ABB PQFS - Page 49

Manual Power Quality Filter PQFS  Electrical design and installation 49
Maximum rms current of the
downstream loads (including starting
current of DC drives):
X1 = ….. Arms
Multiply X1 by
1.6:
X2 = …. Arms
CT cables > 30 meters ?
Select 3 identical CT’s such that:
- rating at primary ≥ X2 - rating at secondary: 5A - Burden ≥ 15 VA - Class 1 accuracy or better
NO
Section of CT cables:
2.5 mm²? (recommended)
Determine the length of
CT cables (meters)
L = … m
X3 = (L x 0.007 x 25) + 10
X3 = … VA
Select 3 identical CT’s such that:
- rating at primary ≥ X2 - rating at secondary: 5A - Burden ≥ X3 VA - Class 1 accuracy or better
Determine the length (m) and
resistance (Ω/m)of
CT cables (meters)
L = … m
R = … Ω/m
X4 = (L x R x 25) + 10
X4 = … VA
Select 3 identical CT’s such that:
- rating at primary ≥ X2 - rating at secondary: 5A - Burden ≥ X4 VA - Class 1 accuracy or better
NOYES
YES
Figure 32: Flow chart for CT determination