We have previously proposed a live simulation model (LSM) that simulates the heat-balance of high-voltage overhead transmission lines during high-temperature operation without requiring meteorological parameters. This can be used to calculate the dynamic line rating (DLR) in real time, although the accuracy of this approach is significantly influenced by measurement errors in the real-time monitoring system. This paper describes how the nonlinear parameter estimation method can be combined with the tabu search algorithm to determine the optimal solutions for systematic deviation corrections in a practical application of LSM. The effects of this optimal solution on LSM are verified using data from a 110-kV transmission line. The accuracy of the deviation corrections is verified through comparisons with field measurements. After correcting the measurement errors, the average error in the real-time DLR calculated by LSM is expected to be less than 1% and the root mean-squared error is expected to be less than 10%.

Frequency response analysis is widely used as a method for the offline diagnosis of winding deformations in power transformers. To apply it to a working transformer, people need to determine how to inject the excitation signal and measure the response signal for windings that bear a rated voltage and current. In this study, a method to obtain the frequency response curve online is proposed. It uses the principle of magnetic field coupling to inject a frequency sweep signal into the windings through a Rogowski coil. Another Rogowski coil sensor placed at the root of a high‐voltage bushing is used to measure the response current signal. Experiments on a 72.5 kV bushing show that metal accessories of the bushing have no influence on the injection or the measurement. The feasibility of this method was verified by experiments on charged 110/35/10 kV transformers at a factory and a working 35 kV transformer in a power station. The results show that it is safe to install the Rogowski coil at the root of the high‐voltage bushing. The excitation signal can be injected into live windings and the response signal is measurable. Strong electromagnetic power frequency noise can be reduced and the frequency response curve can be measured online.

Online frequency response analysis (FRA) is expected to be capable of diagnosing winding deformation defects in operating power transformers. However, there is a lack of available experimental field research on online detection methods of frequency response curves. In this paper, we establish a magnetic coupled online frequency response curve measurement system to execute FRA for operating transformers and apply this system to two working power transformers. The principle, technical process, key requirements, structure, performance, and results of field experiments on the online system are presented. The feasibility of online FRA is analyzed through comparisons with frequency response curves from offline measurements. Our online system does not affect transformer safety and can be installed on some transformers without powering them off. The interference generated by a 500 A load current can be compressed by a factor of 100 to measure an FRA current with an amplitude of tens of μV to several mV. The measured online frequency response curve has approximately the same resonance frequency as the offline measured curve and can thus be used to diagnose winding deformation defects.

It causes a lot of accidents and influences power system security in our country by the transmission line icing, the research and prevention of line icing are in process all the time. At present, the majority of electrical Company adopt electrical signal sensor to measure temperature, but some localization lies in them more or less; the scan time lasts quite a long time in traditional fiber temperature measuring system. However, fiber Bragg grating is an insulator and is small, and it has the advantages of low-price, simple structure, safety, no electromagnetic interference, so are particularly suit for measuring temperature, strain and stress. This paper uses fiber Bragg grating as the sensor of on-line monitoring system of electrical equipment. A novel fiber Bragg grating sensor interrogation system based on a tunable fiber Fabry-Perot(FFP) filter was demonstrated. A reference fiber Bragg grating (FBG) was used as a wavelength reference element. By measuring the wavelength difference between reference FBG and sensor FBG, the drift of tunable FFP filter's cavity length was compensated. A quadratic fit function was made with software based on experiment results. This function showed a good fit to the relationship between the displacement of PZT and control voltage. It was used to calculate the wavelength of the sensing FBG Experiment results show that the measured error caused by the drift of FFP filter's cavity length and PZT's nonlinearity is greatly reduced and a higher accuracy is obtained.

Frequency response analysis is widely used for the offline diagnosis of winding deformations in power transformers. To apply this approach to a working transformer, the magnitude of the response current needs to be measured by using Rogowski coil sensors across a load current. The saturation of the power frequency magnetic field in these current sensors must be prevented to ensure accurate measurement of such small response currents. Here, a method is presented to suppress the power frequency magnetic field using a sensing system including a special connection of three‐phase current sensors based on the sum of the three‐phase power frequency load currents of the transformer being close to zero. Each sensor comprises two secondary coils: a measuring coil and an anti‐saturation coil. The anti‐saturation coils are connected in parallel with one another through small inductors to eliminate the power frequency magnetic field in the cores of the sensors. Theoretical analysis is used to derive a solution for this system. The experimental results verify the proposed method as enabling the sensors to function with a transformer carrying a load current of 2333 A.

A method of measurement the current and the path of a lighting flashover is put forward. When a lighting break an insulator string on high voltage power transmission lines, an impulse current will flow through the string, and an impulse voltage will appear at the tower end of the string. A voltage sensor can measure the voltage pulse. An inductance coil current sensor can measure the current pulse. Contrasting the polar of the sensor signals, we can distinguish the shielding failure and back flashover, and obtain the polarity of the lighting. To establish this method, the authors designed a voltage sensor, a current sensor and an optical fiber transmission system. An impulse current generator was used to generate lighting current about 10 kA, which flow through a 2.5Omega resistance to simulate the lighting flashover. The voltage sensor and the current sensor were place above the resistance to measure the signals. The outputs of the sensors were converted to light signal and transmitted by optical fiber to measurement system. The experiment result shown this method has excellent feasibility.