Strange Amperage readings

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cbasye

Member
I am experiencing a strange problem with some new 350 MCM cables that are being used as a temporary source of power at a remediation site. The power source is 2000 kW, variable voltage 110 to 800, 3 phase, no ground (delta) transformer bank. The cables are the same length, copper construction. They are triple runs per phase, and each triple run feeds a copper bus-bar in the field, where loads are connected. The cables from each phase cross cables from other phases, run parallel to each other, run parallel to opposite phases, etc. as they are run to the field, and they are run across the open ground. The total length is about 240 feet. 2/0 cables feed loads from the field busbars.


Baseline Condition: 3, 350 MCM into box, 2, 2/0 out of box. Currents:

Y9 = 115 amps C2 = 175 amps

Y9A = 508 amps D1 = 155 amps

Y10 = 637 amps



Change 1: Remove all 2/0 from box. Therefore 3, 350 MCM into box, 0, 2/0 out of box. Currents:

Y9 = 200 amps

Y9A = 470 amps

Y10 = 570 amps

Change 2: Remove 1, 350 cable. Therefore, 2, 350 MCM into box, 0, 2/0 out of box. Currents:

Y9 = 214 amps

Y9A = 217 amps

Change 3: Install 2 2/0 loads. Therefore, 2, 350 MCM into box, 2, 2/0 out of box. Currents:

Y9 = 216 amps C2 = 166 amps

Y9A = 306 amps D1 = 146 amps

Change 4: Install 2 more 2/0 loads. Therefore, 2 350 MCM into box, 4, 2/0 out of box. Currents:

Y9 = 309 amps C2 = 160 amps

Y9A = 434 amps D1 = 139 amps

G4 = 131 amps

E3 = 195 amps

So why do we have a total 1240 amps measured on the 350 MCMs with no loads hooked up to them? Why, in change 2, are the amperage readings just about equal, (214 amps) when there is supposedly no load on them? Can an inductive load be imposed on cables of the opposite phase under heavy resistive load, when in close proximity to each other. How about on cables of the same phase? How about under no-load conditions?
 
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ronaldrc

Senior Member
Location
Tennessee
Re: Strange Amperage readings

Wish I could help. But I don't have a clue.

Beam me up Scottie I can't afford these light bills

spacecraft.gif
 
bob

bob

Senior Member
Location
Alabama
Re: Strange Amperage readings

Your question is too confusing. Reference your amp reading to phase A, B & C. We do not know what the Y refers to.
 
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cbasye

Member
Re: Strange Amperage readings

As explanation for the phase designation, I had designated the field feeders to be X, Y, and Z, so that I could then designate the field loads to be A, B, C, and D. So Y9 or Y10 is phase Y, spade #9 or 10 on the transformer output. The amps are measured with a Fluke ammeter, at the transformer output. It is assumed that the measurements would be the same at the field boxes, but they were not read at that point. That might be a place to start.

The real question I am wondering about is if parallel runs of the same phase under heavy load in close proximity to each other can cause a significant power loss.

The next question is whether parallel runs of DIFFERENT phases under the same conditions can cause a power loss. I am trying to decide my cable routing in the future, in trying to alleviate this problem at other sites.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Re: Strange Amperage readings

When you bundle parallel cables, you should have one full set of conductors in each bundle. A,B,C,N, and ground. Routing will not cause the problems that you are seeing. Most Fluke meters are autoranging. Are you sure that you are reading amps and not milli or micro amps, when the load is disconnected?
Don
 
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cbasye

Member
Re: Strange Amperage readings

Good thought regarding autoranging. I will check it out with the site operator.
 
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