3-Phase imbalance - Pursuading the customer.

[Click-Sure]

I'm currently doing a bit in a large commercial property where demand has changed significantly from the original design and having had the clamp meter out there is some quite serious imbalances, along with some circuit running very close to, or at their limits.

The figures I got from my clamp meter during a period of normal demand were roughly:
L1 - 90A
L2 - 37A
L3 - 79A

Its bad, I know, but other than the obvious safety issues how do you reccomend I best go about pursuading the customer to put their hand in their pocket and that things are in dire need of sorting, ASAP.

Any ideas folks?

 

[Spark123]

Assuming a 100A supply, what is wrong?

 

[ericmark]

with some circuit running very close to, or at their limits.

In a commercial property loss of power means loss of money. When told there is a likely hood of power loss places I have worked in have been only too keen to get it sorted.

Think how much will they lose with a power failure. Often they have to evacuate because of lighting levels supplies to fire alarms lifts etc. To empty and fill after the fuse is replaced may take 1/2 hour and for 50 people that is likely to cost £250 each time it blows. Plus loss of trade etc.

 

[conny]

Tell him/her it will cost £xx.xx to put it right now.
If it fails it will cost him £xx.xx at emergency call out rates plus loss of production costing him even more. The thought of losing production and associated profit usually sways them especially if some processes take time to re-start after a sudden shutdown. Re programming machines, firing up boilers, clearing fault codes etc.

 

[ColJack]

any idea how they charge for 3 phase?

do they charge KWH for each phase, or just off the one phase or average???

 

[Lectrician]

They charge for total consumption. You cant get free lecky!

It is unbalanced, but it is certainly not dangerous. It is not hugely unbalanced either, not ideal, but I would not be worrying to much. What is the supply? If it was just a 100amp head (with possibly just 80 amp fuses as per some DNO's), then I would be looking to balance, and also be looking at future possible loading the need to upgrade the supply.

 

[Click-Sure]

Thanks for the comments peeps, its a 200A TP+N supply, so I'm not too worried about overloading in that sense, however I've never really gone into the charging aspect of things, as ColJack picked up on.

I can't imagine its going to be easy to find out how their electricity is charged, but seeing as the DNO's generally (unloess otherwise advised) like 3-phase supplies to be pretty well balanced, I'd imagine there would be some kind of incentive to balance properly, and its along this line that I'll be trying to convince them to strip out their overloaded 16 TP-way Square-D Loadmaster with something more like a 24-Way Merlin Isobar.

The meter doesn't have the phases 'passing through' it like on smaller supplies but is connected to pick-ups strapped onto each phase wire before it heads up into the building on 95mm2 4-core SWA.

 

[Lectrician]

All suppliers that size will be CT metered.

They will not be imposing fines or anything for an unbalanced load. Although they do place in your supply contract that supplies are to be balanced, it is not actively 'policed' and there is no guide as to what they interpret as balanced!

I would not be worrying.

 

[Stoday]

According to the supply conditions, you are supposed to maintain the power factor to 0.8 or better. As it's only recorded and there's no financial incentive, except on the largest supplies, most ignore it.

Even more so imbalance. It's not measured and there's no financial incentive other than the very slight improvement in losses on the factory's wiring.

As for metering, the current in each phase is used, with the voltage, to obtain the true kWh. If the metering's for HV (11kV) there will be a 3-phase voltage transformer for providing a voltage to the meter, as well as current transformers.

Meters for large supplies also measure the kVArh and calaculate the kVA from that and the measured kWh. kVA Maximum Demand is calculated from the half hour totals of kWh and kVArh, that is, it's averaged over a half hour.

 

[bernardgreen]

You could mention to the client that if the un-balance causes other customers to suffer voltage fluctuations on their single phase supplies then the supply company may "request" better balancing is put in place.

 

[Click-Sure]

Thanks for all the helpfull comments folks, its not a factory by the way, its actually a large retail shop! Bit of an overkill on the supply side, but hey-ho.

I think the route I'll go down is that the board is old and choc-a-block with MCBs feeding active circuits and leaves no room for expansion, which is allready neccicary due to a few 'glowing' breakers serving some lighting and power circuits!