V Vladimir Cuk

An analysis of diversity factors applied to harmonic emission limits for energy saving lamps

An experimental investigation of diversity factors for CFLs (compact fluorescent lamps) in combination with LED (light emitting diode) lamps is presented in this paper. Diversity factors were calculated for different configurations of lamps connected to the same feeder in one phase. It was found that the presence of LED lamps with a high apparent power input can lead to considerable damping of harmonics. If the number of CFLs is much greater, this effect was found as very low. Harmonic emission limits for lamps were also analyzed. A conclusion has been made that with a sufficient variety of energy saving lamps phasing out of incandescent lamps should not significantly impact the resultant harmonic distortion.

The development of demand elasticity model for demand response in the retail market environment

In the context of liberalized energy market, increase in distributed generation, storage and demand response has expanded the price elasticity of demand, thus causing the addition of uncertainty to the supply-demand chain of power system. In order to cope with the challenges of demand uncertainty under the unbundled electricity market, the concept of Market-based Control Mechanism (MCM) in retail market environment has been emerging. This paper presents the concept considering demand elasticity as an opportunity in retail market environment for inventing a new bid mechanism. This work formulates demand elasticity model as a Markov decision problem and implements pursuit algorithm as a machine learning technique to evaluate the price elasticity of demand by predicting the price. The performance of the algorithm is compared with the numerical calculation of price elasticity of demand for the given simulation settings.

Considerations on harmonic impedance estimation in low voltage networks

One difficulty in calculating harmonic voltages and currents throughout a transmission or distribution system is the need for a precise model of the linear load, both in magnitude and composition, fed from each bus. It has become evident that the use of equivalents without a comprehensive check on the effects of all impedances actually present can lead to inaccurate estimation of the harmonic voltages and currents. Considerations on harmonic impedance estimation in low voltage networks are presented in the paper. Influences of model abstractions and uncertainties in parameter estimations are analyzed analytically and tested on a model of a real low voltage network. The parameters analyzed include different load compositions, cable lengths, lumping loads and feeders, and medium voltage network representations. It is observed that some of these parameter changes have only a minor effect on the frequency of the first parallel resonance, while other effects have to be included in the calculation to avoid misleading results. This analysis can be used as a guideline when harmonic voltages are estimated in low voltage networks.

Modeling the frequency response of photovoltaic inverters

The increased presence of photovoltaic (PV) systems inevitably affects the power quality in the grid. This new reality demands grid power quality studies involving PV inverters. This paper proposes several frequency response models in the form of equivalent circuits. Models are based on laboratory measurements performed on five different commercially available PV inverters, and fitted to obtain circuit parameters. The proposed models are in good agreement with the measured data.

Monitoring of dips in the MV network for regulation- A case study

Voltage dips constitute to a noticeable part of power quality (PQ) problems but causing major financial losses to industrial and commercial customers. This work involves comparative studies to choose the most appropriate location of monitoring dips for regulation. In this paper, a Dutch MV network is used and dip monitoring locations are considered at different points of connections (POC) where customers are connected. To estimate the number of dips per year, simulations are performed on the network using PowerFactory. The voltage dip profiles at the selected monitoring point are analyzed for phase and line voltage dips. The effects of distributed generation (DG) on the voltage dips are also observed and the transfer of voltage dips from MV to LV network is briefly discussed. To analyze the effects of the expected dips on industrial equipment, severity curves are applied onto the standard dip tables.

Summation of harmonic currents of variable-speed induction motor drives

In this paper, the problem of the summation of harmonic currents of induction motor variable-speed drives (IM VSDs) is analyzed based on computer simulations and field measurements. As a first step, the influence of different parameters on the phase angles of current harmonics of different orders is analyzed using computer simulations. Secondly, harmonic currents of several drives working in parallel were measured on two locations for a period of one week, with a time resolution of 1 s. The measured locations included drives with 6-pulse and 12-pulse rectifier front ends. From the measurements, coefficients for simplified harmonic current summation were calculated, together with their limit values.

Estimation and classification of power losses DUE to reduced Power Quality

A Power Quality problem is defined as a problem that results in voltage, current, or frequency deviations and subsequently in failure, misoperation or premature aging of customers equipment. However, beside these consequences, reduced Power Quality also leads to additional losses in the power system. Three phenomena that lead to additional losses, namely Harmonic Distortion, Unbalance and low Power Factor, are presented in this paper and a method for calculating the losses that they cause in the various parts of a typical industrial installation, such as transformers and cables, are analyzed. Additionally, a classification method for these losses is proposed. The goal was to create a classification method which could be implemented in an instrument which estimates the various losses and present them to the end user in a simple and understandable way.

Experimental investigation on the sensitivity of an industrial process to voltage dips

A voltage dip is an important power quality (PQ) disturbance mainly caused by short-circuit faults. It can cause malfunctioning of sensitive equipment that can lead to the disruption of industrial processes, which usually results in substantial financial losses. One way to solve the problems caused by voltage dips is to identify the weak parts of a process and make the manufacturing process more robust against voltage dips. This paper discusses the sensitivity of a simple industrial process, which consists of a contactor in series with an adjustable speed drive connected to a load, based on experimental tests. The immunity of the sensitive devices to voltage dips are first tested under different conditions, and then compared with the immunity of the process to see the influence of the weak parts on the process. This approach can give insight into setting the limits for voltage dips.

Impact of residual harmonic current on operation of residual current devices

Residual current devices (RCDs) are most commonly used as a part of the protection system in low voltage installations. RCDs are supposed to disconnect the supply whenever the imbalance current between the live conductor(s) and the neutral conductor, i.e. residual current, exceeds the predetermined value. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit, which could result in a lethal shock. However, harmonic components in ground fault current may influence the tripping sensitivity of RCDs, and the protection against electrical shock may not be effective. In the paper, results of theoretical analysis and experiments are presented. Several mechanisms which could influence the tripping sensitivity of RCDs are validated, and their dominant conditions are identified.

Measurement of the harmonic impedance of the aggregated distribution network

This paper presents a method for measurement of the harmonic impedance of an aggregated distribution network using multiple Phasor Measurement Units (PMUs) with the additional capability of synchronized voltage and current spectrum measurement. The perturbations of the harmonic voltages which originate from the higher voltage levels are distinguished based on the measurements from multiple busbars, and used as the input for the calculation. Results of a test case using measurements from a 50 kV network are given to illustrate the method.