

[Darkwood]

I have found out that the phases are not balanced throughout the building. All I can do is wire new loads to the phases with smallest loads

Be careful here when assessing the existing load, if you can get an idea of the design load of the existing not just a measured load as you may have clamped at a period that might not show a true reflection of the normal trend... once your happy with your averge load per phase then yes do as you suggest to rebalance the existing with your new loads.

 

[davesparks]

Stick a data logger on the existing supply for a week and get a proper look at what is going on

 

[gerard]

Stick a data logger on the existing supply for a week and get a proper look at what is going on

I will do exactly that... i'll put power monitor on it tomorrow and see what results are like.

Thanks...

 

[Darkwood]

Stick a data logger on the existing supply for a week and get a proper look at what is going on

A bit OTT tbh unless its fluctuating alot and the existing circuits are hard to identify and trace... a weigh up on of the existing circuits should be enough to guess if your measured reading is reflective of the nature of the design load.

Edit ... the OP already has the equipment so seems the better option - most don't posses this equipment and could be expensive to hire out.... this round to you dave

 

[davesparks]

A bit OTT tbh unless its fluctuating alot and the existing circuits are hard to identify and trace... a weigh up on of the existing circuits should be enough to guess if your measured reading is reflective of the nature of the design load.

Edit ... the OP already has the equipment so seems the better option - most don't posses this equipment and could be expensive to hire out.... this round to you dave

It depends how big and complex the installation is, and how accurate you want/need to be.

I am used to balancing generator supplies at festivals/events so am very mindful of maintaining good balance at all times, bearing in mind the nature of loads as well as design currents.

And for small installation some home energy monitors work as reasonable data loggers when high accuracy is not key. I've got 3 OWL transmitters with 200A CTs I picked up on eBay for next to nowt along with a USB receiver to download/monitor the data. They work quite well when my proper power quality analyser is already in use.

 

[Knobhead]

It's not even worth bothering about. Connect up and get on with the next job.

 

[MacLec]

If you were that fussed you could run 3 phase to each cabin but that would be cost + ott

 

[Silly Sausage]

Use a 3 phase powered, single phase output generator.
Perfectly balanced!

 

[Knobhead]

He could use a Scott T or LeBlanc transformer with 8KW on one leg and 8 + 3KW on the other

 

[gerard]

He could use a Scott T or LeBlanc transformer with 8KW on one leg and 8 + 3KW on the other

I will give it some consideration.

 

[Knobhead]

Hope you’ve got plenty of money.

They’re very rare in this country.