,
Abstract
The Johnson City Power Board is an electric power distributor located in Johnson City, Tennessee, serving over 75,000 customers in 5 counties. JCPB operates and maintains over 2000 miles of 13KV distribution lines and over 120 miles of 69KV transmission.The peak system load on JCPB’s system is 550 MW. JCPB has 30 distribution substations with over 100 distribution feeders. JCPB purchases power from the Tennessee Valley Authority. In March 2010, TVA converted their billing structure to include demand power charges for each distributor. Therefore JCPB decided to implement a conservation voltage reduction plan during peak loading times in order to save on peak demand charges.
Figure 1. Custom dashboard showing station loading, end of line voltages, and voltage reduction status. 17 Boomerang devices are online at the time of the screenshot.
Context
Conservation voltage reduction is a process by which distributors lower the voltage on their system for a short duration. Lowering the voltage on a system will temporarily lower the power demanded by the loads connected to those circuits. JCPB is charged a demand component for each kw demanded by the system in its entirety. Thus, lowering the demand of the system as a whole during peak times will reduce the demand charge from TVA.
Typical factors for percent load reduction are 0.5 to 1.2 for every percent of voltage reduced. ANSI C84.1 allows for a minimum voltage at the end customer’s metering point to be no less than 114 volts during normal operation. JCPB needed to find a way to measure the voltage at the end of the line in order to maintain minimum voltage at the customer’s billing point and achieve the maximum reduction in voltage at the substation.
Figure 2. Monthly load profile with voltage reduction initiated only during peak time of the month.
Problem Definition
JCPB operates an unlicensed 900 MHz radio system for communication with substations and some field devices. Because they are unlicensed, the power output of the radios is restricted to 1 watt. Line of sight is required for these radios to communicate reliably with one another. JCPB’s system is in the hills of the Appalachian Mountains and has many hills and valleys where line of sight communication is difficult. In many cases, multiple repeaters were required to achieve the line of sight between the radios. In order to communicate with any end of line voltage devices using these radios, a large investment would have been needed in radios and repeaters. Additionally, as JCPB’s system grows and changes are made to the feeders and substations, the point on each feeder with the lowest voltage may change. This would require additional investment in radios and repeaters. Installing 900 MHz radios and repeaters to communicate with an end of line voltage sensor would be time consuming and expensive. Each month that JCPB is not receiving the end of line voltages from critical feeders lessens the amount of demand reduction that JCPB can achieve.
Goals of Equipment Application
System automation is required to eliminate any human error in a voltage reduction program and achieve maximum benefit. There is a need to acquire near real-time measurements to adequately bias the voltage regulation devices to achieve maximum benefit. Many products, such as AMI systems, record and report the voltage back to their servers. Often there is a latency between the measurement and the time that it is reported. This could cause either an underperforming system or the voltage to be below the minimum voltage range. In addition to the latency, many AMI vendors do not have an application to allow a SCADA system to access this voltage information. The equipment selected to report the voltage would have to do so with a high degree of accuracy, in near real-time, and be able to interface with our SCADA system.
Solution
JCPB selected the Power Monitors Boomerang device to report the end of line voltages back to JCPB’s SCADA system. Each Boomerang operates over a GSM cellular network and has a static IP address. There is a DNP protocol interface for each device that allows SCADA communication. Since the communications infrastructure is already in place with these devices, there was no need for JCPB to purchase and install additional radios and repeaters. JCPB used a model of the power system to determine which feeders on each substation would have the lowest voltages during peak loading. Using this model, one or two feeders out of each station had the highest load or the longest line that resulted in the lowest voltage out of that station. The ends of these feeders were selected to install a Boomerang device to report the voltage. JCPB personnel visited each feeder with a powered Boomerang device to verify communications. Once communications were verified, the Boomerang devices were installed on the lines and programmed into the SCADA. Voltage measurements for the ends of those lines were now available in SCADA for achieving maximum benefit of the voltage reduction program. Custom scripts for the SCADA system were then written to automate the voltage reduction program. These scripts are programmed to bias the regulators from the end of line voltages and maintain peak performance from the voltage reduction program. Many other scripts were written to automate the entire system, resulting in the voltage reduction program to be called upon only when a new monthly peak is going to be achieved. As the JCPB’s system changes over time, the Boomerang devices are easily relocated without the expense of installing additional communication infrastructure. Hence, the Boomerang devices and custom automation scripts provide JCPB with an efficient and reliable solution for achieving conservation voltage reduction.
Figure 3. Zoom of voltage reduction showing approximate 7 MW reduction in load
Conclusion
The Johnson City Power Board installed 27 Boomerang devices on the system to maximize the benefit of conservation voltage reduction while maintaining above minimum voltage on the customers’ point of service. The conservation voltage reduction program will lower JCPB’s cost of providing power, therefore driving rates down. The Boomerang solution allows for accurate and real-time measurements of end of line voltages and is easily relocated at minimum cost as the system changes. The conservation voltage reduction program in conjunction with the Boomerang devices allows JCPB to operate its power system in a more efficient manner, serve the customers better by keeping rates low, and help the environment by reducing carbon emissions from fossil fuel burning generation plants.
Brandon Horne, PE, MBA
System Design Engineer
Johnson City Power Board
www.jcpb.com
Chris Mullins
VP of Engineering and Operations
cmullins@powermonitors.com
https://www.powermonitors.com
(800) 296-4120
