3-Phase Power Balanced Distribution

It indeed seeks my time as it is causing interruptions on my 3 phase equipment rated +/-15% of nominal voltage. It trips off everytime Vac imbalance. So yeah indeed is neceasaru to solve the puzzle.

Consider installing a Dyn connected, isolation (unit ratio) transformer and shift all the single phase loads to the secondary side of the isolation transformer.

<...+/-15% of nominal voltage. It trips off everytime...>

That suggests that the cabling supplying the <...3 phase equipment...> upstream of the single phase loads is undersized. That would be of great interest to the facility's fire insurance company!

Have the installation inspected, tested and certified for safety without any delay by a qualified local Electrician, and certainly before anyone gets hurt/killed. It could well be that replacing the feeder cables with something that is correctly sized will be the solution to the problem.

Just for info, can this be eliminated since Power is in wye transformer upstream , will a delta distribution transformer to 3 phase loads mitigate the imbalance?

Please focus on the right thing #9⇓. Have a local professional Electrician check, immediately, the sizing of the cables upstream of the <...3 phase loads...> as the indications in this thread are that these are too small for today's job.

How long ago was the last EICR carried out, and what were the findings (rhetorical question - NNTR)? Find this document and carry out action(s) based on the contents. Do it today!

If it cannot be found, get it done again. Today ends at midnight!

Changing to Delta supply for 3 phase loads would require a new transformer and be expensive. Since 3 phase loads are normally balanced you will not correct any imbalance by changes to their supply.

A reply to my post #11 would be appreciated.

Gutmonarch post #13 tells us you have a Y transformer upstream. He previously told us the actual problem is a 3 phase equipment which trips if 3 ph supply is outside certain limits. Other than un-balance changes day to night, no values given, CR4 know nothing.

Does the "Y transformer" mean you have 400/230V 3 phase supply in which all 230V single phase neutrals are earthed/grounded??

This suggests your single phase supplies are 230V. As P.W. Slack has suggested, you may have all your single phase loads on one phase, maximising imbalance.

...and a <...delta transformer...> will not have a neutral connection, so there will be no scope to connect <...single phase loads...> to it.

How are those phone calls to get an EICR done going?

No, it will not.

In the UK it is called an Electrical Installation Condition Report, usually abbreviated to EICR. Call some of them and get some quotes. Today ends at midnight.

Ac voltage unbalance protection for 3 phase loads is distinctive. Motors are not designed to tolerate more than 6% to 10% unbalanced current. A motor with 15% unbalanced current will incinerate itself in very short order. Good overload protection will detect this situation. I’d be interested to know just what equipment is complaining about voltage unbalance.

Capacitors might work in specific cases to lower asymmetrical I squared R losses, but not handling unbalanced loads properly is a sign of a highly distressed power system, as PWSlack has alluded to earlier.

Overload protection, circuit protection and cable sizing are interlinked. There are protocols in British Standard 7671, among other national electrical codes, for co-ordinating the three, and a qualified local Electrician will be able to manipulate these and correct the matter in short order.

There has been no need to address <...I squared R losses,...>. This is only necessary if the installation is charged for power on the basis of power factor, which currently lays outside the domain of this thread.

Unbalanced I squared R losses could be corrected with application of capacitors, for installs where the unbalance is caused by highly reactive unbalanced loads. Otherwise, capacitors would be useless to correct unbalanced conditions. You cannot separate the load characteristic from the supply. 3 phase distribution supply systems are invariably designed to be balanced. It is the load, and only the load, that causes unbalanced conditions.

...which is why the original poster is looking at the wrong thing. GA

Sigh! Gutmonarch has told us

1. In initial post that his load is balanced in day, but not at night. Also that he knows about power factor correction and voltage stabilisers.
2. In post #3, that he has a 3 phase equipment that trips out because supply goes outside +/- 15% volts.

Despite post #11, he does not appear to have measured the incoming supply [voltage & current] to the premises [or to the critical equipment that trips] night or day to see if he is getting an unbalanced supply before any cable voltage drops on-site add to unbalance.

Perhaps he has no instrumentation, built-in or portable? No willingness to go in at night, just finds an equipment has tripped overnight?

CR4 cannot provide instrumentation. There should at least be watt-hour meters for billing, hopefully one per phase - reading these every few minutes should give an idea of current balance. Modern meters might give phase kW voltages, currents & Vars.

The several respondents have done all they can.

Over to Gutmonarch.

Before you can control anything,first you have to measure it.

That is why I suggested an event recorder measuring the voltage/current on all phases,including single phase loads.

After you perform these measurements you can decide where the problem lies.

If the problem turns out to be multiple issues and it is an elephant,you have to accept it and do what is required.

Remember,if you must eat an elephant,you do it one bite at the time.

<...current...> is a feature of the mechanical loading of the motor. <...voltage imbalance...> is a feature of the supply.

If the motor is stalling because of low voltage, then the current will rise until the <...overload protection...> device disconnects it on the basis of current drawn. Dips in <...voltage...> still point towards supply conductor sizing.

If the <...3 phase equipment...> is refusing to operate because of low voltage on any of its input terminals, that indicator still points towards supply conductor sizing, and is not a feature of imbalance.

It would be useful to know...

1. If the source incoming power to the installation were unbalanced at night, even before your loads added different voltage drops in cabling?
2. If the phase currents were unbalanced at night compared to day?
3. If the night-time load is mostly lighting. Fluorescent lighting is likely to cause more harmonics than incandescent?
4. If the 3 phase equipment with +/- 15% limits trips because it has built-in sensing which is set to less than +/- 15%? Maybe limit is adjustable?

I agree with PWSLACK:

Spread out your single phase loads over all phases by measuring amps drawn,but remember,it will never be perfect balance,which is why there is a neutral conductor,to carry unbalanced current.If your facility has a large component of switch mode power supplies,(Such as a data processing center), double the neutral conductor size to handle harmonics that are not seen by a normal VOM.There are VOM's that will read harmonic currents,and the modern switch mode power supplies switch only during the zero portion of the sine wave to reduce harmonic currents.

Once upon a time, we had a project engineer who was known for fast work, finishing projects in quickly and under budget. Once he was assigned to build a new admin building and, as always, he finished in record time. The power plant, however, started complaining that the three-phase lines had become imbalanced and were causing problems.

To make a long story short, we mapped the loads on each phase and measured current flows on each of them both during the day and during the night. Then, we reassigned the loads to minimize the imbalances both for day and night.

Then, the electrical manager sat down with the contractor and project engineer to give them a lecture on how to coordinate with the elecrical department during projects.

The electrical manager described the project engineer, "That guy's hands are faster than his brain."

regards,

Vulcan

What type of loads are on at night that are not on during the day,and vice-versa.

Area lighting?Inside lighting?Heating,cooling?

If it trips on a single phase of 3 phase power,that phase is very unbalanced,and the daytime load may help balance the system.Best thing to do is balance the load as was previously suggested.

Can't tell which phase?Use a 3 phase voltage recorder and monitor for 24 hours,at least.

Missing from the information pool (maybe a puddle) provided is anything about the facility.

Facility in service for some period of time, this trouble simply manifested? All new facility and energy service, cannot get commissioned?

Please fill the pool a little more.

There are many ways to address this problem.I like to keep it simple.

Why not simply balance the loads?Measure all single phase loads and try to make them equal across all 3 phases.K.I.S.S.