34.5-kV Cogeneration Plant

Location: Decatur, Ill.

Client: Archer Daniels Midland

This project consisted of a 34.5-kV substation at the cogeneration plant and six (6) 34.5-kV distribution feeder circuits to five (5) plant site substations and one (1) investor owned electric utility interconnection point. Burns & McDonnell responsibilities included route selection, substation design, distribution line design, and construction administration assistance.

  • Route Selection
  • Substation Design
  • Distribution Line Design
  • Construction Administration

Substation Design

Continuous service, expandability and airborne contaminates were the design criteria for ADM's 34.5-kV cogeneration substation. Burns & McDonnell implemented a reliable breaker and a half scheme with special insulation design coordination to satisfy the design requirements. The substation was designed with a repetitive nature to allow for future expansion on both ends of the main bus. Burns & McDonnell was responsible for structural steel and foundation design, technical specifications and drawings for materials, equipment, relay control boards, transformers and power circuit breaker contracts.

Distribution Line Design

Burns & McDonnell assisted ADM in selecting a line route that would have the least impact on present and future plant operations and expansion while providing circuit availability for expected substation additions. Burns & McDonnell was given total responsibility for design which included develop¬ment of wind and ice loading criteria, conductor sag/tension and vibration design and analysis, insulation, clearance and structure spotting. Struc¬tures were spotted in a complex maze of overhead and underground utilities, railroad tracks, roadways, cooling towers and storage tanks. Additional services included preparing plans and specifications for procurement of materials and construction.

Protective Relaying and Control

The substation protection and control is nearly 100% microprocessor based. Line protection includes ABB DPU 2000 relay systems that communicate with the substation control system. The substation control system consists of an Allen Bradley PLC, which provides all opening, closing, status and alarm signals. The operator interface consists of a gateway to the plant process distributed control system and custom graphics. Microprocessor based metering systems provide continuous load data to the control system.

The substation was designed for future cogeneration systems. Two parallel 34.5-kV lines provide the interconnection with Illinois Power Company. The lines are protected with fiber optic based RFL 9300 charge comparitor line differential relaying systems. Burns & McDonnell coordinated all technical interconnection requirements with Illinois Power.


Substation control and monitoring was incorporated into the cogeneration plant Distributed Controls System (DCS). The DCS acted as the operator interface for substation operation. Breaker control switches were not included as part of the controls design. Breaker controls, indication, and alarming functions were accomplished through an Allen Bradley PLC 5 programmable logic controller located in the plant relay room. The PLC included both digital and analog I/O signal processing. Synchronizing permissive logic was also included as part of the PLC breaker control logic. The PLC interfaced via hardwired connections to the automatic synchronizing equipment located in the cogeneration plant.

Energy monitoring was also included in the PLC. Watthours and Varhours were totalized through direct input of KYZ pulses from the distribution line meters. Instantaneous current, voltage, watt, and var signals were inputs to the PLC were obtained directly from transducers located in the protective relay panels.

A remote I/O rack was installed in the interconnecting utility substation for breaker status, monitoring and line metering functions. Communications to the remote I/O rack was via an underground fiber optic cable between the two substations.

Communications to the DCS was accomplished via the plant local area network. Fiber optic communications modules were installed in the PLC I/O rack. Burns & McDonnell designed operator interface graphics were included in the DCS by the DCS vendor.