IDAX300 and IDAX350

Insulation diagnostic analysers

  • State-of-the-art measurement of moisture content, tan delta/power factor, and oil conductivity using DFR (Dielectric Frequency Response)
  • Dedicated test procedures for power transformers, bushings, and current transformers
  • Automated individual temperature correction (ITC) for accurate comparison with reference data/tests
  • Reliable measurements even in high interference environments
  • Fastest system on the market due to its novel and reliable combination of frequency and time domain measurement data

The IDAX300 and IDAX350 insulation diagnostic analysers are insulation diagnostic instruments based on DFR (Dielectric Frequency Response), also known as FDS (Frequency Domain Spectroscopy). DFR is a measurement technique in which capacitance and losses (dissipation factor/tan delta or power factor) is measured over multiple frequencies to assess insulation condition in test objects such as power transformers, bushings, and instrument transformers. DFR technology is an established test procedure in laboratories that Megger has adapted for field use in the IDAX range of instruments.

This IDAX series consists of:

  • IDAX300: A compact and light three-channel input (red, blue, and ground), three-terminal (generator, measure, and guard) and one ammeter instrument for use with an external computer that runs the IDAX diagnostic software.
  • IDAX300/S: Like the IDAX300, but with two ammeters for two simultaneous measurements.
  • IDAX350: Like the IDAX300/S, but housed in a rugged and waterproof case together with an on-board computer that can also be used to control other Megger instruments.

For extended applications, the IDAX interfaces seamlessly with the VAX020 high voltage amplifier for 2 kV.

In these instruments, the IDAX software incorporates a new ITC corrected frequency sweep specifically designed for assessment of instrument transformers and bushings. Thanks to a novel approach to the combination of time and frequency domain data, the IDAX provides the shortest measurement time in the marketplace for a full DFR measurement from 1 kHz to 10 μHz. Separate reference models are fitted to each data set (time or frequency) prior to transformation and combination, which eliminates the risk of artifacts introduced by approximations or transformation of incomplete data sets.

The IDAX is exceedingly easy to use with an automated test flow and presentation of results in an easy to understand 'traffic light' colours. The IDAX DFR method is now part of international guides and standards e.g., Cigre TB 254, Cigre TB 414, Cigre TB 445, Cigre TB 775, IEEE C57.152-2013, IEEE C57.161-2018.

Technical Documents
Technical guide
A novel approach to DFR measurement speed and fidelity
Technical guide
Analysis of HV bushing internal properties using DFR
Technical guide
Case Study on IDAX300 and VAX020
Technical guide
Case study: Identifying aging and installation issues in an HV bushing
Technical guide
Case study: NB DFR on HV CVTs
Technical guide
Testing bushings with IDAX
IDAX Software
63.9 MB | 24/10/22
What information does a DFR test using the IDAX provide?

DFR test curves are provided for all measurements. Depending on the asset, additional, discrete test results are reported. For example, a transformer report includes the moisture content of the transformer’s solid insulation, the conductivity of its liquid insulation, and the transformer overall insulation’s 50/60 Hz tan delta or power factor value. When testing a bushing, the percent dissipation factor or power factor value is reported at three different frequencies. 

How much time does a DFR test take?

The time required to complete a DFR test depends upon the asset being tested and, in the case of a transformer, its condition. The better the transformer’s insulation health, the longer the test requires. However, a DFR test using the IDAX will generally be less than 20 minutes. For a bushing, a DFR test takes less than 5 minutes.

What makes the IDAX so fast?

Any time that you can perform an entire measurement in only FDS (frequency domain spectroscopy) mode, you have a better, more reliable measurement. A true frequency domain method that speeds up measurement time is accomplished by applying several frequencies simultaneously, and extracting measurement data from the applied frequencies simultaneously. Because the voltage level of each frequency needs to be reduced, the measurements are a bit more sensitive to AC interference, but DC current interference will not affect the measurements. This multi-frequency approach is an advance over the older approach of combining FDS with PDC, which is more sensitive to AC interference and also quite sensitive to DC interference.

The time savings of the multi-frequency method are significant. For example, using three frequencies simultaneously reduces measurement time by about 40%.

Why is having 2 meters in a DFR test set (a feature that is unique to the Megger IDAX range of instruments) important?

The benefit of having two available metering systems in one instrument is the unique advantage of testing two capacitances simultaneously. For example, the IDAX can test two HV bushings at the same time. It can also measure both of a three-winding transformer’s interwinding insulation systems, e.g., CLH and CLT, at once.

No other instrument is capable of simultaneous measurement in the frequency domain. In some dual-channel instruments, both channels share a single ammeter. With these instruments, either half as many measurements are made (i.e., less accuracy), or no timesaving is realized as compared to performing two separate tests.

For which applications do I need a high voltage (HV) DFR instrument like the IDAX 322?

The most commonly used voltage level is 140 V RMS and this is enough for measurement of the CHL insulation of a transformer in most conditions. However, in situations where there is a high level of interference or when measuring CH, CL (of a transformer), reactors, bushings and current transformers (CTs), a 140V RMS signal does not provide a high enough measurement signal-to-noise ratio to get meaningful results. Using a higher test voltage, like the IDAX 322’s 1,400 V RMS/2,000 V peak, in these instances will improve the measurement accuracy and is recommended.

When should DFR be used instead of taking an oil sample or having a constant DGA on the transformer?

Moisture assessment of a transformer’s solid insulation by DFR is more accurate than taking an oil sample for a moisture content test. The latter often results in over estimations of water-in-paper content. However, an oil sample can be taken while the transformer is still energized. A DFR test is performed when a transformer is deenergized. An on-line moisture monitor installed in the transformer provides ‘anytime’ trending of moisture but requires an outage to install and is, thereafter, tracking only one transformer. Therefore, this approach is relatively expensive. As an asset owner, the course of ensuing action that you plan to take under various scenarios should inform the method you choose to assess moisture in your transformers. If one wants an accurate assessment of the moisture content in their transformer’s solid insulation so that they can determine whether or not to process the unit, DFR is an excellent choice.

What is the difference between DRF & SFRA?

DFR and SFRA, Sweep Frequency Response Analysis, are two very different tests that are often confused because they both entail making measurements at many different frequencies. As noted above, DFR assess how the losses in insulation behave as frequency changes. SFRA, on the other hand, assesses how effectively a voltage signal is propagated through a winding at many different frequencies. An SFRA test provides a mechanical assessment of a transformer.