T&D World Magazine
High-Voltage Amplifier Allows Insulation Analysis

High-Voltage Amplifier Allows Insulation Analysis

With Megger’s new VAX020 high voltage amplifier, it is now possible to reliably assess insulation condition using proven dynamic frequency response (DFR) techniques, even in extreme high interference environments, such as HVDC substations. In addition, the new amplifier also eliminates the difficulties associated with testing low capacitance objects, such as bushings and instrument transformers, at low frequencies.

Designed primarily for use in conjunction with Megger’s popular IDAX300 insulation diagnostic analyser, but compatible with all Megger IDAX and IDA instruments, the VAX020 amplifier is a compact lightweight unit that expands the instrument’s test voltage range from 200 V to 2 kV.

This high output voltage, particularly when combined with the advanced digital filtering algorithms used in the IDAX300, greatly reduces the influence of electromagnetic interference, allowing accurate and dependable results to be obtained under conditions where this would have previously been difficult or even impossible.

Speed of operation is another important benefit. Because of its efficient signal acquisition technology and the provision of two separate current measurement channels, the VAX020 + IDAX300 combination provides fast and reliable true ac measurements without the need for dc to ac conversion. Two separate measurements down to 1 mHz on a three-winding transformer can be completed in about 35 minutes, whereas other instruments typically take around two hours.

In addition to allowing the IDAX300 to provide market-leading interference immunity, the VAX020 amplifier extends the capabilities of the instrument to include 50/60 Hz capacitance and tan delta measurements. The high output current capability (50 mA) of the amplifier means that it can be used with test objects with capacitance up to 80 nF at 50 Hz and 67 nF at 60 Hz. Tan delta/power factor measurements can also be made on insulating oils at up to 1,400 V rms.

The new VAX020 high voltage amplifier from Megger has an operating temperature range of -20ºC to +55ºC making it suitable for use in even the toughest of conditions. It is supplied in a custom transport case, complete with a 3 m multicable to link it to an IDAX3, a 20 m high voltage cable, and an interlocking device.

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