Increasing interest has been seen in condition monitoring (CM) techniques for electrical equipment, mainly including transformer, generator, and induction motor in power plants, because CM has the potential to reduce operating costs, enhance the reliability of operation, and improve power supply and service to customers. Literature is accumulated on developing intelligent CM systems with advanced practicability, sensitivity, reliability, and automation. A literature survey is felt necessary with an aim to reflect the state-of-the-art development in this important area. After introducing the concepts and functions of CM, this paper describes the popular monitoring methods for and research status of CM on transformers, generators, and induction motors, respectively. The paper also points out the potential benefits through the utilization of advanced signal processing and artificial intelligence techniques in developing novel CM schemes.

Condition monitoring techniques for electrical equipment-a literature survey

ower transformers are one of the most expensive elements in a power system, and their failure is a very costly event. Power transformers are mainly involved in energy transmission and distribution. Unplanned power transformer outages have considerable economic impact on the operation of electric power networks. To have reliable operation of transformers, it is necessary to identify problems at an early stage before a catastrophic failure occurs. In spite of corrective and predictive maintenance, preventive maintenance is gaining due importance in the modern era, and it must be taken into account to obtain the highest reliability of power apparatus such as power transformers. The well-known preventive maintenance techniques such as dissolved gas analysis (DGA), thermal monitoring, partial discharge measurement, capacitance and tan delta measurements, frequency response analysis, etc. are performed on transformers for a specific type of problem. DGA is a very efficient and reliable tool for the earliest detection of inception faults in transformer and other electrical equipment using insulating oil. Condition monitoring of electrical equipment, such as transformers, helps users in many ways such as planning of maintenance schedule, obtaining knowledge of the health of equipment, estimating the remaining service life of equipment, finding areas of further improvement, refining product specification, etc. Kraft paper (cellulose) immersed in mineral oil is used as the insulation system for the copper windings in large power transformers. As the system ages under load, the paper and oil can degrade, potentially leading to catastrophic failure. Partial discharge (PD) is an important tool for improving the reliability of HV insulation systems. It is a very sensitive and nondestructive method of evaluation of the health of the insulation of any HV equipment. PD always is associated with the degradation of insulation systems in HV equipment. Therefore, PDs need to be detected, measured, located, and reduced to a safe value so that the quality of the insulation system is not affected.

Condition Monitoring of Power Transformers - Bibliography Survey

Online transformer condition monitoring techniques based on transfer function methods, such as transmission-line diagnostics and swept frequency-response analysis, require the injection of a known test signal into the transformer On larger power transformers, a practical method is to use the available bushing tap connection In this paper, we will discuss a custom high-power signal generator that injects high-frequency signals on the bushing tap of the transformer under investigation, as well as a circuit to replace the bushing tap short and allow online operation of the system Finally, the system is demonstrated on a 650 kV transformer

Apparatus for Online Power Transformer Winding Monitoring Using Bushing Tap Injection

Insulation degradation is one of the prime reasons for failures in power transformers. Partial discharge (PD) is considered as one of the primary causes of initiation of insulation degradation. Thus, monitoring of PD in a power transformer at a preliminary stage is the most important task to prevent any catastrophic failure. This paper presents a brief introduction of PD phenomena along with the causes and effects. Various topics of contemporary research related to PD, such as modelling, detection, measurement, and classification, are grouped under different headings with exhaustive up-to-date bibliography. The paper outlines distinctive sensors and technologies based on acoustic, ultra-high-frequency, electric, and hybrid methods. The techniques are compared, and their advantages and limitations are pointed out. The techniques of denoising of PD signal based on signal processing, artificial intelligence, and statistical analysis are summarised. The challenges and trends in future PD research are ...

Detection, Measurement, and Classification of Partial Discharge in a Power Transformer: Methods, Trends, and Future Research

The subject matter of this paper refers to the application of optical spectral diagnostics to the detection of electromagnetic waves generated by partial discharges. The research work refers to creeping discharges at bakelite/oil interface. The analysis of optical spectrum time changes was performed. The influence of voltage on the changes of the creeping discharge optical spectrum was determined. The spectrum distributions were determined in the area of creeping discharges. The results obtained at this stage of the research can constitute a source material for people dealing with issues connected with electrical material science and diagnostics of insulation systems

Optical spectra of surface discharges in oil

On-line partial discharge calibration and monitoring for power transformers

For a hybrid ac/dc power system incorporating voltage source converter-based multi-terminal direct current (VSC-MTDC) grids, it is essential to solve the power flow problems efficiently for reliable operation. This paper presents an efficient ac/dc power flow algorithm considering the complementary constraints of VSC's reactive power limit and ac node voltage. It can be distinguished from the existing works in terms of both modeling and algorithm aspects. First, the VSC model is formulated, in which the interactions between the reactive power limit and the ac node voltage of VSC are viewed as complementary relations. The complementary relations are expressed using a smooth Fischer-Burmeister function. Then, power flow models of the ac grid and dc grid with a constant Jacobian matrix are formulated based on the VSC model, respectively. To efficiently solve the power flow of an ac/dc grid, the structure characteristic of the Jacobian matrix of ac/dc power flow computation is analyzed. It shows that the Jacobian matrix can be approximated as a block-upper triangular one. Based on this characteristic, a decoupled ac/dc power flow computation algorithm is provided. Test results on two hybrid ac/dc systems under different scenarios validate the correctness, convergence, and efficiency of the proposed power flow algorithm.

Efficient Power Flow Algorithm for AC/MTDC Considering Complementary Constraints of VSC's Reactive Power and AC Node Voltage

This letter proposes a method to determine the optimal shift frequency (OSF) for shifted frequency (SF)-based simulation. The SF-based simulation algorithm is briefly introduced, and the error of SF-based simulation is quantitatively analyzed. The OSF that minimizes the error is deduced, which can improve the simulation accuracy. Furthermore, the influence of time-step size on the OSF is investigated. Numerical test results demonstrate the effectiveness of the method in determining the OSF for SF-based simulation.

Determination of Optimal Shift Frequency for Shifted Frequency-Based Simulation

Three-stage implicit integration for large time-step size electromagnetic transient simulation with shifted frequency-based modeling

For the future power grid, the electromagnetic transient (EMT) simulation seems to be the most promising tool for design, operation and analysis. However, it is difficult to establish its EMT simulation model in the EMT simulation software for a large-scale power system. This paper proposes a method to generate a large-scale EMT simulation model on the EMT software CloudPSS using the existing PSASP projects. The correspondence relationship between the transient stability (TS) model on PSASP and EMT model on CloudPSS is analyzed. Besides, the workflow of the project conversion process from PSASP to CloudPSS is presented. Test results on several large-scale cases validate the correctness and efficiency of the proposed project conversion method.

Shilin Gao

Papers

On-line partial discharge calibration and monitoring for power transformers

Efficient Power Flow Algorithm for AC/MTDC Considering Complementary Constraints of VSC's Reactive Power and AC Node Voltage

Determination of Optimal Shift Frequency for Shifted Frequency-Based Simulation

Three-stage implicit integration for large time-step size electromagnetic transient simulation with shifted frequency-based modeling

Generating Large-Scale Electromagnetic Transient Simulation Model on CloudPSS Using PSASP Projects