Abstract
Inter-turn short circuit of field windings (ISCFW) may cause the field current of a generator to increase, output reactive power to decrease, and unit vibration to intensify, seriously affecting its safe and stable operation. Full integration of mechanical and electrical characteristics can improve the sensitivity of online monitoring, and detect the early embryonic period fault of small turns. This paper studies the calculations and variations of unbalanced magnetic pull (UMP), of which the excitation source of rotor vibration is the basis and key to online fault monitoring. In grid load operation, ISCFW are first calculated with the multi-loop method, so as to obtain the numerical solutions of the stator and the rotor currents during the fault. Next, the air-gap magnetic field of the ISCFW is analyzed according to the actual composition modes of the motor loops in the fault, so as to obtain the analytic expressions of the air-gap magnetic motive force (MMF) and magnetic density. The UMP of the rotor is obtained by solving the integral of the Maxwell stress. The correctness of the electric quantity calculation is verified by the ISCFW experiment, conducted in a one pair-pole non-salient pole model machine. On this basis, comparing the simulation analysis with the calculation results of the model in this paper not only verifies the accuracy of the electromagnetic force calculation, but also proves that the latter has the advantages of a short time consumption and high efficiency. Finally, the influencing factors and variation law of UMP are analyzed by means of an analytic model. This develops a base for the online monitoring of ISCFW with the integration of mechanical and electrical information.
Highlights
The requirements for the safe and stable operation of synchronous generators continually increase with the continuous development of power systems
When a field winding inter-turn short circuit fault occurs in a generator, the position of the short circuit and the turn number is fixed in a certain time
In order to determine whether or not the field winding inter-turn short circuit fault occurs, it is very important to study the relationship between unbalanced magnetic pull (UMP) and the generator’s running state
Summary
The requirements for the safe and stable operation of synchronous generators continually increase with the continuous development of power systems. In the motor, owing to mechanical and electrical coupling, the ISCFW will cause partial magnetic poles to short circuit, thereby causing air gap magnetic field distortion This produces the air gap electromagnetic force wave and unbalanced magnetic pull (UMP) differing from normal operation, causing the radial vibration of the motor rotors. A fault experiment on the model machine is conducted, and the experimental results are compared with theoretical calculation results On this basis, the analytic calculations of air gap magnetic motive force (MMF) and magnetic density on inter-turn short circuit faults are conducted; the size and direction of the UMP on the rotor in faults are calculated using the Maxwell stress tensor method, and the analytic calculation models of the UMP are obtained. The conclusion provides the theoretical basis for the further study of rotor vibration response characteristics, and lays the foundation for the online monitoring of rotor inter-turn short circuits with mechanical and electrical information integration
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