4.4.12 3 phase with 4 wire measurement with 3 CT’s and 3 PT’s
Figure 21
The above wiring diagram is used for three-phase measurement in public distribution networks with
3 CT´s and 3 PT’s. The voltage channels of the unit are connected to PT’s (normally 63 V AC
secondary), for supplying line-to-earth voltages, and current channels are connected to CT´s
(normally 1 - 5 A AC secondary). Always protect the voltage inputs with a suitable fuse in each
conductor on the secondary side of the PT. The connection for this type of measurement is as
follows:
Channel: Measured object: Channel: Measured object:
U1 = L1 PT+ I1+ = L1 CT+
U2 = L2 PT+ I1- = L1 CT-
U3 = L3 PT+ I2+ = L2 CT+
Ref = L1 PT-, L2 PT-, L3 PT- I2- = L2 CT-
I3+ = L3 CT+
I3- = L3 CT-
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