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[Guy Holt]

This is one of those things that seems like it would be useful, but really isn't. Even if you see something...What do you plan to do about it? ... a power quality analyzer... is very big $$$$ and still doesn't really give you any more actionable information than the CT-70, unless you are prepared to work on the building's HVAC, lighting, and power systems.

What scope meters can tell you is the nature of the power quality issue, and from there you can figure out whether there is something you can do about.  Most of the time there isn’t, but sometimes there is.  For example, if you are running 3-phase from a small tow plant that you are sharing with a large LED lighting rig and the scope shows a flat-topped voltage waveform, it is a good indication that the LEDs are not power factor corrected (design flaw) and are drawing harmonics.  Non-pfc LEDs draw current only at the peak of the voltage waveform and so cause voltage drop only at the peak causing a flat-topped voltage.  Most scope meters will also do Fast Fourier Transformations (FFTs), which you can use to confirm your suspicions by metering the neutral return current.  If the scope shows mostly triplens returning on the neutral than you know that is your problem. 

Now that you know the problem, you can do something about it.  To eliminate voltage flat-topping and elevated triplen current on the neutral of 3-phase systems, you can use a Harmonic Mitigating Transformers (HMT) just downstream of the generator plant. HMTs are specifically designed to minimize the high neutral returns, voltage distortion, and power losses that result from the harmonics generated by non-linear loads like the electronic power supplies of LEDs (as well as Triac/SCR Dimmers.) By means of a zig-zag secondary winding and phase shifting, a HMT can accomplish substantial improvement in power quality by:

Off-loading of the 3rd, 9th, and 15th harmonic currents from the neutral back to the load.

Cancellation of the 5th and 7th harmonic currents as a result of the 30 degree phase shift between its’ outputs.

3rd harmonic voltage reduction by low zero-sequence impedance.[/li][/list]

The net effect will be a substantial reduction in the voltage waveform distortion, as well as a reduction in the amount of current drawn by the LEDs, a balancing of the load over the three phases, and an isolation of the generator stator from the heating effect of triplen harmonics.

To become familiar with the causes of voltage flat-topping you can read through my previous posts as Tim McCulloch suggests or you can read a series of articles on the subject I wrote for Protocol magazine (available at http://www.screenlightandgrip.com/html/hd_plug-n-play_pkg.html.)  I am in the process of writing an article for Protocol on the use of HMTs to remediate the power quality issues caused by LEDs, so look for that in the pages of Protocol this fall.

Guy Holt, Gaffer
ScreenLight & Grip

[Kevin Conlon]

What scope meters can tell you is the nature of the power quality issue, and from there you can figure out whether there is something you can do about.  Most of the time there isn’t, but sometimes there is.  For example, if you are running 3-phase from a small tow plant that you are sharing with a large LED lighting rig and the scope shows a flat-topped voltage waveform, it is a good indication that the LEDs are not power factor corrected (design flaw) and are drawing harmonics.  Non-pfc LEDs draw current only at the peak of the voltage waveform and so cause voltage drop only at the peak causing a flat-topped voltage.  Most scope meters will also do Fast Fourier Transformations (FFTs), which you can use to confirm your suspicions by metering the neutral return current.  If the scope shows mostly triplens returning on the neutral than you know that is your problem. 

Now that you know the problem, you can do something about it.  To eliminate voltage flat-topping and elevated triplen current on the neutral of 3-phase systems, you can use a Harmonic Mitigating Transformers (HMT) just downstream of the generator plant. HMTs are specifically designed to minimize the high neutral returns, voltage distortion, and power losses that result from the harmonics generated by non-linear loads like the electronic power supplies of LEDs (as well as Triac/SCR Dimmers.) By means of a zig-zag secondary winding and phase shifting, a HMT can accomplish substantial improvement in power quality by:

Off-loading of the 3rd, 9th, and 15th harmonic currents from the neutral back to the load.

Cancellation of the 5th and 7th harmonic currents as a result of the 30 degree phase shift between its’ outputs.

3rd harmonic voltage reduction by low zero-sequence impedance.[/li][/list]

The net effect will be a substantial reduction in the voltage waveform distortion, as well as a reduction in the amount of current drawn by the LEDs, a balancing of the load over the three phases, and an isolation of the generator stator from the heating effect of triplen harmonics.

To become familiar with the causes of voltage flat-topping you can read through my previous posts as Tim McCulloch suggests or you can read a series of articles on the subject I wrote for Protocol magazine (available at http://www.screenlightandgrip.com/html/hd_plug-n-play_pkg.html.)  I am in the process of writing an article for Protocol on the use of HMTs to remediate the power quality issues caused by LEDs, so look for that in the pages of Protocol this fall.

Guy Holt, Gaffer
ScreenLight & Grip

Thank you Guy. I did go back to your posts. Also thanks to all for the info. I have to use what power is around, as do most of us lower level, under funded people. You have all given me more info than i knew existed on the subject. I have three years of EE school and do not ever remember clean AC ever being lectured about. Most likely because we can't fix it. I have meters in my distro, only volts mains in and the two legs have amp meters also. I have never used three phase at this point. Did not intend to bump this post but have had little time to keep up. This should end here as the post reference earlier had all the answers. Thank you all for your time.     Kevin.

[Tim Padrick]

At work I have an Owon SDS6062 (I think that's the one).  It can be battery powered, and it as an FFT function.  I've never used it to look at the mains.

[TJ (Tom) Cornish]

What scope meters can tell you is the nature of the power quality issue, and from there you can figure out whether there is something you can do about.  Most of the time there isn’t, but sometimes there is.  For example, if you are running 3-phase from a small tow plant that you are sharing with a large LED lighting rig and the scope shows a flat-topped voltage waveform, it is a good indication that the LEDs are not power factor corrected (design flaw) and are drawing harmonics.  Non-pfc LEDs draw current only at the peak of the voltage waveform and so cause voltage drop only at the peak causing a flat-topped voltage.  Most scope meters will also do Fast Fourier Transformations (FFTs), which you can use to confirm your suspicions by metering the neutral return current.  If the scope shows mostly triplens returning on the neutral than you know that is your problem. 

Now that you know the problem, you can do something about it.  To eliminate voltage flat-topping and elevated triplen current on the neutral of 3-phase systems, you can use a Harmonic Mitigating Transformers (HMT) just downstream of the generator plant. HMTs are specifically designed to minimize the high neutral returns, voltage distortion, and power losses that result from the harmonics generated by non-linear loads like the electronic power supplies of LEDs (as well as Triac/SCR Dimmers.)

An even simpler way to reduce neutral harmonics and neutral current is to not use the neutral at all.  The vast majority of production equipment (incandescent lamps and stage power excepted) can run on 208/240v power with only a plug change, and maybe not even that if distribution is Powercon-based.

I'm sure there are situations where you can arrive at a show, discover an issue (I would think most distro current meters would include harmonics in their current measurement so I don't know how much a scope meter really adds other than a visual confirmation), order an HMT, wait for delivery, shut down, insert the HMT (how much does this thing weigh anyway?), and carry on in time for the show, but I haven't yet been a part of one.  In my experience this needs to be engineered out beforehand - make the lighting vendor use their own generator, over-engineer the generator to have extra capacity (almost certainly needed anyway for the dynamic component of the load - power amps, lighting rig bumps, etc.), and/or move as much to 208/240v distribution as possible when designing the system in the first place.

I think transformers can serve a purpose, but I think their usage is the right solution in a relatively small number of cases - your HMI lights on a Honda EU, for example.

[Stephen Swaffer]

I am curious how much "bad" or "dirty" power really affects most modern electronics?  I'm not as well versed as some guys on here, but I have tinkered with electronics at the component level since I was a teen- and then a lot of what I had access to was my dad's tube gear. To make a very broad observation, it seems like todays switch mode power supplies provide a much greater degree of seperation from main's noise/distortion than those of years ago.

It seems ironic, we worry about distortion and noise when we plug in electronics, but don't give a second thought when we hook up a motor-yet from what I understand, it seems like motors are probably the most critical.   The physical characteristics of a genny create the sine wave, and a pure sine wave is the most efficient way to drive the armature of a motor- any noise or distortion results in extra inefficiencies and heat- and heat is what kills most motors.

I realize noise spikes are hard on power supply components- and eventually cause insulation breakdown.  But is distortion really a big deal for the electronic load?  Harmonics cause issues with distribution and neutral overloads- so they need to be controlled-same with power factor.

[TJ (Tom) Cornish]

I am curious how much "bad" or "dirty" power really affects most modern electronics?  I'm not as well versed as some guys on here, but I have tinkered with electronics at the component level since I was a teen- and then a lot of what I had access to was my dad's tube gear. To make a very broad observation, it seems like todays switch mode power supplies provide a much greater degree of seperation from main's noise/distortion than those of years ago.

It seems ironic, we worry about distortion and noise when we plug in electronics, but don't give a second thought when we hook up a motor-yet from what I understand, it seems like motors are probably the most critical.   The physical characteristics of a genny create the sine wave, and a pure sine wave is the most efficient way to drive the armature of a motor- any noise or distortion results in extra inefficiencies and heat- and heat is what kills most motors.

I realize noise spikes are hard on power supply components- and eventually cause insulation breakdown.  But is distortion really a big deal for the electronic load?  Harmonics cause issues with distribution and neutral overloads- so they need to be controlled-same with power factor.

Switching power supplies can tolerate quite a bit of garbage. There are people who run LEDs and movers from dimmed power (chopped waveform) out of convenience and it apparently works (setting the channel to 100% output), but you won't find me doing that.

The application Guy has written a lot about relates to getting a large light used for film to fit on a Honda EU7000 generator.  In this scenario, the capacity lost to neutral harmonics is the issue, not gear damage.

In the audio world, noise on the ground is a far more significant problem than noise on the current-carrying wires.  Fortunately this can usually be remedied by bonding the grounds of all of the circuits used for audio together, as it's ground noise between circuits that's the main problem.

The only gear damage stories I've heard of resulted from more significant issues - a loose neutral wire, miswired receptacle (H/G reversal, or wrong voltage on the plug), or lightning.

[Phil Graham]

An even simpler way to reduce neutral harmonics and neutral current is to not use the neutral at all.  The vast majority of production equipment (incandescent lamps and stage power excepted) can run on 208/240v power with only a plug change, and maybe not even that if distribution is Powercon-based.

Yes. And in many industrial environments they simply dispense of the neutral's substantial expense in wire, conduit, and potential de-rating. Round robin single phase drops of XY, YZ, and XZ are common in environments with delta-configured primary power.

In my experience this needs to be engineered out beforehand - make the lighting vendor use their own generator, over-engineer the generator to have extra capacity (almost certainly needed anyway for the dynamic component of the load - power amps, lighting rig bumps, etc.), and/or move as much to 208/240v distribution as possible when designing the system in the first place.

Right. Provide a series of SDS and bond them to an appropriate GEC/GE field. If the SDS are transformers, make sure they have a K-rating appropriate for the nature of the attached equipment.

[Phil Graham]

I am curious how much "bad" or "dirty" power really affects most modern electronics?  I'm not as well versed as some guys on here, but I have tinkered with electronics at the component level since I was a teen- and then a lot of what I had access to was my dad's tube gear. To make a very broad observation, it seems like todays switch mode power supplies provide a much greater degree of seperation from main's noise/distortion than those of years ago.

Modern SMPS, which will have something like a full bridge rectifier, some PFC, and then a half-bridge LLC resonant converter, are pretty immune to the upstream power source at the input voltages common in pro audio.

This can be a different story in the light industrial world, where single phase 480Vrms is common. Here the rectified voltage + a transient can get into the range that exceeds the voltage breakdown ratings of the pair of switching FETs that driver the resonant converter.

The physical characteristics of a genny create the sine wave, and a pure sine wave is the most efficient way to drive the armature of a motor- any noise or distortion results in extra inefficiencies and heat- and heat is what kills most motors.

Motors are generally pretty beefy, and come with their own internal chunk of inductive smoothing. E.g. H-bridge motor drivers for brushed DC motors routinely use hard switching PWM for speed control.

[Stephen Swaffer]

Modern SMPS, which will have something like a full bridge rectifier, some PFC, and then a half-bridge LLC resonant converter, are pretty immune to the upstream power source at the input voltages common in pro audio.

This can be a different story in the light industrial world, where single phase 480Vrms is common. Here the rectified voltage + a transient can get into the range that exceeds the voltage breakdown ratings of the pair of switching FETs that driver the resonant converter.

Motors are generally pretty beefy, and come with their own internal chunk of inductive smoothing. E.g. H-bridge motor drivers for brushed DC motors routinely use hard switching PWM for speed control.

I agree with the 480 volt transients-at a previous job we had inverters that would trip out on overvoltage if they were left connected to line voltage over the weekend while not running.  The POCO voltage would creep up a bit ( we are in a rural part of Iowa quite aways from power plants) then add the transients and the internal caps would charge to the point where the DC bus voltage was too high.

Most motors being used by audio/ lighting guys probably are oversized.   When you get to an application like I work with, with 100 HP motors running in 110+ deg F ambient temps, then any extra heat begin's to be a problem.  This where the industry is focused ( from what I can see ) and why you hear about power quality so much.

Other than for wire sizing in a distro, I think the primary concern for most audio work needs to be making sure the voltage is correct- both at the genny AND at the end of how ever many 100's of feet of extension cord you decide to plug in.   

[Phil Graham]

Most motors being used by audio/ lighting guys probably are oversized.   When you get to an application like I work with, with 100 HP motors running in 110+ deg F ambient temps, then any extra heat begin's to be a problem.  This where the industry is focused ( from what I can see ) and why you hear about power quality so much.

Big motors, and/or motors that aren't inherently self commutating are of course a totally different animal than stuff you drive with a little H bridge :-)

Obligatory large motor driver link:
http://new.abb.com/drives/low-voltage-ac/industrial-drives/industrial-acs800-series/acs800-multidrives

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