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As the price
of extending utility power lines has increased significantly,
photovoltaics have become the preferred source of power in many
applications, including Cathodic Protection.
Cathodic
Protection (CP) works by impressing a current on a metallic
structure that is in contact with the earth, such that the
structure is maintained at a negative voltage (usually about
-.85 to -1.1 vdc) with respect to a copper/copper sulfate half
cell in contact with the earth. Cathodic Protection is used to
protect pipelines, steel tanks, well casings, and even highway
bridges.
Even large
structures in contact with the earth can be protected with a
reasonably sized system. A Cathodic Protection or Corrosion
Engineer should be contacted to evaluate the application and to
specify the ground bed type and dimensions along with the
current and voltage requirements. A system should normally be
sized for some future growth since protective coatings
deteriorate further with age.
ETA
Engineering Inc. has designed a family of Cathodic Protection
Controllers that meet the majority of CP land-based
applications. Normally powered with Photovoltaics, the systems
range in output power from a few watts to 2 Kilowatts. Systems
are available in nominal battery voltages of 12, 24, 48 Vdc with
currents ranging up to 50 Amps. Systems may be paralleled for
higher output currents by setting the controls to the constant
current mode. We can supply complete systems except for the
ground bed, anodes, field wiring, half cell (if used) and a shelter if used. The
controller uses high efficiency components in a DC to DC
"buck" converter topology that gives
conversion efficiencies in the area of (95%). No rheostats or
dropping resistors are used to lower the output voltage, thus
saving the power dissipated in the traditional
"rectifier" systems.
Our
experience dates back to the late 1970's when the first systems
were being designed and installed. In 1993 we redesigned the
electronics to allow a positive ground system from the battery
bank directly to the ground bed. This improves field
installation by preventing "ground loops", and also
minimizes lightning protection problems. The PV module frames
and structures should be grounded, but the PV input cables left
ungrounded. Leakage currents and static build-up are handled by
the module frame grounds, and a diode drop into the positive
terminal of the battery which is grounded. Lightning surge
protection is provided by the PV regulators on the input side
and the PV controller on the negative output side.
PV powered
systems are normally designed for 5 to 10 days of autonomy
(sunless days). The batteries are often protected by a low
voltage cutoff which shuts down the controller before damage to
the batteries occurs. As a PV distributor and control
manufacturer you will find our pricing very competitive. Our
systems usually require fewer PV modules due to the high
efficiency of the ETA controller. |
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