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The measurements which are related to the high-voltage substation grounding system are inevitably affected by electromagnetic interference caused by power frequency and its harmonics. In order to avoid the problem due to interferers, traditional measurements are based on heavy test current injection. In most cases this approach is impractical. In this paper, we evaluate experimentally an effective method for eliminating the effect of interference at power frequency. This approach based on test signal at three frequencies, is slightly different from the power frequency. For that matter, there are two problems: 1. How to choose adequate set of test frequencies, and 2. How to determine optimal intensity of the test current. In this paper, we solve the mentioned problems based on the results of extensive field test measurements at substations 110/X kV, 220/X kV and 400/X kV. We show that the set of suitable test frequencies are: 40 Hz, 60 Hz and 75 Hz. Also shown is a method for finding the optimal intensity of the test current.

The measurement of grounding system impedance of an energized substation is usually required. Consequently, the power system frequency interference and harmonic frequencies may adversely affect the measurement. In order to improve the signal-to-interference ratio, we can increase the intensity of the test current or the test current frequency should be slightly differ-ent from the power system frequency. In the latter case, so called Frequency Shift Method (FSM), the intensity of test current may be relatively low. In this paper, we empirically examine the suffi-cient intensity of the test current. The corresponding field test in the 220/110/10 kV substation is described

The measurement of grounding system impedance may be affected by power system frequency interference and its harmonics. The Shifted Frequency Method (SFM) is potentially insensitive to the electromagnetic interference. In this paper, we evaluate this method in the hydroelectric power plant for two different load conditions of the connected overhead power lines. Presented field tests results further validate and justify the SFM method.

A new practical approach to the shifted frequency method for grounding impedance measurements of high-voltage substation is presented in this paper. The results obtained by the proposed method are compared with the corresponding results obtained by the transition method as well as by the heavy-current injection method. It is shown that the proposed approach gives an accurate assessment of the grounding impedance in the presence of power frequency interference. This method is easy to implement.

The grounding system has an important role to maintain safe and reliable operation of highvoltage (HV) power facility (usually substation). The main task of a grounding system is to discharge maximum ground fault current expected into the soil, without exceeding safety limits for touch and step voltages within the substation and the surrounding area. It is desirable that the substation grounding provides a near zero resistance to remote earth. The prevailing practice is to install a grounding grid of horizontal ground electrodes (buried bare copper conductors) supplemented by a number of vertical ground rods connected to the grid, and by a number of equipment grounding mats and interconnecting cables. The grounding grid provides a common ground for the electrical equipment and for all metallic structures at the substation. It also limits the surface potential gradient. Grounding is traditionally modeled as a pure resistance. This is a good approximation at low frequencies, but as the frequency gets higher, inductance starts to play an important role. National and international standards give detailed guidelines for grounding system design, as well as for testing, under power frequency conditions, but only limited recommendations for high frequency and transient conditions are available. The main performance metrics of the grounding system are: grounding grid integrity, grounding system impedance, and touch and step voltage. The performance metrics should be periodically tested. The goal is to perform the test when the substation is in-service (to avoid interruption of service and costly downtime). Due to conductive interference in the grounding system (usually several amperes, up to about 15 A), caused by power frequency, its harmonics and background noise, the active HV substation is an extremely challenging environment for the measurement on grounding system. This is further compounded by the impact of very low impedance of the grounding system (typically less than 0.5 Ω). Essential data to calculate safety risks in advance is often not available. Measurements are therefore an essential supplement to the theory. Unlike the theoretical approaches, empirical approaches are not widely available in the literature due to the arduous work involved, the difficulty to obtain permissions, and safety restrictions. There is a continual interest in scientific community and standardization bodies to improve the measurement of performance metrics of the grounding system. The drawbacks of actual measurement methods are related to less or more subjectivity and requirements for high level of test current (up to 100 A AC and up to 300 A DC). In this thesis, in order to avoid mentioning drawbacks, we elaborated and experimentally verified the efficient methods. The overall contribution of this thesis is the substantial enhancement of the grounding system measurement by eliminating the current restrictions found in the IEEE standards 80 and 81, respectively. The original works, that constitute the core of this thesis, have been published in referring publications. This thesis is divided into three parts. Part I includes Chapters 2 and 3. Part II includes Chapters 4 to 7. Part III contains Chapter 8. Part I gives an extensive review of published literature related to the analytical and simulation investigations of earth electrode systems. Part I also analyzes the existing methods for measurement performance metrics of the grounding system. Critical review of the constraints inherent in existing methods was given. Part II includes original contributions of the thesis: new method for measurement of grounding grid integrity (Ch.4); an effective method (so called FSM) for eliminating the effect of conductive interference at power frequency (Ch. 5); new method for grounding system impedance measurement (so called FOP-FSM) (Ch.6); new method for measurement of touch and step voltage (so called FEM-FSM) (Ch.7). Our experiment-driven verification approach of the proposed measurement methods is based on totally 49 power facilities (voltage range: 110 kV, 220 kV and 400 kV) in Serbia. Part III gives an extensive review of thesis results. Part III also proposes and elaborates directions for further automation of the proposed measurement methods.