Alstom MiCOM P545 - 6.7.13 CT Vk for Current differential protection; 6.7.14 CT Vk for distance Zone1 reach point; 6.7.15 CT Vk for distance Zone1 close-up fault; 6.7.16 CT Vk for distance time delayed zones

Application Notes P54x/EN AP/La4
MiCOM P543, P544, P545 & P546
(AP) 6-87
AP
6.7.13 CT Vk for Current differential protection
If thro * X/R thro = 2.14 * 5.66
= 12.11
The appropriate equation for K and Vk to be is used from section 6.2
K
> 40 + (0.07 * 12.11) OR K > 65
K > 40.8 OR K > 65
Hence K = 65
Vk  K. In (Rct + 2 RL)
Vk > 65 (RCT + 2 RL)
6.7.14 CT Vk for distance Zone1 reach point
Vk  K
RPA
x IF z1 x (1+ X/R). (RCT + RL) -- From section 6.3
Vk > 0.6 * 2.63 * (1+5.74) * (RCT+RL)
Vk > 10.65 (RCT + RL)
6.7.15 CT Vk for distance Zone1 close-up fault
SIR = Zs / Zzone1
= 3.32 / 38.73 is less than 2; so we need to do this Vk calculation
Close-up fault current = 40kA (primary) = 33.33 A (secondary)
Vk  Kmax x IF max x (RCT + RL) -- From section 6.4
Vk > 1.4 *
33.33 * ( RCT + RL)
Vk > 46.67 (RCT + RL)
6.7.16 CT Vk for distance time delayed zones
Vk
> If (RCT + RL) -- From section 6.5
Vk
> If thro * (RCT + RL)
Vk > 2.14 (RCT + RL)
6.7.17 Vk to be considered
Usi
ng the above sections, the different Vk requirements are to be calculated for all the
functions that will be enabled, or that will be brought into operation. Then the highest Vk shall
be considered for the CT design.