RU2152122C1 - Off-line power supply - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: power supply has synchronous generator with rectifier in armature winding circuit; connected to rectifier DC buses are generator voltage measuring device and voltage regulator whose output is connected to field winding. Generator field winding is designed for operation at voltage lower than rated rectified phase value by phase forcing factor; transistor voltage regulator is provided with current limiting device that functions to limit field current at voltages across generator phase leads lower than rated value. EFFECT: improved overload capacity in starting squirrel-cage induction motors of comparable rating. 1 dwg

Description

 The invention relates to electrical engineering and can be used as a source of electricity in an autonomous generation system.

 The purpose of the technical solution is to increase the overload capacity of a synchronous generator when starting an asynchronous motor with a squirrel-cage rotor of comparable power.

 Known excitation systems of synchronous generators with direct current generators, in which the excitation current is regulated in the excitation circuit of the exciter. The presence of additional electric machines greatly complicates such a generation system, and with a varying load, feedback is necessary to stabilize the output voltage. In static excitation systems with phase compounding, current transformers are used, the primary windings of which are connected in series with the load. Secondary through a rectifier connected to the excitation winding of the asynchronous generator. Within the range from idle to rated load, the voltage constancy in such systems can be maintained with an accuracy of ± (10-15)%. When starting an asynchronous motor of comparable power, the current consumed by it reaches five to seven times. At the same time, a significant voltage drop occurs on the windings of the current transformer, which reduces the overload capacity of the generator. (Voldek A.I. Electric machines. A textbook for students of higher technical schools. -3rd ed. Revised. - L., 1978, 783-786 pp.).

 The closest technical solution is a car synchronous generator with a transistor voltage regulator and an output rectifier. (Theory, design and calculation of automotive electrical equipment. A textbook for engineering schools specializing in automotive electrical equipment "/ L.V. Kopylova, V.I. Korotkov, V.E. Krasilnikov. Edited by M.N. Fesenko et al. - Engineering, 1979, pp. 163-169).

 The transistor voltage regulator contains: a device for measuring the voltage of the generator, including a voltage divider and a zener diode, a regulating device whose functions are performed by a transistor relay with collector feedback, including two transistors, a diode, a voltage divider and a resistance in the feedback circuit. The load of the transistor relay is the generator field winding, which is turned on to the output rectified voltage of the generator.

 Automobile synchronous generator with a transistor voltage regulator operates as follows. Due to the residual magnetic field, the electromotive force induced in the generator windings is rectified by the rectifier and saturates the output transistor of the generator voltage control device. In this case, the rectified voltage of the generator is applied to the field winding. The process of self-excitation begins. When the generator output voltage exceeds the rated voltage, a zener diode breaks through and the voltage measuring device shorts the input of the generator voltage control device. The field winding is disconnected from the rectifier. Generator voltage drops. Thus, the voltage of the generator is stabilized. A car synchronous generator with a transistor voltage regulator and a load connected to the windings through a rectifier is characterized by a rigid external characteristic.

где K_i - кратность пускового тока асинхронного двигателя;
K_p - отношение номинальной мощности асинхронного двигателя к номинальной мощности синхронного генератора;
X_d* - индуктивное сопротивление якорной обмотки генератора в относительных единицах.However, when an active-inductive load is connected to the phases of the generator, the demagnetizing effect of the armature winding leads to a significant drop in the output voltage of the generator. At the same time, the excitation current drops. And, as a result, the process of excitation begins. Therefore, the main disadvantage of such a power source is the low overload capacity when starting an asynchronous motor of comparable power. From the analysis of the direct start of the induction motor from an autonomous synchronous generator without taking into account the transient components of the currents, it follows that the required boost of the excitation current

where K _i - the multiplicity of the starting current of the induction motor;
K _p is the ratio of the rated power of the induction motor to the rated power of the synchronous generator;
X _{d *} - inductive resistance of the armature winding of the generator in relative units.

So, for example, when starting an induction motor with a starting current multiplicity of i _p = 7 (Asynchronous motors of the 4A series. Reference book / A.E. Kravchik, MM Shlaf, et al. - M .: Energoatomizdat, 1982. Size of an induction motor - 4AC 112M4UZ), the rated power of which is equal to the rated power of the synchronous generator (K _p = 1) with the inductive resistance of the generator armature winding in relative units X _{d *} = 1 (Veshenevsky S.N, Characteristics of motors in an electric drive, ed. 6th, - M .: Energy, 1977, p. 331) forcing the excitation current to increase the overload the actual ability of the synchronous generator when starting the induction motor should be K _t = 4.

 Taking into account the transient process, the excitation current must be accelerated.

This goal is achieved in that in an autonomous power source containing a synchronous generator with a rectifier in the armature winding circuit, to the DC bus of which a measuring device and a voltage regulator of the generator are connected, to the output of which a field winding is connected, the field winding is designed for the rated excitation voltage, smaller rectified by I _{p *} times, parallel to which an integration link is connected with a threshold element and a key, the output of which is connected to the input of the device Generator voltage regulation device.

 In the proposed technical solution (see drawing), the autonomous power source contains a synchronous generator 1 with a load in the form of an asynchronous motor with a squirrel-cage rotor 2, to the phases of the armature winding of which 3, 4, 5 a three-phase rectifier 6 is connected, which is connected by DC terminals 7 and 8 to a voltage measuring device 9 on resistors R1, R2, R3 and a zener diode VD1, the output of which is connected to the input 10 of the voltage regulation device 11 on transistors VT1, VT2 and resistors R4, R5, the output of which is connected to the field winding 12 and the reverse diode 13 of the synchronous generator 1, in parallel with which the integration link 14 is connected on the resistors R6, R7 and the capacitor C1 with the threshold element 15 on the resistor R8 and the zener diode VD2 and the key 16 on the transistor VT3, the output of which is connected to the input 10 of the generator voltage control device .

The device operates as follows. After reaching the specified rotation frequency of the synchronous generator 1, the EMF of the winding phases, caused by the residual magnetic flux, is rectified by the rectifier 6 and fed to the excitation winding 12 through the open transistor VT2 of the control device 11. The self-excitation process begins, during which the voltage increases in the phases of the generator 3, 4, 5 and DC buses 7, 8. The resistance of the field winding 12 of the synchronous generator 1 is selected so that the rated field current is at a voltage on DC buses 7, 8, which is even K _f times the stabilization voltage
U _dc = 2.34 • E _fst
where U _dc is the voltage on the DC bus 7, 8 in the mode of voltage stabilization;
E _fst - EMF of the generator phase in voltage stabilization mode.

 The device operates identically in the self-excitation mode and in the direct start mode of the induction motor, when in both cases the voltage on the DC buses 7, 8 is less than the stabilization voltage. In these modes, the zener diode VD1 of the voltage measuring device 9 does not pass current and the transistor VT2 of the voltage regulation device 11 is open. The voltage on the DC busbars 7, 8 is applied to the excitation winding 12. If the stabilization voltage of the generator 1 is much higher than the nominal excitation voltage, then emergency conditions occur for the transistor VT2 of the voltage regulation device 11 according to the maximum permissible collector current and for the excitation winding under thermal heating conditions. The limitation of the excitation current in these modes of increasing the overload capacity is achieved by the fact that parallel to the excitation winding 12 include an integration link 14 on the resistors R6, R7 and capacitor C1 with a threshold element on the resistor R8 and the zener diode VD2 and a key 16 on the transistor VT3, the output of which is connected to the input 10 of the control device 11. A voltage is generated on the capacitor C1 of the integration link 14, repeating in shape the current change through the excitation winding 12. After the voltage on the capacitor C1 reaches the specified magnitude breaks the zener diode VD2. Between the emitter and the base of the key 16 on the transistor VT3 appears voltage. The transistor VT3 opens and acts on the input 10 of the voltage regulation device 11. The field winding 12 is disconnected from the rectifier 6 and the field current decreases, closing through the return diode 13. The capacitor C1 is discharged through the resistor R7. The zener diode VD2 in the threshold device 15 exits the breakdown mode and the transistor switch VT3 is closed. The inhibit signal is removed from the input 10 of the control device 11. The transistor VT2 opens by connecting the field winding 12 to the DC buses 7, 8. After which the process is repeated. The transistor voltage regulator, thus, provides forcing the excitation current at a level that is specified by the parameters of the divider R6, R7. After the phases of the generator 1 reach a voltage higher than the rated voltage under the action of the rectified voltage, the zener diode VD1 breaks through the measuring device 9 and, acting on the input 10 of the control device 11, closes the transistor VT2. The field winding 12 is disconnected from the rectifier 6. The voltage at the generator phases 3, 4, 5 and DC buses 7, 8 drops. The zener diode of the measuring device 9 exits the breakdown mode, taking the signal from the input 10 of the regulation device 11. The transistor VT2 opens and connects the field winding 12 to the DC buses 7, 8. Thus, connecting and disconnecting the field winding 12 from the DC buses 7, 8 , the transistor voltage regulator stabilizes the voltage in the phases of the generator 3, 4, 5.

Claims (1)

A self-contained power supply containing a synchronous generator with a rectifier in the armature winding circuit, to a DC bus of which a measuring device and a voltage regulator of the generator are connected, to the output of which a field winding is connected, characterized in that the field winding is designed for a rated field voltage less than rectified

times
where K _i - the multiplicity of the starting current of the induction motor;
K _p - the ratio of the rated power of the induction motor to the rated power of the synchronous generator;
X _{d *} is the inductive resistance of the generator armature winding in relative units, in parallel with which an integration link with a threshold element and a key is connected, the output of which is connected to the input of the generator voltage control device.