IDAX series of insulation diagnostic analysers
Fastest system in marketplace
By using a multi-frequency test signal at low frequencies, the cumulative measuring time is reduced, and eliminates the need for combining frequency and time domain measurements to quicken the test
Reliable measurements in high interference environments
By measuring entirely in the frequency domain, EMI is minimised
Automated individual temperature correction (ITC)
For accurate comparison with reference data/tests
Dedicated test procedures
For power transformers, bushings, and current transformers
About the product
The IDAX is an insulation diagnostic analyser based on DFR (Dielectric Frequency Response), also known as FDS (Frequency Domain Spectroscopy). DFR technology is an established test procedure in laboratories that, in an innovative effort by Megger, has been adapted for field use in the IDAX range of instruments.
DFR is the measurement of capacitance and losses (tan delta or power factor) over multiple frequencies. The measured DFR curve is dependent on insulation geometry, moisture, oil conductivity, and temperature. By advanced curve fitting to the reference material model, the IDAX calculates moisture content in solid insulation, the oil’s conductivity at 25 °C reference temperature, and tan delta/power factor at 20 °C reference temperature.
In these calculations, ITC (Individual Temperature Correction), another important Megger innovation, is used to translate test data from the test object temperature to the reference temperatures. The IDAX software incorporates an ITC-corrected frequency sweep designed explicitly to assess 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 artefacts 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 that uses an easy-to-understand ‘traffic light’ system.
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.
The IDAX is available in multiple versions:
- 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 – As IDAX 300 but with two ammeters for two simultaneous measurements.
- IDAX350 – As IDAX 300/S but housed in a rugged and waterproof case with an on-board computer that can also be used to control other Megger instruments.
- IDAX322 - AS IDAX 300/S but with built-in 2 kV amplifier for higher signal-to-noise ratio in low capacitive test objects. Ideal for field testing bushings.
For extended applications, the IDAX interfaces seamlessly with VAX high voltage amplifiers; VAX020 for 2 kV and VAX220/230 for 20/30 kV (on request).
Technical specifications
- Test type
- Capacitance and dissipation/power factor
Further reading and webinars
Troubleshooting
There are a few possible reasons and countermeasures for this:
1. The generator output is earthed/grounded.
You should:
- Check the measurement setup and disconnect the ground.
- Change the measurement configuration if you cannot disconnect the terminal of the test object from ground.
2. The generator output is connected to a measuring electrode (input or ground).
You should:
- Check the measurement setup.
- Disconnect measuring or guard electrodes from the generator output.
- Don't connect the generator output to either measuring or guard electrodes.
3. High stray capacitances to ground are present or the test object has a high capacitance.
You should:
- Lower the highest frequency used in measurement.
- Lower the test voltage.
4. If you try to use an old version of the IDAX software (version 3.2 or earlier), but the firmware in the IDAX is for the IDAX software 4.0 or newer, the IDAX software does not understand the incapability and it usually results in error 347.
Please check the IDAX software and if you are using version 3.2 or earlier, upgrade to 4.0 or newer (this new software will automatically upgrade the firmware if necessary).
Values of capacitance measured for different configurations are in disagreement. This includes the UST, GST-Guard, and GST-Ground. When performing a UST measurement, the measuring electrode is connected together with the ground electrode, or is connected to ground:
You should:
- Check the measurement setup and make sure that the measuring electrode is connected to a non-grounded terminal of the test object and that the ground electrode is connected to ground.
- Check cable connectors for damage.
- Measure the resistance between the chassis and guard electrode. It should be 1.2 to 1.4 ohms. If resistance is lower than this, there is a short-circuit in the instrument.
If the measured capacitance is below the limit specified in C-file by MinSpecimenC, then possible reasons and countermeasures include:
- The measured capacitance is higher than 10 pF. However, the specimen size is very small which results in a low value of capacitance:
- Change the limit set by MinSpecimenC to an approximately 10 % lower value than the measured capacitance.
- Select another measurement configuration, if possible.
- If the measured capacitance is lower than 10 pF, then most likely, there is no contact with the test specimen:
- Check connections with the specimen for loose contacts.
- Check the measurement cables for damage.
For more information of actual measured capacitance, please see Message Window.
A measured capacitance above the limit specified in the test plan by MaxSpecimenC is usually due to the large size of a test object, resulting in high values of capacitance:
- Change the limit set by MaxSpecimenC to an approximately 10 % higher value than the measured capacitance.
- Select another measurement configuration, if possible.
- A decrease in test voltage allows for measuring at higher frequencies
If the measured DC current exceeds the limits set in the test plan by MaxDCCurrent, then the most common reason is too low a resistance between the measurement electrode and guard. For example, measuring a UST configuration between high and low voltage windings of a two-winding transformer, the low voltage winding has too low an impedance to ground (inductive voltage transformer connected, internal damage of transformer, neutral connected to ground via a Peterson coil). For a GST measurement, the same applies to guard electrodes, i.e., a guard electrode with too low a resistance to ground may introduce DC currents.
Make sure that the floating electrode has a high resistance to ground. If that’s not possible, use another setup (e.g., measure to ground without use of guard).
It is possible to increase the limit level for DC current in the Measurement Template, but only when the difference is very small and all other possibilities are excluded.
If the measured interference or hum current exceeds the limits set in the test plan by MaxHumCurrent, then the level of interference is very high. Try to reduce the interference level by:
- Disconnecting the still connected busbars that pick up interference.
- Selecting another setup, e.g., a CHG+CHL is much less influenced by interference compared to CHG.
- As a last option, it is possible to increase the limit for hum current in the Measurement Template.
Interpreting test results
Megger’s IDAX software provides an analysis of moisture content, oil conductivity, and temperature corrected, line frequency PF/DF test results. It is important that you supply the insulation temperature of the asset under test for an accurate assessment.
For a new transformer, the moisture content in the solid insulation is commonly targeted to be less than 0.5 % by weight. As the transformer gets older, the moisture content will typically increase around 0.05 % per year for a sealed conservator transformer and by approximately 0.2 % per year for free-breathing transformers. In an old and/or severely deteriorated transformer, the moisture content can be greater than 4 %. The graph below provides moisture interpretation criteria by Megger and different standards bodies. In agreement between them is that moisture content above 2 % in a transformer requires attention.
Recommended criteria for assessment of water, given by percent by weight, in the solid insulation of transformers.
These acceptance criteria are somewhat ‘broad-brush’. Generally, for higher voltage class transformers, less percentage moisture by weight contamination can be tolerated.
The criticality of addressing a wet transformer is also elevated when the transformer is excessively loaded. When coupled with exposure to higher temperatures, such as those resulting from overloading, the transformer insulation may age rapidly. In addition, moisture awareness is a critical data point for system operators who may otherwise unwittingly cause a transformer winding failure through emergency switching and loading, if these activities result in an increase in temperature that exceeds a wet transformer’s bubble inception temperature.