Spectrum Controls, Inc. - Application Note: 1746sc-INI4i Isolated Analog Input used by TECO Energy, Inc.

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Electric Power Generation:
A Spectrum Controls solution without sparks...

Higher electric power demands have resulted in an initiative to improve power generation process control and safety. TECO Energy, Inc. is the parent company to a family of energy businesses, headquartered in Tampa, Florida providing over 550,000 people with energy. One of these businesses, Tampa Electric, working in conjunction with Electro Design Engineering, a systems integrator, recently completed a conversion of an existing coal-fired turbine generator to a natural gas-fired generation system.

The power generation station consists of two Siemens turbines that are fueled from a nearby gas pipeline. This electricity is then fed to the Florida transmission grid. The generators operate continuously and the critical nature of the station requires complete redundancy at the controls and measurement device level.

Don Delp, the maintenance supervisor at Teco Energy indicated that "We cannot afford for the system to fail" due to the high demand cycles. The process involves two stations separated by about a mile:

A metering station measuring pipeline temperature, pressure, flow and valve position.

A regulation station that controls the flow and pressure of the gas supply being used by the turbines.

Each station has a primary and backup Allen Bradley SLC-500 programmable logic controller. Each of these PLCs use Spectrum Controls 1746sc-INI4i isolated analog input modules to monitor these parameters. The critical nature of the application requires the highest level of reliability and protection. Spectrum Controls modules were selected for their build-in electrical isolation that restricts the damages to an absolute minimum. This area of Florida is affected by lightning strikes resulting in electrical transients. Ground loops are also prevalent in power generation installations. These issues are minimized by providing high levels of channel-to-channel isolation for the different input devices such as flow meters, pressure transmitters, and temperature transmitters.

Spectrum Controls I/O modules provide internal electrical isolation. This minimizes the need for external brick isolators and reduces installation time. Here is a wiring example for two (4 to 20mA) sensors. Teco Energy uses Spectrum Controls modules because of their high channel-to- channel isolation, ease of configuration, reliability and high accuracy. These characteristics make them an ideal fit in any energy control system where isolation and reliability is critical.