Harmonics

[ellisd4]

I am not sure if you can provide any technical assistance on a situation we are dealing with that involves a parking garage that has a 3 phase 277V lighting panel of which the total load is HID lighting (metal halide). The 45kva transformer, 480 delta to 480/277Y which feeds this load center was less than two years old when it failed. Upon replacing it and testing the currents we were stunned to find that the neutral current on the secondary was equal to the highest phase, C-phase, around 44 amps. Placing a fluke analyzer on this transformer secondary revealed that the THD on each phase was above 40% and the THD on the neutral was a whopping 90%. At one point the coil temperature of the C-phase was a staggering 420 degrees. Can HID lighting cause this problem and are there any remedies besides just installing a K rated transformer.

Any advice would be appreciated

 

[don_resqcapt19]

Re: Harmonics

Yes, HID ballasts are nonlinerar loads and can cause this type of problem. You can use a K-rated transformer or try a product like this .
If the other transformer coils are not running as hot as the C phase one there may be other problems.
Don

 

[karl riley]

Re: Harmonics

And run an oversized neutral or one neutral per phase.
Karl