Installation manual

UNIPOWER

Installation manual PQ Secure

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

Figure 11

The above wiring diagram is used for three-phase measurement in networks with 2 CT´s and 2 PT’s.

The voltage channels of the unit are connected to PT’s for measuring line-to-line voltages (normally

110 V AC secondary), and the power is calculated in accordance with the Aaron 2-wattmeter

method. The current channels are connected to CT´s (normally 1 - 5 A AC secondary). Two channels

are measured while the third current and voltage are calculated from the measured channels. 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) I3+ = L3 CT+

U2- = L3-L2 PT+ I3- = L3 CT- (Grounded)

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

voltage (

UL3 - L1

) and the current I2. This configuration is normally used in medium

voltage networks.

Note: In this configuration the constants for U1-U3 must be the same. Also the constants for

I1-I3 must be the same. This is because the missing U2/I2 is calculated by the

instrument.