Reactive Power Measurement Research Articles

A New Method for Online Steady-State Power Flow Calculation in Electric Power System

Owing to the given variables are measurable in online power flow calculation, the electrical variables of higher measuring accuracy should be chosen for calculation. Currently the theory of reactive power is deficient and several methods for reactive power measurement are briefly introduced in this paper. The inaccuracy of those methods is pointed out by the relevant references in non-sinusoidal conditions. The measuring accuracy of Active power directly obtained by voltage and current is the same as that of voltage and current. For increasing the accuracy of online power flow calculation, a method substituting voltage magnitude for reactive power is proposed in this paper. The new method eliminates the effects resulted from inaccurate reactive power measurement. The simulation results on software MATPOWER verify the correctness and rationality of the new method.

The Effect of the Accuracy of Reactive Power Measurement on Transmission Node Cost

Power flow calculation is the fundamental of cost analysis of transmission node. In traditional methods, the rationality of the cost analysis is of more concern than the accuracy of the power flow calculation’s results. This paper starts from the reactive data that being used for power flow calculation, expatiate that the method of present reactive power data measurement is inaccurate and explains why it is inaccurate. What reactive power would do to node cost analysis and why it could do so are analyzed considering cost analysis of transmission node. At last, an example of IEEE 9 is used. And it is proved that the fluctuation of reactive power will affect the power distribution of the whole network, as a result affect the generators’ sale of electricity income to loads greatly.

Determination of Geomagnetically Induced Current Flow in a Transformer From Reactive Power Absorption

This paper proposes a technique to estimate geomagnetically induced currents (GICs) in a transformer by measuring its absorbed reactive power. GIC is induced in electrical transmission lines by changes in the earth's magnetic field typically caused by solar magnetic disturbances, and flows into transformers through neutral grounding connections. An assessment of GIC from readily available reactive power measurements is an attractive alternative to the installation of dedicated GIC monitoring equipment on every transformer of an high-voltage transmission network. This technique is verified with electromagnetic transients software simulations and shows good agreement with the historical records captured in Hydro One's GIC detection network during the May 15, 2005 geomagnetic disturbance.

Architecture Design and FPGA Implementation of an FFT based Reactive Power Meter

Reactive power measurement is increasingly paid attention by power industry. A novel architecture to measure the reactive power is proposed in this paper. Architecture is described in verilog and implemented using Xilinx ISE 13.1i. In this method voltage and current signals in time domain are converted to the frequency domain and power on each component is calculated to obtain the total reactive power.

A wavelet-based approach for reactive power metering in modern three-phase grids considering time-varying power quality disturbances

Three-phase reactive power meters that are currently available in the market can accurately measure reactive power only under time-invariant operating conditions. However when considering time-varying power quality disturbances, the performance of these meters is questionable. In future grids, the emergence of active loads characterized by their dynamic operation could possibly lead to time-varying disturbances that will propagate along the distribution networks. In order to address this issue, a time-frequency approach based on wavelet transform is presented in this study to measure three-phase reactive power while taking into consideration the new time-varying operating environment in three-phase systems. A wavelet-based approach for reactive power measurement has been developed and tested under different time-varying power quality disturbances including balanced and unbalanced systems considering different wavelet basic functions of the Daubechies family. Results are analyzed, and recommendations are presented regarding the operating principles of such reactive meters under the new measuring environment.

Comparison of the Performance of Vector Control and Direct Power Control of Induction Generator in Wind Energy Conversion System

The conventional approach for independent control of active and reactive powers handled by the machine is stator flux oriented vector control with rotor position sensors. The performance of the system in this case depends on the accuracy of computation of the stator flux and the accuracy of the rotor position information derived from the position encoder. In vector control, power is controlled by rotor current injection. Direct power control is a rotor side control of a doubly fed induction generator by which decoupled control of stator active and reactive power can be obtained. It is based on the measurement of active and reactive power on the grid side where voltages and currents are alternating at fixed frequency. The active and reactive powers are made to track references using hysteresis controllers. The measurements are taken on stator side and the control is made on rotor side. This control system eliminates the need for rotor position sensing and gives an excellent dynamic performance with simulation results for a variable speed constant frequency induction generator system. The system can be operated below, at and above synchronous speed. The controlling schemes are explained and the modelling of the complete system is done in MATLAB–SIMULINK.

Wavelet-Based Reactive Power and Energy Measurement in the Presence of Power Quality Disturbances

This paper investigates the performance of electronic reactive power/energy meters by evaluating differences that arise as a result of (1) the distinct operating principles of the meter and (2) the presence of stationary and nonstationary power quality disturbances. The paper also includes a comparative study to determine the effectiveness of using orthogonal, bi-orthogonal, or reverse bi-orthogonal wavelets for such application. Moreover, the paper identifies the reactive power quantities required for accurate assessment and monitoring of reactive energy in the presence of power quality disturbances. Finally, the paper provides recommendations on reactive power and energy measurement for future generations of smart meters.

Effect of nonlinear energy on wind farm generators connected to a distribution grid

The wind farm generators are new energies sources in the Algerian electrical networks, as every project their placements are determined by the wind assets of the site suitability (economic evaluation), its proximity to the power grid of which it will be connected (technical assessments). The other problem which is not taken into account or not studied in a satisfactory way is the electrical environments in witch the wind generators are to be subjected. So it is shown in this paper, that in the case of a power distribution under strongly nonlinear loads, the wind farm presents difficulties in maintaining an acceptable power quality, due to the measurement apparatus errors incompatible to this type of non linearity. Wind generator MPPT are controlled and regulated mainly by 3 loops, based on active power, reactive power (sometimes substituted to a power factor) and bus bare voltage measurements. So, in this paper it is shown that in nonlinear condition these parameters are faultily measured. Thus, new relevant definitions and formulation of active power and true power factor correction with other types of power are proved and detailed in order to improve the governor wind farm energy management.

High-precision time domain reactive power measurement in the presence of interharmonics

When interharmonics exist in power system signals, large errors emerge in traditional time domain reactive power measurement. In this paper, we present a novel time domain integral method with good effect of restraining interharmonics, synchronization error, and white noise, as well as the principle of the selection of the sampling periods when employing this approach. The current signal and phase-shifted voltage signal are reconstructed after the harmonic components of signals are extracted, so that the interharmonics are filtered. The influence of the synchronization error on the measurement is reduced through removing the weight coefficients of the reactive components. In the simulation, we apply several cosine windows to the proposed method and analyze signals containing both harmonics and interharmonics. The results show that, in the presence of interharmonics, synchronization error, and white noise (with a fundamental signal-to-noise ratio of 40 dB) all together, the relative errors are within the magnitude of 10−4, which perfectly satisfies the practical requirement.

Mitigating Blackouts via Smart Relays: A Machine Learning Approach

In this paper, we investigate the protective relays used in electric power systems and their role in large-scale blackouts. After reviewing the state of the art, to mitigate future blackouts, we propose a new machine learning approach for protective relays based on binary hypothesis testing, support vector machines (SVMs), and communications between the protective relays and the supervisory control and data acquisition (SCADA), which we call smart protective relays. The goal of smart relays is to classify and discriminate the normal conditions from fault conditions via local measurements. It is shown that the proposed SVM-based smart relays can detect the location of an initial fault using local current, voltage, real power, and reactive power measurements, and by monitoring these metrics, they can make a correct decision even when the state of the system changes after some equipment failure. We show that by making an intelligent decision on whether and when to trip, and communicating the changes observed to SCADA for fast and intelligent decision making, SVM-based smart relays have the potential to mitigate large-scale blackouts and confine them to much smaller areas. By deploying SVM-based smart relays only at relatively few locations where they have the highest probability to be tripped incorrectly, the probability of cascade of failures and a blackout can be greatly reduced.

Microcontroller-controlled reactive power measurement and saving circuit design for residences and small-scale enterprises

In the present day, the requirement for electric energy is increasing rapidly with the advancement of the technology. One of the most effective methods of achieving savings in electrically-operated systems and increasing its efficiency is the reactive power compensation. According to the presently enforced regulation, compensation is mandatory in the industry and it is made at certain intervals, however, there is no arrangement for residences and small-scale enterprises and this issue is neglected. It is possible to make significant amounts of savings if the reactive power compensation is implemented over the whole country. In this study, measurement of the reactive power in single-phase systems has been developed, as well as calculation for directing for energy saving through a microcontroller. In the implemented system, the phase difference between the current and the voltage is measured, and the direction of saving is implemented according to the used reactive power. Implementation results demonstrated that the designed system has a simple structure and small dimensions, it brings up the power coefficient of the system to the optimum level, it reduces the faults to minimum and also reduces the cost. With these features, it is more useful and more economical than the devices sold on the market. Key words: Compensation, reactive power factor, microcontroller, energy savings.

Measurement of Reactive Power in Three-Phase Electric Power Systems by Use of Walsh Functions

This paper presents a new method for measuring of three-phase reactive power (RP) in three-phase systems. Extraction of three-phase reactive power RP from entire instantaneous power signal is achieved by multiplication the phase instantaneous powers with the Walsh function(WF). This method simplifies the multiplication procedure required for the evaluation the tree-phase reactive power components due to the use of the peculiar properties of the WF. In contrast to the existing methods involving phase shift operation between the input voltage and current signals proposed measurement approach does not require the phase shift of the phase current signals to the 2 / π with respect to the voltage signals. Limitations and proposals for future performance enhancements of the suggested method are also discussed. Validity and effectiveness of the suggested method have been tested by use of a simulation tools developed on the base of Matlab 6.5. The results obtained demonstrate that the computational demands can be substantially reduced by using the proposed method.

State Estimation-based Transmission line parameter identification

This article presents two state-estimation-based algorithms for identifying transmission line parameters. The identification technique used simultaneous state-parameter estimation on an artificial power system composed of several copies of the same transmission line, using measurements at different points in time. The first algorithm used active and reactive power measurements at both ends of the line. The second method used synchronised phasor voltage and current measurements at both ends. The algorithms were tested in simulated conditions on the 30-node IEEE test system. All line parameters for this system were estimated with errors below 1%.

A new reactive, distortion and non-active power measurement method for nonstationary waveforms using wavelet packet transform

The definitions of power components that are contained in the IEEE Standard 1459-2000 [IEEE Std. 1459-2000, Definitions for the measurement of electric quantities under sinusoidal, non-sinusoidal, balanced or unbalanced conditions, 2000] are based on the Fourier transform (FT) which is suitable only for the case of stationary waveforms. However, for nonstationary waveforms, the FT produces large errors. Therefore, the power components based on this transform become inaccurate. A new approach based on the wavelet packet transform (WPT) for defining these power components is developed in this paper. The advantages of using the wavelet transform are that it can accurately represent and measure nonstationary waveforms, providing uniform frequency bands while preserving both time and frequency information. In addition, this paper addresses the problem of choosing the most appropriate mother wavelet for power components measurements. The results of applying both approaches to stationary and nonstationary waveforms show that the currently used definitions according to the IEEE Standard 1459-2000 result in large errors for the case of nonstationary waveforms while the proposed approach (WPT based) gives more accurate results in this situation.

A New Signal Processing based Method for Reactive Power Measurements

A new modified Walsh function (WF) based method for the measurement of reactive power (RP) under both sinusoidal and non-sinusoidal conditions is proposed and investigated. Proposed method simplifies the multiplication procedure to evaluate the reactive components from instantaneous power signal using peculiar properties of the WF. One of the advantages of proposed measurement approach is that in contrast to the known existing methods which involve phase shift operation of the input signal, the proposed technique does not require the time delay of the current signal to the 2 / π with respect to the voltage signal. Another advantage is related to the computational saving properties of the proposed approach coming from use of the Walsh Transform (WT) based signal processing method. Proposed method eliminates an influence of the prevalent third order current harmonic to and reduces the effect of the highest order current harmonics on the RP measurement results. The examples are used to illustrate validity and effectiveness of the suggested method for evaluation of the RP. A new method has been tested by use of a simulation tools developed on the base of “Matlab”.

On-line tracking of single phase reactive power in non-sinusoidal conditions using S-ADALINE networks

This paper presents design and implementation of a new on-line single phase reactive power measurement technique under non-sinusoidal conditions. The proposed method expresses the conventional reactive power definition in a suitable state space form to avoid use of quadrature phase shifting method in measurement, thus, improving estimation accuracy. A modified adaptive linear combiner (ADALINE) structure has been introduced which is capable of dealing with off-nominal frequency conditions rather than the existing ADALINE, which provides good accuracy only at nominal frequency. The new topology is able to synchronize itself with the system signals using an efficient fundamental angular frequency deviation estimation algorithm and is called S-ADALINE. The principle and the architecture of this S-ADALINE is well suited for on-line implementation of the proposed reactive power measurement algorithm. Illustrative laboratory test results confirm the validity and accurate performance of the proposed method under both static and dynamic conditions.

Employing stochastic models for prediction of arc furnace reactive power to improve compensator performance

The time-varying nature of electric arc furnace (EAF) gives rise to voltage fluctuations, which produce the effect known as flicker. The ability of a static VAr compensator (SVC), a widely used method for flicker reduction, is limited by delays in reactive power measurements and thyristor ignition. To improve the SVC performance in flicker compensation, a technique for the prediction of EAF reactive power for a half cycle ahead is presented. This technique is based on a new procedure for stochastic modelling of EAF reactive power at an SVC bus. This procedure uses huge field data, collected from eight arc furnaces, to determine the most suitable signal among several candidate signals in view of EAF reactive power prediction. In addition, appropriate orders of autoregressive moving average models are found for reactive power time series. For this purpose, various model adequacy checking methods and some other stochastic analysis methods have been applied on data records. The performance of the compensator in the case of employing predicted fundamental reactive power of an EAF is compared with that of the conventional method by using three new indices that have been defined based on concepts of flicker frequencies and the power spectral density.

A Low-Cost Fault-Tolerant Real, Reactive, and Apparent Power Measurement Technique Using Microprocessor

Errors may creep in when measuring power by conventional methods due to the inductance and capacitance of the coils and the induced eddy current in the metal parts of the instruments through the alternating magnetic field of the current coil. Apart from these, if a fault occurs in any of the potential transformer secondary circuits or the potential coil of the measuring equipment, a conventional meter cannot detect it, which results in underregistration. In this paper, a microprocessor-based threephase real, reactive, and apparent power measurement system is developed, which displays the power being fed to a load under both normal and faulty conditions. The microprocessor provides a simple, accurate, reliable, and economical solution to these problems. A framework of the hardware circuitry and the assembly language program for the evaluation of power values is given, and the problems to which attention should be paid to execute the proposed algorithm using the microprocessor are discussed. Illustrative laboratory test results confirm the validity and accurate performance of the proposed method in real-time.

About the active and reactive power measurements in unsymmetrical voltage dip ride‐through testing

AbstractThe electrical utilities have specified in their recent requirements that wind turbines have to be capable to ride through severe symmetrical and unsymmetrical voltage dips without disconnection. Moreover, the generators are required to produce active and reactive power in order to improve the stability of the grid. For symmetric three‐phase dips, the measurement of reactive and active power, and current is quite straightforward, and several methods can be used. On the contrary, with unsymmetrical dips, very different results are obtained using alternative methods. A recommendation to use active and reactive power calculation method based on the positive sequence of the fundamental component is given. Copyright © 2007 John Wiley & Sons, Ltd.

Primary AC Power Standard Based on Programmable Josephson Junction Arrays

Josephson series arrays have been operated as digital-to-analog converters with fundamental accuracy to generate precision waveforms with accuracies better than one part in 107 at power frequencies. These waveforms have been used in the past to calibrate the sampling voltmeter in the primary standard for electrical power at the Physikalisch-Technische Bundesanstalt (PTB). The present contribution reports the integration of such a Josephson waveform synthesizer into the PTB primary power standard in order to continuously calibrate the sampling voltmeter and thus reduce the uncertainty for the measurement of active, reactive, and apparent power at the 120-V and 5-A levels