With its 34 water wells and 280 sewage lift stations, the Escambia County Utility Authority (ECUA) in Pensacola, Fla., is the largest water provider and wastewater manager for a population of about 85,000 in the Florida Panhandle.
It also is extremely prone to lightning strikes.
There are about 100 thunderstorm days per year along the Florida Gulf Coast, and in a two-week period in July 1995, ECUA lost an estimated $42,000 in equipment from lighting damage. This cost did not include labor, downtime and potential fines associated with down equipment.
Pressure and flow monitoring stations at remote sites near bridges and elevated tanks are even more susceptible. "At these sites, pressure transmitters, flowmeters and related equipment began failing at a seemingly high rate," said Earl Griffin, ECUA instrument and electrical control supervisor.
ECUA decided to install surge protection at all the remote sites thought to be highly exposed to lightning strikes. The authority installed "fine-level" protection at the sites from March to June 1996, and on the instrumentation at three of 34 water wells from September to October 1996. Fine-level protection is designed to protect individual instruments against surges in power lines, antenna lines and signal lines attached to the instrument. (See Table 1.)
In general, surge protective devices are designed to protect sensitive electronic equipment from damaging transient voltages. Under normal operating conditions, they act as a high-impedance connection between power or signal line and ground. When sensing a fast rising voltage, the surge protective device becomes a low impedance short circuit to ground to divert the unwanted energy away from the sensitive electronic equipment. Because the transient condition occurs for a maximum time duration in microseconds, this low impedance state occurs very quickly. After diverting the energy to ground, the surge protective device "resets" itself back to the normal high impedance state.
At the sites Griffin chose, the protection included surge protection of the AC power supplied to the instruments and the Supervisory Control and Data Acquisition (SCADA) Remote Terminal Units (RTUs), surge protection of the antenna input to the SCADA radio, and surge protection for all 4-20mA DC loops. Based on the specifications needed, ECUA installed Transient Absorption Technology (TRABTECH) surge protection from Phoenix Contact, Harrisburg, Pa., at these sites.
In addition to fine protection, ECUA installed "coarse" protection at the main breaker of the stations to protect them against high-level or direct strike surges. Medium-level protection could be eliminated due to the layout of the ECUA water well and lift stations.
"Although we did not keep exact records before or after the installation of the surge arrestors, opinion among ECUA personnel close to the situation is that we realized a significant reduction in lightning-related losses," Griffin said.
Since 1996, ECUA has upgraded and protected additional sites with various TRABTECH products that provide protection on pressure and flow circuits, pH and flow loops, SCADA RF lines and incoming power. In early 1999, Flashtrab Plus Control coarse-level protection was installed on the AC power service at one of the water wells and large water pumping stations. In mid-1999, a Flashtrab Plus Control was installed at one of the major lift stations during a major rehab, and in late 1999 at a second water well during its total rehab.
In 1999, ECUA experienced 22 lightning-related incidents in its water well system that resulted in failed instruments. Of those, only four occurred at sites where some sort of fine-level protection was installed. None of these sites had coarse-level protection.
Currently, ECUA has fine-level protection installed on more than 100 individual instruments located at more than 20 separate locations. A new water pumping station and a new water well currently under construction have been specified to have full surge protection by Phoenix Contact. ECUA’s specifications have been revised to require all new SCADA RTUs to be equipped with fine-level protection. All new construction as well as planned renovations will also include full-surge protection.
"The ultimate goal is to have all of our more than 50 water well sites and more than 275 lift stations properly protected," Griffin said.
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