A 20MVA, 11kV/132 kV, star-delta transformer is being protected
by a biased differential protection
system. The transformer is supplied from 132 kV grids and on full
load operation. Determine the
suitable CTs ratio at both side of the transformer if current at
restraints coil is rated at 5 A. (CT ratios
available: 100/5A, 300/5A, 600/5A, 800/5A, 900/5A, 1000/5A,
1500/5A, 2000/5A, 3000/5A) If
lightning strikes at the secondary of the transformer which
injecting IL=10kA to the system;
(i) Determine the primary...