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September 7, 2020
During the rotation of the generator, as long as there is unbalanced magnetic flux interlinking on the rotating shaft, an induced electric potential will be generated at both ends of the rotating shaft of the generator. This induced potential is called the shaft voltage.
The shaft voltage can be divided into two parts:
1. The shaft voltage generated at both ends of the shaft by cutting the unbalanced magnetic flux when the shaft is rotating;
2. The shaft voltage generated at both ends of the rotating shaft due to the axial leakage magnetic flux.
There are three reasons for the unbalanced magnetic field of the generator and the shaft voltage:
(1) Unbalanced magnetic circuit and asymmetry of air gap caused by manufacturing and installation process, etc., which are unavoidable factors.
(2) Shaft voltage is generated when an asymmetric short circuit occurs inside or outside the generator. This is because the short-circuit part of the stator winding has induced current, which prevents the synthetic magnetic flux from passing through the stator area where the part of the winding is located; at this time, the unshort-circuited part of the stator winding does not have this phenomenon, which is asymmetrical to the stator magnetic circuit. Equivalently, it produces alternating magnetic flux whose axial direction is dominated by the fundamental frequency. If the stator winding leads are located on both sides of the generator's length direction, an asymmetrical external short circuit may also generate shaft voltage.
(3) Grounding of the excitation circuit or short circuit between the rotor winding turns will also produce a strong axial unbalanced magnetic flux. When the shaft voltage reaches a certain value, a closed loop is formed through the bearing and its base to generate a current. This current is called the shaft current.
When the shaft voltage reaches a certain value, a closed loop is formed through the bearing and its base to generate a current. This current is called the shaft current.
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