Power transformer

design feature, cores made of precisely cut sheets, high quality copper winding, clamping structure, voltage adjustment (tappings), well designed tank and conservator, excellent cooling system, and most importantly embedded by protection and control equipment. And of course, stringent tests are carried out to determine conformity to local and international standards. Each production step is operator controlled to ensure the highest quality. Elaborate control procedures and continuous measurements are used to verify the conformance to customer specifications.

In order to achieve better reduced losses and low noise levels with smaller core dimensions, core sheets produced with highly developed technologies are used. Generally, the thickness of core laminations is 0.30 or 0.23mm and it is possible or obtain better results with 0.23mm thick laser treated core sheet. CNC machinery is used for lengthwise and broadways cutting to achieve better results with these low loss core sheets.

The windings are designed in accordance with the temperature rises, insulation and impulse voltage levels, overload conditions, short circuit stresses which are issued in international manufacturing standards. Normally layer winding is used up to 36 kV voltage level and continuous disc winding is used for higher voltage levels. The windings are compressed with pressure segments at the upper and lower yokes in order to encounter the mechanical stresses occurred axially during the short-circuits while the transformer is under service.  Motor drive mechanism is used for the control of on-load tap changer. This control can either be made locally on the transformer or remotely from the control room. The operation of off-load tap changers can either be made on the cover or on the sidewall of the transformer by manual drive mechanism.

On the tanks, there are oil treatment connection valves, oil sampling cocks, lifting lugs, butterfly valves to which radiators are connected and the oil connection valves to other types of coolers in case. All gasket surfaces at the tank are treated with utmost core to prevent unwanted oil leakage. All gasket surfaces are painted with a special point against corrosion. Before painting, outer surfaces of the tanks are sand blasted in accordance with international standards. Conservators are used to compensate the increase of oil volume due to heat. The oil rows from tank to conservator or from conservator to tank through the pipe between cover and conservator depending on expansion and extraction of the oil, air enters or exists the conservator through a dehydrating breather equipped with silica gel particles. To avoid faster aging of the oil, special oil preservation system (Air cell) is used. 

In transformers, the cooling has a special importance to ensure safe operation and to increase the lifetime of the transformer. The heat occurred in the transformers is dissipated at the cooling unit by the help of oil. The simplest and mostly used cooling system is ONAN (Natural Air Cooling with Radiators). ONAF (Radiators Additionally Cooled by Fans) cooling system, in which cooling air is blown to the radiators by fans, is also used.

Transformers are equipped with various protection and control instruments for the operational security. Gases which occur in the transformer for any reason are collected in the Bucholz relay and depending on the volume of gas it gives an alarm or control signal. Pressure relief device replies to the sudden pressure increase that may occur by an arc in the oil of the transformer and gives tripping signal by the contacts on itself. Depending on the oil temperature variations, oil level indicator indicates the oil level in the conservator and gives too low or too high indications by the contacts on itself. Dehydrating breather takes the moisture and dust in the air that enters the conservator and increases service security of the transformer, the amount of silica gel particles in it varies with the amount of the oil in the transformer. Oil thermometer controls the temperature of the oil in the transformer tank and gives alarm and trip signal at the adjusted temperature limit. It gives start and stop signal for the fans used at forced cooling. If remote control is required, PT 100 resistance or 4-20mA output is added to it. Winding thermometer controls the temperature of windings with its monitoring circuit and gives alarm and trip signal at the adjusted temperature limits, like the oil thermometer. Oil flow indicator controls the oil flow at forced oil cooled transformers. It gives alarm signal if oil does not flow for any reason.

Source: Energypac