Harmonic Effects

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ta2drchr

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Location
Overland Park, KS, USA
I have recently installed a single phase 100A service at a bus stop for a real time sign that includes lighting. Inside the sign there is a modem, PC board, thermostatic sensor and LED sign board. Attached to the same circuit, 20A single phase, are 6 T-8 fluorescent bulbs. I am concerned that the ballast, electronic, and its harmonic effects, will shorten the life span of the sensitive electronics inside. Are the effects of harmonic nonlinear loads alot of hullabaloo, or am I right to be concerned?
 
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jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
ta2drchr said:
I have recently installed a single phase 100A service at a bus stop for a real time sign that includes lighting. Inside the sign there is a modem, PC board, thermostatic sensor and LED sign board. Attached to the same circuit, 20A single phase, are 6 T-8 fluorescent bulbs. I am concerned that the ballast, electronic, and its harmonic effects, will shorten the life span of the sensitive electronics inside. Are the effects of harmonic nonlinear loads alot of hullabaloo, or am I right to be concerned?
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The harmonics generated by the modem, PC, and LED screen are just as likely to shorten the life of the electronic ballasts.
 
Besoeker

Besoeker

Senior Member
Location
UK
ta2drchr said:
I have recently installed a single phase 100A service at a bus stop for a real time sign that includes lighting. Inside the sign there is a modem, PC board, thermostatic sensor and LED sign board. Attached to the same circuit, 20A single phase, are 6 T-8 fluorescent bulbs. I am concerned that the ballast, electronic, and its harmonic effects, will shorten the life span of the sensitive electronics inside. Are the effects of harmonic nonlinear loads alot of hullabaloo, or am I right to be concerned?
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Not hullabaloo.
However, the electronic controls most likely operate from DC transformed down from the AC and rectified or have a switch mode power supply. In either case, the electronics is isolated from the supply so I wouldn't be greatly concerned - unless zero crossover detection is used and then there might be a possibility of malfunctioning. Some of our lighting guys haven't quite sussed that out yet.....:roll:

And I'm inclined to disagree with iwire and Jim over the concern about the electronic ballasts. It's not my area of expertise but from the circuits I've seen on the wibbly wobbly web, the circuitry is similar to the ballasts for CFLs.
Essentially a rectifier followed by an oscillator. I don't think it would be troubled by a less than pristine sine wave supply.
 
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jim dungar

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Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
ta2drchr said:
Is there research I can reference with the county Administrators?
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Not really as it is pretty much a non-issue. About the only people that talk about it are the people that want to sell you something to correct a perceived problem.

The office I am in has 14 PC (power supplies + monitors), 35 troffers with electronic ballasts, a computer server and router fed by a UPS, a large screen LED display, two wireless hubs, and a phone system. We have no concerns about the power quality, but then we are just engineers and not people with a product to sell.
 
Besoeker

Besoeker

Senior Member
Location
UK
jim dungar said:
Not really as it is pretty much a non-issue. About the only people that talk about it are the people that want to sell you something to correct a perceived problem.
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It's rather more than a perceived problem and one I've had to quite often address in real life.
 
kwired

kwired

Electron manager
Location
NE Nebraska
OP also says it is a single phase service, not as serious harmonic effects in the neutral here as there is in a three phase wye with harmonic producing loads. If it were a problem then the main solution is larger neutral conductor, but I don't think there is much issue with the particular loads mentioned coexisting on same system together.
 
Besoeker

Besoeker

Senior Member
Location
UK
iwire said:
That seems to be about overcurrent on a neutral, not PCs damaged from other items such as electronic ballasted lighting.
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My comment was in response from Jim D.
About the only people that talk about it (harmonics I assumed) are the people that want to sell you something to correct a perceived problem.
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For the installation jumper linked to, the over current in the neutral was caused by harmonics, particularly the third which adds arithmetically in the neutral of a three phase system.

I've seen lots of capacitor failures as a result harmonics.

Another problem I came across was in a paper mill that had a lot of DC variable speed drives. The harmonic voltage was dreadful - about 15% mostly as a result of the dozens of six-pulse drives. We had the project of upgrading the electronics on a suite of them. We took out the old analogue firing circuits and replaced them with digital units. There was a problem that took a little while to diagnose and rectify. The new firing circuits used a zero-crossover to time the conduction angle. The rather messy waveform confused the timing and resulted in the SCRs firing at the wrong time - big lumps of current.

Just a few examples.

When we tender for a drives project we are usually expected to submit harmonic calculations together with any mitigating measures we think will be required at the bid stage.
 
Besoeker

Besoeker

Senior Member
Location
UK
iwire said:
And it seems none of your examples are of anything at all like the OP and Jim were talking about.
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From the OP:
Are the effects of harmonic nonlinear loads alot of hullabaloo, or am I right to be concerned?
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I think I demonstrated the effects of harmonic non-linear loads isn't hullabaloo.
And I gave a real life example of where harmonics adversely affected electronic circuits.
I would have thought this was pertinent to the question posed.

If you don't, that's fine.
 
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