Characteristics of High Voltage Test Transformers
1) High voltage: The primary voltage of a test transformer is 220V or 380V, but the secondary voltage of a single test transformer often reaches thousands to tens of thousands of volts. Test transformers with secondary voltages exceeding 750kV usually adopt a multi-stage cascade structure.
2) Low current: The rated current of a test transformer is actually the capacitive current of the test object, so it is generally less than 1A. However, for test transformers used in cable and large motor testing, external insulation pollution testing, line corona testing, and other projects, the secondary current can reach several amperes.
3) Short working time: Due to the short withstand voltage time of the tested product, test transformers, except for those used in external insulation pollution testing, line corona testing, and cable testing, generally operate under a short-time duty of 0.5h or 1h.
4) Test transformers are generally single-phase, indoor installations (some are made for outdoor use): they all adopt oil-immersed self-cooling structures, with thicker winding insulation layers, and the high-voltage winding usually has one end grounded.
5) The insulation levels at the beginning and end of the secondary winding of a test transformer are different: the beginning is at high potential, while the end is directly grounded or grounded through an ammeter.
6) High design and manufacturing process requirements: Due to the high operating voltage, the insulation structure has a decisive impact on the overall dimensions of the test transformer. The core and windings generally require vacuum drying, and vacuum oil filling is required for voltages above 100kV.
