Insulation Coordination

A 132 kV transmission line is terminated by transformer at a substation. The transformer is protected by an arrester of rating 120 kV located at the incoming line. The BIL of the transformer is chosen to be 500 kV. The protective ratio required for transformer protection is 1.2. Check whether the transformer is properly coordinated with the arrester if a lightning stroke results in the arrester discharge current of 40 kA. Relationship between discharge current and residual voltage:

Discharge Current	Residual Voltage
10 kA	300 kV
20 kA	360 kV

A 400 kV line shown in figure below is effectively grounded which is protected by L.A. with PR = 3. The transformer has its protection ratio (TPR) = 1.25 with $Z_{c} = 350$ Ω. Determine BIL of Tr. Also find the maximum distance between transformer and lightning arrester so that the insulation coordination is properly met. [IMAGE: Figure from the original paper, showing the 400 kV effectively grounded line protected by a lightning arrester and the transformer.]

A 132 kV line is terminated by transformer and is protected by an arrester of rating 120 kV located at the incoming line. The BIL withstand voltage of the transformer is chosen to be 500 kV. The protective ratio of transformer is 1.2. Check whether the transformer is properly coordinated with the arrester if a lightning strike of 8,000 kV incident at the arrester.

Discharge Current	Residual Voltage
10 kA	300 kV
20 kA	360 kV