b) At Islington substation, two transformers connect the 220kV busbar to the 66kV busbar.
Each transformer is continuously rated at 200 MVA, and has a leakage reactance of 8%.
However, one transformer fails, and a replacement is brought in. The replacement has a
rating of 180 MVA, with a leakage reactance of 10%. Calculate the maximum MVA
load, at 0.9 power factor (lagging), that the pair of transformers can supply.
c) A smart young engineer suggests that the maximum load may be increased by changing
the tap setting on the larger transformer. Calculate the effect of a +2% change on the
200MVA transformer tap setting on the MVA load of the fully loaded transformer at
the maximum load of part b).