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Even then it is still inhospitable – essentially a metal chamber that may contain toxic residues if some burning of insulation materials has occurred – so much so that staff have at times suffered fatalities. The need first to drain the oil and then restore it means that such inspections can easily take a week or more and also carry the risk of spillage that can cause environmental damage.
That description is provided by Jamie Stapleton, digital leader with ABB’s Power Grids Division in the UK. It is, though, a type of procedure that he believes will quickly become redundant as the company looks to provide inspection services using technology that he says is “unique to ABB”. This is its TXplore robot – a remotely operated vehicle that can be lowered into an oil-filled transformer and swim around in it carrying out a full inspection of the interior not just safely but over a much more compressed timescale. “Just one or two days at most,” confirmed Stapleton.
Video images captured
The machine was developed by the company in the US, with five of them now in use. Each weighs only 5kg and can be easily lifted and lowered into a transformer by a single individual. It is then controlled by an operator using commands entered into a PC so that it can capture video images of any area of the transformer’s interior, which are transmitted back to the PC for storage and analysis.
That simple mode of operation is facilitated by some clever capabilities. Perhaps the most striking is that the device swims freely with no umbilical connection to the PC. “We use a wi-fi access point at the transformer opening to communicate with the TXplore through the oil of the transformer,” Stapleton explained. “Since transformer oil is a dielectric fluid, it is possible to have high-frequency communications to control and transmit images from the system. This would not be possible in a non-dielectric fluid such as water.”
Another feature is that the machine’s movements do not introduce any bubbles into the oil which might compromise the transformer’s electrical performance. “Extensive development has been carried out that included oil testing before and after inspections to ensure no bubbles are generated by the robot,” Stapleton confirmed.
Submarine controls
The robot is able to manoeuvre itself by means of a ballast and buoyancy control system similar to that of a submarine. “An internal chamber contains pressurised gas over self-contained oil that can be pumped into or out of a flexible membrane on the outside of the system,” said Stapleton.
“This adjusts displacement to maintain a neutral buoyancy and vertical direction is then controlled through thrusters. The system is set for use in normal transformer mineral oil, but the buoyancy can be adjusted for use in oils of different densities.”
During inspections, images are gathered by four cameras, each of which is paired with an LED light with the light intensity adjustable by the operator to optimise image quality. This is particularly critical, Stapleton noted, because the oil can become very dark in service. Nevertheless he said that the machine’s ability to manoeuvre close to critical points and then illuminate them means that it can return high-quality images even in conditions of high oil opacity.
In fact, more than 20 inspections have been carried out worldwide already by the existing TXplore machines and more of them are in production.
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