Standstill Frequency Response Tests Research Articles

Estimation of Synchronous Machine Parameters by Stand Still Frequency Responses Testing

This paper presents a general method based on the standstill frequency response (SSFR) tests cited in IEEE Std 115-A. The used methodology consists of determining the frequency response of the measured values of the direct axis and quadrature operational inductances. Subsequently, we identify the different models of transfer functions, which are functions of time constants, using curve-fitting techniques. Then considering the time constants as inputs and the parameters of the equivalent circuits of the synchronous machine as outputs. We can identify all the parameters of different topologies of the models, using the numerical Newton Raphson method. The approach used is inexpensive, accurate, and reliable.

Solid-Rotor Induction Motor Modeling Based on Circuit Model Utilizing Fractional-Order Derivatives

This paper presents the Park model of a solid-rotor induction motor. In this model, the dynamic state of the motor is described by integer and noninteger order differential equations. The skin effect in the solid rotor was represented by resistance and inductance with lumped constants, and the fractional inductance was dependent on the frequency of the eddy current induced in the rotor. The parameters of the equivalent circuit were determined by the standstill frequency response test with the stationary machine on the basis of the finite element method analysis of the electromagnetic field. A simulation of the dynamic states of the induction motor with a solid rotor was carried out based on the calculated parameters. The simulation was carried out using a program written in the Matlab environment. The simulations show that the electromagnetic moment during the motor start-up is about 2 times greater than the initial torque in the steady state. On the other hand, the maximum value of the stator current during the start-up is about 1.5 times greater than the effective value of the inrush current in the steady state. A good agreement was obtained between the results calculated from the distribution of the magnetic field by the finite element method and the results obtained on the basis of the equivalent circuit and, in the case of the electromagnetic torque, with the results obtained from the transient state during motor reversal.

Standstill Frequency Response Test and Validation of a Large Hydrogenerator

This paper intends to contribute to the revision process of the IEEE Standard 115 by demonstrating the applicability of the standstill frequency response (SSFR) test on large salient pole hydrogenerators. The presented SSFR tests are carried out on a 55.6-MVA salient pole machine with laminated rotor, non-continuous damper windings, and a nonintegral slot number. The IEEE-115 SSFR test procedure is applied with special care to rotor positioning as well as accurate data acquisition in the low-frequency range. The maximum likelihood estimation method is utilized for machine parameter identification from the SSFR tests. Obtained parameters are compared with design values in addition to the ones obtained using traditional “sudden no-load three-phase short-circuit,” Dalton–Cameron and “open stator d-axis transient time constant” methods. The accuracy of parameters is also confirmed by comparing the measured three-phase short-circuit current waveforms with the ones obtained by simulating the SSFR-based machine models in an electromagnetic transient -type software. Unlike previous SSFR test cases on large salient pole hydrogenerators, accurate results are obtained.

Induction motor inter-turn fault modeling and simulation using SSFR test for diagnosis purpose

This paper presents a new idea to establish a simplified model of the short-circuit turns (SCT), in the stator winding of the squirrel-cage induction motor (IM) using standstill frequency response test (SSFR). This method may offer more precision in parameters estimation independent of variations in motor or load operating conditions since it is at standstill test. However, high-performance field-oriented control, or diagnosis purpose of the IM requires accurate knowledge of the electrical parameters. Furthermore, we propose to model the IM by a multiple cage equivalent circuit (EC) that enables us to take into account the deep bar effect with accuracy.The specific advantage of the proposed method that we can create a true SCT at several levels using fault simulator in order to estimate the EC model parameters in each case of fault severity, with a low probability of risk to the machine being tested, and a relatively modest expense.At the first time the healthy machine is identified and experimentally validated, then the models have been successfully used to study the transient and steady-state behavior of the IM with SCT fault, which a practically oriented scientific value.

Half-Order Modeling of Saturated Synchronous Machine

Non-integer-order systems are used to model diffusion in conductive parts of electrical machines as they lead to more compact knowledge models and also to improve their precision. In this paper, a linear half-order impedance model of a ferromagnetic sheet deduced from the diffusion of magnetic field is briefly introduced. Then, from physical considerations and finite-element simulation, the nonlinear half-order impedance model of a ferromagnetic sheet is proposed, taking into account both saturation and diffusion effects. Next, it has been proved that this model can be successfully included in the equivalent circuits of a synchronous machine (SM), taking into account eddy currents in massive parts of the rotor or damper bars and of small-signal saturation. The new SM equivalent circuit is validated by stand-still frequency response tests performed on the solid salient-pole SM of 125 kVA for variable field excitation conditions. An example of the SM transfer function computation in relation to different magnetization levels indicates the usefulness of this modeling approach for robust control issues.

Standstill frequency response test analyzer by using Excel Macros for educational purposes

AbstractAccurate knowledge characteristics of a synchronous generator are very essential to have an idea of its operation conditions. In the presented paper generator standstill frequency response tests is used as an approach to derive dynamic models and equivalent circuits descriptive of machine behavior for dynamic studies by using Excel Macros. The method is described and applied to a case study. The extraction process for obtaining the parameters is demonstrated. Evaluation of the method with 20 senior under graduate students and 20 junior power system engineers is very positive in terms of their developing confidence in and understanding of this test and deriving the dynamic model. © 2010 Wiley Periodicals, Inc. Comput Appl Eng Educ 20: 474–483, 2012

Standstill Frequency Response Test on a Synchronous Machine Extended With Damper Bar Measurements

Standstill frequency response (SSFR) test data from a salient-pole synchronous machine with reconfigurable damper winding are presented. In addition to the regular measurements, the damper bar currents are measured and used to obtain the stator-to-damper transfer functions. The test is performed three times with physically different damper winding configurations. An extension to the standard SSFR test analysis scheme is suggested, where the stator-to-damper transfer functions are included. The validity of the identified models is substantiated by comparison of the simulated and measured machine response to a drive torque step disturbance. It is found that the damper winding measurements can be incorporated in the analysis scheme to isolate the effect of the damper circuits. However, for a machine of the type studied, also the standard SSFR test procedure yields models that are accurate enough for power system studies.

Numerical pulse test for synchronous machines

PurposeThe purpose of this paper is to propose the numerical pulse test for the parameter estimation of the synchronous machine models.Design/methodology/approachIn order to generate data for the parameter estimation, the numerical pulse test was utilized. This test was implemented within the two‐dimensional finite element analysis (FEA). From the test data, the parameters of the equivalent circuit model were estimated. The differential evolution algorithm was used to minimize the cost function.FindingsThe equivalent circuit model with the estimated values of the parameters matches well with the data generated by the FEA. Thus, the equivalent circuit model with the parameters estimated represents the behavior of the machine accurately.Originality/valuePreviously, the numerical pulse test for synchronous machines has not been introduced. The numerical pulse test takes the real operation point of the machine into account. In the test, phenomena like the changing permeability distribution and the eddy‐currents in the damper bars (windings) are considered unlike in the standardized standstill frequency response test.

Generation of Multisinusoidal Test Signals for the Identification of Synchronous-Machine Parameters by Using a Voltage-Source Inverter

With the standstill frequency-response (SSFR) test, accurate electrical-machine models can be identified. However, it can be a time-consuming method, particularly in case the machine has to be identified at low frequencies. To shorten the required time for identification, in this paper, the response on a broadband signal is measured, resulting in a multisine SSFR test. To generate the broadband signal, a high-power linear amplifier can be applied as a waveform generator. As this signal generator is not commonly available in the field, the application of a voltage-source inverter (VSI) is discussed. The multisine SSFR test with a VSI allows swift evaluation of the influence of frequency, saturation, and cross saturation on the q-and d-axis parameters with a signal generator that is often already available to control the machine. Extensive measurements are performed on several permanent-magnet synchronous machines and the method can be extended to synchronous machines with rotor-field winding. By applying a switching converter instead of a linear amplifier, it can be expected that the identification results are affected by the switching actions. Therefore, multisine SSFR tests with either a VSI or a high-power linear amplifier as well as conventional tests as described in the IEEE standard are performed, and the results are compared.

Semi-analytical method for determining d-axis synchronous generator parameters using the DC step voltage test

The DC step voltage experiment is an alternative and non-destructive time-domain test to extract parameters from electrical machines that follows the standstill frequency response test procedure described in IEEE standard 115A. This work presents a new method for semi-analytically determining the characteristic parameters of the d-axis synchronous machine model. The test is carried out when the machine is at rest and the rotor's position is at d-axis; a DC-controlled power source is applied suddenly at two of the three terminals of the stator machine and the field circuit is short-circuited. Test measurements of d-axis stator voltage excitation and field and d-axis stator current responses were used. Both stator and field current patterns are simultaneously fitted to exponential functions which coefficients are analytically related to the d-axis characteristic parameters of the equivalent circuit. These characteristic parameters come from the conventional two transfer functions: direct-axis operational inductance Ld(s) and the armature to field transfer function sG(s). To validate the proposed methodology, test data is used in the d-axis parameter determination of a 7 kVA, 220 V, 60 Hz synchronous generator.

Experimental Characterization Procedure for a Synchronous Machine Model With Saturation and Arbitrary Rotor Network Representation

This paper sets forth the experimental procedure for obtaining the parameter set of a synchronous machine model with saturation and arbitrary linear network representation for the rotor. The method utilizes a combination of magnetization curves and standstill frequency-response tests. A novel test procedure is proposed for obtaining the turns ratio. The rotor's transfer function and stator leakage inductance are extracted from the frequency response using genetic algorithms.

A Standstill Frequency Response Method for Large Salient Pole Synchronous Machines

In this article, a Standstill Frequency Response Test (SSFR) is proposed, with the aim of determining the direct and quadrature axis operational impedances for salient pole synchronous machines. The method is applied with the rotor at standstill in a given arbitrary position, thus avoiding the difficulties in rotor mechanical alignment and rendering it suitable for large salient pole synchronous machines of hydroelectric power plants.

Estimation of a Global Synchronous Machine Model Using a Multiple-Input Multiple-Output Estimator

In this paper the measurement results of a series of standstill frequency response (SSFR) tests, performed at different magnetization levels, are discussed. For each data set an individual d-axis model is estimated, which allows the variation of the different parameters to be seen as a function of saturation. A global estimator is presented that uses the different data sets to estimate one global model, including the field-toarmature turns ratio. The global estimator is based on an impedance matrix representation of the synchronous machine. This global estimator assumes that only the d-axis main inductance is saturation dependent. The individual estimated models justify this assumption. Finally, the relative additional error of the global estimated d-axis equivalent circuit with the individual estimated ones is studied. The measurement results discussed in this paper are obtained on a four-pole 130 kVA synchronous machine.

Axial flux interior PM synchronous motor: parameters identification and steady-state performance measurements

This paper presents different measurement and identification approaches applied to a nonconventional permanent-magnet (PM) synchronous machine, namely, the novel axial flux interior PM (AFIPM) synchronous motor. The nonconventional geometry of the AFIPM motor requires a dedicated discussion on the parameter identification subject. In the paper, the standstill frequency-response test and the standstill time-response test on the AFIPM prototype are presented. On the basis of these tests, the d- and q-axes circuit parameters are chosen. To confirm the validity of the standstill tests, the load tests have also been performed. Furthermore, the load tests provide some preliminary AFIPM machine performance results and additional information on the saturation phenomena. The d- and q-axes equivalent circuits parameters obtained by the performed measurements are analyzed and compared. Finally, the most appropriate AFIPM machine model is selected.

Influence of saturation on estimated synchronous machine parameters in standstill frequency response tests

In this paper the measurement results of a series of standstill frequency response tests, performed at different magnetization levels, are discussed. For each data set an individual model is estimated, which allows the variation of the different parameters to be seen as a function of the saturation. Further, an estimator is presented which uses the different data sets to estimate one global model, including the field to armature turns ratio. Finally the expected error level of a more traditional saturated synchronous machine model is studied.

Experience with standstill frequency response (SSFR) testing and analysis of salient pole synchronous machines

Standstill frequency response (SSFR) testing and analysis of salient pole synchronous generators and motors performed by the members of the Working Group are summarized. The papers presented in a panel session at the 1997 Winter Power Meeting are condensed into this paper for the benefit of future researchers. The pertinent features of SSFR testing and analysis of salient pole machines are described to point out the differences from those of round rotor turbogenerators extensively published in the literature.

Noniterative synchronous machine parameter identification from frequency response tests

In this paper, a method to identify synchronous machine parameters from standstill frequency response tests is presented. It is common practice to use iterative techniques first to match a set of time constants with the measured response, and then to solve a set of nonlinear equations to obtain the equivalent circuit parameters. However, there is a difficulty of specifying an initial parameter estimate before any iterations can commence. This problem is overcome by the method presented here, which is able to approximate machine parameters straightforwardly and without the need of iterating. It was found that the transfer functions produced by the calculated parameters very closely resemble the measured frequency responses. Should refinements of the solution become necessary, the obtained parameters will still serve as an excellent initial estimate for standard curve fitting procedures.

Characterising the d-axis machine model of a turbogenerator using finite elements

An analysis of a long established fundamental assumption is presented. The assumption that superposition is valid in frequency response derived models is shown to be wrong, because eddy current losses in the solid rotor cannot be superimposed in the machine direct-axis. This implies that network theory is not valid in characterising the d-axis machine model. A machine model structure with one damper winding in the d-axis is derived from finite element analysis. Unequal mutual inductances in the machine d-axis are determined and hence the so-called differential leakage inductances are found and they are frequency dependent. The study is made on a 150 MVA turbine generator by simulating the standstill frequency response test with finite elements.

Standstill frequency response testing and modeling of salient-pole synchronous machines

Standstill frequency response (SSFR) testing and modeling of salient-pole synchronous machines are presented for two machines with integral and nonintegral numbers of stator slots per pole per phase. Frequency responses at different rotor positions have been investigated to explore the effects of rotor position in a machine with a fractional slot winding, as the electromagnetic fields and the armature magnetomotive forces do not precisely repeat every pole. The test results do not show any significant differences for various direct and quadrature axes rotor positions. The authors obtained a negative value of differential leakage inductance as theoretically postulated in the literature. The pertinent features of testing and modeling of salient-pole synchronous machines are described to point out the differences with SSFR testing of round rotor turbogenerators extensively published in the literature.

Finite element analysis of the skin-effect in damper bars of a synchronous machine

The skin-effect in the damper bars of a synchronous machine is analysed by a finite element simulation using SSFR (standstill frequency response test) data. In order to consider this effect in synchronous machine modelling, sub-subtransient parameters are introduced.