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H 40 Four-pole 4 p method Four-pole method 4p is used to measure earthing elements, when the required accuracy is high. In 3p method the displayed value is the sum of the measured ground resistance and resistance of test leads between E terminal of the meter and the measured earth electrode.
In 4p method, the fourth wire, connected between ES terminal and the measured earth electrode, eliminates the effect of lead resistance measurement. Just as in 3p method, it is necessary to disconnect the control connection otherwise it will measure the resistance of the whole earthing system. The method of measuring earthing resistance with 4 poles is presented in Fig. Measurements performed using the grounding resistance meters 4.
The only possibility option in such cases is applying 3p method with clamps. This method uses two auxiliary electrodes, as in 3p method. As the control connection is not open, test current from E terminal of the meter flows through both the tested earthing and other earthing elements.
To determine the current which flows through the tested earthing, measuring clamps are used. Basing on the measured voltage drop on the tested earth electrode and on measured current values, the meter calculates the value of earth resistance. When performing the measurement, pay attention to correctly place the clamps. During the measurement only a part of generated current flows through the tested earth electrode. The rest of the test current flows through the other components of the earthing system.
To ensure the highest accuracy, use clamps of the highest quality. The measurement range achieved by MRU is 0.
The method of 3p measurement is presented in Fig. To perform the measurement of earth resistance, it is necessary to generate current and then to calculate the resistance value basing on the voltage drop. In the city centre, where the buildings are very close to each other, often there is no way to enter auxiliary electrodes into the ground. In such conditions, two-clamp method may be applied. The principle of the two-clamp measurement method is shown in Fig.
The aim of measurement is to measure the earth resistance of the earthing electrode RE1. This method uses transmitting clamp N-1 and receiving clamp C Transmitting clamp is used to generate a voltage in the circuit. Current flowing in the circuit depends on the values of circuit resistance - the lower the resistance value, the greater the current.
Receiving clamp measures the current flowing in the circuit. On this basis the value of earth resistance is calculated. To make 2-clamp method possible, the circuit must be closed to enable the current flow. Therefore the measurement of one, open earth electrode is not possible in this method.
To perform the measurement, a single earth electrode should be connected to another. System of earth electrodes presented in Fig. The substitute diagram shows the value of RE1 earth resistance. As is apparent from the formula below, the value displayed is composed of the measured ground RE1 and the resultant of other electrodes connected in parallel.
Thus the obtained value of earth resistance will be overestimated positive measurement error. This is the error of the method. Since the resultant resistance of the other parallel earth electrodes i. Example Measuring the resistance of the earth electrode as in Fig. Measurements performed using the grounding resistance meters Fig.
This involves sophisticated metering circuit of the meter, but these measurements best reflect the results for a frequency of 50Hz. Additionally important is the internal diameter of the clamp to be able to perform measurements of earth resistance for example on a band iron.
For N-1 and C-3 clamp inner diameter is 52mm 2 inches. The method of two-clamp measurement is shown in Fig. When measuring with two-clamp method it is irrelevant whether the transmitting clamp is at the top or bottom.
Important is the distance between the clamp, in order to avoid the influence of transmitting clamp on the receiving clamps. The recommended minimum distance is 30cm. Details are defined in EN - lightning protection. This standard introduces the concept of earthing impedance. Earthing impedance is defined as ratio of the peak values of the earth-termination voltage and the earth-termination current which, in general, do not occur simultaneously.
This earthing impedance measured by MRU meter - is called the impulse resistance Rd. Earthing e. Impedance in this case is equal to resistance Fig.
For high frequencies, corresponding to the lightning discharge, the conductor should be considered as a transmission line. Then the conductor inductance and capacitance to the ground begin to play a significant role.
Considering the conductor as a pure resistance in this case is a mistake. Such a system has the impedance, depending not only on its resistance , but also on its orientation in the ground. Electrical model for the lightning stroke is shown in Fig.
Inductive reactance of the wire is the reason for which the further parts of the earthing have less influence on discharging the lightning to the ground. The manner of arranging air terminals, conductors and earth electrodes is very important for effective lightning protection and should therefore be made in accordance with the requirements of EN To fulfil this requirement, the test current should have a shape which is created by the lightning stroke.
The shape of the test pulse is shown in Fig. Measurements performed using the grounding resistance meters The meter during the measurement generates a series of pulses with a given shape and amplitude of 1. The shorter the impulse selected for measurement, the greater is the effect of reactance. The impulse method used in measurements in earthing elements differs from the technical method of 4p, which uses test frequencies similar to the mains frequency.
A shielded cable is used for the measurement to eliminate the effect of noise on the measurement result. It is important that the screen of this cable is connected to E terminal of the meter.
During the measurement test leads must be totally unwound and cannot be located on reel in order to prevent additional inductance. During the impulse measurement auxiliary electrodes must be arranged differently than in 4p method.
To avoid inducing a voltage in S conductor by current flow in the H conductor - S conductor should be separated from H. Measuring ground resistivity Designing new earthing systems should take into account local ground conditions. The most important earth parameter is the soil resistivity. Low soil resistivity means easier way of installing an earthing which fulfils pre-defined requirements. Rocky and sand areas, require complex earthing systems and higher costs in order to achieve an appropriate resistance value.
Resistivity model is presented as a cube with dimensions of 1m x 1m x 1m, filled with soil, while electrodes are located on opposite. Such a cube is connected to the voltage. Ratio of the voltage to the flowing current determines resistivity 23 Fig.
This relationship allows users to define the range of the depth at which the resistivity is measured and it amounts to about 0. Performing a series of resistivity measurements, while changing the distance between the probes, we can determine approximately at what depth the lowest resistivity occurs.
This knowledge is of crucial importance for material savings during the construction of earth electrodes. Measurements performed using the grounding resistance meters 0,7l Fig. Example: In order to determine the ground resistivity in the area of its frost penetration zone approx 0. Similar measurement results are evidence of the homogeneity of the ground and the accuracy of tests.
Water pipes or other metal parts buried in the ground may impact the ground resistivity measurements. This will be indicated by significant differences in results obtained in a series of resistivity measurements with the auxiliary probes directed in different directions. In such case it is necessary to change the place of an examination by replacing the probes and entering them into the ground a few meters from the place where the measurement is difficult.
Ground resistivity measurements enable users to determine the optimum depth at which vertical elements of earthing system should be buried into the ground. This saves both time and materials used to construct grounding systems.
Measurements of electric system parameters using combined measuring instruments - EN Introduction The standard HD defines requirements pertaining to acceptance inspections and periodic inspections of electrical systems. Also, it defines requirements pertaining to reporting of inspection results. The present publication is intended to present the way these measuring instruments can be used to perform measurements in accordance with the aforementioned standard. Legal requirements concerning the performance of measurements The HD standard defines two types of inspections: - acceptance inspections; - periodic inspections.
According to this standard, every system must be inspected during assembly, after assembly, and before handover to the user. The acceptance inspection must include comparison of the measurements results with the relevant criteria defined, among others in the multi-sheet IEC standard, so as to check if the requirements given there have been met.
In the case of enlargement or modifications of existing systems, the same full scope of tests must be performed as in the case of a new system. During the performance of the measurements, precautions must be observed to make sure that the inspection will not cause a hazard to persons or pets and that it will not cause damage to the property and equipment even if the tested loop is defective.
The person performing the inspection should be properly qualified and competent with regards to inspections. It must be emphasized that the person performing the inspection is responsible for preparing the system for tests, for conducting the tests, and for proper assessment of the test results E and D license.
An acceptance inspection consists of a visual inspection and a test. A visual inspection must be performed before the test, before the power supply of the system is switched on.
Ochrona przeciwporażeniowa: norma PN-HD 60364-4-41
Measurements of electric system parameters using combined measuring instruments When the phase sequence is correct, the display of the meter will show phase rotation to the right clockwise. The meter also measures the interphase voltage. If necessary, one must check the operation of the protection devices so as to make sure that they have been installed correctly and that their settings are correct. The voltage drop value can be determined by measuring the circuit loop impedance or on the basis of a diagram given in Annex D to the HD standard. III Measurement reports Reports must be prepared from testing of new, extended, or modified installations, as well as from periodic inspections.
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