Mark Halpin

An Evaluation of the Extent of Correlation Between Interharmonic and Voltage Fluctuation Measurements

The existence of a general correlation between measured interharmonics and measured lamp flicker would be very significant. Present measurement and emission limitation standards for voltage fluctuations are based exclusively on the 60 W incandescent lamps response to amplitude modulation of the power frequency. As use of incandescent lamps declines, the need increases to broaden voltage fluctuation quantification beyond lamp flicker. Amplitude modulation of the power frequency is mathematically equivalent to interharmonics summed with the power frequency. This, with the existence of international standards for measuring interharmonics, has suggested interharmonics as a possible basis for characterizing voltage fluctuations more broadly. Moreover, interharmonic measurements may be inherently extendable to quantify the effects of voltage fluctuations on devices other than incandescent lamps. However, any new method that offers advantages in broadening voltage fluctuation measurement must be capable of matching the results of present practices. Therefore, interharmonic measurements must first be demonstrated to be generally correlated to currently accepted flicker severity measurements. The correlation between these measurements is explored in this paper. It is concluded that by using the techniques in this paper, measured lamp flicker and measured interharmonics are correlated to a large extent for most industrial loads.

Evaluating correlations between interharmonics and voltage fluctuations

Amplitude modulation is a well-known cause of voltage fluctuations resulting in light flicker. Amplitude modulation can be more generally quanlified in terms of interharmonics. As the use of 60 W incandescent lamps declines, the need increases to broaden voltage fluctuation quantification beyond light flicker. If interharmonic measurements could be correlated to currently accepted flicker severity measurements, the effort to make inter-harmonic measurements the grounds of general voltage fluctuation measurement could be justified. This relationship between interharmonics and classic light flicker has been explored in this paper. The recommendations in IEC 61000-4-7 and 61000-4-15 for measuring interharmonics and short-term flicker severity, respectively, were followed. Interharmonic measurements were accumulated over 10 minutes in order for them to be easily compared to the short-term flicker measurements.

Evaluating alternatives to voltage fluctuation and flicker measurements based on IEC standard 61000-4-15

Recent work completed by CIGRE/CIRED Joint Working Groups C4.108 and C4.111 has pointed to the general conclusion that there is a poor correlation between measured voltage fluctuation levels (“flicker”) and complaints from network customers. Voltage fluctuation measurement procedures have long been standardized in the IEC flickermeter (IEC Standard 61000-4-15) and historically the correlation between the short-term flicker severity value, Pst, provided by any compliant flickermeter and customer complaints has been very good. In recent times, the correlation has become much worse, prompting multiple investigations by international researchers and technical organizations such as CIGRE and CIRED. This paper is intended to provide theoretical and simulation bases which support one particular modification to the flickermeter which could lead to improved correlation between measured flicker levels and customer complaints.

Simulation-based electrical safety training

Electrical safety has rapidly risen in prominence in industrial applications due to increased awareness of hazards and risks. There are numerous occupational health and safety organizations around the world that now mandate practices and procedures to maximize electrical safety in the workplace. Training workers to meet these requirements typically follows the standard methods based on seminars and short courses which have been widely used for many years. Maximizing electrical safety, however, cannot be achieved by simply memorizing facts or procedures taught in this environment. The critical aspect of electrical safety lies in the actions of the worker in the workplace-what people do in certain situations when given particular information is based on their higher-level thought process and their sequential decisions and actions. It is not possible to fully train workers in this skillset in advance, and the needs in this area are normally addressed on the job by direct observation and personal interaction. In this paper, a simulation-based electrical safety training module is described that allows the participant to move through a simulated environment while making observations and decisions and taking actions. The ability of the participant to recognize key facts and take appropriate actions when faced with simulated electrical safety scenarios can be scored and evaluated in the same manner as a typical computer game with the total score based on the accumulated choices of the participant. A score threshold can then be used to indicate the level to which the participant has mastered the training scenarios. Determining such a total score is exemplary of the necessary changes in assessment required when using virtual learning environments for training purposes.

A Software Suite for Power System Stability Monitoring Based on Synchrophasor Measurements

A software suite—named Grid Stability Awareness System (GSAS)—has been developed to monitor and analyze power grid stability in real time using wide-area synchrophasor measurements. GSAS consists of five analytical and monitoring tools including an Oscillation Monitoring Tool, a Voltage Stability Monitoring Tool, a Transient Instability Monitoring Tool, an Angle Difference Monitoring Tool, and an Event Detection Tool. System architecture and functionalities of the tools are described. The alarming mechanisms implemented in GSAS are also presented. In addition, a series of off-line simulations were developed to test, evaluate, and validate the immediate suitability of the tools for use in an operational environment of a North American utility, and to identify and support potential improvements in the tools. The testing methodology and the procedures to create the simulation cases are also presented. Findings and conclusions are provided at the end of the chapter.

Field test results of a modified flickermeter Block 5 processing algorithm

IEC TC77/SC77A/WG2 is poised to consider maintenance and revisions to IEC Standard 61000-4-15. Based on the results of multiple CIGRE Working Groups and literature publications, it appears that discrepancies between measured short-term flicker severity values and user complaints can be reduced by making modifications to the so-called Block 5 processing algorithm. For such modifications to be fairly considered in the revision of any standard, it is necessary to establish both theoretical and practical/application bases. Prior work has established theoretical bases for changes in Block 5; in this paper are reported the results obtained from modified algorithms used at multiple sites for extended periods of time. Particular attention has been paid to quantify the extent of the differences obtained from the practical perspective of flicker limit compliance.

Evaluation of the IEC 61000-3-11 procedures for the connection of multiple items of equipment

One way to manage voltage fluctuations in power systems is by limiting flicker emissions from individual items of equipment. The limits of voltage fluctuations produced by equipment having a rated input current less than 75 A intended to be connected to a public low-voltage (LV) distribution system are specified in IEC Standards 61000-3-3 and 61000-3-11. Evaluation procedures are included in 61000-3-11 which shall be applied if the equipment cannot meet the technical requirements and is therefore subject to conditional connection. In this case, the equipment has to be connected to a supply having an impedance lower than the reference impedance so that equipment emissions comply with the limits of the standards and manufacturers can declare the equipment to be compliant. Multiple formulas are provided in Clause 6 of IEC Standard 61000-3-11 for the determination of the required system impedance as a function of the reference impedance. One of the formulas supposedly addresses the connection of multiple items of equipment connected at the point of evaluation. The combined flicker effects of multiple items of equipment using the described methods in the standard are presented in this paper. Also, the cubic summation law, which is widely recognized by the industry and the standards, is used to evaluate flicker effects of multiple items. A comparison of these two methods for combining flicker effects is also presented. The results of using the formula provided by IEC Standard 61000-3-11 are shown to be over- or under-conservative depending on the specifics of the situation and the characteristics of the equipment involved.

Equivalent power system impedance estimation using voltage and current measurements

Many power system analyses require knowledge of the equivalent system impedance. A method for estimating the impedance using three-phase voltage and current measurements is outlined in this paper. The 60 Hz phasors are acquired from time samples through a low-pass filter and one-cycle DFT. The phasors are used to calculate the sequence voltages and currents. As long as the system is sufficiently excited, the equivalent system impedance can be estimated by assuming that it and the equivalent system voltage are constant over two sequential cycles. The system is treated as sufficiently excited when the change in real power between cycles is greater than a chosen threshold. To smooth the impedance estimates over time, a moving-average is used. The change in real power threshold and moving-average time constant were experimentally determined.