July 6, 2015

Trends in continuous on-line condition monitoring

Abstract The article describes new trends in the field of continuous on-line condition monitoring of transformers. These trends are related to the following topics: the...

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Abstract

The article describes new trends in the field of continuous on-line condition monitoring of transformers. These trends are related to the following topics: the monitoring system itself and new requirements for, for instance, HVDC and offshore transformers; growing importance of the implementation of continuous on-line monitoring of bushings, dissolved gases and new ultra-high frequency technology for partial discharge monitoring; and finally, the new trend of using IEC 61850 [1] data model and communication protocol in digital substations.

Keywords: comprehensive monitoring, IEC 61850, asset management, DGA monitoring, partial discharge

Introduction

Today, utilities are focusing on improving or maintaining system security by preventing outages on the one hand, and on the other, on reducing operation and maintenance costs of their assets. Both objectives rely on information about asset conditions. As such, an increasing number of power transmission and power generation utilities are equipping their power transformers with continuous on-line monitoring systems. Step by step, this equipment is becoming a standard configuration of power transformers.

New trends for continuous on-line monitoring

Special applications such as HVDC transformers and new applications in offshore environments require a permanent improvement and further development of comprehensive monitoring systems for continuous on-line condition monitoring. There are also new trends involving advanced sensors, such as on-line bushing monitoring, dissolved gas analysing devices and partial discharge detectors. Furthermore, new requirements have to be fulfilled regarding information interchange among sensors, Intelligent Electronic Devices (IED) and monitoring systems by using, for instance, IEC 61850 data model and communication protocol.

Comprehensive continuous on-line monitoring systems

A power transformer consists of several components: transformer tank with active part and oil-paper insulation, conservator, cooling unit, on-load tap changer and bushings, to mention a few. These components can be fitted with various sensors which are integrated into one monitoring IED by means of analogue or digital signals and protocols, building a comprehensive condition monitoring and expert system.

Raw data, acquired from a wide range of demand-specific selectable sensors, is analysed by means of implemented models and stored in the on-line condition monitoring and expert system. This requires a highly flexible and modular design of comprehensive monitoring systems to provide tailor-made solutions adjusted to the application, rating, relevance, condition, operating mode and maintenance of the transformer protection/maintenance scheme. For example, offshore applications have specific requirements regarding mechanical durability, whereas HVDC applications require new analytic models, such as the bushing monitoring model which is impacted by the connected DC converter station. The application of field bus and process control technology offers a very high degree of flexibility concerning the system architecture, possible functionality and future expandability. This concept allows monitoring of all of the transformers at one substation or power plant with only one IED and is, moreover, an important component of higher-level asset management systems.

Data acquisition and processing alone, however accurate, are of limited value if operators cannot prioritise and exploit the masses of generated information. An expert system included in the monitoring device becomes a useful tool to accomplish this. Configurable report generators automatically create user-friendly reports providing information about the status of the transformer and its main components, upon request or to be sent periodically by email.

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