Procedure

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Overview

Insulation systems made of transformers in combination with insulating liquids have not essentially changed in the last 100 years and consist of a combination of mineral oil and cellulose-based paper and compressed cardboard. The dual temperature test method provides comparable results with respect to earlier methods, which depict the traditional life cycle curves for thermally stable and instable cellulose paper. Today, new insulation systems normally contain materials of differing thermal resistance, and the still common methods for the evaluation of thermal performance of an insulation system are less suitable for these new systems. Previously, the methods for determining the thermal resistance of electrical insulation systems composed of liquid and solid insulating materials involved one of the following two processes: either the material was aged in a "sealed-tube test" or ageing was performed on the complete device. Aging the complete device is impractical, especially for larger products, such as power transformers. Similarly, the use of sealed-tube aging is not practical when components having drastically different thermal capabilities. For example, testing of a system with a solid material with an RTI of 200 °C with a liquid having a thermal resistance of 130 °C cannot be performed efficiently. Accelerated ageing temperatures will often result in extremely long ageing times for the solid materials. Moreover, accelerated ageing temperatures will result in extreme, or even hazardous, ageing of the liquid. Transformers for high-speed trains, wind turbines and transformers with alternative liquids currently use materials that differ from mineral oil-cellulose systems. These insulation systems in particular often have hotspot temperatures above the temperatures for traditional systems. ((Figure 1)) Technical Specification IEC/TS 62332-1 describes a method for the thermal evaluation of electrical insulation systems (EIS) for electrotechnical products with combined liquid and solid components. It is applicable to electrical insulation systems (EIS) where the thermal stress is the dominant ageing factor. The thermal evaluation and qualification is carried out by a dual-temperature test procedure. ((Figure 2)) The dual-temperature test method in the model allows for the solid materials to be aged separately from the ageing temperature of the liquid within one device. The model corresponds more with the ageing of an electrical insulation system in service, inside which the solid insulation near the active parts is exposed to much higher temperatures than the large liquid volume. The model contains all primary EIS elements in a relative component ratio so that comparison with an electro-technical product is ensured. The model has a dual temperature control allowing for independent control of the temperatures for the solid and liquid components. This part of the International Standard IEC 62332 is applicable for all EIS containing solid and liquid components where the thermal stress is the dominant ageing factor, without restriction to voltage class. The responsible committee is K 183 "Bewertung und Qualifizierung von elektrischen Isolierstoffen und Isoliersystemen" (AK 183.0.6 "Verfahren zur Bewertung elektrischer Isolierungen") ("Evaluation and qualification of electrical insulating materials and systems") (AK 183.0.6 "Methods for evaluations of electrical insulations") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Responsible national committee

DKE/K 183 - Bewertung und Qualifizierung von elektrischen Isolierstoffen und Isoliersystemen