Arthur W. Kelley

State estimation for real-time monitoring of distribution systems

Utilities currently use historical customer load data to forecast the loads in their distribution feeders for real-time feeder analysis and control. In this paper a three-phase state estimation method is developed to increase the accuracy of this load data. The method is based on the weighted least square approach and uses a three-phase node voltage formulation. The method can handle power, voltage, and current measurements. Test results indicate that state estimation can improve the forecasted load data by using real-time measurements. The effectiveness of branch current measurements were also tested. >

A branch-current-based state estimation method for distribution systems

A branch-current-based three-phase state estimation (SE) method is proposed for distribution systems. The method is tailored for distribution feeders with a few loops. The method is computationally more efficient than the conventional node voltage-based SE methods. To further improve the computational efficiency, it is shown that distribution systems can be reduced without much loss of accuracy in SE. >

Rectifier design for minimum line current harmonics and maximum power factor

A current quantitative computer simulation-based analysis is presented for single- and three-phase rectifier line current harmonics and power factors as a function of the output filter inductor. A finite-output filter inductor is shown to produce minimum single-phase rectifier line-current harmonics and, if used with an input displacement power factor correction capacitor, to produce maximum overall power factor. A filter inductor with near-infinite output is shown to produce minimum three-phase rectifier line-current harmonics and maximum overall power factor; the smallest inductor that approximates a near-infinite inductor is determined.<<ETX>>

Complete characterization of utilization-voltage power system impedance using wideband measurement

Inexpensive portable instrumentation is used to measure the impedance of an example utilization-voltage power system. With the power system in normal operation, line-to-neutral, line-to-ground, and neutral-to-ground impedances are measured over a bandwidth of 20 Hz to 24 kHz. The measured impedance is presented as resistance and inductance which vary with frequency. Based on the measurements, additional calculations are performed to find the resistance and inductance of every conductor in the system. This complete wideband characterization of power system impedance provides valuable data for power quality calculations.

Meter placement for real-time monitoring of distribution feeders

This paper identifies the data requirements for real-time monitoring and control of distribution systems. It points out that in addition to having supervisory control and data acquisition on switches and control equipment, methods are needed to obtain an accurate estimation of data needed for feeder automation functions. A meter placement method is proposed for this purpose. It is shown that the measurements from such a metering scheme can be used with a state estimator to provide the real-time data needed for real-time monitoring of a distribution system.

Instrumentation for measurement of line impedance

This paper presents instrumentation for nondisruptively measuring the impedance of a normally operating line. A small sinusoidal current of known frequency is injected into the line, and line impedance at that frequency is calculated from the magnitude and phase of the injected current and resulting voltage as measured by a network analyzer. Line impedance as a function of frequency is found by repeating the measurement over a range of frequencies. Lumped equivalent circuit models are extracted from the measured line impedance and applied to an example analysis of line voltage distortion.<<ETX>>

Transformer derating for harmonic currents: a wide-band measurement approach for energized transformers

Power system transformers must often be derated where supplying harmonic currents to nonlinear loads. An existing technique uses measurements performed at DC and the fundamental frequency to extrapolate transformer loss for harmonic frequencies. This paper describes an improved measurement technique which allows direct calculation of transformer loss at harmonic frequencies. The measurement is performed on both energized and deenergized transformers in the loaded and unloaded conditions and is supported by theoretical and numerical analysis. Measurements of several distribution transformers show the limitations of the existing derating technique when compared to the method described in this paper.

Line impedance measurement: a nondisruptive wideband technique

Line impedance is the basis for many power system calculations. This paper presents a technique for measuring line impedance as a function of frequency on an energized line in normal operation using commercially available equipment. A small sinusoidal current of predetermined frequency is injected into the line, and a network analyzer calculates line impedance at that frequency from the measured magnitude and phase of the injected current and resulting voltage. The measurement is repeated over a range of frequencies to produce a wideband impedance-versus-frequency characteristic. The element values for lumped equivalent circuit models are extracted from the measurement. These values are shown to be frequency dependent. Inexpensive portable equipment for performing this measurement is also briefly introduced.

An improved calorimeter for measuring the core loss of magnetic materials

Accurate measurements of core loss for distributed-air-gap magnetic materials have traditionally been very difficult to obtain. Wattmeter measurements are affected by very small phase and time-delay measurement errors, while traditional calorimeters measure the sum of excitation winding loss and core loss. This paper presents an improved calorimeter which excludes winding loss and measures core loss alone.

Voltage regulator for contactor ridethrough

This paper describes a simple voltage regulator that allows contactors to ride through power line disturbances such as sags and dropouts. The voltage regulator protects critical equipment in continuous process industries and prevents loss caused by downtime. The voltage regulator is inexpensive and easily retrofitted into existing installations. A field trial of the voltage regulator has been successfully completed.