Fu Chenzhao

Impedance measurement for grounding grids of ultra-high-voltage Huxi substation

In this paper, taking the Shanghai areas first impedance measurement for grounding grids of 1000kV ultra-high-voltage Huxi substation as an example, it introduces the basic situation of substation grounding grids, the test items and the method used to measure the impedance of the grounding grids. The layout of current and voltage lines and wiring in the test of substation grounding impedance are described, the impedance data are analyzed and checked which were measured with non-50Hz-frequency current method. This accumulated the engineering experience of field test and measurement technology for grounding grids of 1000kV ultra-high-voltage substation.

Study on impulse characteristics of 35kv substation grounding grids

In order to analyze the impulse characteristics of substation grounding grids correctly, a grounding grids model is designed and custom-made based on a 35kV substation grounding grids. The impulse characteristics of grounding grids are studied through simulating corrosion, breakage and sealing-off. Meanwhile, the impact of different impulse points and lightning impulse are also analyzed. The result shows that, with the same current injection point, the impulse grounding resistance rises with the front time of lightning impulse declines. With the same lightning current, when the lightning impulse is injected through the corner of grounding grids, the impulse grounding resistance is bigger than that when the lightning impulse is injected through the center of grounding grids. If the grounding grids has fault, the impulse grounding resistance will increase, but the growing rate has close relation with fault type and lightning current. The study may provide a basis for grounding grids design and evaluation.

Research on Field Test of Impulse Grounding Impedance for Small Substation

In this paper, application of a portable instrument to obtain impulse grounding impedance (IGI) characteristics for grounding grid of small substation is introduced. The test currents of 8/20 µs, 10/350 µs and 30/80 µs were chosen as the injection signal sources to the grounding grid respectively with simultaneous measurement of the response transient voltage waveshapes in time domain. The portable instrument and test object for experimental tests are simply described. Field tests were carried out to the grounding grid in a 35 kV substation for 3 consecutive times with different impulse currents, while the corresponding IGI calculated with processing of the impulse current and voltage waveshapes are also given. All of that provides a reference for basic research of lightning protection for the small substation and a better understanding of transient characteristics of grounding grid under the lightning stroke.

Parameters measurement for grounding grids of a 1000kV ultra-high-voltage substation

In this paper, taking parameters measurement for grounding grids of the 1000kV ultra-high-voltage (UHV) Suzhou substation as an example, it introduces the basic situation about the designed grounding grids, the methods used to measure the power frequency (50 Hz) ground resistance (PFGR) and impulse grounding impedance (IGI), respectively. The PFGR data are analyzed and checked which were measured using the non-50Hz-frequency current method with two different instruments. While the measurement of IGI was realized using a small and portable instrument, which can output the 8/20 µs or 10/350 µs lightning currents with simultaneously recording the corresponding voltage waveforms from the grounding grids. All of work accumulated the engineering experience of the on-site test and parameters measurement technology for the grounding grids of 1000kV UHV substations.

Research on impulse impedance measurement for grounding device of transmission tower

For obtaining impulse impedance characteristics for grounding device of UHV 1000 kV transmission tower, a portable instrument is used as the incident wave source to the grounding device, which stably outputs a 8/20 μs standard lightning current with simultaneous measurement of the response transient voltage. Tests and date recording were done to some standard resistances with nominal values, and a typical tower of UHV 1000 kV An-Tong line in Shanghai Power Grid. Transient grounding resistance in time and frequency domain (TGRT and TGRF) are analyzed and compared abased on the measured current and voltage waveforms.

Partial discharge acoustic location measurement based on image fusion technology

Partial discharge (PD) is one of the major causes of insulation degradation/ageing in power equipment, it is significant to detect PD accurately for guarantee equipments safety and reliable operation. To achieve an accurate PD monitoring and PD location, a new type of PD on-line monitoring system was presented in this paper. The PD phenomena taking place of equipments surface and/or interface was detected by 32*32 ultrasonic array sensors, which is capable of collecting and processing multi-sensor synchronized ultrasonic signal came from PD taking place. Based on Acoustic Doppler theory, the measured sound intensity is decided by received the number of entire waves in unit time, which produced by PD. According to the measured sound intensity sequence, a mapping relationship in plane-coordinate between PD event and its location system could be established. Furthermore, 2D image of object is taken by HD camera in this system, the PD location visualization could be achieved by digital image fusion. The system can intuitively show the discharge location in the image and its status in the development and changes, timely find power equipments failure and has extensive application value.

The improved thermal-circuit model for hot-spot temperature calculation of oil-immersed power transformers

Based on improvement of Swifts black-box thermal-circuit model, this paper establishes a dynamic numerical model suitable for different capacity transformers. According to effect factors of the precision of thermal-circuit model, such as winding losses, oil viscosity changes, heat dissipation conditions, et al, this paper proposed ways to modify the model. The model is proved to be precise by comparing results with factory temperature rise test data.

Application of Excitation Function to the Prediction of RI Level Caused by Corona Discharge

Radio interference (RI), as an aftereffect of corona discharge, is an important research topic in the field of electromagnetic compatibility, where excitation function is applied broadly to the prediction of RI level. This paper presents the theory of excitation function method used in the RI level prediction. Then, some practical problems related to this method are discussed. The propagation procedure of corona current is solved by the phase-modal transformation, and the impedance matrix of multi transmission lines is calculated by a double logarithmic approximate model of Carsons Ground-Return impedance. At the same time, in order to calculate the RI level when total line corona is assumed, an analytical formula is deduced for integral operation. Based on the above solutions, an algorithm is presented and applied to the prediction of RI level of a practical overhead transmission line. Comparison of prediction and measurement results indicates that the algorithm proposed in this paper is effective and feasible.