Complex Design: Pork Processing Plant Standby Generating Facility
IEA designed and built an 11.4 MW diesel fired standby power generating plant for a large industrial customer in central Iowa. The system was built in three phases over a 10 year period in order to keep pace with customer load growth. It was originally designed to include three 1.6 MW diesel generators, a single utility feed, and two customer load ties. Several years later, an additional two 1.6 MW engines, a second utility connection and two additional load ties were added. Finally, an additional 1.6 MW engine and a 1.8 MW engine along with an additional utility feed and two more customer load ties were added.
The completed system consists of (see simplified one line):
- Seven diesel generators (11.4 MW total generating capacity) in walk-around enclosures including a 275 gallon day tank in each enclosure.
- A single 12,000 gallon above ground storage tank.
- Three utility services.
- 6 customer load connections.
The system generates power at 4,160 Volts. Utility interconnection is at 4,160 volts via utility owned transformers that step voltage up from 4.16 KV to 34.5 KV. All seven generators are connected to a common emergency power bus. The emergency bus is connected to customer loads via six load tie circuit breakers. Each tie circuit breaker is paired with one of six utility interconnect circuit breakers or automatic reclosers.
The system can be operated in Standby mode (power outage), Import mode (maintain a set KW import level while in parallel with the utility) or in Base Load mode (generators produce a fixed amount of output in parallel with the utility). In addition, each engine can be manually loaded while in import or base load mode. It features Load Sense/Load Demand capability (the system will automatically start or stop engines as required by actual plant loads).
Import mode operation: All seven engines are started, and their output circuit breakers are closed to connect them to the emergency power bus. The system will then soft unload the first of 6 utility connections (the order in which the system connects to and then unloads and isolates from each of the six utility connections is user selectable). Once unloaded, the utility circuit breaker is tripped open. The system then parallels with the utility source and closes tie circuit breaker designated as the number two load. Once the tie closes, the utility source is unloaded and when import level drops to approximately 50 KW, the utility circuit breaker is tripped open. This process (close tie, unload utility, trip utility) is repeated until the last of the six tie circuit breakers has been closed. The system will then automatically maintain the operator selected import level setpoint by varying generator load as facility loads change.
Base load mode: The startup sequence is the same as for Import mode. However, the system will stop taking on additional load at such time as its Base Load Setpoint has been reached. It will then maintain the set load until the system is shut down.
System shut down: Upon command to shut down (or after a programmable time delay following return of stable utility service), the system will unload across the last designated tie circuit breaker, and then the tie will be tripped open. The system will then parallel to the utility source and close the utility circuit breaker designated as the number 5 source. The generators will unload until a preset utility load is reached, and then the tie will be tripped open. This process (close utility, unload to utility, trip tie) is repeated (in reverse order, 5-4-3-2-1) until the last utility circuit breaker has been closed. The system will unload and then all seven generator output breakers are tripped open. The last tie remains closed in order to provide station power for battery chargers, lighting, jacket water heaters and other generating plant loads.