Shoichi Oda

Prediction of starting performance of PM motors by DC decay testing method

This paper presents a method to predict the direct- and quadrature-axis operational impedances and starting performance of PM motors by a simple standstill response testing method using a small-capacity DC power supply unit. In this method, not only the starting performance but also the direct- and quadrature-axis synchronous machine constants (synchronous, transient and subtransient reactances) and equivalent circuit constants are calculated. This proposed strategy, tentatively named the DC decay testing method, is carried out on a 3.7 kW 200 V 22 A 100 Hz four-pole interior PM motor with a damper winding. The results measured by on-load tests and those predicted by the proposed method on starting performance demonstrate the validity and usefulness of the proposed method.

Prediction of starting performance of synchronous motor by DC decay testing method with the rotor in any arbitrary position

This paper presents a novel method to predict the starting performance of synchronous motors. This proposed strategy is based on a simple standstill response testing method using a small-capacity DC power supply unit, tentatively named the DC decay testing method in this paper, and can be applied to standstill synchronous motors with the rotor in any arbitrary position. The proposed testing method is carried out for a 10 kW, 200 V, 31.9 A, 50 Hz, 4P laminated salient-pole synchronous motor with damper winding. The results measured by on-load test and those predicted by the proposed method on starting performance clearly show the validity of the proposed method.

An estimation method of starting performance of squirrel-cage induction motor on DC decay testing method

In this paper, the authors propose a new method to calculate the starting performance of a squirrel cage induction motor by standstill tests using a small-capacity DC power supply. In this method, DC current is first made to flow through the armature winding (two terminals with the third one open). Then the current decay caused by short-circuiting the two phases is recorded. The operational impedance of the induction motor per phase is determined by Fourier transformation of the current decay. The starting performance is obtained by the two reaction theory. Experimental results clearly show that this method is useful for estimating starting performance.

Undesired Locus of Operational Impedance and Consideration of DC Decay Testing Method for Large-Capacity Alternating Current Generator

The DC Decay Testing Method is quite useful at testing large-capacity machines, because it is a simple standstill response testing method and needs only a small capacity of dc power supply equipments. When authors held a field test of the large-capacity alternating current generator (6000KVA-18P), we found that there was an unnecessary small curl in operational impedance locus. And it lead to the error at predicting the machine constants of its generator. So we consider that it is a problm in practice.In this paper, the investigation of measured data and approximate analytical calculation shows that the curl in operational impedance locus is caused by truncating the dc decay current data. So, authors propose a data processing method by data extrapolation which predicts the decay current after the measured data. And the result of applying the Expanded Dalton-Cameron Method to the total decay current is good agreement with the result of the other measuring methods. The proposed method is also applicable in testing the smalland middle-capacity machines and expands the usefulness of the DC Decay Testing Method.

A Method for Identifying Equivalent Circuit Constants for Double Squirrel-Cage Induction Motors

This paper presents a method for identifying equivalent circuit constants for double squirrel-cage induction motors. The proposed strategy is based on a standstill response testing method using a small capacity DC power supply unit, and identifies equivalent circuit constants that accord with the construction of double squirrel-cage induction motors, using characteristics of the rotor-side equivalent circuit constants as inferred from the slot shape of the double squirrel-cage rotor. The proposed method is applied to a 5.5kW-200V-22A-4P-50Hz induction motor with a semi-closed double squirrel-cage rotor. The accuracy and validity of the proposed method are evaluated by comparing the results on starting performance (torque-slip and current-slip characteristics) measured by an on-load test and those predicted by the proposed method.

An expanded dalton-cameron method: DC decay testing method at an arbitrary rotor position

The Dalton-Cameron method is a well-known method for determining direct and quadrature axis subtransient reactance (x′d and x′q) by standstill response testing. This method entails calculating x′d and x′q from the voltage and current measured when a rated-frequency single-phase voltage is applied to each armature winding (U-V, V-W, and W-U) in turn. The authors have developed a new method to calculate x′d, x′q and the impedance loci by applying a dc voltage instead of a single-phase voltage. This method was named the expanded Dalton-Cameron method. The method is a small-capacity standstill test, and is carried out by using the following three steps. The first is to short-circuit the U and V terminals while a dc current flows between these terminals, to measure the voltage and current (VDC and IDC) when the dc current flows between these terminals and to record the dc decay current (i(t)) after these terminals are short-circuited. This same procedure is also performed for the V-W and W-U terminals in turn. The second step is to draw the impedance loci from the measured Vdc, Idc and i(t) by means of Fourier transformation and to divide it into the direct-axis and quadrature-axis impedance loci (Zd(js), Zq(js)). The third step is to calculated the values of x′d and x′q from Zd(js) and Zq(js) and the starting performance on the basis of the two-reaction theory. Experimental and calculated results on starting performance, as well as a comparison with calculated results of x′d and x′q by the Dalton-Cameron method, clearly show that this method is very useful.

A method of predicting transient constants of synchronous machines

It is difficult to determine the subtransient (transient) reactance and subtransient (transient) short-circuit time constants of medium and large synchronous machines by the sudden three-phase short-circuit test because large-capacity equipment is required. This paper describes a new method of measuring these constants by means of a simple test using a small dc power supply. The key points of this method are as follows. (1) A dc voltage is applied to the armature winding (two terminals with the third one open) of a stationary synchronous machine through a resistance. When the two terminals are closed, the winding is short-circuited and the current in the armature winding decays. The whole process of decaying current is recorded. (2) The value of the transient phenomena of the winding calculated from circuit equations (armature, field winding and damper winding circuits) is compared with actual data, and the unknown equivalent circuit constants are identified by the least squares method. (3) Transient phenomena of the sudden three-phase short-circuit are calculated by the two-reaction theory using identified constants, and, hence, these constants are calculated. The transient constants of synchronous machines obtained by the new method agree closely with the observed values.

Equivalent Impedance of Damper Winding in Consideration of End Ring Impedance

The authors examined the subject using the following two methods. (1 } Assuming that the induced bar currents are all of the same phase and are sinusoidally distributed when an alternating field is applied to the axis, the total power absorbed in the damper winding is obtained. The equivalent impedance is calculated with the power assumed to be due to the armature currents. (2) With an alternating field applied to the axis, voltage equations are set forth for a pair of bars at the symmetrical positions for each axis. Each bar current is obtained by simultaneously resolving these equations. The relation where the gap magnetomotive force by such currents is equal to the armature reaction magnetomotive force is used. The results of these two methods agreed well in the actual design. The starting performance of synchronous motors was calculated and compared with the measured values.