Tom A. Short

Advanced Metering for Phase Identification, Transformer Identification, and Secondary Modeling

Advanced metering infrastructure (AMI) offers utilities new ways to model and analyze distribution circuits. Results from two circuits introduce a new method to identify phasing of transformers and single-phase taps using voltage and kilowatt-hour measurements from AMI. In addition to phase identification, we show how to use the same approach to create or check meter-to-transformer mappings. These algorithms are based on linear regression and basic voltage drop relationships. With this approach, secondary connectivity and impedance models can be auto generated. In addition, detection of unmetered load appears possible. Also demonstrated is use of AMI to estimate primary-side voltage profiles.

Site variation and prediction of power quality

We use EPRIs distribution power quality project data to characterize and predict voltage sags and momentary interruptions based on site characteristics. The quality of sites is widely dispersed. Rural sites have many more sags and momentary interruptions than suburban and urban sites. The strongest indicators of voltage sags are: 1) circuit exposure, 2) lightning, and 3) a term with transformer impedance and number of feeders. We develop a linear model for predicting sags and another for predicting momentary interruptions based on site characteristics. We also compare transmission-level power quality to distribution power quality.

Using PQ Monitoring and Substation Relays for Fault Location on Distribution Systems

Fault location is of considerable interest for utilities to improve their reliability and speed storm restorations. Power quality recorders, relays, and other monitors can provide information to help locate faults. In this paper, some basic impedance-based fault-location methods are evaluated on utility measurement data with known fault locations. The main finding is that reasonably accurate fault locations are possible on a wide range of distribution circuits with either feeder-level or bus-level substation monitoring. Another important finding described is how monitoring can be used to estimate the parameters of the fault arc. This can improve fault locations and help with accident investigations, equipment failure forensics, and other hazards related to the power and energy created by the arc

Weather Normalization of Reliability Indices

Weather significantly influences distribution reliability indices, especially duration benchmarks like SAIDI. We explore correlations with various weather parameters including lightning-detection network data, and wind from weather stations. This paper explores a number of ways to account for the variability caused by weather. Approaches include regression models to normalize with weather data as inputs, using outage database indicators of weather, and modifications to the 2.5 beta method of IEEE Std. 1366.

Voltage reduction field trials on distributions circuits

This paper describes field trials of voltage reduction on nine distribution circuits. The median CVR factor was 0.6 on these circuits. Results were normalized using measurements from nearby comparable circuits. Advanced metering infrastructure data on some circuits allowed comparison by customer type. On one circuit, commercial customers had lower CVR factors than residential customers. For residential customers, CVR factors were lower for customers with higher winter loads.

Effect of Single-Phase Reclosing on Industrial Loads

Three-phase reclosers with single-phase tripping are being more widely employed on utility distribution feeders. They have the advantages of increasing reliability for the customers on the feeders, because the majority of distribution feeder faults are single-phase. However, certain difficulties may occur when three-phase industrial and commercial loads, with three-phase transformers and motor loads are interrupted on one phase only. These include overheating of motors, ferroresonance of transformers, tripping of power electronic drives and backfeeding of distribution lines. This paper examines these effects, their severity and mitigation techniques

Voltage reduction results on a 24-kV circuit

This paper describes findings from a field trial of voltage reduction on a 24-kV circuit in North Carolina. The depth of voltage reduction was limited by commercial customers with off-nominal transformer taps and by customers with transformer and secondary issues. Voltage measurements from advanced metering provide insight on the importance of distribution transformers and secondaries when reducing voltage.

Medium-voltage arc flash in open air and padmounted equipment

Arc flash is an important consideration for personnel safety. This paper shows test results for overhead arc flash scenarios and arc flash in a padmounted switch. Both scenarios result in more incident energy than expected. For overhead arc scenarios, longer arc lengths are considered when analyzing arc flash. For the padmounted switch, an equation is developed to help coordinate protective clothing with minimum approach distances and upstream protective relaying.

Arc-Flash Testing of Typical 480-V Utility Equipment

A test program was completed to measure arc-flash incident energy from actual 480-V utility equipment to determine the most appropriate flame resistant clothing for utility workers. The equipment tested included self-contained and current transformer-rated meters, pad-mounted transformer secondary cubicles, power panels, and network protectors. Testing was performed to determine the sustainability of low-voltage arcs in actual utility equipment, to find the most appropriate calculation method to predict the measured incident energy, and to identify any key variables that would effect both duration and heat from this type of equipment.

Efficiency impacts of distribution secondaries

Distribution feeder models do not typically include secondary lines and distribution transformers. In general, sufficient data concerning the secondary impedances and individual customer demands has not been available to accurate assess the losses and voltage drops accrued across these portions of the feeder. However, feeder data collected through GIS and AMI programs may permit more accurate representation of system behavior at the customer level. In this paper, the impacts of typical secondary loss modeling assumptions and circuit configurations are evaluated against models derived from detailed secondary circuit data and field measurements collected by Consumers Energy.