Grounding transient responses measurement

In the following section, typical examples of transient response measurements on grounding electrodes are explained. 

Measurement of Transient Responses on Various Grounding Electrodes... 

Ametani, A., H. Morii, and T. Kubo. 2011. Derivation of theoretical formulas and an investigation on measured results of grounding electrode transient responses. lEE Jpn. B-131 (2) 205-214. 

In general, it is not easy to measure transient responses in a test field, because there is no power source (AC voltage source) and no voltage reference (no ground terminal). Therefore, one has to prepare all the apparatus required for the measurement. For example, one needs ... 

A measured result involves noise due to mutual coupling between a current lead wire and a voltage reference wire, and also the unknown parameters such as soil resistivity and permittivity. An NEA method [38] can simulate a transient only by the geometrical and physical parameters of a given system, and thus, the NEA method is very effective to analyze the transient responses of a grounding electrode buried in soil of which the resistivity and permittivity are unknown. 

It is well-known that a transient response in a circuit is significantly influenced by the impedance of a lead wire used for grounding, connecting circuits, and measurements as explained in Section 7.4.2. In Reference 47, it is said that the grounding of the metallic sheath of a control cable may not be effective at all during a high-frequency transient because of the grounding lead inductance. 

Both coo and h can be measured, e.g., from the system transient response or by exciting the system with steady-state harmonics of frequencies in aband including/o. For low frequencies, the mass velocity and acceleration terms in Eq. 4 are small, so mass displacement z is then proportional to the ground acceleration u. 

This section shows field test results of transient and steady-state responses on grounding electrodes with various shapes, that is, a vertical rod, a rectangular plate, a circular plate, etc. [29]. The field tests were carried out in different seasons over a period of 3 years to obtain reliable results. Then, NEA simulations were carried out using VSTL [39] that is based on an FDTD method. A comparison with the measured results is first made to confirm the accuracy of the VSTL. Then, the VSTL is applied to investigate the reduction of the grounding impedances with various electrodes. 

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