On-line monitoring and diagnosis of transformers have been investigated and discussed significantly in last decade. This study has concentrated on issues arising while on-line transformer winding deformation diagnosis is going to be applied on transformers with various kinds of techniques. From technical perspective, before replacing off-line methods by on-line methods and eventually by intelligent approaches, practical challenges must be addressed and overcome. Hence, available off-line transformer winding deformation diagnosis methods are discussed precisely. Mathematical calculation in on-line short circuit impedance measurement is investigated. On-line transformer transfer function measurement setup is presented. A profound insight to the problems pertaining on-line transformer winding deformation recognition methods, characterizes existing online methods, explains the concepts behind online measurements and striving to open the discussion doors towards challenges are discussed. In the end a 400 MVA step up transformer has been taken as a case in order to clarify the capability of Frequency Response Analysis (FRA) method in fault detection while short circuit impedance could only demonstrate some rough understanding about transformer condition.

Advanced transformer winding deformation diagnosis: moving from off-line to on-line

This paper presents the current status and future trends in the application of the frequency-response analysis (FRA) technique with the transformer in service (online) through bibliographic review and analysis. As a result, three basic stages of the online FRA test have been identified and defined: injection and excitation signal measurement; recording, filtering and processing of measured signals; and curve analysis and interpretation. This work presents an overview of the online FRA technique, useful for subsequent research in this area.

Current Status and Future Trends in Frequency-Response Analysis With a Transformer in Service

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

Systems and methods for implementing online and offline applications are described. Such systems and methods may in some cases provide the same programming interface, regardless of whether the application is online or offline. Such systems and methods may also or instead in some cases provide additional or other possible capabilities, including installation without elevated privileges, simplified data synchronization, sharing of applications and application data, access to data from other applications, and richer client functionality than may be provided by an application such as a web browser.

Online and offline applications

Transformer winding deformation is common among all sorts of transformer failures. Cumulative deformation can eventually burgeon into catastrophic faults and result in entire network outage. It is possible to detect the early signs of faults with continuous online monitoring transformer. However, frequency response analysis (FRA) is considered to be a useful and accurate tool for sufficient detection. This paper aims at proposing a novel diagnostic system for online monitoring power transformer winding deformation based on FRA. In order to realize online monitoring transformer winding, the system uses the capacitive coupling method to inject controllable nanosecond pulses, which function as the excitation signal of winding, and to obtain the response signal. This proposed method may extend frequency range for analysis and perhaps could early detect minor winding movement and looseness. Transformer experiments show great prospect in the application of the system.

Transformer winding deformation diagnostic system using online high frequency signal injection by capacitive coupling

Extending the Multi-Area Thévenin Equivalents method for parallel solutions of bulk power systems

An online signal injection approach based on a special current transformer is proposed as part of a solution for improving the test setup of transfer function diagnostics of transformers. However, the method is general and applicable to many types of substation equipment, such as circuit breakers and transmission lines. The system allows a high-power, high-frequency test signal to be injected directly on a high-voltage bus of an energized system. Due to the self-contained nature of the injector, no external power supplies or signal generators are needed and the design does not need to be ground-referenced. The system can thus be at the bus potential. In conjunction with wireless communication for control, no isolator bushings are required and the device can be constructed as a sleeve to be mounted around the busbar. This allows for economical retrofitting to existing installations. In this paper, the operational need for such an injection device is discussed, followed by the theory behind the proposed concept. Finally, a low-voltage, optically controlled, self-powered prototype is designed and demonstrated online to show the practical validity of the concept.

Online Signal Injection Through a Bus-Referenced Current Transformer

Condition monitoring of transformer windings has become a critical issue for proper asset management schemes in power systems. With the exception of on-load tap changers, transformer windings are the components most likely to fail, causing companies to incur heavy penalties. A new non-intrusive method for diagnosing the condition of transformer windings entitled "Transmission Line Diagnostics" (TLD) has been developed at UBC's research Lab and this paper details the results of validation tests done in the university's high voltage lab as well as at PowerTech's high voltage lab. The method is based on the characterization of the transformer as a long transmission line in the megahertz frequency range. The results show that the TLD method is just as sensitive as current leading methods used (FRA), and more immune to external influences.

Field Validation Tests of the TLD Box for Online Power Transformer Winding Monitoring Systems

An on-line signal injection approach based on a special current transformer is proposed as part of a solution for improving the test set-up of transfer function diagnostics of transformers However, the method is general and applicable to many types of sub-system equipment, such as breakers and transmission lines The system allows a high-power, high-frequency test signal to be injected directly on a high-voltage bus of an energised system Due to the self-contained nature of the system, no external power supplies or signal generators are needed and the design does not need to be ground-referenced The system can be at the bus potential In conjunction with wireless communication for control, no isolator bushings are required and the device can be constructed as a sleeve to be mounted around the bus-bar This allows for economical retro-fitting to existing installations In this paper, the operational need for such an injection device is discussed, followed by the theory behind the proposed concept An example injection core for a 512 kV system is designed to show the practical validity of the concept and numerical simulations are performed for validation It is shown that the injection concept is a viable, high-power, wide-band signal source for on-line equipment testing

T. De Rybel

Papers

Apparatus for Online Power Transformer Winding Monitoring Using Bushing Tap Injection

Extending the Multi-Area Thévenin Equivalents method for parallel solutions of bulk power systems

Online Signal Injection Through a Bus-Referenced Current Transformer

Field Validation Tests of the TLD Box for Online Power Transformer Winding Monitoring Systems

Self-powered on-line signal injection based on a current transformer