WO2023155049A1

WO2023155049A1 - Device for detecting ground faults and electrical system

Info

Publication number: WO2023155049A1
Application number: PCT/CN2022/076379
Authority: WO
Inventors: Huan SHI; Hongming GUO; Wei Liu
Original assignee: Abb Schweiz Ag
Priority date: 2022-02-15
Filing date: 2022-02-15
Publication date: 2023-08-24
Also published as: CN118382814A

Abstract

A device (100) for detecting ground faults and an electrical system (1000) comprising the device (100). The device (100) for detecting ground faults comprises: a stimulating source (110) coupled to a ground (G) and configured to generate a first voltage or a second voltage, the polarity of the first voltage being different from that of the second voltage; a plurality of sampling resistors (R1, R21, R22) coupled between the stimulating source (110) and a power supply (200); a determining module (120) configured to calculate a grounding resistance (Rg1, Rg2) based on a sampled voltage associated with the plurality of sampling resistors (R1, R21, R22); and an auxiliary resistor (R AUX) coupled across the power supply (200). The accuracy of calculating the grounding resistance is improved while the detection of the ground faults has a less response time.

Description

DEVICE FOR DETECTING GROUND FAULTS AND ELECTRICAL SYSTEM

FIELD

Embodiments of present disclosure generally relate to power fault detection, and more particularly, to a device for detecting ground faults and an electrical system comprising the device.

BACKGROUND

In an electrical system, such as an electric drive system where a power source drives a motor, a short circuit between the power source and protective earth may occur. Such ground fault results in undesired situations in the electrical system. For example, in the event of a ground fault, the power supply may connect directly via the protective earth to and drive other loads which are not expected to be driven.

Generally, a module for detecting the ground faults may be provided in the electrical system and designed to measure and calculate the short-circuit resistance when the ground fault occurs. However, the accuracy of the measurement and calculation may be affected by some factors. One of these factors is the wire break of the power supply. In the case of the wire break of the power supply, some of the electrical parameters in the calculation will be changed, which causes the calculated short-circuit resistance to deviate from the actual short-circuit resistance, and therefore the ground faults cannot be identified.

A conventional solution for this problem is to judge whether the wire break of the power supply occurs, and perform different calculations for the wire break and the non-wire break. Unfortunately, the judging of the wire break increases the response time of the detection of the ground faults, and it is difficult to judge the wire break in some cases.

SUMMARY

Embodiments of the present disclosure provide an improved device for detecting the ground faults and an electrical system comprising the improved device.

In a first aspect, a device for detecting the ground faults is provided. The device comprises: a stimulating source coupled to a ground and configured to generate a first voltage or a second voltage, the polarity of the first voltage being different from that of the second voltage; a plurality of sampling resistors coupled between the stimulating source and a power supply; a determining module configured to calculate a grounding resistance based on a sampled voltage associated with the plurality of sampling resistors; and an auxiliary resistor coupled across the power supply.

In some embodiments, the plurality of sampling resistors comprise a first resistor coupled between the stimulating source and a common node, a second resistor coupled between the common node and one of two ends of the power supply, and a third resistor coupled between the common node and the other of the two ends of the power supply. The determining module is configured to calculate the grounding resistance based on a first value of voltage across the first resistor and a second value of voltage across the first resistor, the first value of voltage being measured when the stimulating source generates the first voltage, and a second value of voltage being measured when the stimulating source generates the second voltage.

In some embodiments, the determining module is further configured to determine that the ground faults occur if the calculated grounding resistance is below a threshold value.

In some embodiments, the auxiliary resistor is selected such that if a wire break of the power supply occurs and the calculated grounding resistance is above the threshold value, an error rate of the calculated grounding resistance is below a predefined error rate.

In some embodiments, the auxiliary resistor is further selected such that the power consumption of the auxiliary resistor is below a predefined power consumption

In a second aspect, an electrical system is provided. The electrical system comprises a power supply, a load electrically coupled to the power supply and a device for detecting ground faults according to the first aspect.

DESCRIPTION OF DRAWINGS

Drawings described herein are provided to further explain the present disclosure and constitute a part of the present disclosure. The example embodiments of the disclosure and the explanation thereof are used to explain the present disclosure, rather than to limit the present disclosure improperly.

Figure 1 illustrates a schematic diagram of an electrical system in the event that a ground fault occurs.

Figure 2 illustrates a schematic diagram of an electrical system with a conventional device for detecting the ground faults.

Figure 3 illustrates a schematic diagram of an electrical system according to embodiments of the present disclosure.

Figure 4 illustrates a schematic diagram of the power supply and the device for detecting ground faults according to embodiments of the present disclosure.

Figure 5 illustrates a circuit diagram of the power supply and the device for detecting the ground faults in the case of the most asymmetry of the grounding resistances according to embodiments of the present disclosure.

Figure 6 illustrates an ideal simplified circuit of the power supply and the device for detecting the ground faults according to embodiments of the present disclosure.

Figure 7 illustrates the actual simplified circuit of the power supply and the device 100 in the case of the wire break according to embodiments of the present disclosure.

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

DETAILED DESCRIPTION OF EMBODIEMTNS

Principles of the present disclosure will now be described with reference to several example embodiments shown in the drawings. Though example embodiments of the present disclosure are illustrated in the drawings, it is to be understood that the embodiments are described only to facilitate those skilled in the art in better understanding and thereby achieving the present disclosure, rather than to limit the scope of the disclosure in any manner.

The term “comprises” or “includes” and its variants are to be read as open terms that mean “includes, but is not limited to. ” The term “or” is to be read as “and/or” unless the context clearly indicates otherwise. The term “based on” is to be read as “based at least in part on. ” The term “being operable to” is to mean a function, an action, a motion or a state can be achieved by an operation induced by a user or an external mechanism. The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment. ” The term “another embodiment” is to be read as “at least one other embodiment. ” The terms “first, ” “second, ” and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below. A definition of a term is consistent throughout the description unless the context clearly indicates otherwise.

Unless specified or limited otherwise, the terms “mounted, ” “connected, ” “supported, ” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Furthermore, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. In the description below, like reference numerals and labels are used to describe the same, similar or corresponding parts in the figures. Other definitions, explicit and implicit, may be included below.

Figure 1 illustrates a schematic diagram of an electrical system in the event that a ground fault occurs. As shown in Figure 1, a power supply 200’ is electrically connected to loads 300-1’ and 300-2’ through switches S1’ and S2’ respectively. If ground faults occur in the electrical system, some unexpected loop may be formed in the electrical system. For example, when the switch S1’ turns on and the switch S2’ turns off, the power supply Ue drives the load 300-1’, and the load 300-2’ should not be energized. However, if short-to-ground faults occur at a node N1’ and a node N2’, the current from the power supply Ue will flow to the load 300-2’ via the node N1’, the protective earth G’ and the node N2’, thereby causing the load 300-2’ to be energized, which is undesirable.

Figure 2 illustrates a schematic diagram of an electrical system 1000’ with a conventional device for detecting the ground faults. As shown in Figure 2, a stimulating source Us’ and a plurality of the resistors R1’, R21’, R22’, R31’ and R32’ are provided in the electrical system 1000’ for measuring a grounding resistance Rg1’ of the positive terminal and a grounding resistance Rg2’ of the negative terminal, or measuring the parallel resistance of Rg1’ and Rg2’, so as to identify the ground faults. However, in the event of the wire break of the power supply Ue’, the grounding resistance may not be accurately calculated. In order to address this problem, the electrical system 1000’ may further provide a module for judging the wire break of the power supply Ue’, and thus the grounding resistance can be calculated in different manners in the case of the wire break and the non-wire break.

It is seen that in the conventional solution, the judging of the wire break will increase the response time of detection of the ground faults, and thus the stability and security of the system are adversely affected. Moreover, in some cases, it is difficult to judge the wire break of the power supply. Specifically, the principle of judging whether the wire break occurs is to record voltage values between two nodes under two different power polarity of stimulating source Us’, and then subtract the two recorded voltage values. If there is no wire break, the calculating result is equal to zero, and if there is wire break, the calculating result is not equal to zero. However, in the event that the grounding resistance Rg1’ of the positive terminal is equal to the grounding resistance Rg2’ of the negative terminal, the calculating results are always zero in both cases of the wire break and the non-wire break, and thus it is impossible to judge whether the wire break occurs, and the grounding resistance cannot be calculated accurately.

In order to at least partially address the above and other potential problems, embodiments of the present disclosure provide an improved solution for detecting the ground fault. In such a solution, by means of providing an auxiliary resistor in parallel with the power supply, there is no need for judging the wire break of the power supply during measuring and calculating the grounding resistance, while the measuring accuracy of the grounding resistance is improved and thus the ground faults can be identified properly. Thereby, the measuring accuracy in the case of the wire break of the power supply is improved and within an acceptable range, while the response time of identifying the ground faults is reduced.

Figure 3 illustrates a schematic diagram of an electrical system 1000 according to embodiments of the present disclosure. As shown in Figure 3, the electrical system 1000 comprises a power supply 200 and a load 300 electrically coupled to the power supply 200. The power supply 200 is shown as a DC power source, which may output any suitable voltage, e.g., 3-48V DC. Alternatively, the power supply 200 may also be an AC power source. Moreover, the load 300 may be any electrical load such as motor, and may be directly coupled to the power supply 200, or coupled to the power supply 200 through an electrical switch.

The electrical system 1000 may comprise a device 100 for detecting ground faults. Specifically, the device 100 is coupled to the positive and negative terminals of the power supply 200 and a ground G such as a protective earth, thereby measuring or calculating the grounding resistances of the positive and negative terminals. Then, whether the ground faults occur can be determined by means of the measured or calculated grounding resistances.

Figure 4 illustrates a schematic diagram of the power supply 200 and the device 100 for detecting ground faults according to embodiments of the present disclosure. As shown in Figure 4, the device 100 comprises a stimulating source 110 coupled to a ground G and configured to generate a first voltage or a second voltage, the polarity of the first voltage being different from that of the second voltage. For example, the stimulating source 110 may be a voltage source, and the output voltage polarity of the stimulating source 110 is changed according to an external control or a predetermined setting, thereby generating a forward voltage or a reverse voltage as needed.

The device 100 may comprise a plurality of sampling resistors coupled between the stimulating source 110 and a power supply 200. In some embodiments of the present disclosure, the plurality of sampling resistors comprises a first resistor R1 coupled between the stimulating source 110 and a common node N, a second resistor R21 coupled between the common node N and one of two ends of the power supply 200, and a third resistor R22 coupled between the common node N and the other of the two ends of the power supply 200. The second resistor R21 may have a same resistance value as the third resistor R22, so as to simplify the calculation of the grounding resistances.

The device 100 may comprise a determining module 120 configured to calculate ground resistances Rg1 and Rg2 or a parallel resistance of Rg1 and Rg2 based on a sampled voltage associated with the plurality of sampling resistors R1, R21, R22. Specifically, after obtaining the sampled voltage, the ground resistance can be calculated according to the sampled voltage and the known resistance values of the sampling resistors R1, R21, R22.

Figure 5 illustrates a circuit of the power supply 200 and the device 100 in the case of the most asymmetry of the grounding resistances Rg1 and Rg2. The grounding resistances Rg1 and Rg2 may be represented by (A+1) *r and (A+1) *r/Arespectively, wherein r=Rg1*Rg2/ (Rg1+Rg2) , and A is the degree of symmetry of Rg1 and Rg2. When Rg1 and Rg2 are in the most asymmetrical case (i.e., A=0) , the circuit in Figure 4 can be changed as a circuit as shown in Figure 5. Specifically, in the most asymmetrical case, Rg1 is equal to r, and Rg2 is equal to infinitely great, that is, the branch of the resistance Rg2 may be considered as open circuit, and the resistance Rg2 has a resistance value r. Furthermore, it is assumed that R21=R22=R2 in Figure 5. For purpose of clarity, the calculation of the grounding resistance will be described below with reference to Figure 5.

When the stimulating source Us generates the first voltage Us+, the voltage U _R1+across the resistor R1 can be calculated by the equation below:

Wherein the item

represents the voltage component applied by the forward voltage Us+ of the stimulating source, and the item

represents the voltage component applied by the power supply Ue.

When the stimulating source Us generates the second voltage Us-, the voltage U _R1-across the resistor R1 can be calculated by the equation below:

Wherein the item

represents the voltage component applied by the reverse voltage Us-of the stimulating source, and the item

represents the voltage component applied by the power supply Ue.

Then, the above item of the power supply Ue can be removed by subtracting the equation (2) from the equation (1) as below:

Figure 6 illustrates a simplified circuit of the power supply 200 and the device 100 in Figure 5. The related parameters in the equation (3) can be found in Figure 6. Obviously, by means of applying the forward voltage U _S+ and the reverse voltage U _S-and performing subtraction, the item related to the power supply Ue is removed, and thus the equations (1) and (2) can be simplified as the equation (3) .

If the equation (3) is further transformed, the grounding resistance r can be obtained by the following equation:

In the equation (4) , U _S+ and U _S-are the voltages generated by the stimulating source Us, and R1 and R2 are values of the sampling resistors. Apparently, U _S+, U _S-, R1 and R2 can be preset and known. Moreover, the voltage values U _R1+ and U _R1-can be sampled and provided to the determining module 120. Therefore, after obtaining the voltage values U _R1+ and U _R1-, the ground resistance r, i.e. the parallel resistance of Rg1 and Rg2, is readily determined by the equation (4) . That is, the grounding resistance r may be calculated by the determining module 120 based on a voltage value U _R1+ across the first resistor R1 and a voltage value U _R1-across the first resistor R1, the voltage value U _R1+ being measured when the stimulating source 110 generates the first voltage U _S+, and the voltage value U _R1-being measured when the stimulating source 110 generates the second voltage U _S-.

Although the equation (4) is derived in the case of the most asymmetrical case A=0, it is appreciated that in other cases where the symmetry degree A is not equal to 0, the parallel resistance value r of Rg1 and Rg2 also can be calculated by means of the equation (4) .

In the embodiments of the present disclosure, the device 100 for detecting the ground faults further comprises an auxiliary resistor R _AUX coupled across the power supply 200. As discussed above, the conventional solution of detecting the ground faults should provide the function of judging the wire break of the power supply, since the wire break adversely affects the calculation of the ground resistance. In the improved solution of the present disclosure, there is no need for judging the wire break of the power supply, and by providing the auxiliary resistor R _AUX, when the grounding resistance is calculated, the accuracy of the calculation can be ensured regardless whether the wire break of the power supply occurs. The following will explain why providing the auxiliary resistor R _AUX ensures the accuracy of calculating the grounding resistance without the judging of wire break.

Specifically, in the event that there is no wire break of the power supply Ue, the actual measuring circuit for the grounding resistance is exactly consistent with Figure 6, and thus the grounding resistance can be accurately calculated by the equation (4) . However, if the wire break of the power supply Ue occurs, the actual measuring circuit for the grounding resistance will be changed.

Figure 7 illustrates the actual simplified circuit of the power supply 200 and the device 100 in Figure 5 in the case of the wire break. As shown in Figure 7, the parallel branch of the resistor R _Ue and the auxiliary resistor R _AUX is connected in series with the resistor R22, wherein R _Ue represents the resistance of the power supply branch and may be considered as infinitely great when the wire break of the power supply occurs. In the actual measuring circuit as shown in Figure 7, the real grounding resistance r _real may be calculated by the equation below:

Based on the equations (4) and (5) , the error of the calculation may be obtained as below:

In the equation (6) , since the item

has a small contribution to the error Δr, e.g., about 0.4k～0.5k ohm, this item can be ignored.

As a comparison, in absence of the auxiliary resistor, the branch of R22 is in the open circuit, and the real grounding resistance r _real may be calculated by the equation below:

As a result, the error of the calculation in absence of the auxiliary resistor may be obtained as below:

In the equation (8) , similar to the equation (6) , since the item

has a small contribution to the error Δr, this item can be ignored.

By way of example, it is assumed that U _S+ is +12V, U _S-is -12V, R1 is 2.5k ohm, R2 is 120k Ohm and R _AUX is 22k Ohm. According to the equation (8) , the error Δr′ of the grounding resistance in absence of the auxiliary resistor reaches -60k Ohm. In the event of providing the auxiliary resistor, the error Δr of the grounding resistance r is only about -5k Ohm according to the equation (6) .

It is seen that by providing the appropriate auxiliary resistor R _AUX in parallel with the power supply Ue, even if the wire break occurs, the calculated grounding resistance in the equation (4) is very close to the real grounding resistance and has only a small error, which may fall into an acceptable range. In this situation, the grounding resistance can be directly calculated by the equation (4) without judging the wire break. Since there is no need for judging the wire break, the ground faults can be detected with a less response time, thereby improving the stability and safety of the electrical system.

In some embodiments of the present disclosure, the determining module 120 is further configured to determine that the ground faults occur if the calculated grounding resistance is below a threshold value. The threshold value may be predefined according to the actual conditions of the electrical system, and the calculated grounding resistance may be compared with the threshold value. The calculated grounding resistance being below the threshold value means that the faults related to a short to ground has occurred.

For example, the threshold value for the grounding resistance is predefined as 20k ohm. In the event that the wire break of the power supply Ue occurs, when the calculated grounding resistance is above the 20k ohm, the error rate of the calculating the grounding resistance can be within an acceptable arrange, for example, the error rate is below 15%. When the calculated grounding resistance is below the 20k ohm, the error rate may be increased outside the acceptable arrange, for example, the error rate may be above 15%. However, although the accuracy of the calculated grounding resistance is unacceptable, since the calculated grounding resistance is below the threshold value, it is sufficient to determine that the ground fault has occurred. In this way, the adverse effect of the wire break on the calculation of the grounding resistance is eliminated.

In some embodiments of the present disclosure, the auxiliary resistor R _AUX is selected such that if a wire break of the power supply 200 occurs and the calculated grounding resistance is above the threshold value, an error rate of the calculated grounding resistance is below a predefined error rate. Specifically, it is seen from the equation (6) that if the resistance value of the auxiliary resistor R _AUX is lower, the error will be lower. Therefore, the resistance value of the auxiliary resistor R _AUX should be low enough, so as to ensure that the ratio of the error as calculated in the equation (6) and the grounding resistance is acceptable when the wire break occurs and the calculated grounding resistance is above the threshold value.

In some embodiments of the present disclosure, the auxiliary resistor R _AUX is further selected such that the power consumption of the auxiliary resistor R _AUX is below a predefined power consumption. Specifically, a lower resistance value of the auxiliary resistor R _AUX improves the accuracy of the calculation. However, the lower resistance value of the auxiliary resistor R _AUX will result in higher power consumption, which is undesirable in the electrical system. Therefore, when selecting the resistance value of R _AUX, there is a tradeoff on the accuracy of the calculating the grounding resistance and the power consumption. That is, the auxiliary resistor R _AUX should not be too low or too high, such that the accuracy of the calculation is improved to be within an acceptable range, while the power consumption of the auxiliary resistor R _AUX also is controlled below the predefined power consumption.

While several inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

Claims

A device (100) for detecting ground faults, comprising:

a stimulating source (110) coupled to a ground (G) and configured to generate a first voltage or a second voltage, the polarity of the first voltage being different from that of the second voltage;

a plurality of sampling resistors (R1, R21, R22) coupled between the stimulating source (110) and a power supply (200) ;

a determining module (120) configured to calculate a grounding resistance (Rg1, Rg2) based on a sampled voltage associated with the plurality of sampling resistors (R1, R21, R22) ; and

an auxiliary resistor (R _AUX) coupled across the power supply (200) .
The device (100) of claim 1, wherein the plurality of sampling resistors (R1, R21, R22) comprise a first resistor (R1) coupled between the stimulating source (110) and a common node (N) , a second resistor (R21) coupled between the common node (N) and one of two ends of the power supply (200) , and a third resistor (R22) coupled between the common node (N) and the other of the two ends of the power supply (200) , and

wherein the determining module (120) is configured to calculate the grounding resistance based on a first value of voltage across the first resistor (R1) and a second value of voltage across the first resistor (R1) , the first value of voltage being measured when the stimulating source (110) generates the first voltage, and a second value of voltage being measured when the stimulating source (110) generates the second voltage.
The device (100) of claim 1 or 2, wherein the determining module (120) is further configured to determine that the ground faults occur if the calculated grounding resistance is below a threshold value.
The device (100) of claim 3, wherein the auxiliary resistor (R _AUX) is selected such that if a wire break of the power supply (200) occurs and the calculated grounding resistance is above the threshold value, an error rate of the calculated grounding resistance is below a predefined error rate.
The device (100) of claim 4, wherein the auxiliary resistor (R _AUX) is further selected such that the power consumption of the auxiliary resistor (R _AUX) is below a predefined power consumption.
An electrical system (1000) comprising:

a power supply (200) ,

a load (300) electrically coupled to the power supply (200) ; and

a device (100) for detecting ground faults according to any of claims 1-5.