Hello everyone, I want to validate my calculation of pu transformation for a load flow case which is a case of 30 wind turbines : in fact , i consider the turbines like PQ nodes ( P= nominal power of each turbine = 3 MW and Q = 0 ) i calculate r x b between the branches of cables with these equations:
𝑥 = 2𝜋𝑓. 𝑙. 𝑑 / 𝑏𝑎𝑠𝑒 𝑖𝑚𝑝𝑒𝑑𝑎𝑛𝑐𝑒 𝑏= 2𝜋𝑓. 𝐶. 𝑏𝑎𝑠𝑒 𝑖𝑚𝑝𝑒𝑑𝑎𝑛𝑐𝑒 𝑟= R. 𝑑 / 𝑏𝑎𝑠𝑒 𝑖𝑚𝑝𝑒𝑑𝑎𝑛𝑐𝑒 Where : d is the cable length in km , L : inductance (H/km), C (F/km) , R(ohm/km) 𝑏𝑎𝑠𝑒 𝑖𝑚𝑝𝑒𝑑𝑎𝑛𝑐𝑒 = (𝑏𝑎𝑠𝑒𝑣𝑜𝑙𝑡𝑎𝑔𝑒 )^2 /𝑏𝑎𝑠𝑒𝑝𝑜𝑤𝑒𝑟 The base power for my case is = 30 * 3 = 90 MVA Question 1 : Is my equations for calculation x , b, and r are correct ? (i found in some documents that b= 2𝜋𝑓. 𝐶. 𝑏𝑎𝑠𝑒 𝑖𝑚𝑝𝑒𝑑𝑎𝑛𝑐𝑒/2 (divison by 2) ) which is the correct equation for b ? All the turbines are connected after that with a commun transformer ( tranform 33 kv to 132 kv) so my problem here is how to modelize the transformer. In fact , i found two ways to do that : 1/ by consider only the r and x of the transformer and to put b=0 with a ratio = 1 ( no no additional transformation) 2/ by consider the transformer like a a cable model with r,x and b so the ratio = 0 I tried the two ways for the case of 30 turbines and it gives me almost the same results, but im not sure that gives the same for other cases. Question 2: Can anyone please validates my approach, which is the approriate way to modelize the transformer ?
