JP3068821B1 - Bearing current reduction device for rotating machine - Google Patents

Abstract

The present invention provides a bearing current reducing device that reduces bearing current generated in a rotating machine to prevent wear of a bearing portion, damage and destruction of a rotating shaft, and that does not require maintenance even when used for a long time. I do. SOLUTION: A metal case of a rotating machine and a frame are connected by a conducting wire, and electrostatic force is generated between a rotating metal plate attached to a rotating shaft connected to a rotor shaft of the rotating machine and a metal plate attached to the frame. If the air gap capacity between the stator and the rotor of the rotating machine is set large enough by placing them in a non-contact close position so as to form a capacity, the steep voltage supplied to the rotating machine from the inverter The shaft voltage behavior with respect to changes can be damped without vibration, and the DC component that becomes the convergence value of the shaft voltage also decreases, so the shaft voltage immediately before the discharge is suppressed and the bearing DC that occurs as a shaft voltage discharge phenomenon Can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing current reducing device for an induction machine for reducing a bearing current flowing through a bearing of a rotating machine.

[0002]

2. Description of the Related Art In recent years, it has become common to drive a rotating machine such as an induction machine by a power converter such as an inverter as a method of controlling the number of revolutions. A voltage-type PWM inverter is best known as an inverter driving method. In this type of inverter drive system, a rectangular wave-shaped voltage pulse train having a constant carrier cycle with a pulse width proportional to the amplitude of the modulated sine wave signal is applied to the induction machine, and the current flowing through the stator winding of the induction machine is modulated. The induction machine is driven such that a sine wave equal to the frequency of the sine wave signal flows.

[0003] With the recent development of semiconductor devices for high-speed power, the carrier frequency of a voltage-type PWM inverter has been increased, and the bearing of an induction machine generated due to a steep voltage change generated at the time of switching of the inverter. It has been pointed out that a failure of the bearing portion due to electric current has occurred. This bearing current includes, for example, “the bearing current of an induction motor generated by a PWM inverter”
Chen, IEE Transaction on Energy Conversion, Vol. 11, No. 1, Volume 1, 1
(March 996) (Analysis of Induc)
Tion Motor Bearing Curren
ts Caused by PWM Inverter
s, IEEE Transactions on En
ergyConversion. Vol. 11, No.
1, March 1996),
There is a discharge mode bearing current with the largest amplitude and frequently occurring. In this type of bearing current, the steep rising common mode voltage supplied from the inverter to the winding of the induction machine causes the coupling capacity between the winding of the induction machine and the stator, the coupling capacity between the winding and the rotor, and As a response voltage generated when applied to a closed circuit constituted by the air gap capacity between the stator and the rotor, as a discharge phenomenon of static voltage accumulated in the electrostatic capacity between the stator and the rotor What happens. The shaft voltage accumulated in the capacitance between the stator and the rotor causes the oil film of the bearing to break down to make the bearing conductive, and the shaft voltage accumulated in the capacitance via the bearing is reduced. The discharge current flowing when discharging is the bearing current in the discharge mode.

FIG. 7 is a circuit diagram showing the principle of an induction machine driven by a conventional PWM inverter, and FIG. 8 is an explanatory diagram for explaining waveforms at various parts of the induction machine driven by a conventional PWM inverter. The generation mechanism of the common mode voltage that supplies the common mode voltage to the induction motor winding system by the PWM inverter will be described with reference to FIGS. 7 and 8.

[0005] In FIG. 7, an inverter 101 comprises switching elements 102 to 107 and a DC power supply 108, and R, S and T phase output terminals 109 to 111 of the inverter 101 are connected to a stator winding 113 of an induction machine 112.
, S-phase, and T-phase taps 114 to 116 respectively. The frame ground terminal 117 of the induction machine 112 is connected to the frame ground terminal 118 of the inverter 101.
8 is grounded to the ground.

[0006] in FIG. 8 (a), (b) , (c) the carrier wave signal V _c and each phase of the inverter command value U _R, U _S, by comparison with U _T, ON-OFF control in the inverter 101 This is for explaining the formation of a signal. 8, the horizontal axis is the time axis, and the sine waves shown by the thick lines in FIGS. 8A, 8B, and 8C are the inverter command values (U _R , U _S , U _T ). The waveform shown by the triangular thin line in FIG.
_C. Carrier wave signal V _C is an inverter command value U _R,
When it is lower than U _S and U _T , the corresponding switching elements 102 to 104 are turned on, and the switching elements 105 to 105 are turned on.
The 107 side becomes non-conductive. Conversely, the carrier wave signal V _C is an inverter command value U _R, U _S, is higher than U _T, the corresponding switching elements 102 to 104 side becomes non-conductive, the switching element 105 to 107 side becomes conductive.

FIGS. 8 (d), (e) and (f) show the pair of arms (102, 10) of the switching element shown in FIG.
5) Voltages V _R , V _S , and V _T formed between the midpoint of (103, 106) and (104, 107) and the ground. The relationship in the R phase will be described with reference to FIGS. When the carrier wave voltage V _C is higher than the inverter command value U _R , the switching element 105 becomes conductive, and the voltage V _R between the arm pair (102, 105) and the ground becomes zero. Here, _Ed is a voltage value at both ends of the DC current 108. Next, when the carrier wave voltage V _C is lower than the inverter command value U _R , the switching element 102 conducts, and the voltage V _R between the arm pair (102, 105) and the ground.
It becomes + E _d.

FIG. 8G shows the relationship between the common mode voltages applied to the winding 113.

The potential with respect to the ground at the neutral point 119 of the winding 113, that is, the neutral point potential V _NO is usually equal to the average voltage (Equation 1) of the above-mentioned voltages V _R , V _S and V _T. Become.

[0010]

(Equation 1)

Therefore, at the neutral point potential V _NO , a common mode voltage is generated in which the above-mentioned three phases of the voltages V _R , V _S and V _T are superimposed. That is, the neutral point potential V _NO has PW
A waveform in which three phases of the M switching pattern are superimposed is generated.

FIG. 9 is a common mode equivalent circuit diagram of a conventional inverter-driven induction machine. As shown in the figure,
In the induction machine 112, a coupling capacitance 121 exists between the winding 113 and the stator 120, and a coupling capacitance 123 also exists between the winding 113 and the rotor 122. Further, an air gap capacity 124 exists between the stator 120 and the rotor 122. Here, a case is considered where the induction machine rotates at an appropriate rotation speed and the bearing device 125 is in the fluid lubrication mode. In this case, although the bearing device 125 is in a non-conductive state, the winding 113, the coupling capacitance 121, the coupling capacitance 123, and the air gap capacitance 124 form a closed circuit system 126 as illustrated. When the common mode voltage e _i (t) is applied between the winding 113 and the stator 120 from the inverter 101, the shaft voltage V _rs (t) is applied to both ends of the air gap capacitance 124 via the closed circuit system 126. Occurs. That is, the common mode voltage e _i supplied by the inverter 101
An axis voltage V _rs (t) is generated as a response voltage of the closed circuit system 126 to (t).

FIG. 10 is a simplified common mode equivalent circuit diagram of a conventional inverter-driven induction machine. As shown, the winding 113 is replaced by a series circuit of a resistor 127 and an inductance 128. Winding 113
The coupling capacitance 121 between the stator and the stator 120 is the coupling capacitance 12
9 and 130, the total capacitance 123 between the winding 113 and the rotor 122 is simplified to coupling capacitances 131 and 132. The air gap capacity 124 between the stator 120 and the rotor 122 is determined by the resistance 127 of the winding 113 described above.
, An inductance 128 and coupling capacitances 129 to 132 to form a closed circuit system 126.
When the common mode voltage e _i (t) is applied to both ends of the coupling capacitance 129, the shaft voltage V _rs (t) is generated across the air gap capacitance 124 via the closed circuit system 126. That is, the shaft voltage is generated as a response voltage of the closed circuit system 126 to the common mode voltage supplied by the inverter. As shown in the figure, a resistor 133, an inductance 134, and a switch 135 indicate an equivalent circuit of the bearing device 125. When the induction machine 112 is stopped or rotating at a low speed, the bearing device 125 is in a boundary lubrication state, the switch 135 is always in a conductive state, and no shaft voltage is generated in the air gap capacity 124. Induction machine 1
12 is rotating at a suitable speed, the bearing device 12
5 is fluid lubrication and the switch 135 is normally in a non-conductive state, but is sometimes in a conductive state. Therefore, when the bearing device 125 is in fluid lubrication, when the bearing device 125 is in a non-conductive state, the shaft voltage is accumulated in the air gap capacity 124 for the above-described reason.
When the connection 25 is in the conductive state, the shaft voltage accumulated in the air gap capacitance 124 becomes the resistance 133 and the inductance 13
4 and switching 135. At this time, a series resonance circuit composed of the resistor 133, the inductance 134, and the air gap capacitance 124 is formed. A shaft current charged in the air gap capacitance 124 flows through the series resonance circuit to generate a discharge current. It becomes a current.

FIG. 11 is a time chart comparing a shaft voltage waveform calculated using computer simulation with a shaft voltage waveform actually measured.

FIG. 11B shows an example in which an appropriate circuit constant is set in the simplified common mode equivalent circuit shown in FIG.
In the case where the step-like waveform having the amplitude E _d / 3 shown in FIG. 7A is used as a common mode voltage, a waveform obtained by calculating a shaft voltage generated as a response voltage at both ends of the air gap capacitance 124 using a computer simulation. Show.

FIG. 11C shows a waveform of the shaft voltage actually measured when the bearing device 125 is always in a non-conductive state. As is clear from the figure, the shaft voltage (b) calculated by the computer simulation is almost the same as the shaft voltage (c) actually measured, and is calculated using the computer simulation based on the simplified common mode equivalent circuit. It can be seen that the obtained shaft voltage waveform well reproduces the shaft voltage waveform measured by the actual induction machine.

In the simplified common mode equivalent circuit shown in FIG. 10, the shaft voltage V with respect to the common mode voltage e _i (t) is
_Assuming that the transfer function of the closed circuit system 126 representing the response of _rs (t) is G (S), the transfer function G (S) is defined by the following equation (2) by definition.

[0018]

(Equation 2)

Here, V _rs (S) and E _i (S) are Laplace transform equations of V _rs (t) and e _i (t), respectively.

In the simplified common mode equivalent circuit of FIG. 10, R ₁ is the resistance of the resistor 127, and L ₁ is the inductance of 1
28 of the inductance, the capacitance to C ₁₀ is coupling capacitor 129, C ₁₁ is the capacitance of the coupling capacitor 130, C ₂₀ is the capacitance of the coupling capacitor 131, the capacitance of C ₂₁ is coupling capacitor 132,
When the transfer function G (S) is solved after forming a circuit equation with C ₃ being the capacitance of the air gap capacity 124, the transfer function G (S) is represented by the following equation (3).

[0021]

(Equation 3)

Where ζ is an attenuation coefficient, ω _n is an angular frequency, α
Is a coefficient and A is a coefficient, which are (Equation 4), (Equation 5),
Equations shown in (Equation 6) and (Equation 7).

[0023]

(Equation 4)

[0024]

(Equation 5)

[0025]

(Equation 6)

[0026]

(Equation 7)

When a step-like waveform having an amplitude of E _d / 3 is applied to the induction machine from the inverter, that is, when the common mode voltage E _i (S) is represented by (Equation 8)

[0028]

(Equation 8)

The shaft voltage V _rs (S) generated as a response voltage
Becomes (Equation 9) from (Equation 3) and (Equation 8).

[0030]

(Equation 9)

The first term of (Equation 9) is a DC component, and the second term is a second-order lag element.

[0032]

(Equation 10)

The shaft voltage V _rs (S) vibrates while the DC component V
converge to _rs0 .

When the value of the attenuation coefficient ζ becomes (Equation 11)

[0035]

[Equation 11]

The shaft voltage V _rs (S) does not vibrate and converges on the DC component V _rs0 .

Here, the DC component V _rs0 is an equation shown in (Equation 12).

[0038]

(Equation 12)

Here, (Equation 13) is obtained by substituting (Equation 5), (Equation 6), and (Equation 7) for (Equation 12).

[0040]

(Equation 13)

FIG. 12 is an explanatory diagram for explaining the waveform of the shaft voltage which changes in the conventional inverter-driven induction machine depending on how the value of the attenuation coefficient 減 衰 is selected.

The amplitude E _d / 3 as shown in FIG.
Is applied as the common mode voltage c _i (t), the shaft voltage V _rs (t) generated as the response voltage of the closed circuit system 126 behaves as the initial response of the secondary delay element. Show. That is, when the damping coefficient 内 is within the range shown by (Equation 11), the second-order lag element is over-braking or critical braking, and therefore, as shown in FIG. 12B, the shaft voltage V _rs (t ) Is non-vibrating and the DC component V
converge to _rs0 . Next, when the damping coefficient 内 is within the range shown by (Equation 10), the second-order lag element is under-damped, so that the shaft voltage V as shown in FIG.
_rs (t) converges on the DC component V _rs0 while oscillating. In this case, as the damping coefficient ζ becomes smaller than 1, the degree of vibration increases. In a normal induction machine, the damping coefficient 内 falls within the range of ( _Equation 10), and the shaft voltage converges on the DC component _Vrs0 while oscillating.

FIG. 13 is an explanatory diagram illustrating the common mode voltage, the shaft voltage and the bearing current at the moment when the largest bearing current is generated in the conventional inverter-driven induction machine.

The amplitude E _d / 3 as shown in FIG.
Is applied to the induction machine as the common mode voltage e _i (t), the shaft voltage V _rs (t) becomes the same as that described with reference to FIG. 12C. As shown in the figure, the _waveform converges to the DC component V _rs0 (V _rs0 = 5 V from the measurement result) while vibrating greatly. When the bearing device 125 conducts near the point where the shaft voltage V _rs (t) becomes the maximum peak voltage V _rsmax (V _rsmax 42 V from the measurement result), the shaft voltage charged in the air gap capacity 124 is changed to the bearing device 12 shown in FIG.
5 through a resistor 133, an inductance 134, and a switch 135. At this time, a series resonance circuit including the resistor 133, the inductance 134, and the air gap capacitance 124 is formed, and a current flowing when the shaft voltage charged in the air gap capacitance is discharged through the series resonance circuit is a bearing current. Bearing current i _b
(T) is a damped oscillatory wave as shown in FIG. 13 (c), but the maximum peak current I _bmax (I _bmax = 520 mA from the measurement result) of the bearing current is charged to the air gap capacity 124 immediately before the discharge. Proportional to the applied shaft voltage. In other words, a larger bearing current is obtained as the axial voltage charged to the air gap capacity 124 immediately before the discharge increases. Therefore, the shaft voltage V _rs (t) becomes the maximum peak voltage V
_{When the} bearing device 125 conducts in the vicinity of _rsmax , the shaft voltage accumulated in the air gap capacity becomes maximum immediately before the discharge, so that the largest bearing current is generated at this time.

As described above, in a normal induction machine driven by a PWM inverter, the shaft voltage greatly oscillates,
If the bearing device conducts around the _point where the shaft voltage reaches the maximum peak voltage V _rsmax , the bearing current generated as a shaft voltage discharge phenomenon will have the largest amplitude, causing bearing wear, damage to the rotating shaft, and weathering of lubricating oil. Some may damage or destroy the bearing. Therefore, a bearing current reducing device is used in a rotating machine so that such an obstacle does not occur. Normally, this bearing current reduction device includes a method of insulating the bearing and a method of grounding the rotating shaft.However, the method of insulating the bearing requires a complicated structure and requires utmost care in the assembly process. However, it takes a lot of man-hours, and some rotating machines cannot mechanically insulate the bearing part because of the mechanical structure. ing.

Conventionally, a bearing current reducing device of this type for reducing bearing current is disclosed in Japanese Patent Application Laid-Open Nos. 58-78770, 54-8801, and 63-12.
Japanese Patent Application Laid-Open Nos. 4057 and 58-78769 are known.

Hereinafter, the conventional bearing current reducing device will be described with reference to FIG. As shown in the figure, a conventional shaft current reducing device 13 of a type in which a rotating shaft is grounded.
Reference numeral 6 denotes an earth brush holder 137, an earth brush holder support 138, and an earth brush assembly 139. The ground brush holder support 138 is formed by bending a plate of a conductive material into a substantially L-shape, and the substantially L-shaped vertically turned end has a bearing bracket 140 and a shield ball bearing 141 joined to the bearing bracket 140. The bearing device 125 is mounted on a bearing bracket 140 via a bolt 142, and an earth brush holder 137 described later is mounted on a substantially L-shaped horizontal side. The bearing bracket 140 is used for the induction machine 112.
Is attached to the metal casing 143 of the No. 1 via a bolt 144. Earth brush holder 137 is holder shank 145
And a cap 146, and a holder shank 145.
The ground brush holder 138 is fixed to the horizontal return of the ground brush holder support 138 by a screw or soldering, and a mounting hole 147 for a ground brush assembly 139 described later is provided inside the ground brush holder support 138.
The ground brush assembly solid 139 includes the ground brush 148, the spring 149, the pigtail 150, and the pigtail support 15.
Consists of one. Therefore, the ground brush holder 137
When the ground brush assembly 139 is inserted into the mounting hole 147 of the holder shank 145, and the cap 146 is mounted on the holder shank 145, the ground brush 148 is pressed against the rotor shaft 152 via the spring 149 to contact the rotor shaft 152. The rotor shaft 152 is always provided with the ground brush 148, the pigtail 150, the pigtail support 151, and the cap 14.
6, holder shank 145, ground brush holder support 1
38, bearing bracket 140 and metal housing 14
3 is grounded.

[0048]

As described above, as described above,
In a conventional induction machine driven by a PWM inverter, the inverter 101 turns the winding 113 of the induction machine 112 into the R phase,
A common mode voltage is supplied in which three S-phase and T-phase PWM switching patterns are superposed. further,
A coupling capacitance 121 between the winding 113 and the stator 120;
A coupling capacitance 123 between the winding 113 and the rotor 122;
A closed circuit system 126 is formed by the air gap capacitance between the stator 120 and the rotor 122, and the air gap capacitance is a response voltage to the common mode voltage applied to the coupling capacitance 129 of the closed circuit system 126. A shaft voltage is generated at both ends of the shaft 124. In a general induction machine, the transfer function G (S) representing the response of the shaft voltage to the common mode voltage of the closed circuit system 126 includes a second-order lag element, and the damping coefficient ζ is considerably smaller than one. Therefore, when a stair-like waveform having a steep rise is applied from the inverter 101, the second-order lag element performs insufficient braking, so that the shaft voltage vibrates violently, and the maximum peak voltage V of the shaft voltage
_rsmax increases. When the bearing device conducts around the _point where the shaft voltage reaches the maximum peak voltage V _rsmax , the bearing current generated as a discharge phenomenon of the shaft voltage also increases, leading to wear of the bearing, damage to the rotating shaft, weathering of the lubricating oil, and in some cases, Has a problem that the bearing device is damaged or destroyed.

In the conventional bearing current reducing device for solving such a problem, the ground brush 148 is used.
Is made of a very soft conductive material containing carbon as a main component so as not to wear or damage the surface of the rotor shaft 152 because the spring is pressed against the rotor shaft 152 by a spring 149. There was a disadvantage that the earth brush had to be replaced every two to three months early, and at most six to seven months at the earliest.

As described above, in the induction machine driven by the conventional PWM inverter, since the shaft voltage vibrates violently, there is a problem that the bearing current generated as the discharge current of the shaft voltage becomes large. It is required to reduce or eliminate the current to prevent wear of the bearing portion, damage to the rotating shaft, weathering of lubricating oil, and damage or destruction of the bearing device.

Further, the conventional bearing current reducing device has a problem that maintenance due to wear of the brush needs to be performed every few months, and a reduction method capable of reducing the bearing current without requiring maintenance even when used for a long time. Has been requested.

The present invention solves such a conventional problem and reduces bearing current to prevent wear of a bearing portion, damage to a rotating shaft, weathering of lubricating oil, and damage or destruction of a bearing device. It is an object of the present invention to provide a bearing current reducing device that can reduce bearing current without requiring maintenance even after long-term use.

[0053]

In order to achieve the above object, a bearing current reducing device according to the present invention reduces bearing current of a rotating machine, and is connected to a metal housing of the rotating machine via a conducting wire. A frame, a rotating shaft connected to the rotor shaft of the rotating machine and attached to the frame via a bearing device, and a disk portion mounted on the rotating shaft in a direction perpendicular to the rotating shaft and having the same size as the rotating shaft cross section. Cut out 1
At least one rotating ring, at least one bearing device having an inner ring portion attached to the rotating shaft, and the same size as the outer ring portion of the bearing device attached to the outer ring portion of the bearing device in a direction perpendicular to the rotating shaft. A fixed ring having the same number as that of the bearings obtained by cutting the circular disk portion, and the fixed ring is connected between adjacent fixed rings via a conductive wire, and one of the fixed rings is connected via a conductive wire. A bearing current reducing device for a rotating machine, wherein the bearing is fixed to a frame, and the rotating ring and the fixed ring are alternately arranged at positions where they are not in contact with each other so as to generate capacitance. .

According to the present invention, the bearing current can be reduced to prevent wear of the bearing portion, damage to the rotating shaft, weathering of the lubricating oil, and damage or destruction of the bearing device. Thus, a bearing current reduction device capable of reducing the bearing current without requiring maintenance can be obtained.

Another means for reducing bearing current of a rotating machine is a frame connected to a metal casing of the rotating machine via a conductive wire, and a frame connected to a rotor shaft of the rotating machine via a bearing device. A rotating shaft attached to the frame, a rotating support ring attached to the rotating shaft in a direction perpendicular to the rotating shaft and a disk part cut out of the same size as the rotating shaft cross section, and a concentric circle with the rotating shaft One or more rotating cylinders having different radii attached to the rotating support ring, and a fixed support circle cut out from a disk part attached to the frame in a direction perpendicular to the rotation axis and having a radius larger than the radius of the rotation axis. A ring and one or more fixed cylinders having different radii attached to the fixed support ring concentrically with respect to the rotation axis;
A bearing current reduction device for a rotating machine, wherein the fixed cylinder and the rotating cylinder are alternately arranged at non-contact positions so as to generate capacitance.

According to the present invention, bearing current can be reduced to prevent bearing wear, damage to the rotating shaft, weathering of lubricating oil, and damage or destruction of the bearing device. Thus, a bearing current reduction device capable of reducing the bearing current without requiring maintenance can be obtained.

[0057]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a shaft current reducing device for a rotating machine in which a frame is connected to a metal housing of the rotating machine by a conductor, and a rotating ring attached to the rotating shaft is connected to a rotor shaft via a bearing device. A static ring is fixedly connected to the frame via a mounting wire, and is arranged in a position close to the fixed ring in a non-contact manner, so that a capacitance is formed between the rotating ring and the fixed ring, or By disposing the attached rotating cylinder at a position close to the fixed cylinder attached to the frame in a non-contact manner, a capacitance is formed between the rotating cylinder and the fixed cylinder, and the This is to reinforce the air gap capacity.

A closed circuit system constituted by the coupling capacity between the winding and the stator of the rotating machine, the coupling capacity between the winding and the rotor, and the air gap capacity between the stator and the rotor. The response of the shaft voltage to the common mode voltage is expressed as a transfer function having a second-order lag element, and the stator and the rotation are adjusted so that the attenuation coefficient 伝 達 of the transfer function becomes a sufficiently large value as compared with 1. If the air gap capacity between the actuator and the actuator is set to a sufficiently large value, the second-order lag element of the transfer function of the closed circuit can be operated by overbraking, and the shaft voltage can be monotonously increased without oscillating. It is possible to converge on the DC component while the convergence is achieved. Furthermore, by setting the air gap capacity between the stator and the rotor to a sufficiently large value, the DC component that is the convergence value of the shaft voltage is also reduced, so that the shaft voltage immediately before discharge is suppressed, and the shaft voltage is reduced. This has the effect that the bearing current generated as a voltage discharge phenomenon can be reduced.

Further, the rotating ring and the fixed ring, or the rotating cylinder and the fixed cylinder are arranged in a non-contact manner, and are made of a soft conductive material like a conventional bearing current reduction device. Since there is no place where the ground brush is pressed against the rotating shaft and worn, there is no need for maintenance even after long use.

[0060]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example in which the shaft voltage becomes non-oscillating will be described below as Example 1.

As shown in FIG. 1, the frame 1 is an induction machine 1
Twelve metal housings 143 are connected via the conducting wire 2. The rotating shaft 3 is connected to a rotor shaft 152 of the induction machine 112. A rotating ring 4 (5) having an outer radius r _{1 obtained} by cutting out a disk portion having the same size as the cross section of the rotating shaft having a radius r ₂ is:
It is attached to the rotating shaft 3 in a direction perpendicular to the rotating shaft 3. A fixed ring 6 (7) having an outer radius r _{4 obtained} by cutting a disk portion having an inner radius r ₃ larger than the radius r ₂ of the rotating shaft 3 is:
It is attached to the inner wall of the rotating ring 4 (5) at an interval of distance d of inner radius r ₄ frame 1 in a direction perpendicular to the rotation axis 3. The rotating rings 4, 5 and the fixed rings 6, 7
Each is alternately arranged in a non-contact manner at an interval d so as to form a capacitance between the adjacent fixed ring and rotating ring. The bearing device 8 attached to the rotating shaft 3 includes:
It comprises a bearing bracket 9 and a shielded ball bearing 10 joined thereto.
1 is attached to the frame 1.

The area S ₁ (m ² ) of the overlapping portion of the rotating ring 4 (5) and the fixed ring 6 (7) is the area shown by (Equation 14).

[0063]

[Equation 14]

[0064] The electrostatic capacitance between the rotating ring 4 and the stationary ring 6 putting the C _1, C ₁ are the values (number 15).

[0065]

(Equation 15)

Here, ε ₀ is a dielectric constant in a vacuum.

Similarly, the capacitance between the fixed ring 6 and the rotating ring 5 and the capacitance between the rotating ring 5 and the fixed ring 7 become equal to C ₁ . The combined capacitance C _z formed between the rotating ring and the fixed ring is a capacitance represented by (Equation 16).

[0068]

(Equation 16)

The above (Equation 14), (Equation 15), (Equation 1)
Combined capacitance C _z formed between the all rotary ring and the stationary ring 6) is the capacitance represented by equation (17).

[0070]

[Equation 17]

The air gap capacitance C ₃ ′ between the rotor and the stator of the dielectric machine 112 is determined by the combined capacitance C _z formed between all the rotating and stationary rings, and the stator C of the induction machine 112. The capacitance is a combination of the air gap capacitance C ₃ formed only between the rotor 120 and the rotor 122. Therefore, the air gap capacitance C ₃ ′ becomes the capacitance represented by (Equation 18).

[0072]

(Equation 18)

The condition for the shaft voltage to be non-oscillating is replaced by C ₃ and C ₃ ′ of (Equation 4) described in the conventional example (Equation 1).
(1) is changed to (Equation 19).

[0074]

[Equation 19]

Solving (Equation 19) for C ₃ ′ gives (Equation 2)
0).

[0076]

(Equation 20)

The outer radius r ₁ of the rotating ring, the inner radius r _{3 of} the fixed ring, the distance d between the rotating ring and the fixed ring, or the number of stages between the rotating ring and the fixed ring are appropriately selected. By setting the combined capacitance C _z formed between all the rotating rings and the fixed ring to a sufficiently large capacitance, the air gap capacitance C ₃ ′
Satisfies (Equation 20), the reduction coefficient と な り becomes 1 or more, the second-order lag element of the transfer function of the closed circuit system 126 becomes overbrake, and the shaft voltage monotonously increases without oscillating. While converging to the DC component _Vrs0 .

Further, when the air gap capacity C ₃ ′ is set to a sufficiently large value, as is apparent from (Equation 13),
Since the DC component V _rs0 that is the convergence value of the shaft voltage is suppressed to a small value, the shaft voltage immediately before the discharge is always suppressed to a small value, and the bearing current generated as a discharge phenomenon of the shaft voltage can also be suppressed to a small value.

FIG. 2 is a time chart illustrating a common mode voltage, a shaft voltage and a bearing current in an inverter-driven induction machine equipped with a bearing current reduction device. FIG. 2 illustrates a case where the combined capacitance formed between all the rotating torus and the fixed torus is set to C ₂ -480 pF.

When a step-like waveform as shown in FIG. 2A is applied to the induction machine as a common mode voltage, a sufficiently large air gap that satisfies the condition (Equation 20) that the shaft voltage does not vibrate is obtained. Since the capacitance C ₃ ′ is set, the shaft voltage becomes a non-vibrating DC component V as shown in FIG.
A waveform that converges on _rs0 is obtained. It has been described in the conventional example that the air gap capacity C ₃ ′ is sufficiently large (Equation 13).
As is apparent from the above, the DC component V, which is the convergence value of the shaft voltage,
_rs0 can be kept small. When the shaft voltage is settled at such a low level DC component V _rs0 (V _rs0 = 5 V from the measurement result), if the bearing happens to be conductive, a bearing current as shown in FIG. Since the shaft voltage immediately before the discharge is small, the bearing current having a small amplitude (the maximum peak value of the bearing current is I _bmax =
60 mA).

[0081] Figure 3 is a graph illustrating the relationship between the maximum crest value I _bmax of combined capacitance C _z and bearing currents in the induction motor of inverter drive with a bearing current reduction apparatus. The graph of FIG. 3, in the induction machine with bearing current reduction apparatus, when setting the composite electrostatic capacity formed between all the rotary ring and the stationary ring in a suitable C _z, flows to the bearing The relationship is illustrated by observing the bearing current and measuring the maximum peak value I _bmax of the bearing current. As apparent from FIG. 3, when the bearing current reducing device is not, ie when the capacitance C _z formed between the fixed ring and the rotary ring zero, the maximum wave height value of approximately 520mA bearing current Although but occurs in a rotating ring and induction machine synthetic electrostatic capacitance formed with a bearing current reducing machine set to C _z = 480pF between the fixed ring, the maximum wave height value of the bearing current its It is suppressed to about one tenth (I _bmax = 6
0 mA) It can be seen that the bearing current is effectively reduced.

Next, another example in which the shaft voltage becomes non-oscillating will be described below as Example 2.

As shown in FIG. 4, the frame 1 is an induction machine 1
Twelve metal housings 143 are connected via the conducting wire 2. The rotating shaft 3 is connected to a rotor shaft 152 of the induction machine 112. A rotating ring 4 (5) having an outer radius r _{1 obtained} by cutting out a disk portion having the same size as the cross section of the rotating shaft having a radius r ₂ is:
It is attached to the rotating shaft 3 in a direction perpendicular to the rotating shaft 3. Fixed hollow cylinder 12 of the outer radius r ₄ than the radius r ₂ of the rotary shaft 3 removed the cylindrical portion of larger inner diameter r ₃ (13)
Is inner radius is attached to the inner wall of the frame 1 of r ₄ at intervals of a distance d concentrically from the rotating disk 4 (5) relative to the axis of rotation 3. The rotating toroids 4 and 5 and the fixed hollow cylinders 12 and 13 are alternately separated by a distance d so as to be in non-contact with each other so as to generate capacitance between adjacent fixed hollow cylinders and rotating toroids. Are located. The bearing device 8 attached to the rotating shaft 3 includes a bearing bracket 9 and a shielded ball bearing 10 joined to the bearing bracket 9, and the bearing bracket 9 is connected to the frame 143 via a bolt 11.
Attached to.

The rotating ring 4 (5) and the fixed hollow cylinder 12 (1
The area S ₂ (m ² ) of the overlapping portion in 3) is the area shown by (Equation 21).

[0085]

(Equation 21)

[0086] The electrostatic capacitance between the rotating ring 1 and the stationary hollow cylinder 5 when put the C _2, C ₂ are the values (number 22).

[0087]

(Equation 22)

Here, ε ₀ is the induction rate in vacuum.

Similarly, the capacitance between the fixed hollow cylinder 12 and the rotating ring 5 and the capacitance between the rotating ring 5 and the fixed hollow cylinder 13 are equal to C _2. combined capacitance C _z formed between the circular ring and the fixed hollow cylinder is the capacitance represented by equation (23).

[0090]

(Equation 23)

The above (Equation 21), (Equation 22), (Equation 2)
Combined capacitance C _z formed between the all rotary ring and the stationary hollow cylinder 3) is the capacitance represented by equation (24).

[0092]

(Equation 24)

For the same reason as in Example 1, the outer radius r ₁ of the rotating ring, the inner radius r _{3 of} the fixed hollow column, the distance d between the rotating ring and the fixed hollow column, or the rotating ring and the fixed hollow column. the number of stages of columnar set appropriately, the combined capacitance C _z formed between the all rotary ring and the stationary hollow cylinder is set to a sufficiently large capacitance, the stator and the rotor By setting the air gap capacity C ₃ ′ in a range satisfying (Equation 20), the bearing current can be reduced. Hereinafter, the description that can reduce the bearing current is the same as that of the first example, and thus will be omitted.

Embodiment 1 As shown in FIG. 5, the frame 1 is connected to a metal casing 143 of the induction machine 112 via a conductor 2. The rotating shaft 3 is connected to a rotor shaft 152 of the induction machine 112. A rotating ring 4 (5) having an outer radius r _{1 obtained} by cutting a disk portion having the same size as the cross section of the rotating shaft having the outer radius r ₂ is attached to the rotating shaft 3 in a direction perpendicular to the rotating shaft 3. I have. The inner ring portion 16 (17) of the bearing device 14 (15) is attached to the rotating shaft 3, and the outer ring portion 18 (19) of the bearing device 14 (15).
A fixed ring 20 (21) having an outer radius r _{5 obtained} by cutting a disk portion having a radius r ₃ inscribed in the outer peripheral surface of the rotary ring 4 (5) in a direction perpendicular to the rotary shaft 3 and a distance d outer peripheral radius of the bearing device 14 (15) is attached to the outer peripheral surface of the outer ring portion 18 of r ₃ (19) at a position spaced. The rotating rings 4 and 5 and the fixed rings 20 and 21 are alternately arranged at intervals d so as to be in non-contact with each other so as to generate capacitance between the adjacent fixed rings and the rotating rings. Have been. The fixed ring 20 and the fixed ring 21 are connected via a conductor 22, and the fixed ring 21 is fixedly connected to the inner wall of the frame 1 via a conductor 23.

The bearing device 8 attached to the rotating shaft 3 is
It comprises a bearing bracket 9 and a shielded ball bearing 10 joined thereto.
1 is attached to the frame 1.

The rotating ring 4 (5) and the fixed ring 20 (21)
The area S ₃ (m ² ) of the overlapping portion is the area shown in (Equation 25).

[0097]

(Equation 25)

[0098] The electrostatic capacitance between the rotating ring 4 and the stationary ring 20 putting the C _3, C ₃ is a value shown in equation (26).

[0099]

(Equation 26)

Here, ε ₀ is a dielectric constant in a vacuum.

Similarly, since the capacitance between the fixed ring 20 and the rotating ring 5 and the capacitance between the rotating ring 5 and the fixed ring 21 are equal to C ₃ , all the rotations are equal. The combined capacitance C _z formed between the ring and the fixed ring is the capacitance shown by (Equation 27).

[0102]

[Equation 27]

The above (Equation 25), (Equation 26), (Equation 2)
Combined capacitance C _z formed between the all rotary ring and the stationary ring 7) is the capacitance represented by equation (28).

[0104]

[Equation 28]

In the first embodiment, for the same reason as in the first embodiment, the outer radius r ₁ of the rotating ring, the inner radius r ₃ of the fixed ring,
The distance d between the rotating ring and the fixed ring, or the number of stages of the rotating ring and the fixed hollow cylinder is set appropriately, and the combined capacitance formed between all the rotating rings and the fixed hollow cylinder. By setting C _z to a sufficiently large capacitance, the air gap capacity C ₃ ′ between the stator and the rotor of the induction machine 112 is set to (Equation 20).
Is set to satisfy the range, the bearing current can be reduced. Hereinafter, the description that can reduce the bearing current is the same as that of the first example, and thus will be omitted.

Embodiment 2 As shown in FIG. 6, the frame 1 is connected to the metal casing 143 of the induction machine 112 via the conducting wire 2. The rotating shaft 3 is connected to a rotor shaft 152 of the induction machine 112. A rotation support ring 24 having an outer radius r _{6 obtained} by cutting out a disk portion having the same size as the cross section of the rotation shaft 3 having a radius r ₂ is attached to the rotation shaft 3 in a direction perpendicular to the rotation shaft 3. the r _6, the rotating cylinder 25 to the inner radius and r ₇ and,, r ₈ an outer radius, the rotating cylinder 26 to the inner radius and r ₉ is rotating support ring concentrically with respect to the rotation axis 3 24. Similarly, a fixed support ring 27 having an outer radius r _{4 obtained} by cutting a disk portion having a radius r ₁₀ larger than the outer radius r ₂ of the rotating shaft 3 has an inner radius r perpendicular to the rotating shaft 3.
₄ is attached to the inner wall of the frame 1 and the outer radius is r ₁₁ ,
A fixed cylinder 28 having an inner radius of r ₁₂ and a rotating cylinder 29 having an outer radius of r ₁₃ and an inner radius of r ₁₀ are formed on the fixed support ring 27 so as to be concentric with the rotating shaft 3. Installed. The rotating toroids 25 and 26 and the fixed cylinders 28 and 29 are alternately arranged at non-contact positions so as to form a capacitance between the adjacent fixed torus and rotating cylinder. The bearing device 8 of the rotating shaft 3 comprises a bearing bracket 9 and a shielded ball bearing 10 joined thereto, and the bearing bracket 9 is connected to the frame 1 via bolts 11.
Attached to.

The rotating cylinder 25 (26) and the fixed cylinder 28 (2
Assuming that the length of the portion overlapping in the axial direction of 9) is L, the capacitance C ₄₁ formed between the rotating cylinder 25 and the fixed cylinder 28 becomes (Equation 29).

[0108]

(Equation 29)

The capacitance C ₄₂ formed between the fixed cylinder 28 and the rotating cylinder 26 is (Equation 30).

[0110]

[Equation 30]

The capacitance C ₄₃ formed between the rotating cylinder 26 and the fixed cylinder 29 becomes (Equation 31).

[0112]

(Equation 31)

The combined capacitance C _z formed between all the rotating cylinders and the fixed cylinder is the capacitance shown by (Expression 32).

[0114]

(Equation 32)

The combined capacitance C _z formed between all the rotating cylinders and the fixed cylinders is given by (Equation 33) from (Equation 29), (Equation 30), (Equation 31), and (Equation 32). It becomes capacitance.

[0116]

[Equation 33]

In the second embodiment, for the same reason as in the first embodiment, the inner and outer radii of the rotating cylinder and the fixed cylinder are r ₇ , r ₉ , r ₁₂ , the outer radii r ₈ , r ₁₁ , r ₁₃ , and the rotating cylinders 25 and 26. And the length L of the portion overlapping in the axial direction of the fixed cylinders 28 and 29 or the number of stages of the rotating cylinder and the fixed cylinder is appropriately selected, and the combined capacitance formed between all the rotating cylinders and the fixed cylinder is selected. C
_{If z} is set to a sufficiently large capacitance and the air gap capacity C ₃ ′ between the stator and the rotor of the induction machine 112 is set in a range satisfying (Equation 20), the bearing current is reduced. be able to. Hereinafter, the description that can reduce the bearing current will be omitted because it is the same as that of Example 1.

[0118]

As is apparent from the above embodiment, according to the present invention, the metal casing of the rotating machine and the bearing current reducing device are connected by a conducting wire, and the rotating circle attached to the rotating shaft of the first embodiment. The fixed ring attached to the rotating shaft and fixedly connected to the frame via the ring and the bearing device, or the rotating cylinder attached to the rotating shaft and the fixed cylinder attached to the frame of the second embodiment are brought into close contact with each other in a non-contact manner and statically moved. The shaft voltage generated as a response voltage of the steep rising common mode voltage applied to the induction machine from the inverter by forming electric capacity and reinforcing the air gap capacity between the stator and the rotor of the rotating machine Is operated without vibration, and at the same time, the DC component which is the convergence value of the shaft voltage is also reduced, so that the shaft voltage immediately before the discharge can be suppressed extremely small, which occurs as a discharge phenomenon of the shaft voltage. Can be reduced bearings current, the wear of the bearing unit, damage to the rotary shaft, weathering of the lubricating oil can provide a bearing current reduction apparatus having the effect that it is possible to prevent damage or destruction of the bearing device.

According to the present invention, the bearing current is reduced by bringing the rotating ring and the fixed ring of the first embodiment or the rotating cylinder and the fixed cylinder of the second embodiment close to each other in a non-contact manner. Since a soft conductive material is pressed against the rotating shaft as in the conventional bearing current reduction device, there is an effect that the bearing current requiring maintenance which requires brush replacement in a few months can be reduced. A bearing current reduction device is obtained.

[Brief description of the drawings]

FIG. 1 is a side view of a bearing current reduction device of Example 1 in which a shaft voltage becomes non-oscillating.

FIG. 2 is a time chart illustrating a common mode voltage, a shaft voltage, and a bearing current in an inverter-driven induction machine equipped with the bearing current reduction device.

FIG. 3 is a graph illustrating a relationship between a combined capacitance C _z and a maximum peak value I _bmax of a bearing current in an inverter-driven induction machine including the bearing current reduction device.

FIG. 4 is a side view of the bearing current reduction device of Example 2 in which the shaft voltage becomes non-oscillating.

FIG. 5 is a side view of the bearing current reducing device according to the first embodiment of the present invention.

FIG. 6 is a side view of the bearing current reducing device according to the second embodiment of the present invention.

FIG. 7 is a diagram showing a basic circuit of a conventional induction machine driven by a PWM inverter;

FIG. 8 is an explanatory diagram for explaining waveforms of various parts of an induction machine driven by a conventional PWM inverter.

FIG. 9 is a common mode equivalent circuit diagram of a conventional inverter-driven induction machine.

FIG. 10 is a simplified common mode equivalent circuit diagram of a conventional inverter-driven induction machine.

FIG. 11 is a time chart comparing a shaft voltage waveform calculated using computer simulation with a shaft voltage waveform actually measured in a conventional inverter-driven induction machine.

FIG. 12 is an explanatory diagram illustrating a waveform of an axial voltage that changes in a conventional inverter-driven induction machine according to a method of selecting a value of a damping coefficient ζ.

FIG. 13 is an explanatory diagram illustrating a common mode voltage, a shaft voltage, and a bearing current at the moment when the largest bearing current occurs in a conventional inverter-driven induction machine.

FIG. 14 is a side view of a conventional bearing current reduction device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Frame 2 Conductor 3 Rotating shaft 4 Rotating ring 5 Rotating ring 6 Fixed ring 7 Fixed ring 8 Bearing device 12 Fixed hollow column 13 Fixed hollow column 14 Bearing device 15 Bearing device 16 Inner ring part 17 Inner ring part 18 Outer ring part 19 Outer ring unit 20 Fixed ring 21 Fixed ring 22 Conductor 23 Conductor 24 Rotation support ring 25 Fixed cylinder 26 Fixed cylinder 27 Fixed support ring 28 Rotation cylinder 29 Rotation cylinder

Continuation of the front page (72) Inventor Takahiro Asai 6-2-61 Imafukunishi, Joto-ku, Osaka-shi, Osaka Inside Matsushita Seiko Co., Ltd. (56) Reference Real-life 1983-183070 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) H02K 11/00 H02K 5/16

Claims (2)

(57) [Claims] An apparatus for reducing a bearing current of a rotating machine, comprising: a frame connected to a metal housing of the rotating machine via a conductive wire; and a frame connected to a rotor shaft of the rotating machine and mounted on the frame via a bearing device. A rotating shaft, one or more rotating rings attached to the rotating shaft in a direction perpendicular to the rotating shaft, and having a disk portion having the same size as the rotating shaft cross section, and an inner ring portion attached to the rotating shaft. And at least the same number of bearing rings as the bearings, which are cut out of a disk portion having the same size as the outer ring portion of the bearing device attached to the outer ring portion of the bearing device in a direction perpendicular to the rotation axis, and Wherein the fixed ring is connected between adjacent fixed rings via a conductive wire, one of the fixed rings is fixed to the frame via a conductive wire, and the rotating ring and the fixed ring are static. Alternately placed at non-contact locations to generate capacitance A bearing current reduction device for a rotating machine characterized by being placed. 2. A method for reducing a bearing current of a rotating machine, comprising: a frame connected to a metal casing of the rotating machine via a conductive wire; and a frame connected to a rotor shaft of the rotating machine and mounted on the frame via a bearing device. A rotating shaft, a rotating supporting ring attached to the rotating shaft in a direction perpendicular to the rotating shaft, and a disk portion having the same size as the rotating shaft section cut out, and the rotating supporting circle concentric with the rotating shaft. One or more rotating cylinders having different radii attached to the ring, a fixed support ring which is attached to the frame in a direction perpendicular to the rotation axis and has a disk portion having a radius larger than the radius of the rotation axis cut out, One or more fixed cylinders having different radii attached to the fixed support ring concentrically with respect to an axis are provided, and the fixed cylinder and the rotating cylinder are in a non-contact position to generate capacitance. Alternately A bearing current reducing device for a rotary machine.