Installation manual

UNIPOWER

Installation manual PQ Secure

4.4.2 3-phase measurement with direct voltage, 3 CT´s and neutral (Line-to-neutral voltages)

Figure 10

The above wiring diagram is used for three-phase measurement in low voltage networks. The voltage

channels of the unit are connected directly to the electricity network for measuring line-to-neutral

voltages (230 V) and therefore do not require any instrument transformers (PT). However, the

current channels are connected to existing instrument transformers, allowing the measurement of

high currents, e.g. directly from the secondary side of a power transformer. Always protect the

voltage inputs with a 1A fuse in each conductor (red conductor). The connection for this type of

measurement is as follows:

Channel: Measured object: Channel: Measured object:

U1+ = L1 I1+ = L1 CT+

U1- = (Neutral) I1- = L1 CT- (Grounded)

U2+ = L2 I2+ = L2 CT+

U2- = (Neutral) I2- = L2 CT- (Grounded)

U3+ = L3 I3+ = L3 CT+

U3- = (Neutral) I3- = L3 CT- (Grounded)

Note: In power quality standards such as EN 50160 and the Swedish SS 421 18 11 (low voltage

quality standard) measurements in low voltage networks are always based on line-to-

neutral voltages, i.e. U

num

= 230V. This means that it is important to connect the unit for

line-to-neutral voltages and not for line-to-line voltages.