In 2005, baltimore gas and electric co. initiated a project to address aging and obsolete capacitor control equipment in substations. Unlike the majority of utilities, Baltimore Gas and Electric Co. (BGE; Baltimore, Maryland, U.S.), a subsidiary of Constellation Energy, uses controlled line capacitors instead of load-tap changers on transformers as a primary method to maintain distribution voltage levels. Historically, this has been accomplished through control equipment local to the substation, using station metering as a source and very-high-frequency (VHF) radio-signal-controlled switches to operate line capacitors.

While this method has been successful, advances in technology have since replaced this older method of control. Manufacturers have stopped making the station equipment, and replacement parts are difficult to purchase. In addition, BGE's evolving company enterprise needs made it necessary to move voltage-control information and control functions from local substations to various departments within the company. To resolve these issues, BGE set forth to centralize its capacitor control.

NEW SYSTEM FRAMEWORK

BGE's existing capacitor control system included stand-alone capacitor bank controllers (CBCs) manufactured by Cannon Technologies (Minneapolis, Minnesota, U.S.). Capitalizing on this, BGE's IT and substation control departments formed a joint effort with Cannon's to develop a new system that would remove local radio-controlled capacitors from substations and create a centralized paging control with intercompany web-based access.

The team initiated a system-design concept that replicated the function of BGE's existing station equipment using the Cannon Yukon Advanced Energy Services Platform software. While the Yukon software had the functionality to build complex math functions and link source data from the substation, its VAR control platform required modifications to support BGE's voltage-control needs. To do this, BGE's substation control group created a complex algorithm to replicate the operation of existing substation hardware. BGE's algorithm combined with Cannon Technologies' paged controllers allowed for a means to centrally control capacitors outside the substation.

To help ensure system reliability, BGE's IT department developed redundant paging paths and redundant off-site servers. Cannon Technologies' programmable controllers allowed BGE to use two different paging companies, providing diversified coverage. Redundant servers running Cannon's applications provided the means to integrate current data systems that provide substation analog data, as well as intercompany access via Web Client to view live system conditions and issue manual controls outside the automatic voltage control. Redundant servers also provided flexibility for running development testing for future software releases.

HOW IT WORKS

The system uses a Web Client to build the controlled substation buses and to remotely view and control the capacitor banks on the system. The Web Client feature has eliminated travel time to the substation to adjust a voltage curve or to add or move a capacitor control. In the past, control room operators had an indication of the switched capacitors' status by a gross count of closed capacitors from supervisory control and data acquisition (SCADA). Now, other BGE departments such as planning and customer voltage quality have access to individual capacitor status and can view the VAR and voltage reaction of switched capacitors.

Cannon's Yukon software program is the heart of the system. It allows the flexibility to create an operational control point based on station analog data and combined math and logic equations. It also creates a virtual replica of equipment that was formerly in the substation. The control creates a load-biased voltage control for each substation bus, functionally similar to a load-drop compensator but with some enhancements. One of the features implemented in the software is a bus changeover function. The loss of one bus transferred to an opposite bus in an H-tie configuration will actually transfer the source data in the software. On a single bus application, the loss of a bus will disable the capacitor control in the software, as well.

Additional features include the use of a global control to shift the operational curve by a predetermined percentage. The software program accepts control from BGE's SCADA system. The control is logically linked to the algorithm, which in turn shifts the curve for a faster response to load. This can be applied to all substation buses at once during severe heat conditions to allow an opportunity to advance the voltage response to load on the distribution system on peak forecasted days.

BGE uses a bus-optimized approach where voltage correction is applied by switching capacitors on the feeder most in need of reactive power correction. This approach maintains proper voltage and keeps power factor in check. The actual control algorithm of the Yukon software provides a fixed bandwidth setting and an assignable floating control point. BGE's voltage control works on the principle of a voltage bandwidth setting based on no load with the control point floating on the same vertical axis, but in parallel with actual load conditions. Wherever the load is, it will always be reflected on the zero-load vertical axis. The algorithm contains minimum and maximum voltage setpoints relative to the predicted minimum and maximum load conditions.