By Eric Langford and Danny Tosolini
With the requirement to increase control, improve responsiveness and system reliability, most large utilities have installed automated control and SCADA systems. These systems, while very robust, can be very expensive to install and maintain and are out of reach for many small to medium sized utilities.
Through the use of Intelligent Electronic Devices (IEDs) and advanced monitoring software, St. Thomas Public Utilities Commission has implemented a cost effective monitoring solution that enables the utility to monitor both their electric distribution and their water system.
THE REQUIREMENT
St. Thomas PUC has a peak load of approximately 60 MW serving 13,000 industrial and residential customers. In 1996 St. Thomas PUC identified the need for a Supervisory Control and Data Acquisition (SCADA) system that would meet a minimum set of requirements. These requirements included: real-time monitoring; historical data storage and trending; alarming; fault current recording and waveform capture; ability to control switches, breakers and valves; and flexible communications to field devices. Most importantly, however, the software would have to be easy to use, reliable, and cost effective with strong technical support.
THE SYSTEM
After evaluating several systems, St. Thomas PUC chose Pegasus monitoring software and field devices from Power Measurement Ltd. The utility installed Intelligent Electronic Devices (IEDs) providing them with a solution that met all of their requirements at a competitive price. Furthermore, the system was installed and commissioned by utility staff, thereby eliminating the requirement for specialized vendor or third-party technicians, and expensive long-term support contracts. Addition-ally, the utility staff maintains ownership of their monitoring system and it can be defined, modified and expanded by the utility as required without relying on external service organizations or the manufacturer. Extended support and factory training was provided.
In the main office control room, the Pegasus workstation runs on a Windows NT computer with 3 dial tone phone lines to remote devices. Additional client workstations are used to access this information in the PUC office. The IEDs are used to monitor each of the 4 main feeders in the utility's distribution system. Three IEDs are used with external I/O for the booster stations and two chambers. The IEDs monitor electrical energy consumption as well as water parameters such as water flow, pressure, pH chlorine and counts the cubic meters of water that pass. Remote control functionality has not yet been implemented but will be in a future project.
The control room is only staffed during the day. After hours the IED will send alarm messages to the on-duty trouble man's pager when a pre-defined setpoint condition is exceeded.
REVENUE METERING
Although not initially in the plan, interval Time-of-Use metering on the utility's major loads was added. The utility employs a revenue-class meter that, via telephone line, provides many of the features required for the initial SCADA scope of work, while also providing interval revenue billing on the utility's major loads. As a result, St. Thomas PUC has one system for its distribution system monitoring and for its Automated Meter Reading (AMR). One system means there are fewer maintenance and training requirements, and the use of password protection prevents unauthorized access to restricted information. A monthly report containing the meter readings from the revenue meters is automatically generated with the Report Generation tool and provided to the billing department.
A unique feature of the unit is its dual communication ports that allow the meter to simultaneously communicate with two different systems on different protocols. For example, the unit can be interrogated by the utility's software, and the second communication port can be provided to the customer so the customer can have real-time power and energy information in their Distributed Control System (DCS) or SCADA system.
DEREGULATION
St. Thomas PUC has given itself a competitive advantage for deregulation of the electrical industry.
It isone of the few utilities capable of providing its customers with value-added services such as real-time power and energy information from its revenue meters directly into its customers DCS or SCADA system. Therefore the customer will not have to install check meters and the utility has an accurate profile of the energy consumption of the customer. Furthermore, if there are voltage fluctuations or power disturbances on the distribution system the user can check the revenue meter before contacting the utility.
St. Thomas PUC is able to provide detailed information to its customers about a disturbance. The system will also verify what, if any, power is wheeled through its distribution grid.
If, in the future, the utility is merged with, or purchased by, another utility that already has an extensive SCADA system, then via Modbus, Pegasys can be expanded to communicate with other devices such as PLCs or RTUs.
The overall project costs, including installation and commissioning, were far below that of traditional SCADA systems, while meeting the requirements of a progressive mid-sized utility. The St. Thomas PUC solution is one that can be easily maintained by utility staff and can be scaled as the utility grows.
Danny Tosolini is with St. Thomas PUC and Eric Langford is with Langford & Associates. ET