Utilities are enamored with distribution automation (D/A) over the past decade. Utilities large and small have embarked on numerous studies and pilot projects to demonstrate the technology and to determine whether to launch a full-scale roll out of D/A. The majority of these initiatives have shown positive results produced savings in operating cost and improved system operation. Still, we have not seen major implementations. One major obstacle utilities face when planning full-scale implementation is the cost of the communications system. For many utilities, this cost overrides the potential benefits of D/A.

One example of this communications obstacle is the recording and gathering of voltage readings throughout a distribution network. In the past, utilities had few options for capturing this information and transferring it from the field to the utility operations center. Utilities often used customer phone lines or made time-consuming site visits to download the information.

A new low-cost communications technique to measure line voltages, the Telemetric TVM MicroRTU^™, eliminates the difficulty of gathering accurate and timely line-voltage information. This device, offered by Telemetric Corp. (Boise, Idaho, U.S.), uses a built-in radio that communicates over the control channel of the cellular data network. This network covers 98% of the population in North America and does not require a license or local cellular account. Using this system eliminates the capital cost of developing a communications system while minimizing operating costs.

The integrated cellular radio provides two-way communications between the remote device and the Telemetric Network Operations Center. An intelligent Web server provides the user with instant access to the data over a secure site. For increased ease of use, users can monitor all devices through the utility's existing SCADA system. The TVM can monitor single- or three-phase line voltages and compare the readings to user-configured voltage limits, detecting voltage sags, surges and power outages. Out-of-bounds conditions are reported immediately, while long-term voltage profiles are reported periodically.

Monitoring Voltage Profiles

Idaho Power (Boise) relies heavily on circuit models to ensure reliability of service to end-use customers. As new businesses and neighborhoods are added, the utility must update the circuit models to reflect the circuit extensions and the additional load.

In the past, Idaho Power had two methods for gathering voltage measurements to verify the accuracy of the circuit models. The first method used manual reads from handheld meters at various points on the feeders during peak load periods. Data gathered through this method was infrequent, time consuming and might not always correlate with peak load conditions.

The second method was to temporarily install metering equipment to measure voltage levels at various points on the feeders. The equipment, which could only be installed for short periods of time, required several trips to the field to install, read the data periodically and uninstall.

Idaho Power is conducting a pilot project installing the TVM at geographically dispersed locations throughout its network to evaluate the potential for improving the circuit models while reducing field expenses. The TVM monitors single-phase voltage and reports present voltage levels, power outages and line-voltage fluctuations. Only one site visit is required to install the unit; periodic reports are obtained via the cellular network. If necessary, the utility can reconfigure the TVM via the wireless network.

According to Monty Mericle, T&D development group leader, Idaho Power is constantly working to improve the accuracy of its system monitoring and analysis. The TVM will facilitate the utility's continued effort to fine-tune its system and improve quality of service to customers.

Monitoring Feeder Reclosers

Presently, power-quality engineers at Idaho Power are evaluating the TVM for feeder-recloser monitoring. The TVM can report recloser operations, giving details (time duration and voltage) for each state change. The time and location of the triggering event is also reported. Many utilities monitor line reclosers using a dedicated communications system, but the TVM does not require this large investment. Within a few seconds after an event occurs, the data is available for use in the utility control center. In addition, the TVM gives exact locations of system outages while customer phone calls give only general area information.

Feeder Voltage Profile

An energy management specialist with Progress Energy (Raleigh, North Carolina, U.S.) is evaluating the TVM to quickly and easily install monitoring devices anywhere on the distribution system on an existing communications system. Applications include voltage monitoring, capacitor bank control and recloser communications.

Progress Energy intends to use TVMs to monitor the distribution feeder supply voltage, both near the first customers and at the tail end near the last customers. These units will monitor supply voltage levels and will alarm for over-voltage and under-voltage conditions. This monitoring will help ensure high-quality service to the end customers regardless of their location on the feeder.

Monitoring Power Quality

Several utilities are deploying TVMs at key customer sites to monitor the voltage supply based on the ITI/CBEMA voltage-acceptability curve. This curve specifies acceptable voltage quality conditions that can be tolerated by well-designed computer equipment. For example, the equipment should operate at zero voltage for up to 20 milliseconds without resetting and at a 10% under voltage level indefinitely. The default TVM configuration compares the monitored line voltage to the CBEMA curve and reports any excursion outside of the acceptable zone. This allows the supply voltage at key accounts to be continuously monitored for acceptable quality levels. E-mail or pager-based reports of power-quality events can be automatically sent to either the utility or the customer. In addition, the voltage profile and other data will be saved at the Telemetric Network Operation Center or in the utility's SCADA system for retrieval and analysis.

Final Analysis

Many utilities have been searching for the key that would allow them to implement distribution automation systems on a wide-scale basis. All of the pilot system tests and analyses promised economic savings in system operation and improved quality of service to the end-use customers.

However, in the final analysis, the cost associated with the communications system required to support these DMS systems blocked the implementation. Now utilities have access to an in-place communications system that offers economical utilization rates and is dependent only on the users' report requirements and device configuration. This gives the utility control of the automation system implementation and operation and does not require any capital funding for communications.

H. Lee Smith, principal consultant with HLS Consultant Services, has more than 40 years experience in the electric-utility industry. Smith, who has written more than 40 technical papers and articles, has a Life Senior Membership with IEEE and the Power Engineering Society, and is a Working Group Chair for updating IEEE standard 1379-2000. In addition, he is the U.S. technical coordinator for the development of IEC standard 61850 series, and an adjunct professor at Penn State University teaching power system automation courses.