Arshad Mansoor

Multilevel intelligent universal transformer for medium voltage applications

The solid-state transformer allows add-on intelligence to enhance power quality compatibility between source and load. It is desired to demonstrate the benefits gained by the use of such a device. Recent advancement in semiconductor devices and converter topologies facilitated a newly proposed intelligent universal transformer (IUT), which can isolate a disturbance from either source or load. This paper describes the basic circuit and the operating principle for the multilevel converter based IUT and its applications for medium voltages. Various power quality enhancement features are demonstrated with computer simulation for a complete IUT circuit.

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.

Effects of power line voltage variations on different types of 400-W high-pressure sodium ballasts

This paper presents the results of laboratory tests to determine the effects of voltage sags, interruptions and fluctuations on high-pressure sodium (HPS) lamps and ballasts. The way these ballasted lamps react to sags and interruptions in the laboratory is then compared to a model of the real-world electrical environment created from data gathered during three recent North American power quality surveys. This work also shows how HPS immunity to voltage variations depends significantly on the ballast type and the lamp age.

Lower order harmonic cancellation: impact of low-voltage network topology

Cancellation due to phase-angle diversity between dispersed single-phase nonlinear loads is insignificant for the 3rd and 5th harmonics, but becomes increasingly significant for higher harmonics. Since the transformer connection has a significant effect on the propagation of 3rd harmonic current, most of the focus by international standard organizations such as the IEC for harmonic limits is primarily based on the concern for 5th and 7th harmonic components. However, depending on the low-voltage customer network topology, there may be significant cancellation of 5th and 7th harmonic currents of nonlinear loads. This paper demonstrates the extent of this cancellation based on realistic load harmonic current spectrum and shows how the difference in mainly European and North American low voltage customer network topology greatly impacts this cancellation.

An examination of the rationale for limiting harmonic emissions from low-voltage equipment

Connection of nonlinear loads such as diode bridge rectifiers to AC mains systems results in current flow at power harmonic frequencies. Undesired effects arising from the flow of harmonic currents through power system impedances drive regulatory efforts via standards such as IEC/EN 61000-3-2, which is intended to limit emissions at the product level, and IEEE 519, which limits emissions at the facility level. Simplified linear models based on Ohms law for AC circuits have been used to provide a technical rationale for establishing permissible emission levels given desired maximum voltage distortion. Two such models are critically examined in light of a variety of well-documented cancellation effects. Neither model provides a consistent prediction of voltage distortion levels. This examination leads to the conclusion that regulatory efforts should be guided more by ongoing system monitoring than by theoretical models.

Applying HID high-pressure sodium lamps in a variable-voltage environment

This paper presents the results of laboratory tests to determine the effects of voltage sags, interruptions, and fluctuations on high-pressure sodium (HPS) lamps and ballasts. The way these ballasted lamps react to sags and interruptions in the laboratory is then compared to a model of the real-world electrical environment created from data gathered during three North American power quality surveys. This work also shows how HPS immunity to voltage variations depends significantly on the ballast type and the lamp age.

Enhancing the Power Delivery Infrastructure to Support Expanded Energy Efficiency Initiatives

The objectives of this paper are to examine the benefits of electric end-use energy efficiency as well as the potential cost to enhancing the current electric distribution system, to examine the quantifiable impact of electric end-use energy efficiency as an energy resource, to suggest critical technological advances that must be made to the current electric distribution system to enable greater use of electric end-use energy efficiency, and to summarize a proposed technology R&D initiative.Copyright

Harmonic loading-related performance of power line filters for shielded enclosures

Power line filters (PLFs) are used to maintain integrity of shielded enclosures by preventing unwanted signals from either entering or leaving the enclosure via the power supply conductors. These filters are intended to provide a high insertion loss-typically about 100 dB-above 14 kHz without affecting the quality of the power frequency voltage waveform that is fed to equipment inside the enclosure. Connecting nonlinear loads to these filters will distort the filter input and output voltage waveform, cause increased filter heating, and diminish filter attenuation performance. Most performance specifications require PLFs to have less than 1% fundamental voltage drop under rated load conditions and require a voltage-drop test at rated load. This paper shows that this test is inadequate if the load consists of typical electronic equipment, and proposes a new waveform quality test to augment the test described in military standards commonly used by industry. The new test will identify any degradation in voltage quality caused by the connection of a PLF between a power source and equipment in a shielded enclosure.