Removing moisture is a vital process in transformermanufacture and maintenance because, moisture is the foremost challenge that atransformer might face. Moisture affects the electric resistance of the insulation material and prompts ageing of the transformer.
After a transformer is assembled and before it is filledwith oil, the transformer is dried. Circulating air in the vacuum chamber,vapour phase drying and hot oil spray drying are carried out to ensure dry insulation. The transformerdrying ovens are constructed with a view of protecting the equipment fromhigh internal stresses. Not only does it increases the lifespan, but also improves the improves impact of insulating material.
One of the above mentioned drying methods are chosen basedon their process time and energy consumption. Temperature in HV and LV windingsare monitored and the former is heated when its temperature is less than the latter.
Such a method is employed to improve insulation at lowfrequency heat and is more beneficial than the hot aircirculation system. Hot aircirculation system needs twice the time of vacuum drying to complete thetask. Upgrading hot air vacuum system with
Transformerdrying oven mitigates moisture and enhances functionality of transformersand make them more effectual in the power industry. The transformer is dried byemploying one of the methods namely induction heating, hot aircirculation system, vacuum drying method and gas-phase vacuum dryingmethod.
In hot air circulation method, the transformer is subjectedto a drying oven which allows hot air to pass through it.
Before initiating the hot aircirculation system, the oil tank of the transformer is assembled and oil isfilled outside the transformerdrying oven. The entire setup is monitored with SCADA system which notesinput of parameters in initial condition and those in different drying stages.Such details are inclusive of weight of cellulose paper insulation material, primary winding voltage, material used for winding and its density and cold resisitance.
A vacuum leak test is performed which is followed by heatingthe windings by using combined thermal plate heater and by passing LFHconverter current around the windings. The winding temperature is made uniform in the insulation and winding parts.
After stabilization time is completed, hard vacuum is pulledin the dryingoven chamber which removes considerable amount of moisture from theinsulation material. After releasing vacuum, the aeration valve is opened sothat atmospheric pressure could be raised.
The hot aircirculation system is mainly used for small transformers, which could beupgraded beneficially with LFH. Flexible connections enable hot aircirculation system to be pumped inside the transformer. Hot aircirculation systems support LFH process in larger power distribution andsmall power transformers.
Transformerdrying ovens differ in structure based on processes employed like lesserthan or equal to 100 MVA for which air drying plant is used and for capacitymore than this, phase dryingplant is used to reduce process duration.
The dryingovens are further divided into several modules so that a comprehensiveinstallation is ensured.
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