Dimmers and ground currents

[audio ferret]

I am trying to fix a sound system noise problem, and have some questions
that require electrical engineering expertise. I hope that someone here
can shed some light.

Sound and lighting systems are installed in a large church sanctuary.
The lighting dimmers are fed by a 400 amp delta-wye transformer, whose
480v feeders run in slab, under the sound mix position. The 3 phases and
ground are in PVC.

The distance between the transformer and service entrance is about
250-300'.

With all dimmers running at 50%, we get a substantial amount of signal
contamination in the mixer's mic inputs, largely at 180Hz, though other
harmonics are present.

When the dimmers are at 50%, we measure over 50 amps on ground, at the
transformer. The transformer is also bonded to building steel. The
lighting folks say that this in reasonable, and not excessive. I have
read the large amounts of harmonics are byproducts of SCR dimming, and I
know that the draw across phases varies constantly, because lighting
conditions change a great deal through a service.

My questions to you are:

Is 50 + amps on ground, acceptable with regard to code?
Is there a way to remediate the noise?

thanks

 

[Roy Q.T.]

From: [email protected] (audio ferret)

I am trying to fix a sound system noise problem, and have some questions
that require electrical engineering expertise. I hope that someone here
can shed some light.
Sound and lighting systems are installed in a large church sanctuary.
The lighting dimmers are fed by a 400 amp delta-wye transformer, whose
480v feeders run in slab, under the sound mix position. The 3 phases and
ground are in PVC.
The distance between the transformer and service entrance is about
250-300'.
With all dimmers running at 50%, we get a substantial amount of signal
contamination in the mixer's mic inputs, largely at 180Hz, though other
harmonics are present.
When the dimmers are at 50%, we measure over 50 amps on ground, at the
transformer. The transformer is also bonded to building steel. The
lighting folks say that this in reasonable, and not excessive. I have
read the large amounts of harmonics are byproducts of SCR dimming, and I
know that the draw across phases varies constantly, because lighting
conditions change a great deal through a service.
My questions to you are:
Is 50 + amps on ground, acceptable with regard to code? Is there a way
to remediate the noise?
thanks
---------------------------------------------
So, what you are saying is: when you dim the lights at church to 50%
output you get too much noise from the sound system, mainly from your
mic/mixer., are they Wireless ? do they distort any with no dimming on
the lights...?

Have you tested it by adjusting the lighting with reference to the noise
coming from the sound system ?

It may just need proper shielding & attenuation to over come the
environment
and ambient energy dispelled by the nearby (slab) 3ph lighting system,
or more clearly, probably just relocation to a better area away from any
dimmers & other electrical circuittry.

It's sounds to me like a your ground is suspect too, the problem maybe a
short or dirty ground in the lighting circuits..or..a bad connection.

I've worked on church circuitry & I was amazed at the crazy things
others had done to the electrical system. I found dozens of shorts and
had to restore several antigue cathedral fixtures to normal op again
after decades of disrepair.

more info please: like,
How many dimmers ? check them one by one against the problem & you may
find out more.

Do you also know, How many Amps at the Tr with no dimming and fully
dimmed? Is there a substancial difference in current?

Are you using Wireless mikes ? magnetic flux from power cables will
affect these if physically too close, they'll affect the harmonic signal
from the mikes carrier.

Roy Q.T.
Urban Technician
[I don't make em, I just fix em]

 

[ehsjr]

I am trying to fix a sound system noise problem, and have some questions
that require electrical engineering expertise. I hope that someone here
can shed some light.

Sound and lighting systems are installed in a large church sanctuary.
The lighting dimmers are fed by a 400 amp delta-wye transformer, whose
480v feeders run in slab, under the sound mix position. The 3 phases and
ground are in PVC.

The distance between the transformer and service entrance is about
250-300'.

With all dimmers running at 50%, we get a substantial amount of signal
contamination in the mixer's mic inputs, largely at 180Hz, though other
harmonics are present.

When the dimmers are at 50%, we measure over 50 amps on ground, at the
transformer. The transformer is also bonded to building steel. The
lighting folks say that this in reasonable, and not excessive. I have
read the large amounts of harmonics are byproducts of SCR dimming, and I
know that the draw across phases varies constantly, because lighting
conditions change a great deal through a service.

My questions to you are:

Is 50 + amps on ground, acceptable with regard to code?
Is there a way to remediate the noise?

thanks

I can give only general answers - but first:
Something does not sound right - 50 amps on ground can make
you very very dead.

Did the system ever work properly? If so, something has
gone bad/been changed that causes the problem. If not,
it's a design problem or one (or more) of the parts of
the system is defective. From your description, one
assumes the source of the noise is the dimmed lighting.
Is that proven (either by all lights full on or all
lights full off)?

Break the problem down into elements:
Source identification (which seems to be the lights)
Determine which lighting circuits affect the noise level -
maybe you have a circuit or circuits that are bad
Determine the point(s) and hows of noise ingress: conducted?
radiated? Are you sure *ingress* is at the mic inputs? (For
example, a radiated signal could come in on speaker
wires and make its way back to the mic inputs)

Remedies: shielding, isolating, filtering, elimination at source

Ed

 

[audio ferret]

First, is there any chance you are confusing the terms "ground" and
"neutral"? Is the 50 amps on ground mostly mostly fundamental vs. higher
harmonic content?

There is no chance that I am confusing ground and neutral. The 50 amp
current is on the ground wire.

You can expect small, in the wall, dimmers to be thyristor dimmers that dim
by means of phase control that intrinsically generates noise from the
switching operation. Third harmonic currents from the separate phases will
add up rather than cancel each other in the neutral. It is possible to get
filters to remove the harmonics, but that is probably an expensive way to
go.

These are not small, wall mounted dimmers. These are 3Kw theatrical
dimmers: http://www.etcconnect.com/products/products.asp?251

You might consider wireless microphones so that induction between long wire
runs is minimized.

Replacing wired mics, with wireless, is impractical on this scale. I
have over 130 channels of mic lines between the stage, house, monitor,
and recording splits.

The real solution to your problem would be to use variable transformers or
an induction regulator or some kind of magnetic amplifier device to lower
the lighting voltage. These do not generate harmonics (except possibly some
magnetic amplifier devices) at all. That solution may be rather bulky and
expensive.

Thanks, but I am not sure that replacing the dimming system is practical.

 

[audio ferret]

I am trying to fix a sound system noise problem, and have some questions
that require electrical engineering expertise. I hope that someone here
can shed some light.

Sound and lighting systems are installed in a large church sanctuary.
The lighting dimmers are fed by a 400 amp delta-wye transformer, whose
480v feeders run in slab, under the sound mix position. The 3 phases and
ground are in PVC.

The distance between the transformer and service entrance is about
250-300'.

With all dimmers running at 50%, we get a substantial amount of signal
contamination in the mixer's mic inputs, largely at 180Hz, though other
harmonics are present.

When the dimmers are at 50%, we measure over 50 amps on ground, at the
transformer. The transformer is also bonded to building steel. The
lighting folks say that this in reasonable, and not excessive. I have
read the large amounts of harmonics are byproducts of SCR dimming, and I
know that the draw across phases varies constantly, because lighting
conditions change a great deal through a service.

My questions to you are:

Is 50 + amps on ground, acceptable with regard to code?
Is there a way to remediate the noise?

thanks

I can give only general answers - but first:
Something does not sound right - 50 amps on ground can make
you very very dead.[/QUOTE]

Did the system ever work properly? If so, something has
gone bad/been changed that causes the problem. If not,
it's a design problem or one (or more) of the parts of
the system is defective. From your description, one
assumes the source of the noise is the dimmed lighting.
Is that proven (either by all lights full on or all
lights full off)?

The lighting is indeed a source of the noise. Yes, it is has been tested
with dimmers at full, 50%, and off.

Break the problem down into elements:
Source identification (which seems to be the lights)
Determine which lighting circuits affect the noise level -
maybe you have a circuit or circuits that are bad

We had hoped to find that a hot and neutral had been reversed at the
lighting pin connectors, but that was not the case.

Determine the point(s) and hows of noise ingress: conducted?
radiated? Are you sure *ingress* is at the mic inputs? (For
example, a radiated signal could come in on speaker
wires and make its way back to the mic inputs)

We have the ability to disconnect the console from the amplifier rack
and related equipment, and still had noise show up at microphone inputs.

Remedies: shielding, isolating, filtering, elimination at source

Seems to me that the only way to shield from local EM would be to put
feeders in rigid conduit. That isn't going to happen.

 

[audio ferret]

| I am trying to fix a sound system noise problem, and have some questions
| that require electrical engineering expertise. I hope that someone here
| can shed some light.
|
| Sound and lighting systems are installed in a large church sanctuary.
| The lighting dimmers are fed by a 400 amp delta-wye transformer, whose
| 480v feeders run in slab, under the sound mix position. The 3 phases and
| ground are in PVC.

What is the output voltage of the transformer? 208Y/120 or 480Y/277?
If the latter, how are you getting 120 volts for the sound system?

The sound system is fed by a separate transformer.

| The distance between the transformer and service entrance is about
| 250-300'.
|
| With all dimmers running at 50%, we get a substantial amount of signal
| contamination in the mixer's mic inputs, largely at 180Hz, though other
| harmonics are present.
|
| When the dimmers are at 50%, we measure over 50 amps on ground, at the
| transformer. The transformer is also bonded to building steel. The
| lighting folks say that this in reasonable, and not excessive. I have
| read the large amounts of harmonics are byproducts of SCR dimming, and I
| know that the draw across phases varies constantly, because lighting
| conditions change a great deal through a service.

By "ground" do you mean the wire (with white or gray insulation) that is
wired up to actually carry current, or do you mean the wire (with green
insulation or bare) that is wired up to provide grounding protection?
At what point are you taking this measurement that gets 50 amps?

Green wire ground. Measured at the Delta/Wye transformer.

| My questions to you are:
|
| Is 50 + amps on ground, acceptable with regard to code?

Depends on what you mean. If what you really mean is the neutral wire,
then it may well be in compliance with code given a sufficient lighting
load. But the harmonics may still be a serious safety issue if parts
of the system are not properly rated for it.

I do not mean neutral wire. This is on the GREEN wire.

| Is there a way to remediate the noise?

Yes. But it may be costly. Lots more information is needed to know
what the various options are. One possible option is to operate the
lights and/or the sound system from a line-to-line voltage and not
involve the neutral. But getting all this to be quiet on three phase
is harder than it would be on single phase. If I had been consulted
at the beginning I would have recommended three single-phase 120/240
volt output transformers (each connected to different 480 volt phases
coming in). This would allow better balancing of lights and better
neutralization of harmonic content. But transformers are expensive
to change out, so this isn't likely an option, though supplementing
the power system with a single small 480 volt or 208 volt (input to
120 volt (output) transformer complying with NEC article 647 might
help a good bit.

That's an interesting idea. Thanks.

 

[audio ferret]

It is not immediately clear what technology is used for the actual dimming.
I am not interested enough to go on a wild goose chase. The site seems to be
mostly puffery.

These are SCR dimmers. The site does contain data sheets and manuals,
but they are a bit of chore to retrieve.

 

[w_tom]

Dimmers create harmonics. If the entire load on that
transformer is dimmers at 50%, well, others have discovered
that a neutral wire must be sometimes double the size required
by code due to harmonic and reactance problems. But this
should make it obvious. A substantial voltage increase would
be seen on one or some 300+' wires between transformer and
load side.

Second, get a field strength meter to learn what those
electric and magnetic fields are above the pvc pipe; measured
with all lights off, 100% on, and 50% on. When they worried
about childhood leukemia from electricity, it was not those
big transmission towers that created the hype. That hype was
created by local newsreporters who never bothered to first
look at the numbers. Threat was fields from wire such as the
400 amps inside that pvc conduit. What are your wires doing
especially when dimmers create so much harmonics? That may
explain sound system problems.

As others have noted, 50 amps on the ground wire is well
more than excessive. Measure for significant voltage
increases between both ends of each wire in that 300' pvc
conduit. These problems can be aggravated by harmonics and
reactive loading that is largest when lights are 50% dimmed.
50 amps in ground indicates more serious problems than I have
suggested looking for. It is that bad. Hopefully, some
things suggested here will uncover symptoms of a larger
problem - before someone (especially a plumber) gets hurt.

 

[Roy Q.T.]

50 amps on the grounded (green) conductor spells big trouble to me.
* As in A Danerous Ground Fault ..!.. Some where they must have used a
Ground for a Neutral., Perhaps on a segment of Lighting Circuitry or to
an Outlet Circuit with some small resistive appliance connected to it.

Just Where is this Church Located ?

Roy Q.T.
Urban Technician
[I don't make em, I just fix em]

 

[JC]

The web page mentions different rise times available. Can this be adjusted
by you, and if you adjust it does it make any difference?