DE102005021354A1 - Arrangement for limiting overvoltages on functional parts of converter-fed electrical machines - Google Patents

Abstract

The invention relates to an arrangement for limiting overvoltages on functional parts of converter-fed electrical machines. DOLLAR A task is to provide an arrangement to limit the voltage applied primarily to the bearings and earthing brushes and the high-frequency currents flowing through these components as far as possible. DOLLAR A In the novel arrangement of a parallel to the functional parts capacitor in conjunction with a sliding contact according to the invention, the connecting and connecting lines are designed inductively low in particular and an inventively configured additionally arranged rotary contact device establishes a secure contact to the rotor shaft. DOLLAR A In a second embodiment, one or more rotating contact devices are connected to the rotor shaft between ground point of the housing of the electric machine. With this arrangement, the rotor shaft is directly electrically shorted to the machine housing for both low and high frequency components. DOLLAR A The rotating contact device according to the invention causes in the simplest way a reliable, speed and vibration independent galvanic contact to the shaft, which is equally suitable for both low and high frequency leakage currents. DOLLAR A The arrangement leads to a lifetime extension on the machine bearings and grounding brushes.

Description

The The invention relates to an arrangement for limiting overvoltages On functional parts inverter-fed electrical machines, in particular at warehouses. Such surges can in particular the function of the bearings, but also of other functional parts, such as. Grounding brushes, compromise.

To the Protection of the bearings unacceptable low-frequency voltages and consequent currents for a long time used the known grounding brushes. Limit these grounding brushes in sinus mode in conjunction with other protective measures, such as. Use of insulated bearings, reliably occurring in the warehouse electrical stresses. In addition, earthing brushes provide for the establish the contact protection and to protect the coupled machine in medium and large machines necessary shaft grounding.

When operated with voltage DC link converters, the electrical stresses increase due to the effect of the so-called common-mode voltages of the inverter and the capacity ratios present in each case in the electrical machine. Therefore, in particular in rotor-fed asynchronous machines in addition to the low-frequency shaft voltages capacitively coupled high-frequency shaft and bearing voltages and related high-frequency currents accordingly. These additional stresses are generally countered with improved bearing isolation. By way of example, a corresponding technical solution in the OS 100 37 423 A1 described. Here, a current-insulated roller bearing is described, in which the entire rolling bearing is arranged completely insulated in the machine housing by additional sheet-like thin annular disk elements and a hollow cylindrical element made of suitable insulating material. On its own, however, this technical solution is considered insufficient over longer periods of time, as the bearings nevertheless wear out prematurely. On an additional shaft ground can therefore not be waived, especially in medium and large machines and in the rotor-fed asynchronous machines.

So was in the DE 35 11 755 A1 proposed an arrangement for deriving wave voltages, in which the steep voltage spikes and / or high-frequency voltage components are degraded by the shaft is grounded with an additional current path via a arranged on the shaft side sliding contact and a parallel to the functional parts capacitor. The bearings are also electrically isolated by Isolierstrecken to earth, ground and foundation. By additional measures, the frequency of this derivative arrangement is tuned to the machine-specific frequency on the non-drive side of a turbogenerator.

It has also been proposed to pass the bearing currents past the bearings via conductive sealing rings, see DE 200 07 714 U1 , It should be noted that the electrical conductivity of the sealing ring material can not be increased arbitrarily and still unacceptable storage voltages can arise.

It has also been proposed to add short-circuit disks directly to the bearings which electrically connect the roller bearing inner ring to the roller bearing outer ring. However, the short-circuit discs are to be regarded as wearing parts and thus undesirable in the bearings of medium and large machines, as in DE 200 10 088 U1 described.

In special cases are also used so-called hybrid bearings. Speaking of hybrid bearings one, if the rolling elements of a Rolling out of consist of ceramic materials. Achieve these ceramic rolling elements a high insulation effect, so that the current flow is effective can be interrupted. However, such hybrid bearings are very consuming in manufacturing, are therefore expensive and are not available in all sizes.

The above-mentioned improved bearing insulation in conjunction with the Wave grounding over conventional grounding brushes Although it can significantly reduce the bearing stresses and bearing currents. It However, it can not be ruled out with certainty that dynamic voltage peaks, such as those with voltage DC link converters lead to the breakdown of the lubricating film of such kind bearing. The simultaneously pending at the parallel grounding brush Lead spikes again to short current pulses, which are also erosive to a considerable extent the contact of the grounding brushes damage can.

The in DE 35 11 755 A1 The claim to capacitive wave grounding seems to be promising in principle. The type of contacting set out in the embodiment of this technical solution, however, again consists of a brush sliding contact with the disadvantages described above. Incidentally, the type of arrangement and also listed inductive wiring of the grounding brush itself and the use of specially tuned resonant circuits only in special cases, as in the turbogenerators discussed here in detail, applicable.

The invention is based on the object an arrangement for limiting overvoltages and resulting currents in functional parts of converter-fed electrical machines, to provide the voltage applied across the radial gap of the bearings (in the further machine bearing) and at the same time above the grounding brush, and the high-frequency currents flowing through these components in the first place far enough to ensure that sufficient protection is provided for both components, ie that both the mechanical load bearing capacity of the machine bearing (s) and the electrical protective function of the grounding brush are guaranteed over a longer service life than before.

According to the invention Task with the technical features of the first or the second claim solved. Advantageous embodiments of the two main claims are Part of the dependent Dependent claims. The inventive arrangement for limiting overvoltages on functional parts inverter-fed electrical machines acts prolong the service life on the machine bearings and grounding brushes. Unlike the Previously known from the prior art arrangement of the Function parts connected in parallel capacitor in conjunction with a sliding contact here are the connecting and connecting cables in a special way low in inductance accomplished and the inventively designed rotating contact device provides a secure contact to Wave forth.

In a second embodiment the inventive arrangement for limiting overvoltages Inverter-fed electrical machines are available between functional parts Earth point of the housing the electric machine one or more rotating contact devices to the rotor shaft connected. With this arrangement, the rotor shaft with the housing machine for both low and high as well as for high-frequency components directly electrically short-circuited. In order to can the conventional brush slip ring contact omitted.

The rotating invention Contact device causes in the simplest way a reliable, speed and vibration independent galvanic contact with the shaft, which is equally important for both as well as for high-frequency leakage currents suitable is.

• • unmittelbar an, und/oder neben, und/oder in anderer konstruktiv günstiger Entfernung zu einem oder beiden Maschinenlagern,
• • auf einer zusätzlichen Wellenverlängerung,
• • im Labyrinth der Maschinenlager oder
• • nur auf der Nicht-Antriebsseite der elektrischen Maschine.

It is possible, depending on the particular design of the inverter-fed electrical machine to arrange the rotating contact device according to the invention at different locations on the rotor, eg

• • directly at, and / or next to, and / or at another constructively favorable distance from one or both machine bearings,
• • on an additional shaft extension,
• • in the labyrinth of machine bearings or
• • only on the non-drive side of the electric machine.

In a special design the rotating invention Contact devices these are designed as a protector bearing. Protector bearings have the advantage that they do not take over any bearing function have to and on the other ideal, even with different Speeds of the rotor shaft to establish a safe electrical contact.

Advantageous is it, the Protector bearings as usual roller bearing train. When arranging the Protector bearings on a shaft extension With a smaller diameter, the bearings are very small and small particularly cost-effective compared to the machine bearings. In order to connected at the same time a lower peripheral speed Protector bearing inner ring what the wear effect of the Protector camp reduced.

It is also conceivable e.g. to dimension the protector bearings according to the invention that they are placed in the labyrinth of one or both machine bearings can be so that they are directly at risk Radial gap of the machine bearings act.

In order to the contact between the inner ring on the rolling elements to the outer ring and then on to casing the electrical machine is optimally ensured, it is of Advantage, if the rolling bearings as axially preloaded roller bearings are formed.

A Further improvement of the contacting can be achieved if inside the rotating contactor or protector bearing a contact material is arranged. The contact materials can thereby in pasty or in fluidic consistency.

Advantageous it is when the contact material is formed as a conductive lubricant is that electrically highly conductive non-metallic admixtures, e.g. Contains graphite.

In a further variant of the arrangement according to the invention for limiting of surges are at the or the rotating contact devices or the or the Protector camps laterally on one side or both sides in itself known short-circuit discs arranged to continue the contact to improve.

To turn the rotating contact devices or the Protector bearings against turning Chern, torque brackets are arranged. These torque arms can be performed in a special way inductance, such as a thin-walled plate-shaped metallic cap. The cap material is a magnetically and electrically highly conductive material. The cap is contacted at the cap edge with the grounded housing.

In summary can be found that with the inventive arrangement in a new way a possibility for limiting overvoltages especially the high-frequency type and the resulting streams implemented on functional parts inverter-fed electrical machines is. Mainly By using the Protector bearings are those of conventional brush sliding contacts known disadvantages when leading high-frequency currents overcome.

The invention will be described below with reference to the 1 to 3 be described in more detail.

1 shows the equivalent circuit diagram of the common mode circuit of a stator or rotor-fed electrical machine with grounded shaft at inverter power

2 shows a side view of the rotating contact device according to the invention 10

3 shows the top view of a contact device according to the invention 10 including a possible variant of the electrical connection to the housing 17 the electric machine

According to the invention here on the non-drive side NS of the rotor, a single arrangement for limiting overvoltages is positioned, which consists of a low-inductance capacitor C6, on one side low inductance at an existing central earth point GE of the housing 17 and on the other side via a rotating contact device 10 to the rotor shaft 7 connected. This arrangement acts electrically as a high-pass and thus limits those above the machine bearing 8th and the grounding brush 12 and 11 existing electrical high-frequency stresses to a permissible level. The rotating contact device 10 For example, consists of an otherwise common deep groove ball bearing that on a shaft extension 2 mounted on the non-drive side NS with a small diameter. This deep groove ball bearing is axially biased to ensure that the mechanically unloaded bearing has the necessary running quality and low radial clearance (clearance). The actual contacting takes place via the highly conductive lubricant in the deep groove ball bearing 3 (Fat). To improve the current transition is additionally a known short-circuiting disk 4 used. The deep groove ball bearing has no supporting function and serves only as a contact device. By comparison, such a contact would be in the machine bearings 8th impractical, since the carrying function is adversely affected by current transitions or abrasion of short-circuiting discs used there.

The arrangement acting as a high-pass causes a capacitive shaft grounding and limits the electrical high-frequency stresses of the machine bearings in the sense of the task 8th and their insulation with capacitance C5 and earthing brushes 11 . 12 in a significant way.

In 1 the equivalent circuit diagram of a common-mode circuit of a stator or rotor-fed electric machine with a grounded shaft is shown when supplied by means of a voltage DC link converter. The functionally impressed by the inverter common-mode voltage U0 is above the capacitance C1 between the winding, in which the voltage pulses are fed and the stator housing. When fed into the stator winding, this is essentially determined by the winding parts located in the stator slots. When fed into the rotor winding this is essentially determined by the Läuferwickelköpfe. Parallel to the capacitor C1 is the voltage divider formed by the capacitors C2 and C3. The capacitance C2 is formed by the winding into which the voltage pulses are fed and the runner iron. When fed into the stator winding, this is essentially determined by the stator winding heads and when fed into the rotor winding essentially by the lying in the rotor slots winding parts. The capacitance C3 is present between stator and rotor iron, it is mainly determined by the dimensions of the stator bore and the air gap. The ratio of the bearing voltage to the common-mode voltage U0 is largely determined by the capacitance ratio C2 to C3 and thus of the feed of the electric machine. Parallel to C3 are the voltage divider of the bearings on the drive side DS and the non-drive side NS, formed from the capacity C4 of the machine bearings 8th and the capacity C5 of the storage insulation. The height of the tension above the lubricant gap of the machine bearing 8th depends now again on the capacity ratio C4 to C5. Although this ratio can be influenced within certain limits via the dimensioning of the bearing insulation and thus the capacitance C5, it can not be ruled out that the stresses above C4 will lead to the breakdown of the lubricant gap with all the negative consequences on the bearing life. The rotor shaft 7 is via a conventional brush-sliding contact 12 grounded, the brush itself and its pigtail provides an impedance 11 As in the equivalent circuit diagram, the first on the height of Storage voltage decides. The dynamic peaks in the bearing voltage and the associated leakage currents via the brush sliding contact 12 lead to erosive changes in the brush and slip ring surface in addition to the operational wear.

Parallel to the voltage divider C4 and C5 according to the invention, the rotating contact device 10 together with the capacitance C6 connected to the housing ground GE for high-frequency rotor grounding inductance. With the special design of the contact device 10 together with the capacity C6 and the low-inductance connection 6 The high-frequency currents are taken over and the bearing voltage peaks are lowered to a permissible level, without any disruptions of the lubricant gap in the machine bearings 8th occur. According to the invention, the capacitance C6 for connecting the high-frequency rotor grounding consists of a particularly low-inductance capacitor (<100 nH). The capacitance of the capacitor is chosen to be large compared to C2.

In the 2 and 3 is an example of the basic structural design of a protector bearing 1 as a rotating contact device 10 shown. This is on the wave extension 2 with one opposite the rotor shaft 7 Shrunk smaller diameter. The outer ring of the Protector bearing 1 becomes mechanically strong and electrically safe with a protector housing 16 connected. The protector housing 16 is via the isolated torque arm 5 held via torque arm boltings 13 is attached. The same applies to the Protector housing 16 via the Protector bearing terminal 14 the low-inductance connection 6 connected. On the protector housing 16 are the two Protector bearing caps 9 using several Protector bearing caps 15 attached. To the contact between shaft extension 2 and Protector housing 16 To improve, the electrically conductive lubricant 3 together with the short-circuiting disc 4 in the Protector camp 1 used.

U0

Common-mode voltage

C1

Capacity between the winding into which the voltage pulses are fed and the Stand housing (at Infeed into the stator winding essentially determined by the lying in the stator grooves winding parts; when fed into the rotor winding essentially determined by the Läuferwickelköpfe)

C2

Capacity between the winding into which the voltage pulses are fed and the runs travel (when fed into the stator winding essentially by the stator Infeed into the rotor winding in the essentially determined by the in the winding heads; rotor slots determined winding parts)

C3

Capacity between stator and runner iron (mainly by the dimensions of the stator bore and the air gap determined)

C4

Capacity of the machine bearings (mainly by determines the lubricant gap between rolling elements and races) and parallel spark gap between rolling elements and races

C5

Capacity of the storage insulation

C6

Capacitance for wiring the high-frequency rotor grounding

DS

driving side the electric machine

NS

Non-drive side the electric machine

GE

Frame ground

1

Protector-bearing

2

shaft extension with a smaller diameter

3

electrical conductive lubricant

4

Short disc

5

isolated torque arm

6

low-inductance connection

7

rotor shaft

8th

machinery bearings

9

Protector bearing cap

10

rotating contactor

11

More complex Replacement resistance of the brush sliding contact and the brush pigtail

12

Brush Schleükontakt

13

Drehmomentstützenverschraubung

14

Protector-bearing terminal

15

Protector Lagerdeckelverschraubung

16

Protector case

17

Housing of electric machine

Claims (16)

Arrangement for limiting overvoltages on functional parts of converter-fed electrical machines, in particular on bearings and Er tion brushes, consisting of a capacitor and a sliding contact on the shaft, connected in parallel to the functional parts characterized in that the one or more known capacitors are themselves designed low inductance, low inductance on a terminal side at a nearby existing central earth point or other earthed parts of the Housing of the machine and on the other side of the connection in turn inductance are connected via one or more rotating contact devices to the rotor shaft. Arrangement for limiting overvoltages to functional parts Inverter-fed electrical machines, especially at warehouses and grounding brushes characterized in that the earth point of the housing low inductance via one or several rotating contact devices connected to the rotor shaft is. Arrangement for limiting overvoltages according to claim 1 or 2, characterized in that the rotating contact means immediately, and / or next, and / or in another constructive way better Distance to one or both machine bearings are arranged. Arrangement for limiting overvoltages according to claim 1 or 2, characterized in that the rotating contact device on an additional shaft extension is arranged. Arrangement for limiting overvoltages according to one of previous claims, characterized in that the rotating contact device in Labyrinth of machine bearings is arranged. Arrangement for limiting overvoltages according to claim 1 or 2, characterized in that the rotating contact device arranged only on the non-drive side of the electric machine is. Arrangement for limiting overvoltages according to one of previous claims, characterized in that the rotating contact means are designed as a protector bearing. Arrangement for limiting overvoltages according to claim 6, characterized in that the protector bearings than conventional bearings are formed. Arrangement for limiting overvoltages according to claim 7, characterized in that the rolling bearings as axially biased roller bearing are formed. Arrangement for limiting overvoltages according to one of preceding claims, characterized characterized in that in the interior of the rotating contact device or the protector bearing a contact material is arranged. Arrangement for limiting overvoltages according to one of preceding claims, characterized characterized in that the contact material as a conductive lubricant is formed that electrically highly conductive non-metallic admixtures contains. Arrangement for limiting overvoltages according to one of preceding claims, characterized characterized in that on the rotating contact device or on the Protector bearing laterally one-sided or on both sides short-circuit discs are arranged. Arrangement for limiting overvoltages according to one of preceding claims, characterized characterized in that the connection and connecting lines from grounded housing the electric machine to the rotating contact device or the protector bearing formed in a special way inductance are. Arrangement for limiting overvoltages according to one of preceding claims, characterized in that the torque support on the rotating contact device or the Protector camp at the same time as low-inductance Contacting to the one or more low-inductance capacitors or directly to the grounded housing the electric machine is used. Arrangement for limiting overvoltages according to one of preceding claims, characterized characterized in that the torque arm as a thin-walled plate-shaped metallic cap accomplished is. Arrangement for limiting overvoltages according to one of preceding claims, characterized characterized in that the thin-walled dished Metallic cap made of a magnetically and electrically highly conductive contact material exists and is contacted at the edge of the cap with the grounded housing.