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used for fault identification, and this is the subject of a Cigré Technical Brochure (Ref.783) on DGA Monitoring Systems. This document describes the different types of DGA monitors, and includes an impressive performance evaluation of monitors including Vaisala’s OPT100. In addition to hydrogen, the MHT410 also
measures temperature, which is a key indicator of faults. Moisture in oil is also measured by the device because moisture decreases the dielectric strength, accelerates cellulose (insulation) decomposition, and increases the risk of bubble formation at high temperatures.
DGA MONITORING AT BIO GOLDEN RAAND
Explaining the reasoning behind the installation of the Vaisala MHT410, Laurens Freriksen says: “A power plant transformer is one of the most valuable assets in a power network - ours is around 10 years old and operates continuously. However, there is no redundancy so it is important for us to be able to monitor its condition and performance closely. “We chose the MHT410 because it offered an opportunity for the early identification of potential problems, which is an important risk reduction measure. Early fault identification enables timely corrective measures such as transformer service, oil change, repairs and possibly transformer load management through customer engagement. If the transformer indicates a fault through increased hydrogen levels, it may also be necessary to deploy a multigas monitor such as the OPT100, in order to obtain a full fault diagnosis.”
Data from the MHT410 continuously feeds into the Eneco digital control system, which Freriksen is able to access from his laptop. This means, for example, that he is able to track transformer load on the same screen as the MHT410 measurements. “The digitisation of assets is an important issue for our industry, and this is a good example,” Freriksen adds. “Remote access to live data informs decision making, lowers risk and was an enormous benefit during the Covid lockdown, because it meant that we could check the transformer at any time, from anywhere.” The MHT410 has been set to raise a high level alarm at 100ppm hydrogen and a very high level alarm at 150ppm. In addition, an alarm will be issued if there is a sudden increase in the readings for hydrogen, moisture or temperature. However, Freriksen is pleased to confirm that during the first year of operation there have been no alarms, with hydrogen readings typically ranging between 2 and 15ppm, with no significant effects during periods of high load.
VAISALA MHT410 Designed for quick and easy installation with almost no maintenance requirement, the MHT410 has a low cost of ownership. “This is important,” explains Andreas Hilgers. “However, the cost of DGA monitors is negligible in comparison with the value of the assets that they help protect, or in comparison with the cost of outages. “One of the main advantages of digitisation is
a reduction in the need for unnecessary site visits, so it makes sense to install a Vaisala monitor that does not incur an extra service requirement.” Frans van Hofwegen from Flux TS
As part of an initiative to safeguard reliable power output and reduce risk, a biomass power plant in the north of the Netherlands has installed a continuous transformer monitor. The Vaisala MHT410 continuously measures three key parameters in transformer oil – moisture, hydrogen and temperature. Owned and operated by the energy company Eneco, the Bio Golden Raand plant produces steam for local industry as well as power, with a capacity of approximately 135 MW thermal and 49.9 MW electrical.
Instrumentation Monthly September 2022 39
agrees. He says: “This is a good example of cooperation between Vaisala, Flux and the end- user; combining knowledge and experience to achieve the desired goals. As the first MHT410 that we have installed in the Netherlands, the device at Bio Golden Raand represents a great start to our relationship.” The MHT410 takes measurements with an in-
situ probe, so there is no requirement for pumps or membranes. With no consumables or moving parts that could fail, the instrument is encased in an IP66-rated metal housing equipped with a weather shield. Every unit is individually tested for a pressure of at least 10 bar and also withstands vacuum conditions. Special attention has been given to EMC tolerance; for example, all electrical connections are isolated. In addition, the MHT410 has been designed to tolerate short-term power outages.
SUMMARY For Eneco, the installation of the Vaisala monitor is essentially a risk reduction measure, but as Freriksen explains: “It is very reassuring to have constant visibility of the transformer’s condition. However, the key advantage is that it buys us time - time to plan an effective strategy if oil conditions deteriorate - to optimise the performance of the transformer and to extend its working life. “We are proud to be leading the way in the Netherlands with this form of digitisation, and since the MHT410 was installed, we have received a great deal of interest from our colleagues in other sectors, such as wind power.”
Vaisala
www.vaisala.com
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