Broad River Dam: 3 control levels
Lockhart Power Co. owns and operates a hydroelectric plant located on the Broad River in upstate South Carolina, striving to be a low-cost energy provider for more than 6,000 direct customers and 6,000 indirect customers with a 90-mile transmission network. The utility considered its prior proprietary microprocessor-based control system obsolete in an industry undergoing deregulation and continuing competitive pressures.
The plant’s eight-gate dam feeds a canal that channels water to the powerhouse. The powerhouse contains five turbine generators with a combined power capacity of over 17 MW. The dam and turbine control system receive data from power, flow, and level sensing devices to perform monitoring and control of the dam, generators, and associated equipment.
Lockhart required a control system providing open networking capabilities, and a lower total cost of ownership. The new system needed to coexist with an upgraded design of existing hardwired generator controls, and perform distributed, independent control at the dam and each of the five turbine stations.
Lockhart Power contracted North Fork Electric in Crumpler, NC, a provider of hydroelectric products and systems integration services, to implement the renovation. North Fork Electric proposed a three-tier solution. Level 1 includes new hardwired controls for manual operation of the system. Level 2 includes PLC-based control of the dam and generators in an automatic mode. Level 3 provides PC-based redundant control and monitoring from a central location connected to the plant-wide Ethernet network.
The system uses seven AutomationDirect DirectLogic DL205 micro-modular PLCs with D2-250 CPUs that have PID functionality. Each of the five systems for generator control includes I/O modules for digital and analog I/O, and an Ethernet communications module. The remaining two PLCs are configured in a master/slave arrangement and control the dam gates—located upriver from the powerhouse—via radio modems. Low-cost Ethernet connections for the PLCs also helped.
To reduce maintenance costs, North Fork Electric selected matching I/O components to maximize commonality among systems. The identical analog output modules used on the generators, configured for
To complete Level 2 control, North Fork Electric installed the dam control system. The system controls eight canal gates at the dam, which regulate the flow of water downstream to the turbines. The operator enters the required gate-position setpoints using a second color touch panel connected to the dam control’s master PLC in the control room. Data is transmitted to the slave PLC, located at the dam, via a 900 MHz radio modem. The slave PLC monitors gate positions using proximity switches that count teeth on the drives’ gears and move the gates.
The third tier of control and monitoring uses the LookoutDirect SCADA system, which communicates to the PLCs over an Ethernet network. This SCADA system performs supervisory control and collects data for the plant’s information system.
Edited by Control Engineering with information from AutomationDirect and North Fork Electric.