Description:SYSTEM FOR MEASURING EARTH RESISTANCE

FIELD OF THE INVENTION
[0001] The present invention relates to safety of electrical equipment, and particularly measuring ground resistance in order to maintain safety for the electrical equipment & human being.

BACKGROUND OF THE INVENTION
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] In electrical systems, it is essential to measure the earth resistance accurately to ensure proper safety and performance. Sub-station transformers, in particular, require efficient measurement of earth fault loop impedance to assess and mitigate potential risks. Existing systems lack a comprehensive solution for measuring earth resistance in sub-station transformers.

[0004] Earthing is used for saving man and machine being used in industry from get damaged. Earthing is provided by electrically grounded all metallic parts of electrical equipments. When all metallic parts in electrical equipments are not grounded and if the insulation inside the equipments fails a voltage level gets raised drastically. If the live wire touches the grounded case then the circuit is effectively shorted and fuse will immediately blow. When the fuse is blown then the dangerous voltages are away.

[0005] Thus, earthing is needed for several issues, such as to save human life from danger of electrical shock or death by blowing a fuse i.e. to provide an alternative path for the fault current to flow so that it will not endanger the , to protect buildings, machinery & appliances under fault conditions, to ensure that all exposed conductive parts do not reach a dangerous potential, to provide safe path to dissipate lightning and short circuit currents, and to provide stable platform for operation of sensitive electronic equipments i.e. to maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment .

[0006] Further, lightning, line surges or unintentional contact with higher voltage lines may cause dangerously high voltages to the electrical distribution system. Earthing provides an alternative path around the electrical system to minimize damages in the system.

[0007] In addtion, the earthing is helpful in voltage stablization. There are many sources of electricity. Every transformer can be considered a separate source. If there were not a common reference point for all these voltage sources it would be extremely difficult to calculate their relationships to each other.

[0008] The earth is the most omnipresent conductive surface, and so it was adopted in the very beginnings of electrical distribution systems as a nearly universal standard for all electric systems.

[0009] There are several factors which affect earth resistivity. Some of the factors include soil resistivity, soil condition, moisture, dissolved salts, climate condition, physical composition, location of earth pit, effect of gain size and its distribution, effect of current magnitude, area available, obstructions, and current magnitude.

[0010] The system for measuring earth resistance comprises the following elements:
Sub-station Transformer:
The system includes a sub-station transformer equipped with a plurality of terminals specifically designed for measuring earth fault loop impedance. These terminals provide the necessary connection points for conducting the measurements.

First Test Lead:
The system includes a first test lead connected to a line terminal of the sub-station transformer. This lead is responsible for obtaining a first line reference value required for the measurement of the earth fault loop impedance.

Second Test Lead:
A second test lead is connected to a neutral terminal of the sub-station transformer. This lead is responsible for obtaining a second line reference value required for the measurement of the earth fault loop impedance. The first and second line reference values are added to determine the line resistance.

Third Test Lead:
The system further comprises a third test lead connected to an earth terminal of the sub-station transformer. This lead is responsible for obtaining the earth resistance required for the measurement of the earth loop impedance.

Processing Element:
A processing element is connected to the sub-station transformer. This processing element receives the line resistance values obtained from the first and second test leads, as well as the earth resistance obtained from the third test lead. It uses this information to determine the earth loop impedance accurately.

Display Element:
The system is equipped with a display element that renders the effective resistance up to a panel based on the earth loop impedance determined by the processing element. This allows s to view and monitor the resistance levels conveniently.

In operation, the first and second test leads acquire line reference values, which are then combined to determine the line resistance. The third test lead measures the earth resistance. The processing element receives these values and calculates the earth loop impedance. Finally, the display element presents the effective resistance up to a panel, providing s with crucial information for system analysis and safety assessment.

[0011] Fig. 1 illustrates an environment indicating utilization of grounding, in accordance with prior-art. As illustrated in Fig. 1, a fault current generated during fault in an electrical circuitry is fed to the ground through grounding wire. The amount of current fed to the ground depnds upon resistance of the earth. It must be noted that measured values of resistances of different modules are observed as major power station= 0.5 Ohm, major sub-stations= 1.0 Ohm, minor sub-station = 2 Ohm, neutral bushing. =2 Ohm, service connection = 4 Ohm, medium voltage network =2 Ohm, L.T. Lightening arrestor= 4 Ohm, L.T.Pole= 5 Ohm, H.T.Pole =10 Ohm, tower =20-30 Ohm.

[0012] Resistance of the earth is the resistance between infinite earth and earth electrode. This depends upon mainly three factors, such as a resistance of the electrode measuring the earth resistance, a contact resistance between electrode surface and soil, a resistivity of soil between the electrode and infinite earth.

[0013] The first two factors can be taken as negligible compared to third factor, i.e. resistivity of soil. This is the reason, we generally consider resistivity of the soil only, when we deal with resistance of earth. Further, the resistivity of the soil depends upon the other factors, such as electrical conductivity, chemical composition of the soil, a grain size, and temperature of the soil.

[0014] The electrical conductivity offered by a soil mainly due to electrolysis. That means the resistivity (or conductivity) of a soil is mainly electrolytic in nature. So, concentration of water, salt and other chemical components in the soil largely determines its resistivity. The grain size, uniformity of grain distribution and packing of grains in the soil (i.e. inter grain distance) also the factors for resistivity. Since, this factors control the moisture holding capacity of the soil. The temperature of the soil can also be a factor but when it is very close to freezing temperature. Below, 0oC, the water contained in the soil begins to freeze, which largely affects the electrolysis process in the soil. It is found that, just below the freezing point the resistivity of soil or earth resistivity is tremendously increased.

[0015] Earth resistance is calculated using below-mentioned equation.

[0016] Fig. 2 illustartes an equipment for measuring the earth resistance, in accordance with prior-art. In such conventional method, earth tester terminal C1 & P1 are shorted to each other and connected to the earth electrode (pipe) under test. Terminals P2 & C2 are connected to the two separate spikes driven in earth. These two spikes are kept in same line at the distance of 25 meters and 50 meters due to which there will not be mutual interference in the field of individual spikes.

[0017] If generator handle is rotated with specific speed the earth resistance is obtained directly on scale. Spike length in the earth should not be more than 1/20th distance between two spikes. Resistance must be verified by increasing or decreasing the distance between the tester electrode and the spikes by 5 meter. Normally, the length of wires should be 10 and 15 Meter or in proportion of 62% of ‘D’.

[0018] Thus, there is a need of a system for measurement of earth resistance which may overcome above-mentioned shortcomings of conventional approaches.

SUMMARY OF THE INVENTION
[0019] This summary is provided to describe an apparatus for providing a system for measuring earth resistance. This summary is not intended to identify key or essential inventive concepts of the present disclosure, nor is it intended for determining the scope of the present disclosure.

[0020] According to an embodiment of the present disclosure, The present invention relates to a system for measuring earth resistance. The system includes a sub-station transformer with terminals for measuring earth fault loop impedance. It further comprises test leads for obtaining line reference values and earth resistance, a processing element for determining the earth loop impedance, and a display element for rendering the effective resistance up to a panel.

[0021] According to an embodiment of the present disclosure, a system for measuring earth resistance is described. The system comprises a substation transformer comprising a plurality of terminals. A first test lead is connected with a line terminal of the plurality of terminals for obtaining a first line reference value required for measurement of the earth fault loop impedance. A second test lead is connected with a neutral terminal of the plurality of terminals for obtaining a second line reference value required for measurement of the earth fault loop impedance. The first line reference value and the second line reference value are added to determine a line resistance. A third test lead is connected with an earth terminal of the plurality of terminals for obtaining an earth resistance required for measurement of the earth loop impedance. A processing element determines the earth loop impedance based on the line resistance and the earth resistance. A display element renders effective resistance up to a panel based on the earth loop impedance.

[0022] In one aspect, the earth loop impedance is determined by addition of the line resistance, the earth resistance and an earth fault loop impedance external to supply.

[0023] In one aspect, present invention relates to electrical measurement systems and, more specifically, to a system for measuring earth resistance in sub-station transformers.

[0024] In one aspect, the earth fault loop impedance external to the supply is an impedance between measured without installation of the system.

[0025] In one aspect, the line resistance and the earth resistance are obtained during continuity testing of circuits.

[0026] In one aspect, a circuit breaker is bridged out during measurement of the earth loop impedance.

[0027] In one aspect, the earth loop impedance is measured by one of plugging a loop tester into a socket outlet and an external earth probe.

[0028] In one aspect, the earth fault loop impedance is measured using the external earth probe by touching an external probe directly to an earth bar, a collector, and a connection point of the earth bar.

[0029] In one aspect, the earth fault loop impedance is measured by touching an earth probe to exposed, conductive parts of equipment in the circuits, and exposed metal parts.

[0030] In one aspect, the effective resistance is monitored remotely.

BRIEF DESCRIPTION OF DRAWINGS
[0031] To further clarify the advantages and features of the present disclosure, a more particular description of the disclosure will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered limiting of its scope. The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.

[0032] The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other aspects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

[0033] Fig. 1 illustrates an environment indicating utilization of grounding, in accordance with prior-art;

[0034] Fig. 2 illustartes an equipment for measuring the earth resistance, in accordance with prior-art;

[0035] Figure 3 illustrates an electrical set-up for measuring earth resistance, in accordance with an embodiment of the present invention; and

[0036] Figure 4 illustrates an arrangement for determination of fault loop impedance, in accordance with the present invention.

[0037] Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION
[0038] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein would be contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art. The system, methods, and examples provided herein are illustrative only and are not intended to be limiting.

[0039] The term “some” as used herein is to be understood as “none or one or more than one or all.” Accordingly, the terms “none,” “one,” “more than one,” “more than one, but not all” or “all” would all fall under the definition of “some.” The term “some embodiments” may refer to no embodiments or to one embodiment or to several embodiments or to all embodiments, without departing from the scope of the present disclosure.

[0040] The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features. It does not in any way limit, restrict or reduce the spirit and scope of the claims or their equivalents.

[0041] More specifically, any terms used herein such as but not limited to “includes,” “comprises,” “has,” “consists,” and grammatical variants thereof do not specify an exact limitation or restriction and certainly do not exclude the possible addition of one or more features or elements, unless otherwise stated, and furthermore must not be taken to exclude the possible removal of one or more of the listed features and elements, unless otherwise stated with the limiting language “must comprise” or “needs to include.”

[0042] Whether or not a certain feature or element was limited to being used only once, either way, it may still be referred to as “one or more features” or “one or more elements” or “at least one feature” or “at least one element.” Furthermore, the use of the terms “one or more” or “at least one” feature or element do not preclude there being none of that feature or element, unless otherwise specified by limiting language such as “there needs to be one or more . . . ” or “one or more element is required.”

[0043] Unless otherwise defined, all terms, and especially any technical and/or scientific terms, used herein may be taken to have the same meaning as commonly understood by one having ordinary skills in the art.

[0044] Reference is made herein to some “embodiments.” It should be understood that an embodiment is an example of a possible implementation of any features and/or elements presented in the attached claims. Some embodiments have been described for the purpose of illuminating one or more of the potential ways in which the specific features and/or elements of the attached claims fulfill the requirements of uniqueness, utility and non-obviousness.

[0045] Use of the phrases and/or terms including, but not limited to, “a first embodiment,” “a further embodiment,” “an alternate embodiment,” “one embodiment,” “an embodiment,” “multiple embodiments,” “some embodiments,” “other embodiments,” “further embodiment”, “furthermore embodiment”, “additional embodiment” or variants thereof do not necessarily refer to the same embodiments. Unless otherwise specified, one or more particular features and/or elements described in connection with one or more embodiments may be found in one embodiment, or may be found in more than one embodiment, or may be found in all embodiments, or may be found in no embodiments. Although one or more features and/or elements may be described herein in the context of only a single embodiment, or alternatively in the context of more than one embodiment, or further alternatively in the context of all embodiments, the features and/or elements may instead be provided separately or in any appropriate combination or not at all. Conversely, any features and/or elements described in the context of separate embodiments may alternatively be realized as existing together in the context of a single embodiment.

[0046] Any particular and all details set forth herein are used in the context of some embodiments and therefore should not be necessarily taken as limiting factors to the attached claims. The attached claims and their legal equivalents can be realized in the context of embodiments other than the ones used as illustrative examples in the description below. Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[0047] Fig. 3 illustrates an electrical set-up 300 for measuring earth resistance, in accordance with an embodiment of the present invention. The set-up 300 comprises a smart meter 302 for rendering the electricity units based on usage of electricity. The smart meter 302 may be connected with a consumer unit 304 through a double-pole isolator 306. The consumer unit 304 may comprise a main switch 308 for providing electricity to household appliances. Additionally, the smart meter is connected with a service cut-out 310 for hard cut-off of electricity from the house.

[0048] For determining the earth resistance, an earth fault impedance tester 312 may be utilized. The earth fault impedance tester 312 may measure the earth impedance and may render the value on the display of the earth fault impedance tester 312. The earth fault impedance tester 312 may comprise one or more terminals for obtaining reading. The one or more terminals may be connected with line 314 and ground terminal 316 through probes 318. Determination of the earth resistance is described successively.

[0049] Fig. 4 illustrates an arrangement for determination of fault loop impedance, in accordance with the present invention. Prior to determining the earth resistance, an external earth loop impedance (Ze) test needs to be done. The test, done at a distribution board, provides a loop impedance of the circuit, excluding the installation. After calculating the external earth loop impedance (Ze), a system loop impedance (Zs) test may be performed. The system loop impedance (Zs) includes the circuit tested in the Ze test as well as including the installation resistance.

[0050] The system 400 may include a substation transformer 402 having three terminals, such as a line terminal (L), a neutral terminal (N), and an electrode terminal (E). The system 400 may further comprise a distribution board 404 for distributing the testing probes. Further, the system 400 may further comprise a socket outlet 406 for installation of the testing probes inside the ground.

[0051] A first test lead may be connected with a line terminal of the plurality of terminals for obtaining a first line reference value required for measurement of the earth fault loop impedance. A second test lead may be connected with a neutral terminal of the plurality of terminals for obtaining a second line reference value required for measurement of the earth fault loop impedance, wherein the first line reference value and the second line reference value are added to determine a line resistance. A third test lead may be connected with an earth terminal of the plurality of terminals for obtaining an earth resistance required for measurement of the earth loop impedance. The system 400 may further comprise a processing element connected to the sub-station transformer for determining the earth loop impedance based on the line resistance and the earth resistance

[0052] Alternating Current (AC) impedance of a circuit may be different from its Direct Current (DC) resistance, particularly for circuits rated at over 100 A. The fault loop impedance may be measured using the same frequency as the nominal mains frequency (50 Hz).

[0053] The Ze earth fault loop impedance measurement is made on the supply side of the distribution board and the main means of earthing, with the main switch open and all circuits isolated. The means of earthing will be isolated from the installation’s earthing system (earth rods) bonding during the test. The Ze measurement will confirm the earth fault loop impedance as the sum of the resistances.

[0054] For measuring the external earth fault loop resistance, an Earth Fault Loop Tester may be used. In one implementation, an earth fault loop test option may be selected on a multifunctional tester such as the Megger 1553.

[0055] The test may be performed on the incoming side of the installation. A first test lead may be connected to the line terminal, a second test lead may be connected to the neutral terminal, and a third test lead may be connected to the electrode terminal.?

[0056] A TEST button may be pressed. The measurement should be a low reading ohm value. The value (Ze) may be recorded on the Electrical Installation Certificate. Having obtained the `Ze` value for the installation, the value of `Zs` can be easily calculated for every circuit.

[0057] The maximum measured earth fault loop impedance (Zs) values recorded should be compatible with the Ze + R1 + R2 value of each circuit, irrespective of the requirements of the respective protective device(s). Test results measured using low current tests are not recorded on schedules of test results, it is preferable to record the Zs values calculated from individual test results.

[0058] A formula for determining Zs may be provided below:
Zs=Ze + (R1+R2)
[0059] In above-equation, Zs is equal to the earth fault loop impedance of the circuit tested, Ze is earth fault loop impedance external to the supply, R1 is phase conductor resistance, R2 is earth conductor resistance, and (R1+R2) is equal to sum of the resistance of Line and Earth for the tested circuit.

[0060] Ze is derived from a high current test and R1 + R2 obtained during continuity testing of the circuits. The type of test results recorded and the test method used will be indicated in the appropriate remarks column of the test results schedule.

[0061] The earth fault loop impedance (Zs) may be tested at the furthest point of each circuit. In most cases the circuit breaker needs to be bridged out. The total earth fault loop impedance is measured by plugging a loop tester into a socket outlet, or in some cases with an external earth probe. The value of the earth fault loop impedance is the sum of the resistances. When using an external earth probe, the earth fault loop impedance is measured by touching an external probe directly to an earth bar, collector, and connection point of an earth bar. The same measurement can be done by touching the earth probe to expose, conductive parts of equipment in the circuits and exposed metal parts.

[0062] In some embodiments, for measuring the earth fault loop impedance (Zs), a furthest point may be located on a circuit to be tested. an appropriate earth fault loop tester may be connected with test leads. For example, the test leads may be connected to the line terminal, the neutral terminal, and the earth terminal of the earth fault loop tester. Thereafter, test results may be measured and tested. In an example, if the circuit is Residual Current Device (RCD) protected then “No trip” function of the earth fault loop tester must be selected to avoid nuisance tripping of the RCD. In an implementation, if the earth fault loop tester does not have “No trip” option then the RCD must be linked out. Further, the obtained value of Zs must be verified that the value of Zs is within the accepted limit.

[0063] Advantages of the Invention:
The system for measuring earth resistance offers several advantages over existing solutions:
Accurate Measurement: The system ensures accurate measurement of earth resistance in sub-station transformers, promoting enhanced safety and system performance.
Comprehensive Solution: The combination of line reference values and earth resistance provides a comprehensive measurement approach, allowing for a more accurate assessment of earth fault loop impedance.
Convenient Display: The display element renders the effective resistance up to a panel, providing s with real-time information for analysis and decision-making.

[0064] As according to the present invention, the system for measuring earth resistance described herein offers an efficient and comprehensive solution for accurately determining earth loop impedance in sub-station transformers. Its various components, including the sub-station transformer, test leads, processing

[0065] There are some treatments to be followed for minimizing the earth resistance. For example, removal of oxidation on joints and joints should be tightened, pouring sufficient water in earth electrode, usage of bigger size of earth electrode, connection of electrodes in parallel, and making earth pit of more depth & width- breadth.

[0066] The figures and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of the embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible.
, Claims:We claim:
1. A system for measuring earth resistance, the system comprising:
a sub-station transformer comprising a plurality of terminals for measuring earth fault loop impedance;
a first test lead connected with a line terminal of the plurality of terminals for obtaining a first line reference value required for measurement of the earth fault loop impedance;
a second test lead connected with a neutral terminal of the plurality of terminals for obtaining a second line reference value required for measurement of the earth fault loop impedance, wherein the first line reference value and the second line reference value are added to determine a line resistance;
a third test lead connected with an earth terminal of the plurality of terminals for obtaining an earth resistance required for measurement of the earth loop impedance;
a processing element connected to the sub-station transformer for determining the earth loop impedance based on the line resistance and the earth resistance; and
a display element for rendering effective resistance up to a panel based on the earth loop impedance.

2. The system as claimed in claim 1, wherein the earth loop impedance is determined by addition of the line resistance, the earth resistance and an earth fault loop impedance external to supply.

3. The system as claimed in claim 2, wherein the earth fault loop impedance external to the supply is an impedance between measured without installation of the system.

4. The system as claimed in claim 1, wherein the line resistance and the earth resistance are obtained during continuity testing of circuits.

5. The system as claimed in claim 1, wherein a circuit breaker is bridged out during measurement of the earth loop impedance.

6. The system as claimed in claim 1, wherein the earth loop impedance is measured by one of plugging a loop tester into a socket outlet and an external earth probe.

7. The system as claimed in claim 6, wherein the earth fault loop impedance is measured using the external earth probe by touching an external probe directly to an earth bar, a collector, and a connection point of the earth bar.

8. The system as claimed in claim 6, wherein the earth fault loop impedance is measured by touching an earth probe to exposed, conductive parts of equipment in the circuits, and exposed metal parts.

9. The system as claimed in claim 1, wherein the effective resistance is monitored remotely.