Ground Resistance Measurement Method Based on

High-Frequency Pulses

Yuhe Zhang

and Hao Zhang

Chengdu University of Technology, Chengdu, China

Chengdu Onise Electronic Technology, Co., Ltd, Chengdu, China

Keywords: Measuring Device, High-Frequency Pulses, Impact Ground Impedance.

Abstract: In recent years, many substations have expanded accidents due to lightning strikes, most of which are

related to unqualified grounding resistance of the ground grid, so vigorously strengthening the regular

monitoring of the ground resistance of the ground grid has become an important task. At present, the

common use of high and low voltage and low frequency AC, high voltage low and high frequency AC, high

and low voltage variable frequency AC, high and low voltage DC, etc. flows through the measured body,

testing the ground resistance, impedance, the AC or DC used, the frequency is single, and the rising and

falling edges are slow, and the ground impedance is inductive impedance, capacitive impedance or pure

resistance impedance can not be well reflected. In order to solve the above problems, a grounding resistance

test method based on low-voltage high-frequency pulse voltage is proposed.

INTRODUCTION

1.1 Brief Introduction

The grounding device of the generator, substation

and transmission line is the fundamental guarantee

and important measure to maintain the safe and

reliable operation of the power system and ensure

the safety of electrical equipment and personnel

[

Jianwei Guo, 2008]. The grounding device not only

provides a common reference ground for various

electrical equipment, but also can quickly disperse

the fault current or lightning current in the event of a

fault or lightning strike, limit the rise of the ground

potential, and ensure the safety of people and

equipment [

Huadong Huang, 2013]. At present, many

power grounding systems are limited by technical

conditions, only pay attention to the measurement of

power frequency characteristics, but with the gradual

development of science and technology, the stability

of the power system has been greatly improved,

therefore, the main accidents at this stage are mainly

caused by impulse current and lightning current.

When the inrush current flows into the grounding

device of the generator and substation, if the

grounding resistance value of the ground grid is

large, it will cause the potential of the ground grid to

rise abnormally, causing the local potential

difference of the grounding system itself to exceed

the safe value [

Guanghui Song, 2016]. At this time, the

inductive component of the grounding grid cannot

be ignored, and the real state of the grounding grid

can not be well reflected by traditional measurement

methods.

In order to better reflect the real state of the

grounding grid, this paper proposes a high-frequency

pulse digital grounding resistance tester. Using

low-voltage high-frequency pulse voltage as the test

power supply, that is, 20KHz, square wave voltage

with a duty cycle of 50%, input to the ground point

under test, the square wave current of 20KHz flows

back to the tester through the far ground loop, by

testing the peak voltage of the three-point square

wave, the MCU calculates the grounding resistance

of the ground point under test, at the same time,

through the LCD display, the voltage waveform of

the measured point is displayed, and the grounding

resistance of the measured point is determined

whether it is capacitive, inductive or purely resistive

through the change of the rising edge and falling

edge of the square wave; And observe the changes of

the rising edge and falling edge of the square wave,

and roughly determine the size of the stray

inductance or stray capacitance.

Zhang, Y. and Zhang, H.

Ground Resistance Measurement Method Based on High-Frequency Pulses.

DOI: 10.5220/0012280300003807

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 2nd International Seminar on Artiﬁcial Intelligence, Networking and Information Technology (ANIT 2023), pages 253-256

ISBN: 978-989-758-677-4

253

1.2 Current Situation at Home and

Abroad

At present, there are many ways to measure

grounding resistance, such as the three-pole method,

the four-pole method, and the frequency conversion

method, and in lightning detection, the most

commonly used method is the tripolar method

measurement. However, because there are many

influencing factors when measuring grounding

resistance, such as grounding wire resistance value,

grounding body own resistance, contact resistance

between grounding body and soil, etc., traditional

measurement methods can not well exclude the

influence of the above factors, so the following

measurement methods are proposed.

Power frequency high current method: the use of

injected larger current, so that it can measure the

depth deeper, but also the reverse method to

eliminate the power frequency interference, can

more accurately measure the resistance of the

ground resistance. However, it is precisely because

of the introduction of a large current that it means an

increase in cost and is difficult to achieve.

Heterogeneous frequency method: this method

uses alternating current, can well eliminate the

interference of power frequency current in the earth,

compared with the large current method, the

implementation degree of this method is greatly

improved, and the implementation cost is also

reduced, but because the current is small, the depth

of current penetration into the earth is also small.

Initially, voltammetry was used for ground

impedance measurement, and the experiment was

very primitive. In the fifties and sixties of the last

century, the former Soviet Union's E-type shaker

replaced the voltammetry, and the power supply was

a hand-cranked generator. In the 70s, the domestic

grounding impedance meter came out, and the ZC

series (such as ZC-28, ZC-29) was better than the

E-type shake meter in structure, measurement range,

index value, and accuracy. However, due to the

hand-cranked generator, the accuracy is not high. In

the 80s, the digital ground impedance meter was put

into use, and the stability was far higher than that of

the shake meter pointer type. The birth of clamp

resistance meters in the 90s of the last century broke

the traditional test method. In recent years, due to

the use of computer control technology, intelligent

ground impedance measuring instruments have been

produced, such as the Italian HT234. So far, there

have been high-current measurement methods such

as current and voltage method, interference

compensation method, frequency differential beat

method, difference frequency compensation method,

quadrupole method, as well as anti-interference

grounding shake meter, oscillator-frequency

selection voltmeter method, spectrum analysis

method, frequency conversion method and other

small current measurement methods.

In order to suppress the interference of

measurement, a method based on white noise was

proposed earlier, but it was not applied due to the

limitations of the measurement range and error. At

the end of the 90s of last century, a method based on

higher-order spectroscopy was proposed, and

research was carried out from the theoretical and

simulation aspects. In order to eliminate the error

and interference when measuring ground impedance,

in the 90s of last century, Chinese scientific and

technological personnel successively proposed the

double potential pole lead method, the additional

series resistance method, the potential pole lead

midpoint grounding method, the potential difference

method, and in recent years, the multi-pole method

was proposed. At the same time, foreign people have

also proposed the direct current method, numerical

calculation method, Berent compensation method,

and the Jopa-Laidi method in the operating state.

TEST METHODS

2.1 Working Principle

The grounding resistance test principle, as shown in

Figure 1, is the equivalent circuit for a

high-frequency pulse tester to test the grounding

resistance.

Figure 1: Tester Equivalent Circuit.

Among them, R1 is the current sampling

resistance inside the tester, and H outputs a

high-frequency square wave signal of 20KHz, which

flows back into the tester through R grounding and

R remote current loops.

ANIT 2023 - The International Seminar on Artiﬁcial Intelligence, Networking and Information Technology

254

Figure 2: Test Principle.

Through the trigger signal rising edge trigger,

delay 18uS, synchronously collect V1, V2, V3

voltage, and calculate the measured ground

resistance value as follows.as shown in Figure 2.

𝑉1 −𝑉2

𝑅1

𝑉2 −𝑉3

The delay is 18uS, synchronous acquisition, is

the flat section of the acquisition at the high level of

the square wave, which is equivalent to DC, so the

measured resistance is DC resistance. Observe the

V3 waveform, if the high level of the V3 waveform

does not have a flat section, or the flat section is too

short, it indicates that there is an inductance in the

grounding system, and the measured ground

resistance is not a pure resistance.

Through the change of the rising edge of the

waveform of V3, it is possible to know whether

there is an inductance in the grounding system, and

inductance is the most important parameter affecting

the shock response. When there is an inductance in

the grounding system, the rising edge of V3's

waveform slows down, as shown in Figures 3 and 4,

the larger the inductance, the slower the rising edge

of V3. Therefore, the response of the grounding

system to the impact is judged, because the lightning

signal, the harmonic component is many, and the

Figure 3: Grounding System Inductance 10uH.

frequency is high, and there is inductance on the

grounding system, which has the greatest impact.

Figure 4: Grounding System Inductance 1mH.

Shock response testing of grounding systems

requires a lightning current waveform with a steep

wave head and a large amplitude, as well as

extremely high voltages. Such devices are generally

bulky and bulky, making them impractical in field

testing. Through the rising edge change of the square

wave signal of the high-frequency pulse tester, to

observe whether there is inductance in the grounding

system under test, you can roughly understand the

impact response of the grounding system, without

quantitative testing.

2.2 Results and Simulations

For multi-point grounding systems, the test

grounding resistance can be unbroken by the

grounding wire. For example, transmission towers,

each tower must be grounded, and the top shielded

wire between the tower and the tower, that is, the

grounding wire, is equivalent to that each tower is

connected to the ground. When testing the grounding

resistance of a tower, existing testing techniques

require untying the grounding wire. Using a

high-frequency pulse grounding resistance tester,

you can do without untying the wires. as shown in

Figure 5. Transmission Tower Grounding Equivalent

Circuit.

Figure 5: Transmission Tower Grounding Equivalent

Circuit.

I0 is the current flowing through the ground

resistance of the tower under test, and I1 and I2 are

Ground Resistance Measurement Method Based on High-Frequency Pulses

255

the current flowing through the parallel tower.

Z=R+jX

It can be seen that the inductive reactance is

proportional to the frequency, and the capacitive

reactance is inversely proportional to the frequency;

Transmission line, taking model IJ-70 as an example,

the unit length resistance is: 4.6*10^(-4)Ω/m,

inductance is: L=1.27uH/m, capacitance is:

0.118uF/m.

The distance between the tower and the tower is

calculated in 500 meters, 50Hz power frequency

signal.

The inductive reactance is:

XL=2πfL=2*3.14*50*1.27*500*10^(-6)=0.2Ω;

The capacitive reactance is:

XC=1/2πFC=1/(2*3.14*50*0.118*500*10^(-6) )

=53.98Ω

20KHz square wave signal

The inductive reactance is:

XL=2πfL=2*3.14*20*10^3*1.27*500*10^(-6)=

79.8Ω

The capacitive reactance is:

XC=1/2πFC=1/(2*3.14*20*10^3*0.118*500*10

^(-6) )=0.13Ω

Due to the existence of the grounding wire

inductance, the impedance of the square wave signal

of the 20KHz test is large, the current flowing

through I1 and I2 is small, most of the current flows

through I0, and the grounding of the parallel pole

tower has little impact on the grounding resistance

test of the tower under test and can be ignored, so

the grounding wire can be solved when testing

multi-point grounding.

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