Case Histories
• Industrial Grade UPS Systems Protect Electric Generating Plant Control Room
• Power Generating Plant Uses Industrial Grade UPS System to Back-Up Critical Controls
• Glass Making Plant Uses UPS System To Ensure Continuous Operation
• Nuclear Power Station Installs New UPS System
• Nebraska Nuclear Power Plant Upgrades UPS System
• New Hampshire Utility Uses Industrial Grade UPS Systems At Several of Its Power Stations

Power Generating Plant Uses Industrial Grade UPS System to Back-Up Critical Controls

The Conemaugh Electric Generating Station is located on a 1,750-acre site along the Conemaugh River, 13 miles northwest of Johnstown, Pennsylvania, in Indiana County. Employing over 200 people, the Conemaugh Station is a major component of the billion dollar power development in the Chestnut Ridge region. Operated by Penelec, a division of GPU, the station was constructed by investor-owned utilities representing four eastern states and the District of Columbia.

In 1988, the station installed two new Honeywell TDC 3000 distributed control systems (DCSs), one for each of the stationās two generating units, to monitor the power production process. As part of this system upgrade, an uninterruptible power supply (UPS) system was installed to provide backup power for these critical Systems which cannot afford to shutdown during the power generation process.

The DCS monitors all the major functions of the boiler/turbine generator operating cycle. The fuel system determines the rate at which coal is sent into pulverizers for firing. Air used in the combustion process is supplied by forced draft fans monitored by the DCS, as well as the speed at which pumps feed water into the boiler. The DCS also monitors the tur- bine governor which controls the generator speed by controlling the amount of steam going into the turbine. These and other auxiliary functions are all monitored by the DCS.

Because of this high degree of reliance, it is critical that the DCS operate continuously. If the process would suddenly lose power, the plantās power production of 850 MW of power would be jeopardized. The cost of an outage to the plant is approximately $125,000 a day.

The quality of power feeding the DCS is also a concern. Because it is a computer- based system, it requires a clean, transient-free supply for proper operation. Power line aberrations such as surges, sags and brownouts can cause errors in critical data readings and computations, as well as damage to the DCS.

To make sure it is receiving peak performance form the new DCS, despite the loss or quality of incoming electric power from the utility grid, the Conemaugh Station installed two 40kVA capacity UPS systems manufactured by Solidstate Controls, Inc. (SCI). Each system is made up of an inverter and battery charger. The batteries can provide up to 1 /2- hour of continuous power to the control room. This is an adequate amount of time to ride through most power outages. Besides providing battery back-up power, the UPS system also provides a clean, conditioned source, free of transients that can cause poor performance or premature component failure in the DCS.

The UPS system used in the application is an industrial grade unit, specially designed for harsh environments such as those found in fossil-powered Generating plants. The majority of UPS systems on market are designed for the clean, controlled environments of computer rooms and are usually not suitable for industrial surroundings. The UPS system employs ferroresonant technology that uses

passive electronic and magnetic components in its design. This type of unit is better suited to industrial environments than UPS systems using more complicated power devices with complex feedback circuits which must be protected from harsh environments. The UPS at Conemaugh is located in an area about 100 feet from the control room.

The decision to use this type of UPS System was based on past experience with a similar unit. The control system that was being replaced had also used a ferroresonant UPS from SCI to back-up a computer that was part of that system. This I 5kVA UPS, used continuously for over 25 years, is still being used to provide emergency power to other boiler flame scanners, auxiliary boilers, gas/coal firing, turbine supervisory and vibration monitoring controls at the Conemaugh plant.