The reasons for carrying out electrical measurements on transformers can be divided into three main categories:

• Commissioning test
• Periodic state assessment
• Disturbance analysis

Commissioning tests are very often carried out directly on site by the transformer manufacturer before the transformer is switched on for the first time. However, some customers carry out additional manufacturer-independent commissioning tests for quality assurance purposes. For a better evaluation and classification of a transformer, it is very useful to carry out a fingerprint measurement before the initial commissioning. Based on this, it is possible to interpret all subsequently determined measurement results much more effectively and accurately.

Periodic condition assessment tests are also carried out. However, only selected diagnostic tests (e.g., capacity and dissipation factor measurements) are then usually carried out if no abnormalities are detected in the oil analysis.

Within the scope of a malfunction analysis, various types of abnormalities are clarified. The most common type of abnormality to be clarified is an abnormal oil analysis value. Other examples are the tripping of the Buchholz relay of a transformer or a warning signal (e.g., overtemperature) in the control technology. In these cases, the execution of electrical measurements is unavoidable.

An initial estimation of the electrical measurements required to clarify a specific error can be found in the technical note "Overview of error types on transformers and their detection using diagnostic measurements and online monitoring systems".

The electrical measurements can be divided into two groups:

Basic measurements are classical measurement methods that are used for a first solid estimation of the condition of a transformer.

The following measurements belong to the basic measurements:

• Capacitance and dissipation factor measurements on bushings
• Capacitance and dissipation factor measurements on windings
• Ratio measurement
• Short-circuit impedance measurement
• Resistance measurement
• Dynamic winding resistance measurement (tap changer test)

The advanced measurements include measurement procedures that are used for an in-depth clarification of possible anomalies. These measurements are particularly necessary if you want to reliably determine the ageing condition of the transformer. If there is a suspicion of a malfunction (fault analysis), the advanced measurements should definitely be carried out.

• Frequency response measurement
• Partial discharge measurement
• Dielectric response
• Hysteresis curve

We offer a wide range of electrical measurements and are happy to advise and support you in choosing a test programm that suits your needs. Based on our experience, we have designed ready-made service packages that are tailored to the typical occasions of a transformer test.

Independently of this, we also offer individual combinations of measurements or individual measurements.

Event 1: Periodic condition assessment

For periodic condition assessment, we recommend the regular execution of electrical measurements as a preventive measure.

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Event 2: Commissioning

During commissioning, there is an opportunity to create a fingerprint of the transformer to obtain comparative values for future measurements.

This makes it easier to classify and assess certain error patterns. In addition to that, anomalies can be detected earlier.

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Event 3: Fault analysis

In case of a malfunction or a specific fault, we recommend the Advanced IBN-2 service package.

With the help of these measurements, various sources of malfunctions can be identified and, you will receive additionally a detailed status assessment.

Information on further additional services that may be relevant for you can be found in our comprehensive product description in the download area at the bottom of this page.

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