Over Voltage on LV Side

The widely varying current measurements suggest that indeed the loads are unequally balanced, or possibly there is a ground fault on the yellow phase.

Would the equipment operate on 207V? If so, swap it over to the yellow phase.

Replace the client-side paper.insulated cable. Moisture can cause a phase to ground leakage that could give you these results, and would be indicative that more severe problems could be in the offing (like fire or electrocution of an unwary worker). If this does not resolve the issue, measure the current draw on each phase to determine if there is significant difference between phases. If the low voltage phase does not evidence significantly higher current than the other two phases, it is most likely a supply side problem, and these measurements should be sufficient documentation to get the power company to address the problem.

Your customer have a power factor problem-

I understand the most of load are mono-phase

as consultant we maybe help you with more system details .

Joshua Gabriel SAADA

Engineer consultant.

Alternative Power Systems
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A ground fault seems to be one of the likely explanations. However, severely unbalanced loads would also cause these symptoms. So I stand by that part of my answer.

Your method of switching off various loads in order to find the problem is right on target. GA for that part.

In the OP's locale, it appears that electrical practices are not up to date. Therefore, there may not even be any ground fault detection or interruption.

Welcome to CR4. There is lots of good info here, and many interesting discussions (along with a few weird ones).

Well I agree with Tornado,

We once had the same problem at my university were by the university technician had conected all the 4 big hostels on the Red phase , the kitchen on the Blue phase and the Admin on the Yellow,Initially the russian design had to be that all the loads are evenly distributed among the three phases, Problem came when the demand in the hostel and kitchen was high at all times, this lead to a very big voltage drop on red and Blue and a suprising voltage increase on the Yellow phase were by equips were blowing out. The Utility company was called and they had to inspect their transformer and they thought of changing the tap position but everything seemed to be fine not till they told the university technician to balance the loads on all phases. This cleared the problem. So you should balance the loads.

if you have access to the transformer (star) there should be a NER (neutral earthing resistor (67.5 ohm i think) measure the current and voltage - it will give you an idea of the earth fault and if it exists.

personally i think you must ballance your loads (later stadge)

trip all your load and check under no load (0 current) what happens.

to confirm that it is the tx or supply you can isolate tx - disconect feeder cable - power up - measure tx (feeder side where cable use to be), if still unbalance, it coul only be supply.

if not replace paper lead cable when all is of and fault still there

There is a fault or cable interruption somewhere along the circuit.

Disconnect the trasnsformer first at the primary side from your load,check cables and test the output phases red/netral,yellow/neutral and blue/neutral to find out if the problem is from the transformer or not.If u get normal single phase voltages with equal value in all the three cables and to neutral,then the transformer and utility supply is out of suspicion.Switch off power.

Go ahead to test your load cables step by step by putting off all load breakers from mains panel,test for continuity and makesure all live to live and live to neutral cables are free with normal continuity test resistance value.

Further continue the test by switching on the breakers as well as manually pressing in contactors,for loads using contactors(no voltage test) and test for good continuity for each circiut and sub-circuit.You may also use load test with power.let all load be in off position(ie if u have normal voltage at the trasformer to the main panel),put on a load at a time,check or test all three cables to neutral,if ok,put off that load and put on another load and test or check your voltage,continue this method untill u get to where the problem is(ie where the three phase and neutral voltages are not same)

By the time you exhaust the tests,u might find the problem and then clear it properly.

Patrick Whowha

Rgards.

When you say on LV side it will be considerred that the Primay supply is well balanced.

Have tested it?

In AC current measurements are not that simple when you need a precision measurements. For coparison purposes any conventional Meter will suffice.

But for this case you have to ensure some more points in consideration:

1. Ensure Ballanced load on all phases that is Resistive load, but some variations may be there & you have to keep those in mind.

2. In my view if you use a singleload one one by one, it will better for comparison.

Check for an earth fault. There will be no earth fault equipment "recognised as an MCB with a test button" fitted at your users premises, or any other private User in Kenya unless the User has contracted an electrician to install one at his own expense.

Is the User's Distribution Board earthed at all? Check the integrity of the earth.

Ceck the voltage in the morning, during the day and in the evening for fluctuations, and then present the Utility Company with this record.

A common trick used by the Utility Company Electricians is to select higher output voltages on the tranformer in a vain attempt to squeeze a bit more amperage out of the transformer, and then as the transformer is being overloaded the voltage drop becomes more acceptable. Catch is the transformer is not always overloadloaded. This practice has flourished since the Utility companies are short on funds to upgrade older system to meet growing demand

It is possible to claim for voltage fluctuations

Dear all,

It seems like the neutral is disconnected between transformer and your client, that's why, higher current (yellow) has less current and vise versa.

Regards

I would like you to look for ground faults:

If you have a long grounded cable or even a spool of insulated wire; take one end outdoors a least 15 meters away from all man-made structures: underground pipes, utility poles, towers, buildings, etc. Stake this end in damp soil (you can just strip the insulation, weight it with soil and pour water on the soil) and measure the voltage difference from the other end. (A high impedance voltmeter should work better with dry soil.)

Take precautions not to get a shock. (Don't touch both reference and equipment.)

Measure the voltage between the reference wire/cable and equipment ground. Use a portable voltmeter. Note that equipment ground is really the neutral voltage of the utility company equipment!

You can test structures like the grounding electrode wire at the transformer, the service entrance, branch circuits, neutral, other grounding electrodes, etc.

You should also measure these voltages with the main breaker off.

If any voltage is abnormal, we would like to know. I would worry most about differences you find.