Trihal cast resin dry type transformers (ENG) - Trinet

5. Dimensioning the transformer• To prevent the windings overheating :☞ The first solutioninvolves oversizing the transformer or limiting its load if it is a piece of equipmentwhich is already installed.Standards organisations UTE, CENELEC, ...) have adopted or are currently studyingderating equations such as :K = [1 + 0,1 * (Ì Hi 1,6 * Ti 2 )] -0,5See chapter 1 Hi = harmonic numberTi = harmonic factor expressed as a % of the transformer’srated intensi ty• Example 1A 1000 kVA transformer delivers a current which includes the following harmonics :H5 = 25 % H7 = 14 % H11 = 9 % H13 = 8 %K = [1 + 0,1 * (5 1,6 * 0,25 2 + 7 1,6 * 0,14 2 + ...)] -0,5The calculation gives k = 0,91 : the transformer will only supply 910 kVA.• Exemple 2We want to determine the size of a transformer needed to supply 1000 kVA withharmonics of number H = 6 x n Ù 1, with n = 1,2, ...etc and with a factor of 1/H(typical case of a six-phase rectifier).By limiting the calculation to number 29, the coefficient K will be 0,87.K = [1 + 0,1 * (5 1,6 *0,2 2 + 7 1,6 * 0,14 2 + 11 1,6 * 0,09 2 ...)] -0,5The minimum power for the transformer becomes 1000 / 0,87 = 1150 kVAF:Dcial/MK/MKT/InfoMK/Anglais/GENERAL/TIGEA09 6