GB1605317A

GB1605317A - Method and apparatus for testing the efficiency of rotor discs

Info

Publication number: GB1605317A
Application number: GB14353/74A
Authority: GB
Original assignee: MAN Maschinenfabrik Augsburg Nuernberg AG
Current assignee: MAN AG
Priority date: 1973-04-14
Filing date: 1974-04-14
Publication date: 1989-07-19
Also published as: FR2624619A1; DE2318999C1; IT1205880B; NO113583C; NO741311L

Abstract

a) A method for testing the power of rotor discs of the same type for hysteresis motors, particularly in gas centrifuges. b) When the rotor disc 4 is stationary, the current through the windings of the stator 2 is compared with a reference value. c) Method applicable to testing gas centrifuge components. <IMAGE>

Description

(54) METHOD AND APPARATUS FOR TESTING THE EFFICIENCY OF ROTOR DISCS (71) We, MASCHINENFABRIK AUGSBURG MURNBERG AKTIENGESELLSCHAFTS of 8000 München 50, Postfach 50 06 20, Germany, a German Body Corporate do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a process for testing the magnetic and electric characteristics of equally shaped rotor discs for hysteresis motors for gas centrifuges.

To guarantee that rated power and rated efficiency are achieved, the rotor discs of hysteresis motors must have quite specific magnetic properties, whereby inconsistencies in the hardening process and in the composition of the material for the rotor disc cause disturbances in a manner which is still unknown and to some extent not reproducible. Whereas it is likely that these disturbances will be only trivial in the case of a single motor of liberal design operating at part load, the individual hysteresis motor for a large-scale industrial separation plant having some 105 gas centrifuges must, for cost reasons alone, be designed sparingly just to give its rated power in continuous service, and disturbances in efficiency can cumulatively have such an effect that the entire power supply can be jeopardized.

Hitherto. the practice has been to take a specific number of rotor discs selected from a batch delivered and to test their characteristics under operating conditions. The results of the separate tests. which take some 3 hours per disc, allowed sufficiently accurate inferences to be made about the untested discs. Although only random samples were tested, a considerable effort was nevertheless involved, as a test under operating conditions involved installing the rotor disc in a gas centrifuge, evacuating the housing and running up the centrifuge.

Since a high-tensile steel, such as X 2 NiCo Mo 1895 (i.e. steel with 18% Ni, 9% Co. 5% MO) which is submitted to a hardening process, can be used for rotor discs on account of the required strength properties, the rotor discs have properties which vary to such an extent, even within one delivered batch, that there is no altemative to submitting each single rotor disc to a separate test.

The objective of the invention is to devise a process for testing the rotor discs of hysteresis motors which, while involving little time and measuring equipment, enables their output to be adequately checked.

According to the invention a process for testing the magnetic and electric characteristics of equally shaped rotor discs for hysteresis motors for gas centrifuges is suggested, comprising fixing the rotor adjacent a testing stator, applying a predetermined voltage to the testing stator, measuring the resulting current in the testing stator and comparing this current with a predetermined rated current value.

The main advantage of this process is that the time for installing a rotor disc in a test motor, for accelerating and decelerating and for running off a separate test programme is saved in the case of each rotor disc. The test appliance must no longer, be capable of running up a motor from stand-still: it suffices if a reading is taken of the current flow in all phases of the stator winding and this reading is compared with the specified value, which has a certain permissible tolerance scatter.

In a series of running tests it was demonstrated that the invented process of measuring current at a standstill makes it possible to establish the reproducibility of the correlation of characteristic motor data to the standstill current within the measuring accuracy and thus to check the electric and magnetic properties of rotor discs for hysteresis motors.

As long as the shape, material and crystalline structure of the rotor discs which are compared are equal within prescribed and usual tolerances.

a one-time determination of a rated value is all that is required to give sufficiently accurate particulars of real power absorbed, shaft power, pull-out torque, power factor and efficiency.

Beyond this, it is possible to use automated test equipment to print out all the above-mentioned data automatically in the form of a test report, whereby no special requirements have to be met in setting up the test equipment, whereas a running test calls for completely vibration-free, armoured test stands in view of the high speeds involved (several 104 r.p.m.).

In a preferred embodiment, the same stator is used for each rotor disc. The use of the same stator for measurements eliminates a relatively large tolerance band which would be multiplied in the measurement of shaft power as set down in the invention. In addition, it is possible to develop a test appliance which can be used at the manufacturing place of the rotor discs and thus prevents the delivery of defective items. This fact is of particular significance where, as for example in the manufacture of gas centrifuges, extremely large quantities are involved.

According to another preferred embodiment, the predetermined voltage Is applied to the stator with an amplitude and frequency equal to those which are applied to it when the hysteresis motor is running at its rated speed.

This approximates the testing conditions to the rated operation, thereby eliminating further tolerances which could arise in correlating measured values to rated values.

Preferably the predetermined rated current value is equal to that which is measured on a stationary master rotor disc the characteristics of which have already been tested in use. This makes it possible to carry out random checks to monitor the rated value or to obtain quickly applicable rated values without changing the known running test and without theoretical relationships having to be considered for this purpose.

To keep appliances for performing the process as simple and inexpensive as possible a spacer is placed between the stator and the rotor disc, the spacer having a shape and magnetic and electric characteristics equal to those of the space between the stator and rotor disc in a running hysteresis motor.

In case of gas centrifuges, the space between the stator and rotor is a high vacuum. The thickness of the spacer must be identical to the distance of the air gap. The spacer can be exchanged if it is won or damaged, whereas the measuring stator is retained. In this case, a previously measured rotor disc can be used to calibrate the new spacer.

Preferably the testing stator has properties equal to those of a stator of a running hysteresis motor and the rotor disc of which has properties equal to those of said master rotor disc. This guarantees optimum obtainable reproducibility of the measuring result: beyond this, it is possible to select from the quantity of mass produced stators several which are absolutely identical. which serve lo produce several absolutely identical test appliances.The costly production of special testing slators equal to each other can therefore be avoided.

The invention will now be described with reference to an embodiment shown by way of example in the accompanying drawing.

In Figure 1, motor torque at rated speed is plotted against standstill current; above and below the curve the limit of the correlation tolerances is shown. It is evident that a singlevalue torque M is associated with each value of the standstill current Ist. The correlation between torque M and current l,t is obtained as follows: The inenia moment of the rotor disc is exactly determined by an oscillating motion; by measuring speed and time the acceleration during the run-up can be determined and then be used to determine the torque at the rated-speed. After that the standstill current passing through the rotor disc used for this purpose is measured according to the procedure described above.

A stator voltage of 280V and a frequency of 1()40 Hz is used for the measurement. Starconnected power factor compensation capacitors each of 0,6 pF are provided.

In Figure 2 an applicance is shown for performing the testing. A stator 2 is mounted in the end disc I of a casing of a gas centrifuge.

This end disc 1 serves as a measuring stator.

A spacer 3 is mounted on top of it. A test rotor disc 4 is mounted concentrically and plane parallel on top of the spacer 3. Usually the rotor disc is kept stationary by friction force between its bottom surface and the spacer surface. For exceptional light weight rotor discs clamping means can be provided. The current flowing from a generator 5 to the stator 2 is read off at a measuring point 6.

WHAT WE CLAIM IS: I. A process for testing the magnetic and electric characteristics of equally-shaped rotor discs for hysteresis motors for gas centrifuges comprising fixing the rotor adjacent a testing stator, applying a predetermined voltage to the testing stator, measuring the resulting current in the testing stator and comparing this current with a predetermined rated current value.

2. A process according to claim 1. wherein the same stator is used for each rotor disc.

3. A process according to claim I or claim 2.

wherein the predetermined voltage is applied to the stator with an amplitude and frequency equal to those which are applied to it when the hysteresis motor is running at its rated speed.

4. A process according to any one of Claims 1-3, wherein the predetermined rated current value is equal to that which is measured on a stationary master rotor disc the characteristics of which have already been tested in use.

5. A process according to any one of Claims 1-4, wherein a spacer is placed between the stator and the rotor disc, the spacer having a shape and magnetic and electric characteristics equal to those of the space between the stator and rotor disc in a running hysteresis motor.

6. A process according to any one of Claims 1-5, wherein the testing stator has properties equal to those of a stator of a running hysteresis motor the rotor disc of which has properties

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

in setting up the test equipment, whereas a running test calls for completely vibration-free, armoured test stands in view of the high speeds involved (several 104 r.p.m.).

In a preferred embodiment, the same stator is used for each rotor disc. The use of the same stator for measurements eliminates a relatively large tolerance band which would be multiplied in the measurement of shaft power as set down in the invention. In addition, it is possible to develop a test appliance which can be used at the manufacturing place of the rotor discs and thus prevents the delivery of defective items. This fact is of particular significance where, as for example in the manufacture of gas centrifuges, extremely large quantities are involved.

According to another preferred embodiment, the predetermined voltage Is applied to the stator with an amplitude and frequency equal to those which are applied to it when the hysteresis motor is running at its rated speed.

This approximates the testing conditions to the rated operation, thereby eliminating further tolerances which could arise in correlating measured values to rated values.

Preferably the predetermined rated current value is equal to that which is measured on a stationary master rotor disc the characteristics of which have already been tested in use. This makes it possible to carry out random checks to monitor the rated value or to obtain quickly applicable rated values without changing the known running test and without theoretical relationships having to be considered for this purpose.

To keep appliances for performing the process as simple and inexpensive as possible a spacer is placed between the stator and the rotor disc, the spacer having a shape and magnetic and electric characteristics equal to those of the space between the stator and rotor disc in a running hysteresis motor.

In case of gas centrifuges, the space between the stator and rotor is a high vacuum. The thickness of the spacer must be identical to the distance of the air gap. The spacer can be exchanged if it is won or damaged, whereas the measuring stator is retained. In this case, a previously measured rotor disc can be used to calibrate the new spacer.

Preferably the testing stator has properties equal to those of a stator of a running hysteresis motor and the rotor disc of which has properties equal to those of said master rotor disc. This guarantees optimum obtainable reproducibility of the measuring result: beyond this, it is possible to select from the quantity of mass produced stators several which are absolutely identical. which serve lo produce several absolutely identical test appliances.The costly production of special testing slators equal to each other can therefore be avoided.

The invention will now be described with reference to an embodiment shown by way of example in the accompanying drawing.

In Figure 1, motor torque at rated speed is plotted against standstill current; above and below the curve the limit of the correlation tolerances is shown. It is evident that a singlevalue torque M is associated with each value of the standstill current Ist. The correlation between torque M and current l,t is obtained as follows: The inenia moment of the rotor disc is exactly determined by an oscillating motion; by measuring speed and time the acceleration during the run-up can be determined and then be used to determine the torque at the rated-speed. After that the standstill current passing through the rotor disc used for this purpose is measured according to the procedure described above.

A stator voltage of 280V and a frequency of 1()40 Hz is used for the measurement. Starconnected power factor compensation capacitors each of 0,6 pF are provided.

In Figure 2 an applicance is shown for performing the testing. A stator 2 is mounted in the end disc I of a casing of a gas centrifuge.

This end disc 1 serves as a measuring stator.

A spacer 3 is mounted on top of it. A test rotor disc 4 is mounted concentrically and plane parallel on top of the spacer 3. Usually the rotor disc is kept stationary by friction force between its bottom surface and the spacer surface. For exceptional light weight rotor discs clamping means can be provided. The current flowing from a generator 5 to the stator 2 is read off at a measuring point 6.

WHAT WE CLAIM IS: I. A process for testing the magnetic and electric characteristics of equally-shaped rotor discs for hysteresis motors for gas centrifuges comprising fixing the rotor adjacent a testing stator, applying a predetermined voltage to the testing stator, measuring the resulting current in the testing stator and comparing this current with a predetermined rated current value.
2. A process according to claim 1. wherein the same stator is used for each rotor disc.
3. A process according to claim I or claim 2.

wherein the predetermined voltage is applied to the stator with an amplitude and frequency equal to those which are applied to it when the hysteresis motor is running at its rated speed.
4. A process according to any one of Claims 1-3, wherein the predetermined rated current value is equal to that which is measured on a stationary master rotor disc the characteristics of which have already been tested in use.
5. A process according to any one of Claims 1-4, wherein a spacer is placed between the stator and the rotor disc, the spacer having a shape and magnetic and electric characteristics equal to those of the space between the stator and rotor disc in a running hysteresis motor.
6. A process according to any one of Claims 1-5, wherein the testing stator has properties equal to those of a stator of a running hysteresis motor the rotor disc of which has properties

equal to those of said motor rotor disc.
7. A process for testing the magnetic and electric characteristics of equally-shaped rotor discs for hysteresis motors for gas centrifuges substantially as herein described with reference to the accompanying drawing.