# why does my Generator Controller stop measuring current with large number of single phase loads

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#### Darren

I have a camp supplied with 4x 500 kVA generators. Supplying mostly single phase loads, lights, aircon tv's washing machines, dryers. There is also a kitchen that has several 3 phase loads.

During the day on low load, around 70 amps p/phase generator the unit controllers report the current correctly. When the workers return to camp around 530 and switch on the aircons, tvs, etc. The load requires, at 200amps p/phase (from fluke).

The problem is at around 530 the reported current starts dropping to zero. Without the current the generators cannot load share.

The layout is, each generator has a 4 pole syncro breaker on to a main bus. Each generator is connected to earth at the star point and there is an addition MEN on the bus. This earth is wired via PE cable back to the frame of each generator and the star point. The controllers measure current in each phase via CTs ( 3 phases not neutral) the control is wired directly to the S1 terminal of each CT and common return to the controller. The common return is earthed.
I have measure current returning on the PE cable from the( main bus to the generator) it is in the order of 15 amps for each generator. When the neutral is reading 50 amps.

I am wondering if the earth current or the single phase loads could somehow be cancelling out the current summation going to the controllers. As I said earlier low loads it fine, but on high loads, zero current is report. On occasion at high loads one or two phase would report roughly 1/5 of the load.
Has anyone experienced this before

ps the CT and Controllers are rated at 1000/5

#### PhilCorso

Darren... please provide a tabulation of current and voltage measurements, during light and heavy load conditions, for Gen-Set, as follows:

1) Currents: Ia, Ib, Ic, In, and Ipe!

2) Voltage: Vab, Vbc, Vca, Va-n, Vb-n, Vc-n, Va-pe, Vb-pe, Vc-pe, and Vn-pe

Regards, Phil Corso

#### PhilCorso

Darren... further to my earlier response; at hi-load when the Current "displays" indicated zero:

3) were there any indications that any of the gen-sets were in distress?

4) were you able to confirm, via a Clamp-on ammeter, that the currents were, indeed, zero?

Phil

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#### Darren

1) Ia 317, Ib 307, Ic 325, In 50, and Ipe 15!

2) Vab 400, Vbc 399, Vca 400, Va-n 230.8, Vb-n 231.8, Vc-n 230.7, Va-pe 230.8, Vb-pe 231.8, Vc-pe 230.7, and Vn-pe 0.1

3) No indication of distress, the generators were not fully loaded.

4) Yes I was able to confirm I had a Fluke power analyzer on the out cables to the bus and I also placed a clamp meter on the CT cables to the controller. Using the CT ratio the two current measurements were in agreement

#### PhilCorso

Darren… presuming the 3 ph-ph voltages are those at the bus to which the generators are all connected, as well as the Ph-N and Ph-Pe, then the Voltage-Unbalance-Factors, VUF, are less than 0.2%! Additionally, the Ampere-Unbalance-factor, AUF, for the three line-currents you cited, is about 3%.

Thus far, it can be said that voltage-unbalance is not the problem. And, the AUF is certainly acceptable considering the large number of single-phase loads. Even the presence of current in the neutral (about 16% of average) is expected)! But, what is of concern is the presence of current in the Pe conductor! This is indicative of an inadvertent connection of a single-phase load being connected to PE instead of the neutral-bus! Continuing the quest for info following are additional questions:

5) The three line-currents is puzzling; are they for one generator or the total of all five?

6) Does each set of CTs have 4-wires connected to its respective controller, i.e., 3-Ph wires and a common?

7) Is the common-wire grounded at one location; the CT, or the controller?

8) Do you have the luxury of sectionalizing and de-energizing parts of the system so that the Neutral and Pe connections can be separated?

Phil

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#### Darren

> 5) The three line-currents is puzzling; are they for one generator or the total of all five?

yes they are for a single generator feeding to a bus. But all generators where showing the around the same current when I measured this

> 6) Does each set of CTs have 4-wires connected to its respective controller, i.e., 3-Ph wires and a common?

yes

> 7) Is the common-wire grounded at one location; the CT, or the controller?

only once at the CT

> 8) Do you have the luxury of sectionalizing and de-energizing parts of the system so that the Neutral and Pe connections can be separated?

As there is an MEN link in the main bus and the star point of the generators is earthed. I believe there may be current division between the neutral and PE cable back to the star point. I am thinking of removing the MEN link in the mainbus as this is an island power station and one generator is always connected to the bus when it is energised. Providing a solid bonded earth neutral at the starpoint

#### PhilCorso

Darren... If you send me a simple SLD (Single-Line-Diagram) or even a hand-drawn sketch, I may be able to provide additional trouble-shooting ideas!

Phil ([email protected])