Online DGA is a practical and effective approach to transformer monitoring that has been shown to reduce costly unplanned downtime and maintenance in locations around the world. But how can you be sure that your monitor will work as expected when operating in areas of temperature extremes, high humidity, rain, snow, dust, and more?
In order to cope with these challenges, several design principles should be taken into account to ensure the long-term, accurate operation of your DGA monitor. As well as ensuring that the construction is robust enough to avoid reliability issues, there are other points to consider too – for example, does the device use consumables (gas bottles, batteries, and so on) that need to be replaced regularly?
Vaisala has a long history of designing and manufacturing sensors for tough environments. Not only are our sensors used in measurement applications from the tropics to the arctic, they’re even used on Mars. As a result we’ve learned several important lessons when it comes to reliability.
The housing of an online DGA monitor is one of the most important elements in terms of ensuring reliable performance in all environmental conditions. It needs to be both tough (made from a material such as stainless steel) and well sealed, including all inputs and outputs. We recommend using IP66 housings, which protect the internal components against dust and powerful jets of water. An IP66-rated housing will offer the highest level of water protection for devices that are not actually submerged under water (i.e. IP67 or IP68).
In addition to the housing, the design of the device itself also has a bearing on its reliability. Are there moving parts or components that can wear out, such as membranes, pumps, valves, hoses, or batteries? If so, how durable and reliable are they? For example, magnetic pumps are ideal for use in online monitors as they do not rely on a mechanical seal that is subject to leakage and eventual breakdown.
One of our customers, Sharjah Electricity and Water Authority (SEWA) in the UAE, a desert country where summer temperatures regularly exceed 50°C, recently wanted to implement online DGA monitoring. In addition to high temperatures, the monitor would also have to withstand high humidity, sand storms, and the presence of corrosive chemicals.
The goal for SEWA was to move toward an online condition-based system of maintenance for their transformer fleet. They had piloted other online devices, but these suffered from reliability issues – and in fact ended up doing more harm than good in terms of the monitoring and maintenance program.
We recommended our online hydrogen, moisture, and temperature monitor MHT410. The goal was to demonstrate that our system could withstand the harsh climatic conditions while continuously delivering reliable information on the health of the customer’s power transformers.
The Vaisala MHT410 directly and continuously measures dissolved gasses and moisture in a representative sample of transformer oil, providing a reliable overview of both the hydrogen trend and moisture data. The system is housed in a metal enclosure with an IP66 rating to protect against dust and moisture and – as it has no moving parts, membranes, or batteries – is virtually maintenance free.
By examining the indicators and analyzing the health trends of the transformers, the MHT410 is making it possible for SEWA to identify developing faults early and improve their operational and maintenance planning. In this way the MHT410 is helping SEWA extend the lifespan of their assets, prevent revenue losses due to unexpected downtime, reduce the need for costly unplanned maintenance, and lower the total cost of ownership.
Read more of single gas DGA Monitor MHT410 »
Read more of multi-gas DGA Monitor Optimus DGA »