Transformer plays a vital role in grids and its internal hot-spot temperature is a crucial monitoring parameter. In this paper, three groups of temperature rise tests with the load rate of 70%, 100%, and 125% were carried out on a 110 kV transformer with built-in distributed sensing fiber. Based on the distributed temperature sensing technology, the temperature distribution of winding was acquired. Accuracy of IEC, Susa, and Swift thermal models was compared. To eliminate the non-negligible error in cooling process, a modified-Susa model based on driving factor and steady-state temperature rise was proposed. Using this, the top oil temperature prediction error during operation and cooling is reduced. In addition, the real-time tracking of hot spots and analysis of overall temperature gradient of windings was implemented. The accuracy of different hot spot calculation models was also compared. Results show that the prediction accuracy of each model is satisfactory during the operation, but the error during the cooling process cannot be ignored. The refined temperature distribution of the winding was also obtained by the high-resolution Brillouin optical time-domain analysis sensing method. Periodic temperature fluctuations and local hot spots inside windings are perceived, which is confirmed to be closely related to winding geometry.

The temperature distribution and deformation of the transformer windings cannot be measured in a distributed manner by the traditional method and failure location cannot be performed. To solve these problems, we present a transformer winding temperature and strain based on a distributed optical fibre sensing detection method. The design of the optical fibre winding composite model is developed and simulated winding temperature rise test and local deformation test distinguish between measuring the winding temperature and the strain curve. The test results show that the distributed optical fibre can transmit wire strain efficiently. Optical fibres, in the process of winding, have a certain pre-stress. Using the Brillouin–Raman joint measuring method, one can effectively extract the optical fibre temperature and strain information and measure the length of the winding direction of the temperature and strain distribution curve to a temperature measurement precision of ±2 °C and strain detection accuracy of ±50 με. The system can carry out local hot spot and deformation localisation, providing new ideas for the transformer winding state monitoring technology.

In order to realize distributed measurement of transformer winding temperature and deformation, a transformer winding modification scheme with a built-in distributed optical fiber was designed. By laying a single-mode fiber and a multi-mode fiber on the transformer winding, the Brillouin optical time domain reflection technique (BOTDR) and the Raman optical time domain reflection technique (ROTDR) are used to measure the strain and temperature of the winding to complete the more accurate winding deformation detection. The accuracy of strain and temperature sensing of this scheme was verified by simulation. Then, according to the scheme, a winding model was actually wound, and the deformation and temperature rise tests were carried out. The test results show that this scheme can not only realize the deformation detection and positioning of the winding, but can also realize the measurement of the winding temperature; the temperature measurement accuracy reached ±0.5 °C, the strain measurement accuracy was 200 με, and spatial resolution was up to 5 m. In this experiment, the deformation location with the precision of 2 turns was realized on the experimental winding.

In view of the current situation that the load difference is not considered in the existing research on public standby transformer, the reliability Markov model and public standby planning model of distribution transformer unit based on public standby mode are proposed. When the transformer fails, the standby transformer is preferred to replace the faulty transformer. The power failure time of the user is shortened from the transformer maintenance time to the standby installation and operation time. The state transition rate is the installation and operation rate of the standby transformer, and the replaced faulty transformer is converted to the standby transformer in the unavailable state. This paper applies the scheme decision analysis method to the field of engineering control, and applies the combination of the compound matter element analysis and the subjective and objective weight to the quantitative calculation of correlation entropy. This method solves the current situation that transformer faults are difficult to measure and calculate quantitatively, and it can accurately predict the healthy development trend of transformers, which has a good guiding value for the use and maintenance of transformers. At the same time, the public standby measures of distribution transformer can better solve the problem of long transformer fault repair time with a small amount of capital investment, effectively shorten the recovery time of fault outage and reduce the impact of transformer fault. The standby measures of distribution transformer have an obvious impact on the reliability of distribution system.

The insulation condition of oil-pressboard insulating bushings is commonly evaluated by measuring the dielectric loss factor and capacitance at power frequency. However, systematic investigations into the influence of aging and moisture defects on frequency-domain dielectric spectroscopy (FDS) characteristics are still insufficient. To address this issue, a 10 kV high-voltage FDS measurement system was independently developed. The system has an output voltage range of 0~10 kV and a test frequency band of 1 mHz~10 Hz, with excellent measurement stability and high test accuracy. The standard deviation of dielectric loss of the system is on the order of 10⁻⁴ and the relative error is less than 5%. It also features reliable weak current detection capability and thermal stability. Based on this system, the dielectric spectral characteristics of oil-pressboard insulation models with different moisture contents and aging levels were investigated under various temperatures and applied voltages. The results indicate that the dielectric spectrum shifts toward higher frequencies with increasing temperature. Moreover, the low-frequency dielectric loss of degraded insulation increases linearly with the applied voltage, and the rate of increase shows a positive correlation with both moisture content and aging duration. As insulation degradation becomes more severe, the voltage-dependent characteristic frequency moves toward higher frequencies. This frequency refers to the characteristic frequency where the dielectric loss of insulation presents an obvious linear variation with the change of applied voltage. Unaged and dry bushings exhibit only weak voltage dependence at 0.01 Hz, whereas bushings aged for 28 days with a moisture content of 4.121% demonstrate pronounced voltage dependence at 10 Hz. These results provide a valuable technical basis for diagnosing coupled aging and moisture defects in oil-pressboard insulated bushings.