Power station makes use of HYDAC transformer care unit (TCU) to maintain critical transformer availability and is wowed by extent of improvements.
BACKGROUND
A peaking power station in Queensland uses two gas turbines to provide peaking power.
“A peaking power station generally only runs to provide electricity during peak demand,” HYDAC Fluid Power Engineer Albert Dobis points out.
“Typically, peaking power stations run gas turbines or diesel fuel turbines because they are easy to quickly start and run when needed and turn off when no longer needed.
“In this case the station has two gas turbines, with each generating unit supplying power to the grid via two critical 190MVA ABB transformers, which were manufactured and commissioned in 1999.”
Mr Dobis explains that the transformers are “oil submerged”, meaning that the insulating paper inside the transformer is fully submerged in oil.
“There are in fact 45,000L of insulating oil in each transformer, and what happens over time is that the insulating paper in the transformer degrades with the degradation of the oil,” he says.
“Transformer insulating oil has some gases in it, typically up to 10%, which contribute to the oil ageing and the insulating paper degrading over time.
“Therefore, it's important to keep the oil clean and free from contaminants such as gases and moisture to increase the life of that insulating paper.”
PROJECT OBJECTIVES
According to Mr Dobis, the power station approached HYDAC to assist it to slow the oil ageing process down to a minimum by reducing oxygen and moisture levels and thereby increase the remaining cellulose's lifespan.
“Reducing oil changes to a minimum and increasing the safety and availability of transformers by reducing the gas and moisture in the oil and thereby maintaining or increasing dielectric strength and reducing risk of failure were of significant importance to the station,” Mr Dobis emphasises.
HYDAC SOLUTION
HYDAC’s solution was to connect a TCU to the transformer to assist with the removal of gases, moisture, and particulate.
“Particulate in closed transformers is often not too much of a problem because it's a closed system that’s well sealed from the environment,” Mr Dobis points out.
“Therefore, there's not much of particulate that can get into the system, but the gases and moisture from condensation are an issue. It’s here that the TCU shows itself as a great product from HYDAC.”
Mr Dobis explains that the TCU operates via a vacuum chamber that removes all the gases and moisture in the oil.
“It works on a very small flow rate because it's permanently installed. This means that it’s designed over time to slowly remove the gases from the oil without shocking the system,” he says.
“Many companies use higher flow offline polishing units to quickly reduce the gas and moisture content in the oil and then leave the transformer for the next 12 months. However, the downside here is that it can cause hydraulic stress on the transformer.
“Also, with these systems you remove the water that has mainly been formed due to paper insulation degradation.”
Mr Dobis says the HYDAC TCU approach is centred on preventing the oil and paper insulation from being degraded and aged in the first place, and the consequent need for regeneration or oil services, which are usually costly.
HISTORICAL RESULTS
At the time of installation oxygen levels were around 17,500ppm and water content 10 to 11ppm.
Six months after installation, oxygen levels reduced 62% to 6720ppm and the water level reduced by about 30% to 7.5ppm.
Gas in the oil reduced from 8.32% to 2.2% over the period.
CUSTOMER BENEFITS
Benefits of lower oxygen content have resulted in less consumption of oxidation inhibitors or similar protection groups in the oil and the extension of the remaining life of the oil and cellulose.
“The customer recounted that this was the first experience of purchasing a product that delivered exactly what was promised by the sales guy,” Mr Dobis concludes.
Further application areas
Critical large power grid transformers and oil and gas (LNG trains) distribution and power transformers are also suitable applications for the TCU among many others.
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