Got "Dirty" Power?

[Parker]

Ok, let me start by saying this: I am by no means a certified electrician.

My theatre has what the O&M exec staff flippantly refer to as "dirty" power.
Example: every now-and-then the lights (and I mean ALL of them) briefly flicker all at once. Not enough to be an issue as far as safety, but noticeable.

I have noticed this in other theatre spaces as well... mostly other high schools.
Is this an issue at your space?
Anyone know the "real" reason why this happens?
Can anything be done to fix it (short of hiring out a complete re-wire of the entire system)?

 

[Footer]

I have seen more dimmer cards fried because of this then I can count, specificly the Johnson System's CD-80 Retrofit kit had huge issues with this.

This can either be a problem that the buildings service is not large enough or the areas service is not large enough. It usually means that the power in the building fluctuates regularly when elevators, A/C's, heating, and other large loads come on.

I spent the summer working for a little theatre in the middle of nowhere Missouri. The town had 70 people living in it and a 400 seat theatre. My dimmer rack was 48 dimmers made up of CD80 packs. We had the largest service in town at 300 amps for the entire building. I could easily tell when it was middle of the day and everyone in town had their A/C's on. I could tell when the A/C in our building kicked on. I asked when I got there about adding another 24 dimmers for one show and after looking at the power situation, we could not do it. It was not that the building did not have the ability to take on another feed, it was that there was simply not enough power in the town. They would have had to add more power infrastructure to the substation to give us more power.

 

[dmx]

I'd suspect this is caused by excessive loads on your transformer, probably exaggerated by the activation of HVAC equipment, resulting in the brief dimming of your fixtures. You can confirm this if you have a Furman or related rack-mounted power conditioner with a voltage indicator. You should see a drop in voltage when the HVAC is triggered.

Just my own 2cents. Maybe this helps?

--Matt

 

[ajb]

There are a huge number of situations that can fall under the umbrella of "dirty power", which is why I hate that term and wish dearly that it would go away. It can mean:

-Voltage spikes (surges) (pretty much always a utility/force of nature problem)
-Voltage sags due to undersized feeders
-voltage sags due to utility problems
-Power outages
-Voltage waveform distortion due to large nonlinear loads (like phase-chopping dimmers, switch mode power supplies)

Voltage sags and spikes can be a symptom of a loose or open neutral, which is VERY bad--huge fire and life safety hazard.

If all of your lights are flickering at once, then you probably need to call your utility.

I did work in one building that had undersized service feeders to the point that turning on the table saw would cause the entire building to dim. You could also tell how bright the stage lighting was at any given time because the lobby lights would get dimmer as the stage lights got brighter.

What can be done depends on the root cause. Any decent commercial electrical contractor can bring out a recording meter that they can leave hooked to your service for a week that will record any changes in current and voltage. That will give you a good picture of exactly what is going on.

It's unlikely that you would need to rewire the entire place, but you might need to upsize some feeders or upgrade the building service, or the utility might need to do some work on their side of the service entrance.

 

[STEVETERRY]

There are a huge number of situations that can fall under the umbrella of "dirty power", which is why I hate that term and wish dearly that it would go away. It can mean:

-Voltage spikes (surges) (pretty much always a utility/force of nature problem)
-Voltage sags due to undersized feeders
-voltage sags due to utility problems
-Power outages
-Voltage waveform distortion due to large nonlinear loads (like phase-chopping dimmers, switch mode power supplies)

Voltage sags and spikes can be a symptom of a loose or open neutral, which is VERY bad--huge fire and life safety hazard.

If all of your lights are flickering at once, then you probably need to call your utility.

I did work in one building that had undersized service feeders to the point that turning on the table saw would cause the entire building to dim. You could also tell how bright the stage lighting was at any given time because the lobby lights would get dimmer as the stage lights got brighter.

What can be done depends on the root cause. Any decent commercial electrical contractor can bring out a recording meter that they can leave hooked to your service for a week that will record any changes in current and voltage. That will give you a good picture of exactly what is going on.

It's unlikely that you would need to rewire the entire place, but you might need to upsize some feeders or upgrade the building service, or the utility might need to do some work on their side of the service entrance.

There is a saying: "The cheapest power quality tool is a screwdriver".

Before you think about rewiring, get a licensed electrician to perform an infrared scan and torque check of all the applicable switchgear in the building. Often, a loose neutral or phase conductor can produce these kinds of artifacts.

ST

 

[derekleffew]

There is a saying: "The cheapest power quality tool is a screwdriver". ...

That Terry guy doesn't know the difference between a screwdriver and an Allen wrench (hex key).

After all connections have been verified, if the problem persists, one will likely want to have a qualified technician perform an analysis with a BMI, [EDIT:] (as ajb said previously).http://www.controlbooth.com/forums/members/ajb.html

 

[STEVETERRY]

That Terry guy doesn't know the difference between a screwdriver and an Allen wrench (hex key).

After all connections have been verified, if the problem persists, one will likely want to have a qualified technician perform an analysis with a BMI, [EDIT:] (as ajb said previously).http://www.controlbooth.com/forums/members/ajb.html

Actually, the original quote referred to wiring devices, and it's more punchy without a comprehensive list of lug tightening tools attached, don't you agree?




A more generic description of Power Quality Analyzers lives in the glossary under PQA. I've actually never heard "BMI" applied as a generic name. But what do I know, anyway?

ST

 

[Dionysus]

I also hate the term 'dirty power' as it can be so ambiguous. I've also heard poor power factor called as such.
Which by the way correcting poor power factor (which makes your electrical service less 'efficient') sometimes helps when you have too much load (especially when it's non-linear inductive loads causing the main problem).

Something else that can cause issues is having improper distribution of loads across the phases on your feeder. Not a fun thing at all (actually can be very bad).

I have to go with the consensus and say "Contact a reputable licenced electrician" who has the proper experience to deal with this issue. Not every electrician is properly equipped or experienced to deal with this possible group of issues.

I don't know what your building's service is like at all, as they can greatly differ. But there are a million different things that could be adding to your issues from things 'ground leaking' to poor Power Factor, to harmonics caused by various things to feeder size issues, loose connections, overheating feeders or other components, etc, etc, etc...

Fully addressing all the electrical issues in a large complex can be very time consuming and thus expensive. I remember tracing down a ground leak in a YMCA, took me a whole day! Started from the main distribution (yay for digital service equipment, told me which phase without having to open it up), to this panel, that panel, that circuit.... Joy.
Or dealing with large capacitor banks in a factory designed to balance the power factor on large inductive loads.... Melted screwdriver... not fun. I'm happy I was getting coffee when that happened.... Idiot. Go. Boom. (He was fine actually, but really scared, and down one screwdriver).

 

[JD]

The best place to start is to figure out if it is even your problem to begin with. In other words, is the local utility is at fault? You can make all the changes in the world, but if its bad off the street, then there is nothing in-house you can do to fix it. Since I believe you said it is building wide, this may be the case. An electrician can make that determination. The problem is where to go from there. This often then becomes a long term phone war where the utility claims everything is ok, but you know it is not.

To satisfy personal curiosity, you may want to take a walk down the street and see what's feeding you. Often you may find it staring you in the face. Even then, getting it fixed may be a go-round.

 

[derekleffew]

... Something else that can cause issues is having improper distribution of loads across the phases on your feeder. Not a fun thing at all (actually can be very bad). ...

Can you elaborate on this, as recently another member shattered my belief system on this topic.

 

[mrtrudeau23]

Our mainstage space has, what our chairperson calls, dirty DMX. This is mostly apparent with our wonderful ColorSource color scrollers (loud enough to rival the sound system). I've noticed a few of them over the past years that twitch the scroll when they are sitting still. It's an interesting little phenomenon that doesn't seem to affect the lights at all, which is good.

This same space also has a Unison system that is also rather dated, comparatively, that likes to shut the lights off for a few seconds after you turn them on. Also, with the Unison system, we have an older Sensor rack, which needs to be reset when changing settings (Normal dimming to Dimmer Doublers, etc) and when this happens, the theatre goes dark for about five to ten seconds. It also likes to leave lights on when the board is shut down.

 

[JD]

Can you elaborate on this, as recently another member shattered my belief system on this topic.

Balancing phases becomes important when you are dealing with an undersized source, as sometimes happens on tour. A properly designed system should be able to withstand total imbalance with no ill effect. (In theory, it shouldn't matter on tour either, if promoters would only read the technical rider!)

 

[STEVETERRY]

Can you elaborate on this, as recently another member shattered my belief system on this topic.

Let's cut to the chase from that thread:

"There is no doubt that aiming for approximate phase balance is desirable. However, as I previously stated, if the system and its feed from utility power is properly designed, there should be no ill effects from imbalance. For a portable generator where the dimming system is a high percentage of the generator capacity, phase balance does indeed become more critical.

Two items to keep in mind:

1. The very layout of a dimmer-per-circuit system with one third of the dimmers on each phase works statistically in your favor to achieve balance, without any intervention from you. You would actually have to work very hard to purposely achieve a material imbalance.

2. As cues are set, there is no practical way to consider phase balance in the process. However, see point 1 above.

One situation which may require more diligence on phase balance is where the feeder is heavily derated against the connected load. If you have 2400 amps of lights plugged into a 400A three-phase feed, now you need to be hypervigilant about the actual current being drawn. This is where a permanent four-display (3P +N) true-RMS-responding ammeter on the feeder is a great tool.

I reiterate my previous statement that making phase balance part of the production checklist and hookup is generally of little value."

ST

 

[xander]

/hijack

I spent the summer working for a little theatre in the middle of nowhere Missouri. The town had 70 people living in it and a 400 seat theatre. My dimmer rack was 48 dimmers made up of CD80 packs. We had the largest service in town at 300 amps for the entire building. I could easily tell when it was middle of the day and everyone in town had their A/C's on. I could tell when the A/C in our building kicked on. I asked when I got there about adding another 24 dimmers for one show and after looking at the power situation, we could not do it. It was not that the building did not have the ability to take on another feed, it was that there was simply not enough power in the town. They would have had to add more power infrastructure to the substation to give us more power.

Hey, I was ME there a few years. That building has serious power issues...Don't get me started on the houselights...

/end hijack

 

[DavidNorth]

Our mainstage space has, what our chairperson calls, dirty DMX. This is mostly apparent with our wonderful ColorSource color scrollers (loud enough to rival the sound system). I've noticed a few of them over the past years that twitch the scroll when they are sitting still. It's an interesting little phenomenon that doesn't seem to affect the lights at all, which is good.

This same space also has a Unison system that is also rather dated, comparatively, that likes to shut the lights off for a few seconds after you turn them on. Also, with the Unison system, we have an older Sensor rack, which needs to be reset when changing settings (Normal dimming to Dimmer Doublers, etc) and when this happens, the theatre goes dark for about five to ten seconds. It also likes to leave lights on when the board is shut down.

Mike,

My guess on the ColorSource scrollers is that the power supply has a weak DMX receiver chip, a faulty DMX cable or a problem in the data distribution system feeding the power supply. This certainly can be resolved and we'd be glad to help.

On the balance of the system, you definitely do not have "dirty DMX." When you bring up lights on the Unison system [followed by lights going off and back on] is likely only occurring when you first turn on lights for the day. If so, this is a bug in the Sensor rack code where it is sensing for proper airflow before the rack fan finished spooling up.

The need to hit [Reset] on the rack after changing firing mode is also a software bug. Both of these can be resolved. Contact us when you get a chance.

As far as lights coming when the board is turned off, well, many people have this issue and there have been several threads on this. If you wish, you can change your DMX last look hold time from the default of 180 seconds down to something less. The lights will fade out after that time expires.

Hope that helps. Give us a ring.

David
ETC

 

[Dionysus]

Let's cut to the chase from that thread:

"There is no doubt that aiming for approximate phase balance is desirable. However, as I previously stated, if the system and its feed from utility power is properly designed, there should be no ill effects from imbalance. For a portable generator where the dimming system is a high percentage of the generator capacity, phase balance does indeed become more critical.

Two items to keep in mind:

1. The very layout of a dimmer-per-circuit system with one third of the dimmers on each phase works statistically in your favor to achieve balance, without any intervention from you. You would actually have to work very hard to purposely achieve a material imbalance.

2. As cues are set, there is no practical way to consider phase balance in the process. However, see point 1 above.

One situation which may require more diligence on phase balance is where the feeder is heavily derated against the connected load. If you have 2400 amps of lights plugged into a 400A three-phase feed, now you need to be hypervigilant about the actual current being drawn. This is where a permanent four-display (3P +N) true-RMS-responding ammeter on the feeder is a great tool.

I reiterate my previous statement that making phase balance part of the production checklist and hookup is generally of little value."

ST

I have to agree with ST entirely. As a part of a theatre show, or otherwise you'd really have to TRY to unbalance your phases. There are really few circumstances that could cause this, save for someone deliberately loading up one phase over others.
However if there were to be a major imbalance not only would you not be able to draw as much total power, you'd also possibly overheat the one conductor, not to mention the effect on the 'neutral' which carries the imbalance.

Really in reality, I've only heard of a few instances where an imbalance occurred. By the nature of how electrical distribution systems are designed this generally is next to impossible.