J. Gutierrez

Power System Frequency Measurement Under Nonstationary Situations

A new method for the measurement of the instantaneous power-system frequency is proposed. It is based on the frequency estimation of the voltage signal using three equidistant samples. An algorithm is developed that diminishes the variance of the estimation. The procedure is applied to the case of single- and three-phase networks, and uncertainty in the frequency estimation is obtained with simulated signal and severe conditions of signal quality. A frequency variation has been assumed as plusmn2 Hz around the nominal value, with a maximum rate of change of 1 Hz/s. The uncertainty of 25 mHz and 3.5 mHz has been obtained for single- and three-phase signals, respectively. A low-cost virtual instrument has been developed to make frequency measurements over the actual voltage signal.

Power Quality Factor for Networks Supplying Unbalanced Nonlinear Loads

A single indicator [i.e., the power quality factor (PQF)] in the range between 0 and 1 is suggested in this paper to integrally reflect the power transfer quality of a general three-phase network feeding unbalanced nonlinear loads. The prominent power quality aspects considered in the paper are the following: 1) the voltage and current harmonic levels; 2) the degree of unbalance; and 3) the phase displacement factor in the different phases at the fundamental frequency. A network that supplies balanced sinusoidal currents at balanced sinusoidal voltages with zero phase displacement between the corresponding currents and voltages yields a PQF of unity. The measurement of the PQF is discussed. Practical examples illustrate the use and relevance of the new quality factor.

Environmental knowledge, unlearning, and performance in hospitality companies

Purpose – The Spanish hospitality industry is facing environmental challenges which require organisations and individuals to learn new skills and practices and create new environmental knowledge. The aim of this paper is to analyse the relationships between an unlearning context and environmental knowledge.Design/methodology/approach – This paper analyses the relationships between an unlearning context and environmental knowledge and tries to identify whether environmental knowledge impacts on business outcomes through an empirical study of 127 Spanish hospitality companies.Findings – The results support the hypothesis that, in order to create environmental knowledge and hence foster the application of new environmental knowledge, companies need to provide and support an unlearning context.Research limitations/implications – It is important that managers provide an appropriate unlearning context to support the openness of individuals to new ideas and environmental awareness.Originality/value – This study ...

Voltage quality analyzer

The Voltage Quality Analyzer is a virtual instrument for diagnosing voltage quality of three-phase signals: instantaneous frequency deviations, harmonic spec- trum, total harmonic distortion and instantaneous symmetri- cal components. Accurate measurement of the instantaneous frequency and the harmonic content are obtained and the three-phase electrical waveforms and their symmetrical components are displayed. A voltage quality factor in the range between 0 to 1 is defined and measured.

The geometric algebra as a power theory analysis tool

In this paper, a multivectorial decomposition of power equation in single-phase circuits for periodic n-sinusoidal /linear and nonlinear conditions is presented. It is based on a frequency-domain Clifford vector space approach. By using a new generalized complex geometric algebra (GCGA), we define the voltage and current complex-vector and apparent power multivector concepts. First, the apparent power multivector is defined as geometric product of vector-phasors (complex-vectors). This new expression result in a novel representation and generalization of the apparent power similar to complex-power in single-frequency sinusoidal conditions. Second, in order to obtain a multivectorial representation of any proposed power equation, the current vector-phasor is decomposed into orthogonal components. The power multivector concept, consisting of complex-scalar and complex-bivector parts with magnitude, direction and sense, obeys the apparent power conservation law and it handles different practical electric problems where direction and sense are necessary. The results of numerical examples are presented to illustrate the proposed approach to power theory analysis.

Instantaneous line-frequency measurement under nonstationary situations

A virtual instrument for the measurement of instantaneous power-system-frequency is proposed. It is based on the frequency estimation of the voltage signal using three equidistant samples. An algorithm is further developed that diminishes the variance of the estimation. The procedure is applied to the case of single and three-phase networks and relative errors in the frequency estimation are obtained. Low cost hardware, consisting of compatible PC, standard data acquisition card and signal conditioning module, has been used in conjunction with a software application developed with LABVIEW/spl trade/. Finally, measurements using single and three-phase signals, simulating severe conditions of signal quality, were performed. A variation of the frequency throughout the measurement time has been assumed, according to a sinusoidal signal of 5 Hz, within a /spl plusmn/1 Hz margin. The developed tool has been proven, with worst case data and relative errors of 0.1% and 0.025% having been obtained for single and three-phase signals, respectively.

Analysis of instantaneous NSV&C in polyphase systems

(N-1)-phase N-wire systems are analyzed into an orthonormal-coordinate system using the fundamental laws of polyphase systems and the condition of zero neutral-current. N-dimension voltage vectors are referenced to a virtual star-point and the current vectors are decomposed into three mutually orthogonal components, two of them are responsible of the active power. Without the condition of zero neutral-current, results are modified: the current vector is decomposed into a power-current vector and a complementary current vector. Only the first component transports the instantaneous collective power, the other is useless. The analysis is valid for a general situation and shows the condition of line losses minimization after compensation with active power filters.

Voltage quality index

A voltage quality index (VQI) is proposed for evaluation of the voltage quality aspects (QAs) of three-phase voltage signals: instantaneous frequency-deviations, total harmonic distortion and instantaneous symmetrical components. A VQI in the range between 0 to 1 is defined and measured. Accurate measurement of these Qas and VQI are obtained with a virtual instrument: the voltage quality analyzer (VQA)

Power factor optimization with switched-LC networks

A new reactive power compensator consisting of a set of parallel LC branches, which can be automatically switched, is proposed. This permits operation under nonsinusoidal conditions and time-varying loads. A control system, which measures the equivalent admittance on the load side, and sets the optimal LC configuration to minimize the reactive component of the line current, has been used. Thus, the synthesized compensator presents an equivalent harmonic-susceptance which is approximately equal (as given by its discrete structure) to that of the load (with opposite sign) within the appropriate frequency range. Numerical simulation and experimental results are presented.

Non-active power multivector

This paper is a new contribution to the clarification of the non-active power concept. It is based on a Generalized Complex Geometric Algebra (CGn) spanned by a frequency-domain vector space.The classic definition of this quantity is usually associated to the use of the scalar product of voltages and currents rms values. We show that the non-active power can be deduced directly from the power multivector [12]. A simple application example is provided to illustrate the clear capabilities of the suggested concept.