Example Problem

Setting Calculations for ICTs operating in grid.

Example: A 220/132kV S/S has two ICTs operating in parallel having capacity 200 and 100 MVA. Its HV side and IV side CT ratios are as shown in figure. AS ICTs are under loaded either alarm or load trimming scheme is not provided. Reactance data for HV and IV grid sources and ICTs is as shown in following table. For both ICTs delta tertiary is closed. Calculate the HV side and IV side backup relay settings for both ICTs.

Table-1: % Reactance Data for ICTs
SrNo	ICT Name	Capacity	% Reactance
			Primary-Secondary	Primary-Tertiary	Secondary-Tertiary
1.	ICT-I	200 MVA	13%	37%	26%
2.	ICT-II	100 MVA	12%	35%	25%

Table-2: Source Reactance Data
SrNo.	Source	Positive Sequence Source Reactance X1S	Zero Sequence Source Reactance X0S
1.	HV Side grid of the Substation	4.5%	7.0%
2.	IV Side grid of the Substation	11.0%	17.0%