Miniature robots speed up power generator inspections

Thursday, 28 April 2016
The DIRIS inspections system. Photo: GE

As robots continue to be miniaturised, they are seeing wider applications, one of which is in maintenance, to ensure the continued efficiency and safety of machinery.

Alinta Energy will now have robotic inspection technology in all of its gas-fired plants in Australia and New Zealand — GE's miniature robots will provide inspections of 19 generators across the continent.

The robots were developed by Alstom Inspection Robotics, which was acquired in 2015 by GE. They can inspect generator components without having to remove the rotor, thus reducing the risk of damaging the part, and cutting down unnecessary downtime — an important consideration in critical sectors like power generation.

At the centre of the rotor-in-place inspection package is the DIRIS Small robot, which can send probes through air gaps as small as 9mm in order to conduct critical testing of the generator components.  The DIRIS has a slender arm, with a camera, a light source, and a compact mirror that provides the camera with a 360 degree view.

Once the robot slides into the air gap between the rotor and stator, it inspects the stator bore surface and the rotor body surface, feeding the video to the service engineer.

The engineer can use the video to check for deterioration, spot delamination of the core packets, and the presence of foreign objects or contamination. The robot can also detect stator-core short circuits, which , if allowed to remain, can cause core burning, which is costly and time-consuming to repair.

DIRIS can also inspect the tightness of the wedges in the generator, which have to be well-secured to prevent vibration. If it finds any problems, it can flag the necessary fix.

Despite having sourced the robots from GE, Alinta Energy noted that the DIRIS system can run on generators manufactured by a wide range of Original Equipment Manufacturers, providing a consistent, single, inspection service.

Another component in the package called TurboRotoScan inspection tests the condition of the rotor retaining rings, which must be regularly checked as they are subject to extreme mechanical stress during operations, and stress corrosion cracks can lead to abrupt failure of the rings, and irreversible damage to the generator.

With the ability to conduct detailed inspections with the rotor in place, the process now takes two or three days, rather than three weeks in generator downtime. The robotic inspection can also determine if repairs are needed, and the urgency of that need, allowing better planning of maintenance and engineering downtime.

With major inspections requiring much less downtime, Alinta Energy could justify increasing the frequency of major inspections, from once every eight years, to once every four years, doubling the opportunity to pick up component deterioration, while still vastly improving machine availability.

GE says it is now working on combining robotic inspection with predictive maintenance. A software platform would monitor the condition of a generator during operations, while robotic inspections and sensors fitted to the machines provide real-time data, allowing analytical software to predict component failure, so they can be scheduled for replacement prior to a catastrophic failure.


The DIRIS inspections system. Photo: GE