Study of the Possibility of Parallel Operation of Induction Elements of Different Types
Abstract Generated abstract
This paper examines the conditions under which a selsyn receiver in an indicator pair and a selsyn transformer can operate in parallel from a single transmitter without unacceptable disturbance of indicator readings. Using the two-reaction method together with experimentally measured equivalent parameters, the authors analyze the torques arising from parallel connection and relate their reduction to added active resistance in the synchronizing winding circuits. Calculations and tests on SS-408 and SS-410 selsyns with a BS-405 selsyn transformer identify permissible resistance ranges and indicate an optimal mode with ballast resistances of about 200 to 250 ohms per phase and an amplifier input resistance of at least 5 kilohms. The proposed procedure is presented as applicable to other selsyn types.
Full Text
UDC 621.313.334.654.94
STUDY OF THE POSSIBILITY OF PARALLEL OPERATION OF INDUCTION ELEMENTS OF VARIOUS TYPES
V. K. Yasel’skii, V. G. Fomin, V. S. Moskvin
(Presented by the scientific seminar of the Faculty of Physics and Engineering)
On the basis of calculations of induction elements carried out by the two-reaction method and of experimental investigations, the article gives certain recommendations for selecting the optimal mode of parallel operation of selsyns of types SS-408, SS-410, and BS-405, which may also be extended to other types of selsyns.
Illustrations 3, bibliography 1.
In computing technology and in monitoring and control systems, selsyn remote transmissions of one type or another find wide application. In the circuit of single-phase supply of the transmitter and receiver, useful work on the receiver axis is obtained only through the work of the primary device rotating the transmitter axis. Therefore the circuit has found application mainly in devices where only the turning of a pointer is required on the receiver axis. When it is necessary to have significant torques on the output shaft of a remote transmission, a selsyn-transformer circuit is used.
However, the need often arises for parallel operation of the selsyn receiver of an indicator pair and a selsyn-transformer from one transmitter (Fig. 1); for example, for visual indication of the position of the shaft of a selsyn transmitter and simultaneous supply of a signal, proportional to the angle of rotation of the transmitter shaft, to a computing device.
Fig. 1. Parallel connection of a selsyn indicator pair and a selsyn-transformer
The theoretical analysis of the conditions for the possibility of parallel operation of different types of selsyns presents known difficulties. The solution of the problem is substantially simplified when experimentally obtained data are used in the calculations.
When salient-pole selsyns and nonsalient-pole selsyns with a damping circuit in the transverse axis are used in transformer synchronous transmission, a synchronizing torque appears on their axes [1], which is purely reactive in the sense that it is proportional to the difference \(x_d - x_q\), where
\(x_g\) and \(x_d\) are the total reactance of a phase of the synchronizing winding when its axis coincides, respectively, with the longitudinal and transverse axes of the selsyn rotor.
In accordance with the two-reaction method, the value of the torque \(M_1(M_2)\) on the axis of the selsyn transmitter (receiver) can be calculated by the formula:
\[ M_1=-M_2=\frac{3}{4}E_\phi^2 \frac{(x_d-x_q^1)(r_q^{1\,2}+r_i^2+x_q^{1\,2}+x_d^1 j x_q^1)-x_d^2(r_q^1-r)} {\left[(r_d^1+r)^2+(x_d^1+x_d)^2\right](r_q^{1\,2}+x_q^{1\,2})}, \]
where \(r\) is the active resistance of a phase of the synchronizing winding; the remaining transient equivalent parameters are determined according to the equivalent circuits [1].
It follows from the expression given that parallel connection of a selsyn transformer with an indicator pair causes the appearance of resultant torques on the axes of the selsyns. This may lead to a change in the readings of the selsyn indicator.
The magnitude of the torques, and consequently their effect on the readings of the selsyn indicator, can be reduced by increasing the values of the active resistances in the circuits of the synchronizing winding of the selsyn transformer. Obviously, the selsyn transformer will not affect the indicator pair if the maximum torque produced during rotation of the selsyn transformer is at least less than the friction torque of the receiver selsyn of the indicator transmission pair.
To determine the optimal conditions for parallel operation of selsyns, it is necessary to know the equivalent transient parameters along the longitudinal axis \((r'_g, x'_d, z'_d)\) and along the transverse axis \((r'_g, x'_g, z'_g)\), which can be determined experimentally, as well as the variation of the output signal taken from the single-phase winding of the selsyn transformer at different values of the resistances in the circuits of the synchronizing winding and of the load resistance (the input resistance of the amplifier).
Fig. 2. Experimental curves of the dependence of \(U_{\text{out}}\) on the values of ballast resistances \(R_\phi\) in the phase circuits and the load resistance \(R_n\).
The active resistance of the synchronization winding \(r\), as a rule, coincides with the ohmic resistance for direct current and is measured by ordinary methods (using a resistance bridge, an ammeter, and a voltmeter). To determine the resistances of a phase of the synchronizing winding along the longitudinal and transverse axes, one may use measurement of the parameters by the consumed current and power.
The calculations and experimental studies carried out for an indicator pair constructed with selsyns SS-408 and SS-410, and for a selsyn transformer of type BS-405, show that the range of permissible resistance values in the circuits of the synchronizing winding and of the load resistance is bounded above by the dashed curve shown in Fig. 2. The same figure gives a family of curves showing the course of variation of the signal \(U_{\text{out}}\), taken from the single-phase winding of the BS-405 selsyn, for different values of ballast resistances.
\(R_\phi\) in the phase circuits and the load resistance \(R_n\). The dependence of the maximum current value in the circuit of the synchronizing winding of the selsyn-transformer on the value of \(R_\phi\) is shown in Fig. 3.
As follows from the experimental dependences presented, the optimal mode of parallel operation of the indicated selsyns occurs at ballast-resistance values in the phase circuits equal to \(200 \div 250\ \Omega\), and with an input resistance of the amplifier of no less than \(5\ \mathrm{k}\Omega\).
Fig. 3. Dependence of the maximum current value in the circuit of the synchronizing winding of the selsyn-transformer on the value of \(R_\phi\).
The method considered for determining the conditions under which parallel operation of an induction pair and a selsyn-transformer is possible may also be extended to other types of selsyns.
REFERENCES
- D. P. Mkrtchan, V. V. Khrushchev. Single-Phase Selsyns, Leningrad, Sudpromgiz, 1967.