Eyes for oil: condition monitoring in lubrication

A new oil degradation sensor can pre-empt failure in everything from wind turbine gearboxes to diesel generators.

Lubricating oil in wind turbine gearboxes has to be checked a couple of times a year to make sure it is still doing its job in reducing friction between large rotating cogs.This process involves sending an engineer up a 90m-turbine tower and turning the moneymaking turbine off for at least an hour, following an incident where an engineer was killed after being pulled into a gearbox.

When today’s engineer finally makes it to the breezy summit of the temporarily redundant wind turbine, they may be frustrated to find that the gearbox oil is absolutely fine and doesn’t even need changing.

Tan Delta claims that its OQS oil sensor could save engineers wasting their time on such pointless trips up and down turbine towers. The stainless steel, palm-sized sensor that has been developed in Rotherham can provide real-time information on the condition of gearbox oil in wind turbines.

It is able to continuously and accurately monitor every aspect of the oil’s condition, from contamination caused by moisture, water or metallic elements, to oxidisation or the general degradation of the oil’s lubricating performance.

According to Chris Greenwood, Tan Delta’s managing director, the sensor measures energy loss within the oil by looking at the oil’s capacitance and inductance levels.

‘That makes a big difference because if you’re using capacitance alone you’re looking for a very small change over a very large scale,’ said Greenwood.

‘We’re taking that energy loss and applying our algorithm to that to introduce the temperature stability and get a clean signal to give us a very accurate and repeatable output.’

You’ve got 600 litres of synthetic oil that’s very expensive. It costs about £3,000 to change the oil in a wind turbine

Chris Greenwood, Tan Delta

But how will wind turbine managers know when they need to change the oil?

When the oil degrades beyond a certain threshold, a signal is sent to a server or a website to prompt engineers into action.

While the sensor has been installed in approximately a dozen wind turbines around the world, Greenwood struggles to see why all wind turbine owners wouldn’t want to monitor the condition of gearbox oil in real time.

‘You’ve got 600 litres of synthetic oil that’s very expensive. It costs about £3,000 to change the oil in a wind turbine,’ said Greenwood.

Greenwood explained that oil is also a very good indicator of the wear on any rotating equipment and monitoring the oil can identify faults within a gearbox or an engine. ‘More than 80 per cent of all faults are caused by the lubrication,’ he said.

Similarly, the sensor can, and is, being used in many other industries that have large gearboxes.

‘Mining and mineral processing are really good for us. Large gearboxes are used for crushing, grinding, mixing and transporting minerals from A to B,’ said Greenwood, explaining that Australia and South Africa are Tan Delta’s key markets.

While the sensor is also being used here in the UK in gearboxes at several mines, it is more commonly found in food manufacturing machine gearboxes.

The sensor can also be used in combustion engines to monitor the condition of engine oil, which faces far more aggressive conditions than the lubricant oil found in relatively sedentary wind turbine gearboxes.

Greenwood explained that the costs of large industrial engine failures due to oil degradation can be catastrophic. ‘Let’s take a diesel generator, for example,’ said Greenwood. ‘If that goes bang, it costs £25,000 to take the thing off the site, never mind repairing it. The crank shaft is another £150,000 and the replacement engine is half a million.’

Tan Delta Systems is hoping to develop two new versions of the OQS sensor for applications in high temperature and explosive environments. The current sensor can withstand temperatures between -20°C to 120°C but this temperature range means that it cannot be used in many environments where oil is used.

‘We’re looking at an application in thermal transfer oils that are used to distribute head,’ said Greenwood. ‘Let’s say you’re a food manufacturer and you’ve got lots of large ovens. Generally, they would have a boiler and a pipework system containing lots of oil that is heated to more than 350°C and then pumped around the system to create heat efficiently.’

Greenwood explained that Tan Delta sees this as a particularly good area because oils used to transfer heat degrade quicker due to the temperatures they are exposed to. ‘Our current sensor would pick up all the contaminants but it won’t survive that sort of temperature,’ he said.

According to Greenwood, the explosive gases found at the bottom of mines also mean that the sensor cannot be used in such environments because it’s not intrinsically safe.

This relatively inexpensive oil sensor could offer large financial and labour savings for a wide variety of markets, particularly those that have overlooked it thus far, such as the wind energy sector.