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Working with non-PFC ( power factor correction ) ballasts


Bradley Mowell
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I have four Arri 6/12 electronic ballasts that are non-PFC ( power factor correction ) that operate at 190-250v. Each ballast has a green ground, black hot, and red hot. 

I’ve read that non-PFC ballasts return a lot of excess current on the neutral wire because of low power factor (these are rated at 0.7 PF) but how does that apply to ballasts that operate at 190-250v that have no neutral wire? I’m using 240v location power rather than a generator, so how/where does the excess current from a non-PFC ballast return on a neutral wire in the distribution system?  I’m assuming all current is “cancelled out” at 240v between the black hot and red hot. But if, somehow, there IS still excess current, where does it go?

 

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1 hour ago, Ed Conley said:

I believe that is a PFC ballast though.

 

I wish it was, Ed. Unfortunately, the plate shows 0,7…and emails with Arri confirm it’s non-PFC (no active line filtering). Unless I’ve misinterpreted what I’ve been told, which is entirely possible. 
 

BTW, thanks a bunch for the advice about a year ago. Worked like a charm, sir. 

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Interesting. The Harry Box tech handbook states that all 12k and above are now PFC but this is  Fourth Edition 2013 Edition.

How old is the ballast?

anyhoo-
the  "excess" power returning on the neutral matters because in a normal load if all phases are balanced then there should be no load on the neutral but w/o PFC things get weird and the neutral will see excess load and you need to factor in this extra load when sizing the cables and the generator.

It still maters when using house power too.

On 240v the excess power still exists.

With a .7 PF 30% of the current does not cancel out.

You'll notice on the spec sheet
12,000 watts
Line Power 18,000 VA
Nominal Current 72amps @ 250v

So that ballast is a power hog since the PFC is so terrible or non existent according to Arri.

looks like if it had a PFC  of 0.97-0.98

it would be 55amps @240v

Ref: Set Lighting Handbook
Fourth Edition
Harry Box




 

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35 minutes ago, Ed Conley said:

Interesting. The Harry Box tech handbook states that all 12k and above are now PFC but this is  Fourth Edition 2013 Edition.

How old is the ballast?

The ballasts are all retired rental stock. I’d guess they’re about 20 years old…definitely pre-4th edition. I bought 1st and 3rd edition copies of Box’s book to try to find more info about these particular ballasts. 

35 minutes ago, Ed Conley said:

the  "excess" power returning on the neutral matters because in a normal load if all phases are balanced then there should be no load on the neutral but w/o PFC things get weird and the neutral will see excess load and you need to factor in this extra load when sizing the cables and the generator.

It still maters when using house power too.

On 240v the excess power still exists.


I’ve read the section(s) on power factor correction in each of the three editions of Box’s book, but what I don’t understand is this:

On 240v single-phase house power, how can excess power return on a neutral wire when the ballasts don’t have a neutral wire? 😂

Edited by Bradley Mowell
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On 8/15/2021 at 11:01 PM, Bradley Mowell said:

I have four Arri 6/12 electronic ballasts that are non-PFC ( power factor correction ) that operate at 190-250v. Each ballast has a green ground, black hot, and red hot.  I’ve read that non-PFC ballasts return a lot of excess current on the neutral wire because of low power factor (these are rated at 0.7 PF) but how does that apply to ballasts that operate at 190-250v that have no neutral wire? 

You are correct that without a neutral in their mains cable these ballasts will not contribute to the elevation of return current on the system neutral of a distribution system – only smaller non-pfc ballasts operating line-to-neutral will do that.  But, elevated neutral current is not the only adverse effect the harmonic currents drawn by these ballasts have on a distribution system whether it is single phase or three phase.

Ed has already pointed to one: they draw an excessive amount of power (72A) compared to a power factor corrected ballast (55A).   Since this watt-less power does not contribute to  illuminating a set, it effectively reduces the capacity of your service. But that is not all.  The current they draw is severely distorted by their large smoothing capacitors, which only draw current during a very brief period as the voltage waveform peaks. Since the ballast draws power for only a brief period, it draws a spiked current waveform with a high crest factor and harmonic content.  This distorted current will have an adverse effect on the distribution system whether it is single phase or three phase.

First, since the load of the light is only on the peak of the voltage waveform, in high impedance systems like generators, voltage drop occurs only at the peak, resulting in the flat-topping of the voltage waveform in the entire distribution system. Which means all connected loads encounter a chopped voltage waveform. Since the switch-mode power supplies of smaller HMIs, Kinos, and LEDs also only draw current at the peak of the voltage waveform, they can be starved of power.

Second, since the harmonic currents drawn by these ballasts oscillate at high frequencies they travel on the perimeter of conductors (skin effect).  Since more current is traveling through less copper the effective resistance of the conductor increases leading to further voltage drop, but more importantly an exponential increase in I2R heat loss, resulting in the possible nuisance tripping of breakers, and the overheating of conductors and the generator stator.

Power factor correction circuitry is expensive - adding up to 25% to the cost of a ballast.  For this reason, the manufacturers of HMI ballasts only incorporate it where it is absolutely necessary.  Now a days all HMI ballast greater than 4kw include power factor correction because it is essential to the reliable operation of the ballast and connected loads. Which means you will need to take several precautions in using them.

First, oversize  generators and transformers by a factor of two.  Second, oversize your feeder cables. Finally watch out for voltage flat-topping using a digital mulit-meter or power quality analyzer like GenNet IoT that can read peak voltage as opposed to rms voltage (the rms value of flat-topped voltage is the same as a sinusoidal voltage waveform.)

This is a complicated subject, I strongly recommend you read a series of articles I wrote for Protocol Magazine (the qtrly journal of ESTA) on Production Power on a Budget and Power Quality in the Age of LEDS available at our website at http://www.screenlightandgrip.com/html/hd_plug-n-play_pkg.html. Harry box cites these articles in the latest edition of his handbook.

Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental and Sales in Boston

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Guy,

I seriously appreciate the info and will be sure to double my feeders and oversize the power source. 

In regard to capturing peak voltage, I’m assuming a clamp meter would be best. Do you have an inexpensive make and model that you recommend?

Also, any idea if the Fluke 41B Power Harmonics Analyzer is a good unit?

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If you are looking for a Power Quality Analyzer there are a number of options. At a list price of $1495, the Fluke 41B Power Quality Analyzer was Flukes’ entry level single-phase scope meter.  It combined the ease of use of a digital multimeter, the visual feedback of an oscilloscope and the power of a harmonics analyzer in a single instrument. It provided numeric values for rms, peak and total harmonic distortion (THD) for the complex voltage and current waveforms generated by motion picture lights. A bar graph showed the distribution of harmonics in complex waveforms, while its scope provided a graphic representation of both voltage and current waveforms. I use the past tense because, unfortunately, the 41B has been discontinued.

Flukes’ entry level scope meter is now the 43B Power Quality Analyzer which sells for about $3800. Besides offering all the same capabilities of the 41B, the 43B trends voltage, current, frequency, power harmonics and captures voltage sags, transients, and inrush current. As far as I know (Fluke’s product line is constantly changing) the 43B is the only instrument that combines the capabilities of a Power Quality Analyzer, a 20 MHz oscilloscope, a multi-meter and data recorder in a single tool.

The next step up in Power Quality Analyzers in Fluke’s product line is the 434-II, which sells for about $6900. It offers all the same capability as the 43B, but for all three phases simultaneously. It also offers a cool bar graph screen that combines power quality parameters (RMS Voltages, Harmonics, Flicker, Dips, Interruptions, Rapid Voltage Changes, Swells, Unbalance, Frequency, Mains Signaling) all on one screen. The length of a bar increases if the related parameter is further away from its nominal value. The bar turns from green to red if an allowed tolerance requirement is violated.

These two options have several drawbacks.  They are expensive but are available for rental in major markets.   Their screens are poorly designed and exhibit dead scan lines after a while.  The dead scan lines don’t affect their measuring capability, so they are just a nuisance. The screens can be swapped out for a couple hundred bucks at independent service shops (Fluke charges a lot more). The final drawback is that they are cluttered with features that have no benefit to set lighting technicians.

The latest in metering technology designed specifically for set lighting technicians is GenNet IoT.  Employing the latest Internet of Things (IoT) technology, GenNet IoT provides an unprecedented level of accessibility to the critical information required to manage generators and power distribution by delivering it to an operator’s phone, tablet, or laptop via 4G LTE wireless technology.

It has an embedded web server that can display not only comprehensive power quality measurements but also engine data using standard internet browsers and allows for device configuration from the browser. To help you interpret the vast amount of information it generates (such as phase loading, voltage and power levels, power factor, and power quality measurements), its embedded web server presents real time, historical, and event information in easily understandable browser-style graphic displays. If a generator is equipped with InteliVision 5, GenNet IoT will also display critical engine data such as oil pressure, fuel level, and water temperature.

To alert operators to problems before they can get out of hand, GenNet IoT also offers configurable event triggers. Max/Min limits can be set for any measured parameter. If any of the limits are exceeded, GenNet IoT will dispatch an e-mail alarm alerting you of the event. For example, to alert operators of a voltage unbalance that can degrade the performance of a generator and connected loads, its web server displays numerical and graphic phasor representations of the voltage of each phase, its phase angle, the average voltage, and will push an email alarm to your mobile device if the % (-) sequence harmonics (VNeg) exceeds two percent. Gen Net IoT’s email alarms can be a show saver for set lighting technicians since it is easy to miss load induced power quality issues in the thrash to get the first shot of the day.

Gen Net IoT can also be used to prevent engine failure in Tier 4 generators caused by “wet stacking.” Wet stacking is the build-up of carbon in a generator’s engine caused by light loading. Generators need to operate at high temperatures to completely burn diesel fuel. When run under light loads, less heat is generated in its combustion chamber, leaving some fuel unburned. The unburned carbon coats the fuel injector nozzles, compromising their ability to adequately vaporize fuel. This, in turn, further lowers the combustion temperature and allows more unburned fuel to clog the fuel injectors. If left unchecked, wet stacking can result in premature engine failure. Operators of Tier 4 generators must be particularly vigilant. Tier 4 generators are more efficient, but they are also more vulnerable to the effects of light loading. They need to operate under higher loads (at least 75% of the nameplate rating) to reach the temperatures necessary to prevent carbon buildup and engine failure. With the reduced loads characteristic of sets lit predominantly by LED fixtures, wet stacking is an increasing concern for operators of Tier 4 generators.

GenNet IoT prevents wet stacking by controlling a digital load bank to “auto-load” a generator. It does so by a Modbus control signal over ethernet that will initiate a digital load bank to automatically apply load to a generator in a step fashion if the lighting load drops below 75%, and to decrease the load it applies if the combined load begins to exceed 75%.  In this fashion, GenNet IoT assures that the generator is sufficiently loaded to prevent wet stacking and premature engine failure. A tremendous benefit with Tier 4 generators when operating under the reduced load of sets lit predominantly with LED fixtures.

To take one more thing off the plate of a generator operator, GenNet IoT can also automate the process of ghost loading. To maintain voltage unbalance within a narrow range when the impedance of the system neutral is high, GenNet IoT can control a companion load bank manufactured by Simplex specifically for it. If GenNet IoT senses unbalanced phases, it will trigger the load bank to apply load to the low phase in 5kVAR load steps.  In this fashion GenNet IoT can maintain balanced phases thereby reducing deleterious unbalanced voltages.

To further customize the load bank for film production Simplex has engineered it to apply an inductive load rather than the resistive load of standard industrial load banks. An inductive load offers several benefits in motion picture production. Without the tremendous heat generated by resistive coils, an inductive load bank eliminates the requirement for loud cooling fans and is thereby nearly silent in operation which permits the generator to be closer to set. An inductive load also corrects the leading power factor of motion picture lights these days.  HMIs, Kinos, and LEDs are capacitive loads that cause voltage to lead current. Typically ghost loading is required when powering sets lit predominantly by LEDs. By applying an inductive load, Gen Net IoT corrects the power factor of the system (by pulling voltage back in phase with current) while maintaining a 75% load on the generator to prevent wet stacking. 

One Gen Net IoT on its own provides unparalleled access to the critical info required to manage a generator. Multiple Gen Net IoTs in a wireless 4G network, provides the ability to manage multiple generators from a central location. When there is more than one operator, Gen Net IoT enables them to share data and work in shifts – allowing them to get needed rest during overnights.

One drawback to GenNet IoT is that it is only available for rental (most lighting technicians couldn’t afford one anyway.) As part of their rental model, a GenNet IoT customer support technician also receives the email alarms and is on hand to offer advice on how to correct the problem. It’s a whole new world from when I started in this business thirty years ago.

Guy Holt, Gaffer, ScreenLight & Grip, Lighting equipment sales and rentals in Boston.

P.S. In the interest of full disclosure I am involved in the development of GenNet IoT and so get overly excited about its features.

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