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

Industrial Grade UPS Systems Protect Electric Generating Plant Control Room

Fossil-powered electric generating plants depend on industrial grade Uninterruptible power supply (UPS) systems to keep their critical control systems up and running. Electricity is produced by burning coal to heat water, which then creates steam to rotate a turbine at high speeds. The turbineās motion drives a generator to create electricity. The entire process is controlled by sophisticated electronic control systems that require a steady stream of electrical- power in order to keep the plant functioning in a safe and efficient manner.

The importance of maintaining the continuous operation of these control systems is underscored by the cost of a shutdown. If the power was lost, the water tanks would overflow, pumps would stop, the boilers would shutdown and all power production would cease. It would take between 18 and 24 hours to restart the plant at a cost of about $250,000. Additionally, it would cost the utility about $70,000 an hour in lost customer billings.

A major coal-burning power plant in the Midwest recently upgraded the UPS systems protecting its plant control rooms. The operation has two identical generating units, producing a total of 2.6 million kw. Each unit has a control room with a Bailey Network 90 distributed control system (DCS) that regulates heat production, fuel intake and output.

The quality of power feeding the DCS was another major concern. Because it is a computer-based system, it requires a clean, transient-free supply for proper operation. Power line

irregularities such as surges, sags and brownouts can cause errors in critical data readings and computations, as well as damage to the DCS.

The UPS system was specified to be an industrial grade unit of a ferroresonant design, which is especially ideal in the harsh environments of a power plant where coal dust and fly ash are present in the atmosphere. The majority of UPS systems on the market are designed for the clean, controlled environments of computer rooms and are usually not suitable for industrial surroundings. A ferroresonant system, however, 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.

After presenting their needs to several vendors, they selected UPS systems manufactured by Solidstate Controls, Inc., Columbus, Ohio. They chose this vendor because of their willingness to add custom features to the UPS units. These included special screens to keep out animals and birds, as well as additional system operation indicators and metering. There was also a need to deliver the units without the transformers in the cabinets. The location where the units were to be positioned required tilting them to get them into place. This would hove been nearly impossible with the transformers in the cabinets. After the units were situated, the transformers were then installed.

For maximum protection, each control room has two complete ferroresonant UPS systems made up of a regulated rectifier, an inverter and electronic throw over switches. The protected loads are divided between the two systems as an extra measure of security. There are separate plant batteries and battery chargers for each generating unit. The individual inverters have a capacity of 45kVA, while each battery charger is rated at 250 amps. In the event of a power outage, the UPS system transfers the load to battery power without any interruptions in the flow of power to the control room. In addition to 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.