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Harmonic Issue between HID Fixtures and Gens

Harmonic Issue between HID Fixtures and Gens

Harmonic Issue between HID Fixtures and Gens

(OP)
I have and issue with operating approximately 530 HID fixtures in a Parking Garage on generator.  Under normal  condtions running on Utility the load of the 277 volt HID fixtures is as follows:

A Phase : 122 Amps
B Phase : 133 Amps
C Phase : 120 Amps
Neutral :    115 Amps - The ballasts produce a lot of 3rd Harmonics.

The generating system in the building is comprised of 3-Paralleled 2MW-3516 Cats with SR4B Generators (0.7947 Pitch), 277/480V,1800 RPM.

When the Parking Garage HID lighting fixtures are operated on generator with 3 gens running the load is as follows:

A Phase : 128 Amps
B Phase : 139 Amps
C Phase : 122 Amps
Neutral : 118 Amps

When the Parking Garage HID lighting fixtures are operated on generator with 2 gens running the load is as follows:

A Phase : 132 Amps
B Phase : 143 Amps
C Phase : 122 Amps
Neutral : 134 Amps

When the Parking Garage HID lighting fixtures are operated on generator with 1 gen running the load is as follows:

A Phase : 137 Amps
B Phase : 154 Amps
C Phase : 126 Amps
Neutral : 201 Amps

The phase voltages are well within tolerances under all above conditions.  The phase currents vary somewhat on generator, but the neutral current doubles and sometime triples under certain conditions (whole building running on generator).

The readings from above are from tests with just operating the Parking Garage on generators.  When the whole building is operated on generator the neutral current in the parking garage doubles when operating 3 gens and triples when operating on 2 gens.  2 gens is the minimum to support the entire building's load at this time.

The Ballasts in the lighting fixtures are Advance HX-HPF, Cat. No. 71A5492 for 150W Metal Halide Lamp.

This appears to be a harmonic issue with respect to the parking garage HID lighting fixtures and the generators.  If you have any ideas, your input would be greatly appreciated.

Thanks,

RE: Harmonic Issue between HID Fixtures and Gens

Where are you measuring the neutral current in each case?  

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

RE: Harmonic Issue between HID Fixtures and Gens

(OP)
At the panel in the parking garage feeding the lighting fixtures.

RE: Harmonic Issue between HID Fixtures and Gens

When more generators are added the impedance of the neutral current path is lower and the neutral current increases.
With one generator running the neutral impedance is 1 X.
With three generators running the neutral impedance is 1/3 X
The harmonic voltages do not change, but when the impedance of the path of the harmonics is lowered the current increases proportionally.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Harmonic Issue between HID Fixtures and Gens

I would wonder if there were multiple paths for the neutral current in the cases with multiple generators running and you might not be capturing all the current.  I would also check the generator neutral grounding of each machine very carefully.  

A power quality meter or scope could give you a breakdown of the neutral current waveform.  

You're making these measurements with a clamp-on current probe?  These can give erroneous readings if the jaws don't mate up completely or there is a little schmutz on the steel surfaces.  

Are there any actual problems or complaints other than the high neutral current?  



 

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

RE: Harmonic Issue between HID Fixtures and Gens

(OP)
This is working opposite to what you are stating, the neutral current is increasing as generators go off line.

RE: Harmonic Issue between HID Fixtures and Gens

(OP)
DPC,
I'm using an RPM meter to record and capture the waveforms. The generators are not bounded as they are in close proximity of the utility network switchboard which is bonded.  The utility service consists of 6-1000 KVA transformers networked together.  The neutral current consists of most the 3rd harmonic.

RE: Harmonic Issue between HID Fixtures and Gens

It appears that the line currents are higher for the single generator case than two, three, or utility power. HID (and other ballasted lamps) tend to be constant power devices. So, as the voltage drops (higher source Z), the currents go up. Not only the fundamental (60Hz) component, but the harmonics. If the ballasts are not electronic with power factor correction, this effect will be greater.

Take a 'scope or analyzer that allows you to observe both the current and voltage waveforms. I'll bet that the voltage waveform is being 'flat-topped' due to the non-linear nature of the ballast loads and that this is worse when the source impedance is higher.

You might have to install some harmonic filtering on the lighting panel. Or refit with better (electronic, p.f. corrected) ballasts. Given the labor to install 530 ballasts, the filter is probably the way to go.  

RE: Harmonic Issue between HID Fixtures and Gens

So the generator neutrals are run to the switchboard neutral bus and not grounded locally at the generator?  

Any changes to the loads other than these lighting fixtures when you ran your tests?

It appears that the network with one generator on is presenting a lower impedance to the triplen current, but it's clear to me why this would be.  

Do you get similar results regardless of which one of the three generators is on?     

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

RE: Harmonic Issue between HID Fixtures and Gens

I tend to agree with PHovnanian as to the likely cause.

Dave - did you lose the word 'not' from your third sentence?
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Harmonic Issue between HID Fixtures and Gens

A "softer source" will generally increase the harmonic currents.We have had many cap banks blow and breakers trip when the source is switched from utility to geny.There is a parallel connected transformer device called a neutral current eliminator that you may wish to google.This will remove the harmonics from the neutral.

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