Study On 1000kV Series Voltage Ratio Standards At Power Frequency

Power Frequency Voltage Ratio Standard is the key equipment to carry out frequency voltage measurement traceability and delivery .Focusing series voltage transformer as the main object of study, a set of 1000kV standard voltage transformer is developed and a deep research on all aspects of its performance and application in practice is given in this paper.This paper firstly introduces the development situation and characteristics of power frequency ratio standard at home and abroad, gives a comprehensive summary of all types of standard apparatus and corresponding methods of traceability and pointes out two major difficulties faced on the establishment of a higher voltage level of power frequency voltage ratio standard with the further enhancement of voltage level: the first one is to develop higher voltage grade and higher accuracy level of standard equipment; the second one is to develop the accuracy and reliability of the standard apparatus for traceability. Relative researches on these two aspects are carried out in this paper.Based on the T-equivalent model of transformer and voltage in series summation principle, this paper analyzes the measurement process and its influencing factors of the transformer voltage coefficient. And then series-type voltage transformer (STV) principle is proposed and mathematical model is established. The error characteristics of STV are given through the theoretical analysis and calculation on equivalent circuit. The results show: By series capacitor connection on one side of HVIT could compensate a large leakage reactance resulting from great winding insulating distance between high and low voltage of HVIT and reduce the error of HVIT so that the overall error of STV performance is optimized; by parallel connection of a high voltage capacitor with a suitable capacity between the grading rings of the upper standard TV, the resistance of upper and lower of STV can be balanced, sharing half voltage respectively, which give full play to the difficulty of reducing voltage transformer insulation design for STV.Based on the principle of series transformers, a feasibility analysis is conducted on the development of 1000kV series standard voltage transformer (SSTV). On this basis, design plans are proposed and the corresponding design parameters are given respectively for the various key issues of the development of 1000kV SSTV, such as winding design, error compensation, insulation structure design, the body design of transformers. The results indicate: with the winding design of the 500kV standard TV , the electric field strength of all parts are to meet the engineering requirements and the error of 0.01 grade is to meet the accuracy requirements; through the design of the first and second voltage winding shielding electrode structure of HVIT, its space electric field distribution tends to be homogenization, the error of 0.02 grade to meet the accuracy requirement adopting series capacitor compensation; pertinent designs on shell strength, sealing properties, explosion-proof performance of the prototype are to meet the relevant design standards.Using finite element analysis software ANSYS, the following conclusions are drawn after the electric field simulation and analysis on the non-uniformity electric field structure of the prototype design 1000kV SSTV: the main factors of the distribution of the electric field on casing pipe are the shape of the high-voltage conductor connecting block and the inner diameter and height of the ground connection shield, so electric field distribution of the internal part of the casing pipe and disc insulator could be improved by changing the shape of high-voltage conductor connecting blocks; electric field distributions of the grading ring on the top of the ground connection shield and of the external of the casing pipe could be improved by adjusting the height of the ground connection shield; electric field distribution of the internal part of the casing pipe and disc insulator could be improved by changing the inner diameter of the ground connection shield. As for HVIT, high-low voltage shielding electrode and arc corner radius in the end of the core shielding are the main affecting factors of the internal electric field of HVIT on the condition that the inner dimensions of the calculation model of the shield are determined.Lastly, a traceability method of semi-insulating transformer voltage summation is proposed based on the principle of voltage summation in accordance with the principle and structural characteristics of series voltage transformer. After the experiment of measurement traceability method and its reliability of 1000kV series standard voltage transformer, the following conclusions are drawn: error performance impact of proximity effect on series-type voltage transformer is far less than that of the cascade-type voltage transformer, generally no more than2×10^-5; by adopting the measurement of traceability methods with semi-insulating transformer voltage summation and voltage coefficient on prototype of 1000kV SSTV respectively, the consistency is fairly good and the aviation is less than 3×10^-5.Test results show that the insulation level and error performance of the prototype are to meet the design requirements; In addition, after comparison with the two methods, semi-insulating transformer voltage summation method has obvious advantages for its less equipment used, relatively simpler measuring circuit, easier data to handle and smaller uncertainty of the measurement.