Interconnect Voltage Change and Digital Controls Upgrade

In 2019 and 2020, IEA commenced work on a complex project at an existing site where IEA had seven generators bussed to a common bus and connected to six customer loads by individual tie breaker & recloser combinations. IEA generated and interconnected to customer loads at 4,160 volts. In response to voltage upgrades planned by the local utility and transmission suppliers, IEA would now be required to interconnect at a single point at 24.9 kV

Challenges:

·         Source and install a new 4,160/24.9 kV main transformer rated at 12/16/20 MVA (rating dependent on cooling fans configuration);

·         Source and install a new 3,000 amp, 4,160 volt single interconnect tie breaker and a fully digital control system to replace the old analog control system and programmable logic (PLC) controller.

Solution:

The control system upgrades were necessary due to the change from six bus tie connections to a single tie point. Along with the old PLC and its software that could not be readily upgraded or modified.  Due to the age of the system, IEA chose to demolish all existing conduit and wiring for the old control system.  All new conduit and wire were installed between the generators, tie circuit breaker, utility recloser and all switchgear section. To upgrade the system, IEA chose to utilize a Woodward Controls based control architecture along with an Allen Bradley Control Logix PLC. Each generator was then retrofitted with an EasYgen controller and touchscreen interface, and the main utility Recloser and bus tie breaker were fitted with Woodward LS5 circuit breaker controllers.

With the new Control Logix PLC installed, IEA now had the capability for multiple start modes to include:

·         Isolate mode – Operating on generators only with utility source available.

·         Import mode – Operating in parallel with utility maintaining a minimum utility import.

·         Baseload mode – Operating in parallel with utility at a fixed level of production.

·         Standby mode* – Operating on generators when a utility outage occurs.

*This function operates independent of the Control Logix PLC through the Woodward Controller only as to maximize reliability in case of PLC failure.

To abide by the utility interconnect agreement an SEL 700GT protective relay was selected to provide all required protective functions. This replaced the existing individual discrete logic relays, removing multiple potential failure points.

Construction and startup activities took approximately 4 months to complete. IEA coordinated the installation and testing with the manufacturing plant’s production schedules to minimize risk of impacting plant operations.