PROTECTION SYSTEM DISCONNECTS EQUIPMENT AS LIGHTNING NEARS.
For ultimate protection, disconnecting and grounding electrical and
electronic equipment I/Os is an effective and cost-effective method of protection from
damaging lightning-induced electrical surge currents. Now, a new protection system
does this for you, automatically!
by Dan Young, President, Rabun Labs, Inc.
Damage to electrical and electronic equipment from lightning and other
atmospheric charges and discharges continues to be a problem despite the
numerous available countermeasures. Grounding devices, surge supressors,
lightning arrestors, standby power sources and line conditioners all have
been tried, and, when installed properly, each protects equipment with some
effectiveness. Grounding has the greatest effect upon the success of most
conventional protection equipment and devices.
Problems persist because so many variables affect grounding: soil
composition, buildings with poor grounds (or no ground at all) and areas that
seem like a "magnet" to lightning. This new technology developed by Rabun
Labs, Inc., of Plant City, Florida, is new to some industrial applications,
but has been proven to be very effective in the protection of communications,
scientific, and irrigation equipment for some time. In fact, this system is
specified to protect the irrigation equipment
(computer control systems, pump stations, etc.) at the 1996 Olympics
facilities in Atlanta. Other installations include protection of G.P.S.
receivers for NOAA, sensitive seismic measuring and reporting equipment for
the U.S.G.S., protection of the computer control systems in asphalt and
aggregate plants, and to protect the
equipment at the Royal Swedish Academy of Sciences' astrophysics research
station which has the best image quality solar telescopes in the world,
located in Spain, just to mention a few.
The trend in industry, is to take advantage of innovations in technology by
using more and more state-of-the-art automated and computer-based systems and
control equipment. Since this trend allows you to stay up-to-date and
competitive by increasing efficiency of operation, it would seem that to use
a state-of-the-art
equipment protection system, like the one described here, only makes good
sense as well.
In most any type of plant or facility, damage to equipment can get incredibly
expensive, fast! Chances are if your plant is like most, it could take
several days to get back on-line once damage occurs, and you don't have to be
a mathematician to figure out the production losses, in addition to the cost
for repairing/replacing the
damaged equipment, not to mention upset customers.
This "active" protection system is state-of-the-art and dramatically
different from passive surge suppressors or lightning arrestors because it
literally detects lightning when it is typically 2-5 miles away, and when the
intensity of the lightning reaches a level that can cause equipment damage,
it takes action by automatically
disconnecting/isolating the AC power, telephone, coax lines and remote
sense/control I/O connections to your equipment and grounds them for a period
of time--from 5 seconds to 20 minutes or more, depending on the application.
When the storm has subsided or moved a safe distance away, the system
automatically restores all connections to your equipment. Equipment
protection by isolation is the only sure method and is recommended by the
International Telegraph and Telephone Consultative Committee (CCITT), in
their document COM V-15-E.
Ordinary surge suppressors and lightning arrestors can be effective, but
offer no protection until a damaging voltage surge is literally on the wiring
connected to your equipment. Also, supressors and arrestors have a finite
life--this means they will only work for a specific number and level of
surges, then their effectiveness is
reduced or they cease to function completely. That's why you hear people say
"I had it hooked to a surge suppressor and it still got fried".
Here's how the protection system works:
Lightning releases a tremendous amount of radio energy when a strike occurs;
it's not unusal for a bolt to have up to 30 million volts and thousands of
amps of electrical energy. To gain a perspective, a strike having only 1
million volts and only 1 amp would be equal to a radio station having a 1
Million Watt transmitter. The typical
commercial radio station has 50,000 watts at most, considerably less than a
"small" lightning bolt! Many man-made devices, intentionally or not, emit
radio energy in the same frequency range, but at a much lower power level.
The technology of this system is designed to detect the radio energy from
lightning and to filter out frequencies known to be occupied by man-made
radio energy. The system identifies specific signal profiles and lightning
signatures. The system also responds to the corona charge build-up when a
storm is "building". A bargraph displays the atmospheric disturbances as they
are detected and lets you see them.
Once the electronic evaluation confirms that the received radio energy is
from nearby lightning, the disconnect cycle timer activates. All the
equipment protection switching circuits then perform the actual
disconnecting, shunting and grounding functions for AC power, coaxial cable,
telephone lines, remote sense lines, etc.
An internal audible alarm sounds each time lightning is detected and a
digital counter shows you the number of times the system protected your
equipment. The system also protects its own detector from damaging high-level
atmospheric discharges while operating in the protect/disconnect mode. If
power is lost during a storm,
the system automatically operates from its' built-in stand-by batteries, so
your equipment is still protected.
Relay protection:
Surge currents are prevented from damaging equipment in the event they "jump"
across the disconnect relay contacts because the connections to protected
equipment are disconnected, shunted and grounded.
Shunting can be explained as follows: If you were to pull a plug out of a
wall outlet, all three prongs (ground, neutral and hot) would be disconnected
from power. If you were to connect all three prongs together (shunt them),
and then connect them to ground, you would accomplish something similar to
what this system does in
protect mode to the AC power input of the protected equipment.
So, if a surge current were to "jump" the relay contacts, with all three legs
of the power input at the same ground potential, the current would go to
ground--not into the equipment. The same shunting methodology is used on
coax cables, telephone lines, remote sense/control lines, etc. For the best
protection, the system uses
an external ground connection.
The protection system utilizes a Remote Detection Unit (RDU) that actually
detects the lightning and sends signals to the Model AI-1800 control unit
which causes the equipment protection disconnect circuitry to be activated.
The RDU can be physically located up to 500' from the control unit for ease
of installation and
immunity from noisy AC power lines. This protection system can be utilized
in all types of plants & facilities, but as a "real life" example, we will
describe how this new system operates in an asphalt plant environment. We
chose this example because these plants have a large cross-section of
equipment types and problems, some of which are probably found, to some
degree, in your operation.
The plant control room usually contains the most significant amount of the
equipment that is "vulnerable" to damage from lightning. Sensitive load cell
transducers in truck scales and throughout the plant are also extremely
sensitive to damage from lightning as well as all the variety of electric
motors (fractional to 100+horsepower is typical). This new system provides
protection for all of these areas of concern.
For a computer-controlled plant:
When the plant is in normal operation and lightning is detected, the Model
AI-1800 system will alert the plant operator via the built-in audible alarm
and visually via the bargraph. If preferred, automatic and systematic plant
electrical equipment power-down sequence can be initiated by the Model
AI-1800 system when interfaced with the plant control computer. The plant
control computer system will control and assure that the proper sequential
power-down operation occurs.
Once the computer has completed the power-down, the Model AI-1800 system will
then automatically disconnect/isolate and protect the computer, truck scale
system, radio and telephone or intercom equipment from AC power and all
external sensor/data lines and radio antenna inputs when lightning is once
again
detected. Once the storm has moved a safe distance away and approximately 10
minutes has elapsed since the last detected lightning strike, the Model
AI-1800 system will automatically reset and restore AC power (for the
computer, scales and radio) and all connected sensor/data lines, radio
antenna and telephone connections so that normal plant operation may resume.
Manual shut-down by the plant operator after notification of lightning being
detected is a user-selectable option. If the computer has a UPS, the Model
AI-1800 system can automatically switch the computer to it when disconnecting
equipment from AC power.
For a non computer-controlled plant: In the control room, the plant operator
will be alerted by the Model AI-1800's built-in audible alarm and visually
via the bargraph, and must manually initiate a properly sequenced electrical
equipment power-down.
Once completed, all motor contactors will be de-energized (disconnecting the
motors from AC power) and the Model AI-1800 system will then go into an
automatic mode which will maintain all motors de-energized and
disconnect/isolate plant control, sensor, data and low-voltage wiring from
associated equipment (i.e. load
cells,etc.) truck scales, radio system, etc., when lightning is once again
detected until the storm has subsided or moved a safe distance away and
approximately 10 minutes has elapsed since the last detected lightning
strike. At that point, the Model AI-1800 system will automatically reset and
allow nomal plant power-up operations to resume.
For both type plants, during weekends and after hours when all plant
equipment is shut-down (but all I/Os are still electrically connected to
external wiring), automatic/instantaneous disconnect and isolation of AC
power, sensor/data lines and radio antenna inputs to the computer, truck
scales and radio system occurs
simultaneously when lightning is detected. Once the storm has moved a safe
distance away and approximately 10 minutes has elapsed since the last
detected lightning strike, the Model AI-1800 system automatically restores
all connections so that normal plant operations occur at the start of the
next business day.
The Model AI-1800 system provides protection to those sensitive load cells
located in the scales and plant by the protection switching that occurs. The
load cell wiring is disconnected and isolated from it's related equipment and
simultaneously the wiring going to the load cells is shunted together and to
ground so that in the event of a nearby lightning strike, the induced surge
would be minimized and taken to ground instead of being dissipated in the
load cell, which destroys it. The CLS series contol line switchers can also
be wired to parallel the load cell wiring so that when lightning is in the
area and the system disconnects the A-C power, the wiring going to the load
cells is shunted to ground during the protection cycle, but is not
disconnected from equipment. This assures that calibration is not affected by
installation of the protection system from any insertion loss from the relay
contacts. The disconnect switchers used with this system can disconnect up to
100 pair of control/sensor wires in addition to power, coax, etc.
In addition to providing the equipment protection described, the Model
AI-1800 Control unit also has Power Quality Monitoring capabilities built-in.
A second bargraph displays surges, noise and other power line anomolies
continuously as they occur and solid-state LED indicators will constantly
report the line voltage
condition: a green LED indicates normal line voltage; a red LED indicates a
high line voltage; and a red LED indicates a "sag" or low line voltage.
These indicators remain illuminated until reset so you can see the power
quality at your plant continuously. This capability will save motors and a
lot of times explain "weird" computer behavior as well as let you see if some
new piece of equipment has introduced problems on the line. Many times you
may have a "neighbor" that utilizes large amounts of power to start their
equipment (like rock crusher motors, etc.) and you seem to have "problems"
about the same time of day, and neither you or the power company know
why---now you will know and be able to see it. The power quality monitoring
feature
also provides outputs for interface to recorders or computer to record the
power line activity, if needed. The system has a built-in digital event
counter that will record and display the number of power line anomolies or
equipment disconnect cycles.
This system is also utilized in the office area to protect computers and
office equipment connected to AC power and telephone lines for modem
operation, and also in truck scale house facilities.
It is ironic that the equipment protection "technique" that many have always
trusted is the most effective: Disconnect or unplug the equipment--the only
solution that makes sense. That's precisely what this system does, it just
does it automatically for you. The KISS theory still works.
