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Defining "Clean Power"
Systems
By Arthur S. Kelm
HISTORY
After working over 40 years in the
professional recording industry and the past 10 years of that involved in
the high end A/V market, I have lost track of the number of times I have
heard the term "clean power" used to describe someone's power
system.
Whenever I raise the question "What do you mean
by clean power?" I have never heard the same answer twice. It is like
asking, "What is the best way to ground an audio and video system?"
Everyone has their own interpretation.
The reality is, you can define "clean power"
through testing and measurements. The same holds true for "grounding
systems". I have compiled over 200 performance and noise readings of
systems over the past 10 years, everything from industrial warehouse developments,
to world-class production facilities in Los Angeles, condominiums in The
Four Seasons hotel in San Francisco, to the upper east side of New York
City and many points in between.
From my personal experience, I know that power and
grounding is the heart of any electronic system. Keeping voltage distortion,
current harmonic, Normal Mode Noise and Common Mode Noise to a minimum in
a power distribution system, is ABSOLUTELY necessary for reliable operation.
This is even more true for hard drive based audio and video systems. The
unfortunate reality is that utility power and generator power is, simply
put, not adequate for critical load applications.
THINKING ABOUT POWER IN A DIFFERENT WAY
In order to control power quality, one has
to first look at the source of the power and how it is being distributed
around the facility/system. For years sensitive electronic loads have been
segregated from other equipment in the recording and post-production environment
(sometimes not exactly correctly). I would suggest that we define and apply
a minimum performance standard for all electrical systems that feed critical
loads. I would also take this practice and include heavy technology-driven
homes. I have been involved in homes that have over $2,000,000.00 in sensitive
equipment installed. Ideally all loads need to be divided into categories
and isolated from one another. When engineering a new system, I would suggest
that we then define loads into three basic categories.
PROPOSED CATEGORIES:
1) Motor Loads
(refrigeration, air conditioning and water pumps)
2) Lighting and convenience loads (microwaves, coffee
makers, dimming circuits, ect.)
3) Sensitive electronic loads (control systems, audio
and video equipment)
Motor loads
If we were to put all of our motor loads on the same panel (or sub panels),
we would be able to control the negative effects of spikes and dips that
are common whenever a motor starts up (this is common when you see your
lights dim when an air conditioning unit turns on). Having dedicated panels
and circuits will eliminate this problem.
The next benefit to this approach allows us to add "Power Factor"
correction to the system. All motors are inductive loads; the efficiency
of the load is measured in PF (power factor). The goal is to achieve a number
of 1 or 100% efficiency. When power factor correction is added to a system,
the system is more efficient and leads to lower electrical bills. It also
extends the life of the equipment. This solution can only be achieved when
loads are isolated.
Lighting and convenience loads
These loads are generally not a problem. The exception are fluorescent light
ballast and SCR dimmer circuits. Keeping these loads separate from other
loads will make any negative effect much simpler to isolate and solutions
simpler to engineer.
Sensitive electronic loads
These are the most critical loads to protect and condition. They require
at minimum the following.
1. A properly engineered and installed grounding system.
2. Electrostatic triple shielded isolation transformer, including RF filtering
along with Spike and Surge Suppression.
3. Breaker panel with high quality bolt-in breakers, copper bus bars and
isolated ground bus bar.
4. Additional high quality TVSS and filtering installed in panel board.
5. Stranded wire to feed receptacles.
6. Hospital grade receptacles. (provide cleaner, tighter, and therefore
lower impedance connection to a plug)
Electrical wiring should be a minimum of 12 gauge
for a 20 circuit. I prefer to up-gauge all wiring one size (that means #10)
and make all the conductors the same gauge. My first choice is to run wiring
in ridged or flex steel conduit. Second choice is steel MC cable.
The next factor to consider is the length of wiring
to the receptacle. I recommend that the power panel be located as close
as possible to the main components of the system. This allows the impedance
of the system to be as low as possible. In studio and theater applications,
this should be kept to less than 50 feet. For audiophile/stereo applications,
wire should not exceed 20 feet.
The above recommendations should be the foundation
of any system. Depending on your specific needs, additional power conditioning
may be required. The most basic conditioning (after TVSS (Transient Voltage
Surge Supressor) and RF filtering) is voltage regulation. This will be required
if you are in an area that has recurring utility power fluctuations. Regulation
can be accomplished a few ways; the most basic is a stepper transformer.
These types of units monitor the output voltage of the transformer and changes
taps on the primary of the transformer to adjust the output to the proper
voltage.
The next option would be to use an inverter system.
This unit's approach is to takes the incoming AC voltage and turns it to
DC then back to AC again, generating a new low distortion sine wave. The
third approach would be a "full on line" UPS system. This is basically
an inverter system with batteries.
SETTING A NEW STANDARD FOR SYSTEM PERFORMANCE
I would like to now put some numbers to what I would
be defining as a "Clean Power" system. (These measurements were
taken with a Powervar Power Probe115 and Fluke 43 Power Analyzer)
System With No Load
1. Common Mode Noise Less than 30mv
2. Normal Mode Noise Less than 10mv
3. Voltage distortion Less than 1.5%
4. Resistance to earth Less than 5 Ohms
System With Load
1. Common Mode Noise Less than 100mv
2. Normal Mode Noise Less than 20mv
3. Voltage distortion Less than 1.5%
4. Resistance to earth Less than 5 Ohms
The reason for the two different standards is reflected
noise from the individual components' power supplies. One must consider
that all power supplies have reflected noise. I refer to this as a component's
"footprint". As with motors there are solutions to help correct
these issues.
I would consider a system achieving the above criteria
a "Certified Ground One Power System".
In closing, I understand that my views and recommendations
may seem a bit extreme to some, however, I believe that in this day and
age of overly hyped power products, there is a need to establish a minimum
standard for power system performance.
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