JPS6096150A - Axial current preventing device of rotary electric machine - Google Patents

Abstract

PURPOSE:To suppress an axial current inexpensively and simply by flowing a current for cancelling the axial current to a rotational shaft. CONSTITUTION:When an axial current flows to a rotational shaft 2, the axial current is immediately detected by an axial current detecting sensor 4. A signal outputted from the sensor 4 is outputted to an axial current generating coil 8 through a buffer 5, a phase inverter 6 and an amplifier 7. The signal inputted to the coil 8 is preset to substantially the same current value as the axial current of the shaft 2 and to reverse phase. Accordingly, when the axial current flows to the shaft 2, a current for cancelling the axial current is immediately flowed form the coil 8 to the shaft, thereby resulting in suppressing the axial current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a shaft current prevention device for a rotating electrical machine, which suppresses shaft current flowing through the rotating shaft of a rotating electrical machine such as a generator or an electric motor.

[Technical background of the invention and its problems] As is generally known, in rotating electric machines, shaft voltage is generated on the rotating shaft due to unbalanced magnetic circuits or manufacturing irregularities. This axial voltage can cause axial current to flow through the bearing and damage the bearing at the moment the bearing's oil film breaks locally, so conventionally an insulating plate was placed between the bearing and the blanket supporting it. Measures are being taken to prevent shaft current.

By the way, among power generating apparatuses mounted on ships and the like, there is a shaft-driven power generating apparatus in which a generator is provided between a main engine and a propulsion propeller, and the generator is driven by the main engine. In such a shaft-driven power generator, each rotating shaft is directly connected, so the bearing supporting the propulsion propeller, the generator bearing, the main engine bearing, and the intermediate bearing between them supporting the rotating shaft are used. A large number of bearings are provided. It is necessary to install insulating plates between the bearings and the brackets 1 to 1 in all of these many bearings to prevent shaft current.

However, the provision of insulating plates on such a large number of bearings poses problems in terms of bearing structure and has the disadvantage of being extremely expensive.

[Object of the Invention] An object of the present invention is to provide a shaft current prevention device for a rotating electrical machine that can suppress the shaft current at low cost and easily even in a device having a large number of bearings.

[Summary of the Invention j The feature of the shaft current prevention device for a rotating electric machine according to the present invention is that it constantly monitors the shaft current flowing through the rotating shaft, and when the shaft current flows, the shaft current flows through the rotating shaft at almost the same current value as the shaft current. It is configured to flow currents of opposite phases and suppress the shaft current flowing to the rotating shaft.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to FIG.

In the figure, 1 is a rotating electrical machine, 2 is a rotating shaft of the rotating electrical machine 1,
3 is a bearing that rotatably supports the rotating shaft 2, and 10 is a main engine directly connected to the rotating shaft 2.

Reference numeral 11 denotes a shaft current prevention circuit provided in accordance with the present invention, which has a function of flowing a current having almost the same current value and an opposite phase to the rotating shaft 2 in response to the shaft current generated in the rotating shaft 2; In the case of the figure, the structure is as follows. Numeral 4 is a shaft current detection sensor that detects the shaft current flowing through the rotating shaft 2 and outputs a signal corresponding to the shaft current, and for example, a known current transformer or the like can be used. A buffer circuit 5 converts the output signal of the shaft current detection sensor 4 into impedance, and the buffer circuit 5 can be omitted depending on the case. 6 is a phase inversion circuit that inverts the output signal of the buffer circuit 5 to the opposite phase; 7 is an amplifier circuit that amplifies the output signal of the phase inversion circuit 6 to a predetermined level; and 8 is an output signal that is applied to the rotating shaft 2 by the output signal of the amplifier circuit 7. A known current transformer or the like can be used as an axial current generating coil that flows a current having a current value substantially the same as that of the axial current and having an opposite phase.

In such a circuit configuration, when a shaft current flows through the rotating shaft 2, the shaft current is immediately detected by the shaft 1 current detection sensor 4, and a signal corresponding to the shaft current is output.

The signal output from the shaft current detection sensor 4 undergoes impedance conversion in a buffer circuit 5, and is converted into a signal with an opposite phase in a phase inversion circuit 6. The signal inverted by the phase inversion circuit 6 is amplified to a predetermined level by the amplifier circuit 7 and output to the shaft current generating coil 8. Here, the signal input to the shaft current generating coil 8 is set in advance so that a current having substantially the same current value as the shaft current of the rotary shaft 2 and having an opposite phase flows therethrough.

Therefore, when an axial current flows through the rotating shaft 2, a current that cancels the axial current flows from the axial current generating coil 8 to the rotating shaft 2, and as a result, the axial current is suppressed.

In the embodiment shown in FIG. 1, the shaft current detection sensor 4 and the shaft current generation coil 8 are separately provided on both shafts of the rotating electric machine, but the second
As shown in the figure, it may be replaced with one rotating shaft 2 of the rotating electric machine 1, and of course the same effect can be obtained in this case as well.

In another embodiment shown in FIG. 3, the shaft current prevention circuit 11 is further improved to be 1C, and the phase inversion circuit 6 is omitted in contrast to that in FIG. 1, and the polarity of the shaft current generating coil 8 is is wound so that the polarity is opposite to that of the shaft current detection sensor 4. This embodiment is constructed so that currents of opposite phases flow through the rotary shaft 2 depending on the polarity of the shaft current generating coil 8, so that the number of parts can be reduced and, moreover, the same effect as that of FIG. 1 can be obtained.

[Effects of the Invention] As described above, in the present invention, when a shaft current is about to flow through the rotating shaft, a current is immediately flowed through the rotating shaft to cancel this shaft current, and the shaft current is electrically suppressed. Therefore, there is no need to insulate the bearings, and even in systems with a large number of bearings, such as shaft-driven power generators, it is possible to prevent shaft currents at a very low cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an axial current prevention device for a rotating electrical machine according to the present invention, and FIGS. 2 and 3 are schematic diagrams showing other embodiments of the present invention. 1... Rotating electric machine 2... Rotating shaft 3... Bearing 4... Shaft current detection sensor 5... Buffer circuit 6... Phase inversion circuit 7... Amplification circuit 8
...Axis current generating coil 10...Main engine Ill 11.
...Axle current prevention circuit (87JJ) Agent Yoshiaki Inomata (and 1 other person) Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) A rotating electrical machine characterized by being provided with a shaft current prevention circuit that, in response to the generation of shaft current flowing through the rotating shaft, causes a current having approximately the same current value and an opposite phase to the shaft current to flow through the rotating shaft. shaft current prevention device. (2) The shaft current prevention circuit includes a shaft current detection sensor that detects the shaft current flowing in the rotating shaft and outputs a signal corresponding to the shaft current;
A phase inversion circuit that inverts the output signal of this shaft current detection sensor to a signal with an opposite phase, an amplifier circuit that amplifies the output signal of this phase inversion circuit to a predetermined level, and a rotation that is the output signal of this amplifier circuit. The axial current prevention device for a rotating electric machine according to claim 1, comprising an axial current generating coil that causes a current of substantially the same current value and opposite phase to the axial current of the shaft to flow through the rotating shaft. . (3) The shaft current prevention circuit includes a shaft current detection sensor that detects the shaft current flowing in the rotating shaft and outputs a signal corresponding to the shaft current;
An amplifier circuit that amplifies the output signal of the detection coil of this shaft current detection sensor to a predetermined level, and a current that is approximately the same current value as the shaft current and has an opposite phase is caused to flow through the rotating shaft in accordance with the output signal of this amplifier circuit. The axial current prevention device for a rotating electric machine according to claim 1, characterized in that the axial current generating coil is wound with a polarity opposite to that of the detection coil of the axial current detection sensor.