WO2012159163A1

WO2012159163A1 - A machine for testing magnetic cores

Info

Publication number: WO2012159163A1
Application number: PCT/AU2012/000578
Authority: WO
Inventors: Peter TEDORE; Charles Walker
Original assignee: Aem Cores Pty Ltd
Priority date: 2011-05-23
Filing date: 2012-05-23
Publication date: 2012-11-29

Abstract

A machine (10) for testing magnetic cores (5) is disclosed. The machine includes a housing (20) and at least two core encircling assemblies (200) mounted to the housing (20). Each core encircling assembly (200) is adapted to support an excitation coil (270) and an induced voltage coil (275). Each core encircling assembly (200) includes a first or upper segment (280) and a second or lower segment (290). The first and second segments (280, 290) are movable relative to each other between an open condition for loading a core (5) and a closed condition for testing the core (5). The second segment (290) may be moved towards the first segment (280) by means of a telescopically movable bridge (220). Each core encircling assembly (200) further includes a multi-contact connector having a first contact set 252 mounted to the first segment 280 and a second contact set mounted to the second segment.

Description

A MACHINE FOR TESTING MAGNETIC CORES

PRIORITY DOCUMENTS

The present application claims priority from Australian Provisional Patent Application No

201 1901991 entitled "A machine for testing magnetic cores" and filed on 23 May 201 1 , the entire content of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to the testing of properties of magnetic cores such as those used in transformers. In particular, the invention relates to a machine for testing magnetic properties such as hysteresis characteristics and power loss of magnetic cores.

BACKGROUND OF THE INVENTION

Magnetic cores are designed to meet certain performance standards in terms of magnetisation properties and power loss (efficiency). The performance of a core is often measured in terms of the magnetising force (H) required to produce a particular magnetic flux density (B). For a given core size and material, a B-H curve may be plotted by experimental testing and compared with a standard curve to determine whether the properties of the core are acceptable. Testing the properties of magnetic cores is important for purposes of quality assurance and control. A test may enable a core

manufacturer to detect process faults, material fluctuations and even operator mishandling, and to rectify such problems before a batch of cores is dispatched to a customer.

Testing a magnetic core involves energising a core by applying a varying current through a primary winding around the core. A varying magnetic field is created in the core which induces a voltage into a secondary winding around the core. The excitation current and induced voltage are measured and the B and H values computed. A manual testing apparatus may be used to perform the test whereby a variac is connected to a power meter with either a single phase, or three phase test lead around the core. This process is cumbersome and inefficient when testing a large volume of cores as the equipment must be manually connected and disconnected for each test.

An automated core testing machine may also be used whereby a core is placed on a test bench and a core encircling assembly, or "clamp", carrying primary and secondary coils is extendable through the centre of the core to close an inductive circuit. Although this type of core testing machine is an improvement over the manual testing apparatus, there are still significant drawbacks. The core encircling assembly, when closed, forms a primary and secondary winding around the test core. The physical size of the assembly will result in a given mean turn length of the windings around the core. It is desirable to have the windings as close to the core as possible to achieve the most accurate test results. For a testing machine capable of testing cores of variable size, it becomes problematic to be testing both small and large cores with the same core encircling assembly. The core encircling assembly must be sized appropriately for testing larger size cores, which will result in test inaccuracies when testing smaller cores using the same assembly.

An object of the present invention is to ameliorate one or more of the above described difficulties or at least provide a useful alternative to arrangements of the type discussed above.

Other advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, several embodiments of the present invention are disclosed.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a machine for testing magnetic cores, the machine including:

a housing; and

at least two core encircling assemblies mounted to the housing, each core encircling assembly adapted to support an excitation coil and an induced voltage coil, each core encircling assembly including:

a first segment;

a second segment, the second and first segments movable relative to each other between an open condition for loading a core for testing and a closed condition for testing a core; and a multi-contact connector having a first contact set mounted to the first segment and a second contact set mounted to the second segment, the first and second contact sets providing an electrical connection for the excitation and induced voltage coils in the closed condition.

In one form the second segment includes a telescopically movable bridge having a first (upper) end and a second (lower) end. In one form, the first contact set is mounted to a first end of the first segment and the second contact set is mounted to the first (upper) end of the bridge.

In one form, the bridge is movable to the first end of the first segment to engage the first and second contact sets. The bridge may be actuated by a pneumatic actuator although it is not limited to this. Any suitable form of actuation may be used. In one form, the second segment includes a flexible guide portion connected to the first end of the bridge and adapted to guide wires forming the excitation coil and induced voltage coil. The flexible guide portion may be in the form of a chain. In a preferred form, the first segment of each core encircling assembly is an upper portion and the second segment of the core encircling assembly is a lower portion.

The core encircling assemblies may be interchangeably mountable to the housing which enables the machine to be easily reconfigured to suit the particular core size to be tested.

In one form, the core encircling assembly includes a rigid joiner connecting the first segment to the second segment.

In one form, the rigid joiner is in the form of an interface plate, the interface plate mountable to the housing.

In one form, at least one of the core encircling assemblies may be mounted to the rear of the housing. This configuration may be suited to an application where cores are transported on a conveyer system (for example in a production line).

The machine may be configured to test toroidal cores although this should be understood to be an exemplary example only. The machine is configurable to test cores of varying cross-sectional area and diameter. In a preferred form, for a test core, the machine measures the required magnetizing force (H) for a predetermined magnetic flux density (B).

According to a second aspect of the invention there is provided a machine for testing magnetic cores, the machine including:

a housing containing electrical components including an excitation transformer and an induced voltage measuring device; and

at least two core encircling assemblies mounted to the housing, each core encircling assembly supporting an excitation coil drivable by the excitation transformer and supporting an induced voltage coil connectable to the induced voltage measuring device, each core encircling assembly including:

a first segment;

a second segment, the second and first segments movable relative to each other between an open condition for loading a core for testing and a closed condition for testing a core; and a multi contact connector having a first contact set mounted to the first segment and a second contact set mounted to the second segment, the first and second contact sets providing an electrical connection for the excitation and induced voltage coils in the closed condition.

In a further aspect, the invention may be said to reside in a machine for testing magnetic cores, the machine including:

a first core encircling assembly adapted to support an excitation coil and an induced voltage coil and movable from an open condition for loading a first core to a closed condition for testing the first core;

a second core encircling assembly adapted to support an excitation coil and an induced voltage coil and movable from an open condition for loading a second core to a closed condition for testing the second core, the first core larger than the second core;

wherein, the excitation and induced voltage coils of the first core encircling assembly form respective closed loops around the first core when the first core encircling assembly is moved to its closed condition and the excitation and induced voltage coils of the second core encircling assembly form respective closed loops around the second core when the second core encircling assembly is moved to its closed condition.

In a further aspect of the invention there is provided a core encircling assembly for use in a machine for testing magnetic cores, the assembly including:

a first segment;

a second segment, the first and second segments movable relative to each other between an open condition for loading a core for testing and a closed condition for testing the core;

a multi-contact connector having a first contact set mounted to the first segment and a second contact set mounted to the second segment, the first and second contact sets providing an electrical connection for the excitation and induced voltage coils in the closed condition; and

an interface plate connecting the first segment to the second segment and removably mountabje to a housing of the machine.

A specific embodiment of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. This embodiment is illustrative, and is not meant to be restrictive of the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present invention will be described in detail with reference to an embodiment of the invention shown in the following drawings in which:

FIGURE 1 is a perspective view of a machine for testing magnetic cores; FIGURE 2 is a perspective view of the machine with a rear mounted core encircling assembly;

FIGURE 3 is an exploded view of the machine as shown in Figure 1 ;

FIGURE 4a is a perspective view of a core encircling assembly in an open condition;

FIGURE 4b is a perspective view of a core encircling assembly in a closed condition;

FIGURE 4c is a schematic illustration of the excitation coil and induced voltage coil routed inside the core encircling assembly;

FIGURE 5 is an exploded view of the core encircling assembly as shown in Figure 4a;

FIGURE 6 is a perspective view of the second (lower) segment of the core encircling assembly;

FIGURE 7 is an exploded view of the second (lower) segment of the core encircling assembly as shown in Figure 6;

FIGURE 8 is a sectional view of the second (lower) segment of the core encircling assembly; and FIGURE 9 is a simplified schematic diagram of the core testing process.

In the following description, like reference characters designate like or corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

Referring to Figure 1, there is shown a perspective view of a machine 10 for testing magnetic cores. The machine 10 includes a housing 20. The housing 20 houses electrical and electronic equipment for testing magnetic cores including for instance, a CPU 70, audio amplifier 50 and impedance matching transformer 60 (as shown in Figures 3 and 9). The machine is capable of testing magnetic cores of varying shapes including toroidal cores, C-cores and other stackable laminated core geometries. These types of cores are typically used in transformers. The machine is also capable of testing a variety of materials types including nickel iron and silicon steel.

Also shown in Figure 1 is a computer touch screen 30 and a label printer 40 mounted to the housing 20.

The machine 10 illustrated in Figure 1 further includes two core encircling assemblies 200 and 300 that are mounted to the housing 20. Each core encircling assembly is adapted to support an excitation coil and an induced voltage coil. This is more readily explained with reference to Figures 4a, 4b and 4c which show one of the two core encircling assemblies 200. In Figures 4b and 4c there is also shown an outline of a core 5 to be tested. In this illustration the core 5 is a toroidal core and the core encircling assembly 200 loops around or encircles the core 5 when in a closed condition for testing.

The core encircling assembly 200 shown in Figure 4a could also be described as a test clamp or a connector assembly. It has the appearance of a clamp in that it has an open condition shown in Figure 4a and a closed, or "clamped", condition shown in Figures 4b and 4c. In the closed condition shown in Figures 4b and 4c current can flow through an excitation (or primary) coil 270 housed within the core encircling assembly 200 to magnetise the test core 5. The magnetic field of the test core 5 then induces a voltage in an induced voltage (or secondary) coil 275 which is also supported by the core encircling assembly 200 as is illustrated schematically in Figure 4c.

The core encircling assembly 200 includes a first or upper segment 280 and a second or lower segment 290. The first segment 280 is clearly visible in Figure 1 as it projects from a top plate 24 of the housing 20. The second segment 290 is not visible in Figure 1 as it is disposed within the housing 20 and below the top plate 24.

The first and second segments 280 and 290 are movable relative to each other between an open condition for loading a core 5 for testing, as shown in Figure 4a and a closed condition for testing a core 5 as shown in Figure 4b. With the preferred embodiment of the invention, this relative movement is achieved by having a telescopically movable bridge 220 as part of the second segment 290. This bridge is best shown in Figures 4b and in the exploded view of Figure 7.

A multi-contact connector, having a connector socket 250 and a connector plug 260 is shown in Figure 4a. The connector socket 250 has a first contact set 252 comprising female terminal pins mounted to the first segment 280. The connector plug 260 has a second contact set 262 comprising male terminal pins mounted to the second segment 290. The female and male terminal pins 252 and 262 are shown most clearly in Figures 5 and 7 respectively. The connector socket 250 includes a holder 256 with receptacles for receiving a terminal pin bush 254 which is screwed into the holder 256. The female terminal pins 252 are fixedly secured into the bush 254. The holder 256 engages with an adaptor 258 which is fastened to the end of arm 238 of the first segment 280 of the core encircling assembly 200. The structure of the connector plug 260 is similar to the connector socket 250, however the adaptor 268 of the plug 260 is fastened to the bridge 220.

Now referring to Figure 4c, an excitation coil 270 and an induced voltage coil 275 housed within the core encircling assembly 200 is shown schematically. The excitation coil 270 may have four turns and the induce voltage coil or secondary coil 275 may have six turns. While the number of turns for each of the coils 270 and 275 may vary depending on the exact design requirements, a single turn for each coil is shown in the schematic drawing of Figure 4c for clarity. A flexible guide or conduit portion in the form of a chain 224 is provided within the second or lower segment 290 to guide and protect convolutions of the coils 270 and 275 as is most clearly shown in Figure 8. The core encircling assembly 200 will now be described in further detail. The first or upper segment 280 includes a support post mounting plate 234. a support post 236 and an arm 238 as is clearly shown in Figures 4b and 5. Each of the aforementioned plate, post and arm components define a conduit for receiving and supporting the excitation and induced voltage coils 270 and 275 respectively. The arm 238 terminates in the connector socket 250.

The second or lower segment 290 of the core encircling assembly 200 includes a telescopically movable bridge 220 that is shown most clearly in Figure 7. The bridge 220 has a first (upper) end 221 and a second (lower) end 222 as shown in Figure 7. A connector plug 260 engages with the first end 221. The second end 222 of the bridge 220 is mounted to an adaptor 21 8 and a coupling plate 216 that is secured to a threaded portion 212 of a piston 210 that forms part of an actuation element 202 in the form of an pneumatic actuator. While a pneumatic actuator is illustrated in the Figures, in other embodiments of the invention, alternative actuation elements 202 may be used. A retainer nut 208 and a locking nut 214 are provided to lock the body of the pneumatic actuator 202 to a cylinder mounting plate 204 and to lock the end of the piston 210 to the second end 222 of the bridge 220 respectively.

The flexible chain 224 is shown in a sectional view partially within the bridge 220 in Figure 8. The chain 224 has a first end 225 that connects to the first end 221 of the bridge 220 and a second end 225' that connects to a retainer 226.

Fixing plates 242 and 244, most clearly illustrated in Figure 5 and cover plate 246 partially enclose the bridge 220 and connect the cylinder mounting plate 204 to an interface plate 230. This provides complete modular assembly as shown in Figure 4a that can be readily separated or attached to the housing 20. The interface plate 230, or any other suitable rigid joiner, is used to connect the first segment 280 to the second segment 290.

Referring now to Figure 3, it can be seen that core encircling assembly 200 and a similar core encircling assembly 300 can simply be dropped into respective slots 23 formed within adaptor plates 22. The interface plate 230 of the core encircling assembly is removably mountable to an adaptor plate 22. Once the core encircling assemblies 200 and 300 are in place, a top plate 24 can be installed to provide the assembly illustrated in Figure 1.

As can be seen from Figure 1 , the core encircling assemblies 200 and 300 differ in size. The core encircling assembly 200 is larger and is intended to be used to test large toroidal cores, for instance having mass up to 75kg and core diameter up to 700mm. The machine 10 is highly adaptable. A single housing 20 containing a single set of electrical components which may include for instance a single excitation (or impedance matching) transformer 60 can interface with two, three or more core encircling assemblies. Each core encircling assembly is modular allowing the machine to be easily reconfigured to meet particular customer requirements. The number and size of core encircling assemblies used will be determined by the range of core sizes and material to be tested. Figure 2 shows a housing 20 having a core encircling assembly 400 mounted on its rear. This arrangement may be suitable for integration into a production line where cores are transported on a conveyor system and may obviate, or at least reduce, manual handling requirements of the cores to be tested. The core encircling assembly 400 is mounted to the housing 20 by wedge shaped support bracket 28 and adaptor plate 26 as shown most clearly in Figure 2.

Referring to Figure 9 there is shown a simplified schematic of the test process used by the machine 10. A computer 70 generates a sinusoidal waveform which is used to excite the excitation coil 270 in the core encircling assembly 200. The computer 70 outputs the waveform to a USB analogue/digital converter 80 which generates an analogue signal at the desired test frequency. The output of the converter is input to an audio amplifier 50 with a fixed gain. The output of the audio amplifier 50 is then fed to a primary coil of the excitation (or impedance matching) transformer 60. The output of the impedance matching transformer 60 is then fed to the excitation coil 270 (primary) in the core encircling assembly 200. The current flowing through the excitation coil 270 is measured by way of a voltage drop across a shunt 90 which is amplified by a selectable gain shunt amplifier 100 and fed back to the analogue/digital converter 80 which samples the waveform. The voltage induced in the secondary coil 275 in the core encircling assembly 200 is attenuated or amplified by a selectable gain voltage amplifier 55 and fed back to the analogue/digital converter 80 and sampled. In this way, the analogue/digital converter 80 acts as an induced voltage measuring device. The computer 70 then analyses the resulting current and voltage waveforms and calculates the flux density (B) and magnetising force (H). These two values will form one point of the B-H curve for the core. The above steps are repeated until all specified test points have been tested and graphed. The resulting B-H curve is then compared against a user specified reference curve, displayed on the monitor 30, and a pass/fail decision made. If the core passes, a label is printed by the label printer 40 shown in Figure 1 , and is applied to the core.

It will be understood that the term "comprise" and any of its derivatives (e.g. comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied. The reference to any prior art in this specification is not, and should not be taken as, an

acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge of the technical field. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

THE CLAIMS:

1. A machine for testing magnetic cores, the machine including:

a housing; and

a first segment;

a second segment, the first and second segments movable relative to each other between an open condition for loading a core for testing and a closed condition for testing the core; and

a multi-contact connector having a first contact set mounted to the first segment and a second contact set mounted to the second segment, the first and second contact sets providing an electrical connection for the excitation and induced voltage coils in the closed condition.

2. The machine as claimed in claim 1 wherein the second segment includes a telescopically movable bridge having a first end and a second end.

3. The machine as claimed in claim 2 wherein the first contact set is mounted to a first end of the first segment and the second contact set is mounted to the first end of the bridge.

4. The machine as claimed in claim 3 wherein the bridge is movable to the first end of the first segment to engage the first and second contact sets.

5. The machine as claimed in claim 3 wherein the second segment includes a flexible guide portion connected to the first end of the bridge and adapted to guide wires forming the excitation coil and induced voltage coil.

6. The machine as claimed in claim 4 wherein the flexible guide portion of the second segment is a chain.

7. The machine as claimed in any of the preceding claims wherein the first segment of the core encircling assembly is an upper portion and the second segment of the core encircling assembly is a lower portion.

8. The machine of any of the preceding claims wherein the at least two core encircling assemblies are interchangeably mountable to the housing.

9. The machine as claimed in claim 8 wherein the core encircling assembly includes a rigid joiner connecting the first segment to the second segment.

10. The machine as claimed in claim 9 wherein the rigid joiner is in the form of an interface plate, the interface plate mountable to the housing.

1 1. The machine as claimed in claim 4 wherein the bridge is actuated by a pneumatic actuator.

12. The machine as claimed in any of the preceding claims wherein at least one of the core

encircling assemblies is mounted to the rear of the housing.

13. The machine as claimed in any of the preceding claims for testing toroidal cores.

14. The machine as claimed in any of the preceding claims configured to test cores of varying cross-sectional area and diameter.

15. The machine as claimed in any of the preceding claims for measuring the required

magnetizing force (H) for a pre-determined magnetic flux density (B).

16. A machine for testing magnetic cores, the machine including:

a housing containing electrical equipment including an excitation transformer and an induced voltage measuring device; and

a first segment;

a second segment, the second and first segments movable relative to each other between an open condition for loading a core for testing and a closed condition for testing a core; and

17. A machine for testing magnetic cores, the machine including:

18. A core encircling assembly for use in a machine for testing magnetic cores, the assembly including:

a first segment;

an interface plate connecting the first segment to the second segment and removably mountable to a housing of the machine.

19. A machine for testing magnetic cores substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

20. A core encircling assembly as hereinbefore described with reference to and as illustrated in the accompanying drawings.