When Utility Structural Systems began
investigating the grounding concerns of the electrical industry, our research
led us toward the new application called POLY-GROUND®
that maintains the same reliability as POLY-SET®
with the additional ability to solve the grounding needs of the utility
industry.
Grounding is important to an operating utility because it is
part of the “return wire” of the electrical circuit.
Grounding
is related to a “safety valve” of an
electrical system, both to protect the system itself and the personnel working on the
system.
Important aspects in dealing with the electrical problems in a system are:
All electrical equipment must be grounded because of a possible short circuit inside the
equipment.
Electrical sensors, relays, etc. require a reference, which is the ground.
Harmonics created by semi-conductor based switching devices and unbalanced loads depend
upon “good grounds” to stabilize the electrical system.
The speed of discharging a lightening strike keeps both the conductor and equipment from
being damaged.
An electrical ground is also referred to as the NEUTRAL, COMMON or GROUND.
Ground connection points are arranged so that under normal circumstances there will be
no excessive flow of current in any portion of the neutral conductor.
POLY-GROUND®
for pole installation has the
equivalent of 15 to 25 times more surface area than a 5/8 inch by 8 foot ground rod at
each pole installation. By increasing the area in which electrical energy can use the
earth’s crust, the electrical system can operate more efficiently and therefore
requires less maintenance.
Grounding systems are broken into four categories:
Workman’s Safety
System’s Safety
Lightning Protection
Harmonics
1. Workman’s
Safety
The purpose of good grounding is protection from electric shock forthe workmen in the field. If excessive voltage is encountered due to
accidental high voltage contact or by lightning, a good ground is required
on each pole to form the preferred path to ground rather than passing
through the workman. POLY-GROUND®
will potentially increase the protection for the workmen by up to 500%.
These are the potential dangers
under fault conditions:
Touch Potential
Step Potential
2.
System Protection
Due to the combining of all the electrical operating systems that
presently form the North American Electrical Grid, protection of the
complete system has become a very necessary and difficult science needed to
keep the whole system working. The fast acting relays necessary to
accomplish system protection are dependent upon good grounding throughout
the system. If POLY-GROUND®
is installed on each pole in the system the results could potentially be
improved by up to 500%.
3.
Lightning Protection
The goal for shielding transmission and distribution lines is to
attract the static charges from the clouds and to dissipate the charge into
the earth’s crust, which is an infinite reservoir of electrons. The movement
of the clouds through the atmosphere creates a charge on the cloud in which
the positive charges go to the bottom of the cloud and the negative charges
go to the top of the cloud. When the voltage buildup between the potentially
charged clouds and the earth or grounded static or grounded structure has
risen above the break down value of the air between these entities, a
“feeler” of electrons makes an invisible journey to the clouds and leaves a
narrow ionized path, which becomes a good conductor between the two points.
Lightning is the positive discharge from the rain cloud that follows the
ionized path formed by electrical “feelers” that are traced from the earth
to the cloud. This narrow path of ionized air becomes a conductor and
results in the concentrated, positive charges that accumulate on the bottom
of the rain cloud being discharged in the form of lightning into the earth’s
crust. Lightning discharges can be in excess of 5000 amps. POLY-GROUND®
provides your system with added efficiency due to the increased
effectiveness of every ground.
4.
Harmonics
The recent realization among electrical engineers is the effect of
harmonics on the electrical system as a whole. The basic curve plotted by
the rise and fall of an A.C. voltage in the standard 60 cycle system of the
United States is a perfect sine wave. Harmonics are extra rises and falls
that occur in the original sine wave that follow at multiples of the
original period and is super imposed on the original curve. When all of
these are combined a ragged non-sine wave is created. This can make the peak
of the wave 50% to 70% higher than the expected wave. This is sometimes
called the “unsolicited load” and must be accommodated for by relay
protection used on the line for system protection. These harmonics are
caused by unbalanced loads; such as those produced by single phase motors
and the use of semi-conductor based switching devices, e.g., power supplies
used in computers, and temporary faults on lines or in equipment. These
harmonics can be eliminated when the power flows through a grounded “Y” to a
delta transformer. This is accomplished by the use of a strong ground at the
transformer bank. By using POLY-GROUND®on your transformer bank
you have provided a higher capacity ground.
In
areas where the soil resistivity is relatively high
(greater than 30 ohm-meter), it may not be possible to
obtain a low ground impedance of the grounding system.
Of all the possible solutions that a utility can opt to
change, and given the fact that the resistance of the
grounding electrode itself is negligible, the most
opportune, immediate improvement can be made by changing
the soil resistivity around the ground rod itself. The
soil resistivity is the single most important factor
affecting the resistance of the grounding system. And
yet, it is the most often overlooked.
Since soils condition is constantly changing, why not
put something around your pole, or grounding electrode
that actually maintains a constant state of conductivity
no matter what the surrounding soil may do. Moisture
contents of soils are constantly changing with the
seasons. When moisture contents of the soil rise above
20% by weight, the resistivity of that soil decreases.
But when the moisture content goes below 20%, the
resistivity rises at a phenomenal rate. Below are some
examples of varying soil resistivity’s expressed in
ohm-meter:
Soil Resistivities
(Approximate
Ohm-Meters)
Soil Description
Median
Min.
Max.
Topsoils, loams
26
1
50
Inorganic clays of
high plasticity
33
10
55
Fills-ashes,
cinders, brine wastes
38
6
70
Silty or clayey
fine sands with slight plasticity
55
30
80
Porous limestone,
chalk
65
30
100
Clayey sands,
poorly graded sand-clay mixtures
125
50
200
Fine sandy or
silty clays, silty clays, lean clays
