GB2553908A

GB2553908A - Ferrite core, current mutual inductor and current leakage protection switch

Info

Publication number: GB2553908A
Application number: GB1711964.5A
Authority: GB
Inventors: Ma Feng; Allab Farid
Original assignee: Schneider Electric Industries SAS
Current assignee: Schneider Electric Industries SAS
Priority date: 2016-07-25
Filing date: 2017-07-25
Publication date: 2018-03-21
Also published as: NZ734059A; CN107658092B; GB201711964D0; CN107658092A; AU2017208249B2; RU2017126617A; AU2017208249A1; RU2738254C2; RU2017126617A3

Abstract

A ferrite core 200 comprises a first portion 210 formed by a first ferrite material 201 with a temperature dependent permeability and a second portion 220 formed by a second ferrite material 202, different from the first, with a temperature dependent permeability and where the overall permeability of the core 200 is dependent on the permeability of the first and second materials 201, 202 and the proportions of the first and second materials used in the core 200. The first ferrite material 201 may have a higher permeability than the second ferrite material 202 over a given temperature range and/or a lower Curie temperature. The upper temperature limit of a predetermined temperature range may be between the Curie temperatures for the said materials 201, 202. The materials may be different grades of manganese zinc (Mn-Zn) ferrite. The core 200 may have an annular shape and the first and second core portions 210, 220 may also be annular, where the proportions of first and second material may be set by the height of the respective annular portions 210, 220. Further ferrite core portions may also be included. The core 200 may be used in a zero-sequence current mutual inductor of a current leakage current protection system.

Description

(56) Documents Cited:

GB 1369817 A GB 0708121 A US 3065181 A1 JPS63208210

GB 0734243 A DE 002512811 A1 US 2985939 A1 (71) Applicant(s):

Schneider Electric Industries S.A.S (Incorporated in France) rue Joseph Monier, 92500 Rueil-Malmaison,

France (including Overseas Departments and Territori es) (72) Inventor(s):

Feng Ma Farid Allab (74) Agent and/or Address for Service:

Murgitroyd & Company

Scotland House, 165-169 Scotland Street, GLASGOW, G5 8PL, United Kingdom (58) Field of Search:

INT CL H01F Other: EPODOC, WPI (54) Title ofthe Invention: Ferrite core, current mutual inductor and current leakage protection switch Abstract Title: Ferrite core including materials with different temperature dependent permeabilities (57) A ferrite core 200 comprises a first portion 210 formed by a first ferrite material 201 with a temperature dependent permeability and a second portion 220 formed by a second ferrite material 202, different from the first, with a temperature dependent permeability and where the overall permeability of the core 200 is dependent on the permeability of the first and second materials 201, 202 and the proportions of the first and second materials used in the core 200. The first ferrite material 201 may have a higher permeability than the second ferrite material 202 over a given temperature range and/or a lower Curie temperature. The upper temperature limit of a predetermined temperature range may be between the Curie temperatures for the said materials 201,202. The materials may be different grades of manganese zinc (Mn-Zn) ferrite. The core 200 may have an annular shape and the first and second core portions 210, 220 may also be annular, where the proportions of first and second material may be set by the height of the respective annular portions 210, 220. Further ferrite core portions may also be included. The core 200 may be used in a zero-sequence current mutual inductor of a current leakage current protection system.

200-^

FIG. 2

1/5

100

Permeability

110

120

Wt /i ***:♦

130 **

101

I

102 ζ 103

25°C

FIG. 2

2/5

300

Temperature (Ό)

FIG 3

400'^s^

30 00 00 120 150

Temperature (X;)

FIG. 4

3/5

500

. 6

4/5

5/5

FERRITE CORE, CURRENT MUTUAL INDUCTOR AND CURRENT LEAKAGE PROTECTION SWITCH

Technology [0001] Embodiments of the present disclosure generally relate to a magnetic core formed by a magnetic material and a current leakage protection device, and more specifically, to a ferrite core, a current mutual inductor and a current leakage protection switch.

Background [0002] Current leakage protection switch is mainly used to provide protection upon a current leakage failure of a device or in the presence of danger of electric shock for human beings. Having an overload and short circuit protection function, it can be utilized to protect circuits or provide protection for overload and short circuit of electric motors. The current leakage protection switch generally includes a zero-sequence current mutual inductor. For example, a current mutual inductor in the current leakage protection switch usually employs a zero-sequence current mutual inductor to detect unbalanced current in the main circuit, and the current leakage protection switch immediately cuts off the power supply of the main circuit once the designed release threshold is reached in order to switch off the circuit with failure.

[0003] At present, a material for a magnetic core of a zero-sequence current mutual inductor is usually selected from a ferronickel alloy or a nano-alloy material. However, processing techniques of the two materials are complicated, and attributes of their raw materials, the later processing and transportation of the magnetic core demand strict control. During the manufacturing the end product of the current mutual inductor, both the ferronickel and nano-alloy magnetic core materials need to be protected with a casing to ensure that the performance of the magnetic core will not be damaged during transportation. Moreover, as the ferronickel and nano-alloy magnetic core materials are vulnerable to magnetization, the iron loss will be significant.

[0004] Therefore, there is a need for providing an improved magnetic core to at least partially solve various defects existing in current magnetic cores formed by traditional magnetic core materials and thereby improving the performance of existing current mutual inductors and current leakage protection switches.

Summary [0005] The embodiments of the present disclosure provide a ferrite core, a current mutual inductor and a current leakage protection switch.

[0006] According to a first aspect of the embodiments of the present disclosure, there is provided a ferrite core. The ferrite core including a first portion formed by a first ferrite material which has first permeability that changes with a temperature, and a second portion formed by a second ferrite material different from the first ferrite material, the second ferrite material having second permeability that changes with the temperature. The ferrite core has overall permeability that changes with the temperature. The overall permeability is determined based on the first permeability, the second permeability, a first proportion of the first portion in the ferrite core and a second proportion of the second portion in the ferrite core. The first proportion and the second proportion are determined so that the overall permeability is higher than a threshold within a predetermined temperature range.

[0007] In some embodiments, the permeability of the first ferrite material may be higher than that of the second ferrite material within an operation temperature range. In some embodiments, a Curie temperature of the first ferrite material may be lower than that of the second ferrite material. In these embodiments, the upper temperature limit of the predetermined temperature range may be set between the Curie temperature of the first ferrite material and the Curie temperature of the second ferrite material. In some embodiments, the first ferrite material and the second ferrite material may include Mn-Zn ferrite materials of different grades, respectively.

[0008] In some embodiments, the ferrite core may include an annulus ferrite core and the first portion and the second portion may each form two annulus segments of the annulus ferrite core. In these embodiments, the first and second proportions can include respective proportions of heights of two annulus segments to that of the annulus ferrite core.

[0009] In some embodiments, the ferrite core may further include a further portion in addition to the first and second portions. The further portion is formed by a further ferrite material other than the first and second ferrite materials. The overall permeability is determined based on the permeability of the respective ferrite materials and the respective proportions of the portions in the ferrite core. The respective proportions are determined so that the overall permeability is higher than the threshold in the predetermined temperature range.

[0010] According to a second aspect of the embodiments of the present disclosure, there is provided a current mutual inductor. The current mutual inductor includes the ferrite core according to the first aspect. In some embodiments, the current mutual inductor may include a zero-sequence current mutual inductor.

[0011] According to a third aspect of the embodiments of the present disclosure, there is provided a current leakage protection switch. The current leakage protection switch includes the current mutual inductor according to the second aspect.

Brief Description of the Drawings [0012] Through the following detailed description with reference to the accompanying drawings, the above and other objectives, features, and advantages of example embodiments of the present disclosure will become more apparent. Several example embodiments of the present disclosure will be illustrated by way of example but not limitation in the drawings in which:

[0013] Fig. 1 schematically illustrates a curve graph of the relation between the permeability of multiple ferrite materials and the temperature;

[0014] Fig. 2 schematically illustrates a ferrite core according to the embodiments of the present disclosure;

[0015] Fig. 3 schematically illustrates a curve graph of the relation between the permeability of a first ferrite material in the ferrite core according to the embodiments of the present disclosure and the temperature;

[0016] Fig. 4 schematically illustrates a curve graph of the relation between the permeability of a second ferrite material in the ferrite core according to the embodiments of the present disclosure and the temperature;

[0017] Fig. 5 schematically illustrates a curve graph of the relation between overall permeability of the ferrite core according to the embodiments of the present disclosure and the temperature;

[0018] Fig. 6 schematically illustrates a simplified circuit diagram of the ferrite core according to the embodiments of the present disclosure utilized in a current mutual inductor;

[0019] Fig. 7 schematically illustrates a comparison diagram of actual measurement results of three ferrite materials and a nano-crystalline material utilized in the simplified circuit diagram shown in Fig. 6 and a simulation result of an ideal current mutual inductor utilized in the simplified circuit diagram shown in Fig. 6; and [0020] Fig. 8 schematically illustrates a curve graph of the relation between the simulated release current and the temperature in the case that the ferrite core according to the embodiments of the present disclosure utilizes two ferrite materials with different proportions.

[0021] Throughout the drawings, the same or similar reference symbols are used to indicate the same or similar elements.

Detailed Description [0022] Principles of the present disclosure will now be described with reference to various example embodiments illustrated in the drawings. It should be appreciated that description of those embodiments is merely to enable those skilled in the art to better understand and further implement the present disclosure and is not intended for limiting the scope disclosed herein in any manner.

[0023] As mentioned above, at present, a current mutual inductor in a current leakage protection switch generally adopts a zero-sequence current mutual inductor and the material of the magnetic core of the zero-sequence current mutual inductor is usually selected from the ferronickel alloy or nano-alloy materials. However, processing techniques of the two materials are complicated, and attributes of their raw materials, the later processing and transportation of the magnetic core demand strict control. During the manufacturing the end product of the current mutual inductor, both the ferronickel and nano-alloy magnetic core materials need to be protected with a casing to ensure that the performance of the magnetic core will not be damaged during transportation. Moreover, as the ferronickel and nano-alloy magnetic core materials are vulnerable to magnetization, the iron loss will be significant.

[0024] Compared with the ferronickel material and the nano-alloy material, the ferrite core material is distinguished by its high initial permeability and sophisticated processing technique. As the soft magnetic ferrite can obtain high permeability even without using rare materials, such as nickel, and its powder metallurgical method is suitable for mass production, the costs of ferrite core material are low. In addition, since the ferrite core material can be sinter, it has considerable hardness and insusceptibility to stress, hence being convenient in application.

[0025] The present major application of the ferrite magnetic ring is in fdtering, such as common mode induction. The ferrite materials with different permeability are selected according to different frequencies on which the interference suppression is to be performed. The higher the permeability of the magnetic ring is, the greater the resistance at the lower frequency will be and the smaller the resistance at the higher frequency will be. It is convenient to use for it only needs to surround directly on the cable to be filtered without the need to be grounded, as required by other filtering manners, thus posing no special requirements on the structural design and circuit board design. When used as a common mode choking coil, it does not incur signal distortion, which is quite valuable for wires that transmit high-frequency signals.

[0026] To eliminate various defects existing in the traditional magnetic cores and to improve the performance of the traditional current mutual inductor and current leakage protection switch, the embodiments of the present disclosure propose to form a ferrite core with the ferrite core material. The formed ferrite core is utilized in a zero-sequence current mutual inductor and thus providing a higher cost-performance ratio option for the magnetic core material of the zero-sequence current mutual inductor.

[0027] A comparison of the traditional magnetic core and the ferrite core according to the embodiments of the present disclosure leads to the finding that a casing is required to protect the magnetic core utilizing the ferronickel and nano-alloy magnetic core materials in order to avoid performance degradation of the magnetic core during transportation. In contrast, the ferrite core according to the embodiments of the present disclosure does not need a protective casing and allows winding secondary copper wires directly on the materials. It is only possible for the zero-sequence current mutual inductor made of the ferronickel alloy or the nano-alloy to be manufactured in a round shape, while the ferrite core according to the embodiments of the present disclosure can be manufactured into non-circular mutual inductors according to specific design requirements.

[0028] Meanwhile, the current ferronickel and nano-alloy magnetic core materials are vulnerable to magnetization and have a greater iron loss, while the ferrite core according to embodiments of the present disclosure has more favorable performance in these aspects. The ferrite core according to the embodiments of the present disclosure and its application in the current mutual inductor and current leakage protection switch will be described in detail in the following with reference to the drawings.

[0029] Fig. 1 schematically illustrates a curve graph 100 of the relation between the permeability of multiple ferrite materials and the temperature. In Fig. 1, the horizontal axis represents the temperature in Celsius (°C) and the vertical axis represents the permeability. Although Fig. 1 depicts the relation between the permeability of the ferrite materials and the temperature with a Mn-Zn ferrite material as an example, it is to be understood that the principles of the embodiments of the present disclosure can be applied likewise to other proper types of ferrite materials. The scope of the present disclosure is not limited in this regard.

[0030] As shown in Fig. 1, curves 110, 120 and 130 illustrate the relation between the permeability of Mn-Zn ferrite materials of three different grades and the temperature, respectively. It can be seen from the curve graph 100 that the Mn-Zn ferrite material is a soft magnetic material with a very low iron loss and the initial permeability can range from 4000 to 30000 (not shown in Fig. 1). Furthermore, it can be seen from curves 110, 120 and 130 that the Mn-Zn ferrite materials of different grades have different permeability-temperature curves, and that the magnetism of the Mn-Zn ferrite materials of all the grades begins to stop after the Curie temperature (Tc).

[0031] For example, in Fig. 1, the Curie temperatures 101, 102 and 103 of the Mn-Zn ferrite materials represented by curves 110, 120 and 130 are approximately 100°C, 120°C and 140°C, respectively. Additionally, as can be seen from the curve graph 100, in general, the Mn-Zn ferrite material with higher permeability has a lower Curie temperature, while the Mn-Zn ferrite material with lower permeability has a higher Curie temperature. For example, the permeability of the ferrite material represented by curve 110 is higher than that of the ferrite materials represented by curve 120 and curve 130 in the range of lower temperatures, but its Curie temperature is relatively low.

[0032] As mentioned above, the ferrite core according to the embodiments of the present disclosure needs to meet various specific design requirements. For example, in the case that the ferrite core is applied in a zero-sequence current mutual inductor in a current leakage protection switch, the ferrite core may be required to still have effective permeability under, for example, 140°C and the permeability may need to be sufficiently high at a lower temperature to ensure the operation reliability of the current leakage protection switch.

[0033] Therefore, in order to achieve these requirements, the embodiments of the present disclosure can solve the problems of high design demand for operation environment temperatures and sufficiently high permeability under a lower temperature or the like by stacking two ferrite materials of different grades and then winding wires on them to produce an end-product current mutual inductor.

[0034] Fig. 2 schematically illustrates the ferrite core 200 according to the embodiments of the present disclosure. As shown in Fig. 2, the ferrite core 200 includes a first portion 210 formed by a first ferrite material 201 and a second portion 220 formed by a second ferrite material 202 different from the first ferrite material 201. In some embodiments, the ferrite core 200 may include an annulus ferrite core (as shown in Fig. 2). In these embodiments, the first portion 210 and the second portion 220 can form two annulus segments of the annulus ferrite core.

[0035] However, it is to be understood that the principles of the embodiments of the present disclosure may be applied likewise to ferrite cores of other proper shapes. The scope of the present disclosure is not limited in this regard. According to the embodiments of the present disclosure, the first ferrite material 201 and the second ferrite material 202 have different characteristics that the permeability changes with the temperature. These characteristics of the first ferrite material 201 and the second ferrite material 202 will be described below with reference to Fig. 3 and Fig. 4.

[0036] Fig. 3 schematically illustrates a curve graph 300 of the relation between the permeability 310 of the first ferrite material 201 in the ferrite core 200 according to the embodiments of the present disclosure and the temperature. Fig. 4 schematically illustrates a curve graph 400 of the relation between the permeability 410 of the second ferrite material 202 in the ferrite core 200 according to the embodiments of the present disclosure and the temperature. In Fig. 3 and Fig. 4, the horizontal axis represents the temperature in Celsius (°C) and the vertical axis represents the permeability.

[0037] Although the first and second ferrite materials 201 and 202 are depicted as having particular permeability 310 and 410 changing with the temperature, it is to be understood that the principles of the embodiments of the present disclosure may be applied likewise to ferrite materials with other proper permeability-temperature curves. The scope of the present disclosure is not limited in this regard.

[0038] As shown in Fig. 3 and Fig. 4, the first ferrite material 201 has first permeability 310 that changes with the temperature, while the second ferrite material 202 has second permeability 410 that changes with the temperature. In some embodiments, the permeability 310 of the first ferrite material 201 in the operation temperature range (such as the temperature range of about -40°C-90°C shown in Fig. 3) may be higher than the permeability 410 of the second ferrite material 202. Therefore, the ferrite core 200 can utilize the characteristic of the first ferrite material 201 that it has high permeability within a lower temperature range.

[0039] In some embodiments, the Curie temperature 301 of the first ferrite material 201 (for example, about 100°C) may be lower than the Curie temperature 401 of the second ferrite material 202 (for example, about 150°C). Therefore, in a higher temperature range where the first ferrite material 201 losses its permeability property, such as in a range from 100°C to 150°C, the ferrite core 200 can mainly utilize the second ferrite material 202 to perform the function of the permeability. In some embodiments, the first ferrite material 201 and the second ferrite material 202 may include Mn-Zn ferrite materials of different grades, respectively.

[0040] As mentioned above, forming the ferrite core 200 with the first ferrite material 201 and the second ferrite material 202 with different characteristics that the permeability changes with the temperature may take advantage of the advantageous properties of the two kinds of ferrite materials at a lower temperature range and a higher temperature range, respectively, thereby the performance of the magnetic core may be improved, such as broadening its operation temperature range and increasing its permeability or the like. Such improvement will be described in the following with reference to Fig. 5.

[0041] Fig. 5 schematically illustrates a curve graph 500 of the relation between overall permeability 510 of the ferrite core 200 according to the embodiments of the present disclosure and the temperature. Moreover, as a comparison, Fig. 5 also depicts the permeability 310 of the first ferrite material 201 and the permeability 410 of the second ferrite material 202. The horizontal axis in Fig. 5 represents the temperature in Celsius (°C) and the vertical axis represents the permeability. It is to be understood that as the horizontal axis in Fig. 5 is not drawn to scale for the sake of clarity, the shapes of the curves of the permeability 310 and 410 shown in Fig. 5 are different from that depicted in Fig. 3 and Fig. 4.

[0042] Furthermore, Fig. 5 schematically illustrates a curve of a permeability threshold 520 which can be set by those skilled in the art according to actual application environments and requirements of the ferrite core 200. In some embodiments, the threshold 520 can have different values with change of the temperature (as shown in Fig. 5). In the example technical scenario as depicted in Fig. 5, the overall permeability 510 of the ferrite core 200 needs to be higher than the threshold 520 in the temperature range of about -25°C-140°C. As can be seen from Fig. 5, neither the permeability 310 of the first ferrite material 201 nor the permeability 410 of the second ferrite material 202 can meet this requirement.

[0043] As shown in Fig. 5, the ferrite core 200 formed by the first portion 210 of the first ferrite material 201 and the second portion 220 of the second ferrite material 202 has the overall permeability 510 that changes with the temperature. The overall permeability 510 is determined based on the first permeability 310, the second permeability 410, a first proportion of the first portion 210 in the ferrite core 200, and a second proportion of the second portion 220 in the ferrite core 200, where the first proportion and the second proportion are determined such that the overall permeability 510 is higher than the threshold 520 in a predetermined temperature range (such as -25°C-140°C). In this manner, the ferrite core 200 can meet the specific design requirements, such as the specific design parameters proposed when utilized in a zero-sequence current mutual inductor and/or a current leakage protection switch, for instance, the release threshold. For example, the ferrite core 200 is able to satisfy design requirements on the release threshold.

[0044] In an embodiment in which the ferrite core 200 includes an annulus ferrite core, the first proportion and the second proportion may include the proportions of the heights of the two annulus segments to that of the annulus ferrite core 200, respectively. In an embodiment in which the first ferrite material 201 and the second ferrite material 202 have different Curie temperatures 301 and 401, an upper limit of the predetermined temperature range may be set between the Curie temperature 301 of the first ferrite material 201 and the Curie temperature 401 of the second ferrite material 202. For example, in the embodiment shown in Fig. 5, the upper limit 140°C of the predetermined temperature range is set between 100°C and 150°C.

[0045] Those skilled in the art can appreciate that the principles of the embodiments of the present disclosure are not limited to forming different portions with two different kinds of ferrite materials to further form a ferrite core, and it is possible to similarly employ three, four or more kinds of ferrite materials to form their respective portions to form a ferrite core finally.

[0046] Hence, in some embodiments, the ferrite core 200 may further include other portions (not shown) apart from the first portion 210 and the second portion 220. The other portions are made of other ferrite materials except for the first ferrite material 201 and the second ferrite material 202. In these embodiments, the overall permeability 510 can be determined based on the permeability of the respective ferrite materials and the respective proportions of the portions in the ferrite core 200, where the respective proportions are determined such that the overall permeability 510 is higher than the threshold 520 in a predetermined range of temperature (such as -25°C to 140°C). As such, advantageous properties of more ferrite materials can be utilized to further improve the performance of the ferrite core 200 at the expense of increasing design complexity and costs of the ferrite core 200.

[0047] As mentioned previously, the ferrite core 200 according to the embodiments of the present disclosure can be applied to various technical scenarios. In some embodiments, the ferrite core 200 may be applied to a current mutual inductor, particularly a zero-sequence current mutual inductor. Further, the current mutual inductor or the zero-sequence current mutual inductor may be used in a current leakage protection switch. A specific implementation that the ferrite core 200 according to the embodiments of the present disclosure may be applied to a current mutual inductor will be described below with reference to Fig. 6.

[0048] Fig. 6 schematically illustrates a simplified circuit diagram 600 of the ferrite core 200 according to the embodiments of the present disclosure utilized in a current mutual inductor. It is to be understood that the simplified circuit diagram 600 is only a conceptual schematic circuit diagram, which merely illustrates circuit modules or units that are closely related to the present description and other components or units that may be necessary to implement the circuit are omitted.

[0049] As shown in Fig. 6, the simplified circuit diagram 600 may include an alternating current generator 610, a magnetic core 620 and a resistor 630. Moreover, the simplified circuit diagram 600 further illustrates a voltage 640 induced on the resistor 630.

[0050] To compare the ferrite core 200 according to the embodiments of the present disclosure with the existing magnetic core materials or various individual Mn-Zn ferrite materials, different magnetic cores 200 formed by Mn-Zn ferrite materials of three grades of 10k-1, 12k-1 and 15k-1 and a nano-alloy are measured in the simplified circuit diagram 600 and the results are summarized in the following Table 1. In addition, Table 1 also lists a simulation result with an ideal current mutual inductor for comparison. In this Table 1, Il represents the current in the simplified circuit diagram 600 (not shown), while U2 represents the voltage 640 on the resistor 630 in the simplified circuit diagram 600.

Table 1

Il(mA)	U2(mV) measurement
	15k-l ferrite	10k-l ferrite	12k-l ferrite	nanocrystalline -1	ideal current mutual inductor
1	0.203	0.186	0.180	0.170	0.180
3	0.519	0.527	0.531	0.520	0.539
5	0.899	0.893	0.887	0.870	0.898
7.5	1.330	1.343	1.331	1.319	1.346
10	1.805	1.772	1.776	1.732	1.795
15	2.658	2.673	2.669	2.600	2.693
20	3.541	3.561	3.545	3.460	3.590
23.5	4.194	4.178	4.172	4.058	4.218
26	4.632	4.620	4.624	4.514	4.667
30	5.342	5.339	5.322	5.202	5.385

[0051] Fig. 7 schematically illustrates a comparison diagram 700 of the actual measurement results of three ferrite materials and a nano-crystalline material utilized in the simplified circuit diagram shown in Fig. 6 and a simulation result of an ideal current mutual inductor utilized in the simplified circuit diagram shown in Fig. 6. As shown in

Fig. 7, the curve 710 represents the curve of the ideal current mutual inductor, curve 720 represents the curve of the 15k-l ferrite material, curve 730 represents the curve of the 10k-l ferrite material, curve 740 represents the curve of the 12k-l ferrite material, and curve 750 represents the curve of the nano-crystalline material.

[0052] It can be seen from the above data that the curves 720, 730 and 740 of the three 5 ferrite materials are very close, which indicates that they have very close characteristics.

Besides, curves 720, 730 and 740 are very close to curve 710 of the ideal current mutual inductor, which demonstrates that the three kinds of ferrite materials have a very low iron loss and are apparently better than the nano-crystalline material measured at the same time. Therefore, the curve graph 700 proves that ferrite materials of different grades with particular permeability and the same size can achieve the function of the current mutual inductor of the current leakage protection product.

[0053] Returning to referring to Fig. 6, the embodiments of the present disclosure solve the problem of function loss of the current leakage protection product caused by a high temperature by stacking two ferrite core materials of different grades. This is achieved by adjusting the proportion relation between the first ferrite material 201 and the second ferrite material 202 according to different design requirements (the volume of the current mutual inductor, the temperature of the application environment and the output characteristic requirements).

[0054] Through theoretical deduction, it can be obtained that the equation of the 2 1 inductance of the ferrite core 200 is as follows: N yCtqrij + μ₂8₂), where N represents the number of turns of the secondary winding of the coil of the ferrite core 200, 1 represents the circumference of the magnetic path, μι and μ₂ represent the first permeability 310 and the second permeability 410 of the first ferrite material 201 and the second ferrite material 202, respectively, Si and S₂ represent the cross-sectional area of the first portion 210 and the second portion 220, respectively, which are associated with the volumes of the first portion 210 and the second portion 220, respectively.

[0055] With the inductance of the ferrite core 200 obtained through the above equation, the specific value of current 640 can be derived on the basis of the values of the elements in the circuit diagram 600. Through simulation by changing the proportion relation between the first ferrite material 201 and the second ferrite material 202, the curve graph of the relation between the simulated release current and the temperature in Fig. 8 can be depicted.

[0056] Fig. 8 schematically illustrates a curve graph 800 of the relation between the simulated release current Ι_Δη and the temperature in the case that the ferrite core 200 according to the embodiments of the present disclosure utilizes two ferrite materials with different proportions. The horizontal axis in Fig. 8 represents the temperature in Celsius (°C) and the vertical axis represents the release current Ι_Δηΐη milliamperes (mA). As shown in Fig. 8, the curve 810 represents the case that only the first ferrite material 201 is used, curve 820 represents the case that only the second ferrite material 202 is used, various other curves between the curve 810 and curve 820 represent the curves in the cases of different proportions between the first ferrite material 201 and the second ferrite material 202, and curve 840 represents the design threshold of the release current.

[0057] The design value of the release threshold 840 of a current leakage protection product is generally between 15mA and 30mA. It can be seen from Fig. 8 that the outputs are different under different proportions between the first ferrite material 201 and the second ferrite material 202. If the second ferrite material 202 is 100%, then the release threshold will exceed 30mAin the environment of -25°C, which fails to meet the design requirement. If the first ferrite material 201 is 100%, then the current leakage protection product might loss function when the temperature is as high as 90°C, which is even more unacceptable.

[0058] Therefore, by adjusting the proportion relation between the first ferrite material 201 and the second ferrite material 202, it can be ensured that there is a sufficient output current of the current leakage protection product in the temperature range from -25°C to 140°C to meet the requirement of the release threshold. It can be seen from Fig. 8 that the above particular requirement of the current leakage protection product in this specific example can be met under the condition represented by the curve 830 that the proportions of the first ferrite material 201 and the second ferrite material 202 are 30% and 70%.

[0059] In a word, a magnetic core material of a zero-sequence current mutual inductor utilized in a conventional current leakage protection switch is generally a ferronickel alloy (permalloy) and a nano-alloy material. The embodiments of the present disclosure provide a novel magnetic core material (namely, ferrite) to form a magnetic core which can in turn serve as the zero-sequence current mutual inductor utilized in the current leakage protection switch. Besides, the embodiments of the present disclosure further solve the application problems caused by high permeability and a low Curie temperature of the ferrite material.

[0060] The ferrite core material has high initial permeability and a low iron loss. It has sophisticated processing technique and it is convenient to transport, and thus it is considerably competitive compared with the ferronickel and nano-alloy materials in costs. During the process of manufacturing the end-product of the current mutual inductor, the ferrite core does not need a protective casing and the wires can be wound directly on the magnetic core body. Compared to the ferronickel and nano-alloy material, this can save materials and improve production efficiency during producing the end-product current mutual inductors. The magnetic core material can be applied to current leakage protectors to reduce the cost for the current leakage protection product and the economic benefits are significant.

[0061] Through the embodiments of the present disclosure, the magnetic core material of the zero-sequence current mutual inductor provides an option with higher cost-performance ratio for the current leakage protector utilized for power distribution of the current terminal. The ferronickel and nano-alloy magnetic core materials utilized at present need a casing to protect the magnetic core materials to avoid performance degradation of the magnetic core during the transportation. In comparison, the ferrite core does not need a protective casing and can wind the secondary side copper wire on the material body directly. Furthermore, it is only possible for the zero-sequence current mutual inductor made of the ferronickel and nano-alloy to be manufactured in a round shape, while the ferrite core can be manufactured into non-circular current mutual inductors according to specific requirements. Lastly, the ferrite core is basically free from the influence of magnetization, has a low iron loss, and can ensure stable output for secondary side.

[0062] The embodiments of the present disclosure can stack ferrite materials of two different characteristic grades and enable the ferrite combination to provide stable and reliable output according to the design requirement through a particular design relation, thereby meeting the requirement of current leakage protection. In an application of the current leakage protection switch, a current mutual inductor can be formed by magnetizing the ferrite and performing secondary winding.

[0063] The Curie temperature of the ferrite is a characteristic of the material. When the temperature exceeds the Curie temperature, the electromagnetic output feature of the material will disappear, and when the temperature drops below the Curie temperature, the electromagnetic feature will recover immediately. Under different characteristic grades, the initial permeability is in inverse proportion to the Curie temperature, where the Curie temperature is high if the initial permeability is low and the Curie temperature is low if the initial permeability is high. Therefore, the embodiments of the present disclosure further solve the problem of a high temperature of the application environment that may arise during utilization of the ferrite material to guarantee that the current leakage product can still provide current leakage protection when the environment temperature is too high.

[0064] In description of embodiments of the present disclosure, the term “includes” and its variants are to be read as open-ended terms that mean “includes, but is not limited to.” The term “based on” is to be read as “based at least in part on.” The term “one example embodiment” and “the example embodiment” are to be read as “at least one example embodiment.” [0065] Although the present disclosure has been described with reference to various embodiments, it should be understood that the present disclosure is not limited to the disclosed embodiments. Particularly, the present disclosure is intended to cover various modifications and equivalent arrangements included in the scope of the appended claims.

Claims

Claims:

1. A ferrite core, comprising:

a first portion formed by a first ferrite material, the first ferrite material having first permeability that changes with a temperature; and a second portion formed by a second ferrite material that is different from the first ferrite material, the second ferrite material having second permeability that changes with the temperature, the ferrite core having overall permeability that changes with the temperature, the overall permeability being determined based on the first permeability, the second permeability, a first proportion of the first portion in the ferrite core, and a second proportion of the second portion in the ferrite core, and the first proportion and the second proportion being determined so that the overall permeability is higher than a threshold in a predetermined temperature range.

2. The ferrite core according to Claim 1, wherein the first permeability of the first ferrite material is higher than the second permeability of the second ferrite material in an operation temperature range.

3. The ferrite core according to Claim 1 or 2, wherein a Curie temperature of the first ferrite material is lower than that of the second ferrite material.

4. The ferrite core according to Claim 3, wherein an upper temperature limit of the predetermined temperature range is set between the Curie temperatures of the first and the second ferrite materials.

5. The ferrite core according to any of Claims 1 to 4, wherein the first and second ferrite materials include Mn-Zn ferrite materials of different grades, respectively.

6. The ferrite core according to any of Claims 1 to 5, wherein the ferrite core includes an annulus ferrite core, and the first and second portions each form two annulus segments of the annulus ferrite core.

7. The ferrite core according to Claim 6, wherein the first and second proportions include respective proportions of heights of the two annulus segments to that of the annulus ferrite core.

5

8. The ferrite core according to any of Claims 1 to 7, further comprising a further portion in addition to the first and second portions, the further portion being formed by a further ferrite material other than the first and second ferrite materials, the overall permeability being determined based on the permeability of the respective ferrite materials and the respective proportions of the portions in the ferrite core, and the respective

10 proportions being determined so that the overall permeability is higher than the threshold in the predetermined temperature range.

9. A current mutual inductor, comprising the ferrite core according to any of Claims 1 to 8.

10. The current mutual inductor according to Claim 9, wherein the current mutual inductor comprises a zero-sequence current mutual inductor.

11. A current leakage protection switch, comprising the current mutual inductor

20 according to any of Claims 9 to 10.

Intellectual

Property

Office

Application No: GB1711964.5 Examiner: Mr John Watt