Installation manual

UNIPOWER

Installation manual PQ Secure

4.4.5 HV 3-phase measurement with 3CT’s and 2PT’s (Line-to-line voltages)

Figure 13

The above wiring diagram is used for three-phase measurement in electricity networks with 3 CT´s

and 2 PT’s. The voltage channels of the unit are connected to PT’s (normally 110 V AC secondary),

for supplying line-to-line voltages, and current channels are connected to CT’s (normally 1 - 5 A AC

secondary). Two voltage channels are measured and the third is calculated in the measuring

instrument. Always protect the voltage inputs with a 1A fuse in each conductor (red 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-L2 PT+ I1+ = L1 CT+

U1- = L1-L2 PT- (Grounded) I1- = L1 CT- (Grounded)

U2+ = L3-L2 PT- (Grounded) I2+ = L2 CT +

U2- = L3-L2 PT+ I2- = L2 CT - (Grounded)

I3+ = L3 CT +

I3- = L3 CT - (Grounded)

Note: If this method is used, the recorder will automatically calculate the third line-to-line

voltage (U

L3 - L1

). This configuration is normally used in medium voltage networks.