Oil Cooling Type Power Transformer 250kVA with CE Certification

SummaryTransformers immersed in insulating fluid with natural self cooling (ONAN), three-phase, 50/60 Hz. For indoor or outdoor use. Hermetically sealed, CRGO Silicon steel, High-strength cold-rolled steel tank. StandardThe transformers described in this catalogue are designed and tested in accordance to IEC/BSEN 60076. FeaturesCommon power ratings: 30, 50, 80,100,125,160, 200, 250, 315, 400, 500, 630, 800, 1000, 1250, 1600, 2000, 2500 kVA. This transformer is designed for voltages of ≤ 36 kV. Specific figures are not given for this parameter because of the wide variety of voltages used. Transformers can be supplied on demand to run at two different primary voltages, the shift between these input voltages has twobasic alternatives:• with a primary tap changer which can be switched with no load and no applied voltage• or by changing terminals under the cover.The secondary voltage under no load is allocated at 400V, 415V, 433V, though other voltages can be supplied on demand. When usage requires two voltages, transformers with two simultaneous voltages can be supplied. In this case the no-load voltages are set to 400V(230V),415V(240V),433V(230V) .The connections normally used are as follows:• For rated power levels of 160 kVA or less: Yyn0• For rated power levels over 160 kVA: Dyn11.• Dyn5, Yd11 and others can customaized.As per IEC /BSEN 60076 standards these areset in accordance with the highest voltage for the material,being the level immediately above the rated voltage.Material maximum admissible voltage12kV17,5kV24kV36kVWithstand voltage28kV38kV50kV70kVBasic insulation level75kV95kV125kV170kVAs per IEC/BSEN 60076 , in normal operating mode: • 60º K max. in oil • 65º K average in windings Other temperature rise levels on demand. Transformers covered must have one of the following oil expansion systems: a) an external conservator tank b) an air chamber under the cover c) a hermetically sealed elastic tank ROOQ recommends option (c), which is the one considered in this catalogue, as it has the following advantages: 1.Smaller size, as there is no need for an conservator tank or air chamber, making for easier transformer transportation and placement. 2.Lower overall weight. 3.Increased sturdiness and less risk of leaks, there being no weak points such as welds between the expansion tank    and the cover, oil level gauge, Silicagel air breather, etc. 4.Low maintenance due to the absence of elements such as the drier, over-pressure valves and liquid level indicators. 5.No degradation of insulating liquid (oil) by oxidation or absorption of moisture, as there is no contact with the air. The liquid therefore remains in ideal condition. 6.Better conservation of seals due to lack of contact with air, which means that they stay more flexible. Construction detailsI- MAGNETIC CIRCUITOriented grain, very low loss magnetic plate is used following IEC/BSEN 60076. The type or class of plate is chosen on the basis guaranteed noise level and losses. The net cross section is maintained constant in limbs and yokes throughout the magnetic circuit, as a special configuration does away with the need for cross-section reducing grip bolts (section reduction).The limbs and yokes are joined by 45º lugless joints, with complete one-piece yoke, and stacking is arranged so that each plate profile is staggered with regard to the previous one, thus minimising the effect of the gap. The profile is stepped, with the number of steps required to obtain the best coefficient of useful surface area.II- LOW VOLTAGE WINDINGThis winding is located next to and concentric with the magnetic circuit. Two clearly different types of wire are used depending on the allocated current:- Rectangular cross-section with rounded edges. - Strips with conditioned edges.In the former case each wire is insulated with thermal class A cellulose paper or class H enamel. Strips are used bare.The rectangular wire winding is set up in a complete layer configuration with one or more concentric channels for cooling.The insulation between layers is always B status resin impregnated.The width of the strip on strip type winding with conditioned edges covers the whole axial width of the coil, so that each turn is a layer of winding. As the strip is wound a layer of type B resin impregnated paper is wound with it. This polymerises during the drying cycle, giving the winding the strength to withstand the mechanical stresses entailed by short circuits as per IEC 60076 standards.III- HIGH VOLTAGE WINDINGThis is wrapped around the low voltage winding to lie concentric with it, separated by an insulation structure giving the level of insulation desired.The conductors used are of two types:• circular cross-section wire• rectangular cross section strips.The conductors are insulated with thermal class H enamel. The rectangular section wires or strips have thermal class A paper or thermal class H enamel. With both types of wire, the winding configuration is anti-resonant in one section,