frako PQC - Voltage Measurement

Installation | 23
FRAKO | Operating Manual | Power Quality Controller – PQC
Fuses
The instrument power supply circuit AUX must be protected externally by one or two
fuses, either:
– 2 A time delay, 250 V AC (PQC Type: PQC xxx240x-xx) or
– 2 A time delay, 500 V AC (PQC Type: PQC xxx480x-xx).
One such fuse is required in the phase line when the power is from a phase – neutral
connection, but two fuses must be installed, one in each phase, if a phase – phase
connection is used.
Please refer to the diagrams in Section 5.2.10 “Connection diagrams for all PQC
types”, for further information.
5.2.6 Voltage measurement
Depending on the instrument type, the PQC can measure one, two or three AC volt-
ages. The voltage measurement inputs are electrically interconnected via high resist-
ances. See Section 3 “Technical data” for the measurement ranges. DC voltages
cannot be measured.
The PQC voltage measurement inputs are designed for 100 – 690 V AC networks.
It is possible to measure medium voltages using an x/100 V transformer.
It is not necessary to provide external overcurrent protection in the voltage measure-
ment circuits since these are safety impedance-protected. In this case, a short-cir-
cuit-proof cable (double insulated stranded wire) must be used to connect the voltage
measurement inputs.
Instrument types with single-phase measurement:
For single-phase measurement, the terminals L and N/L are connected as shown in
the diagrams in Section 5.2.10 “Connection diagrams for all PQC types”. The voltage
can be measured between any two phases or between any phase and neutral.
Instrument types with 3-phase measurement:
For 3-phase measurement, the terminals L1, L2, L3 and N are connected as shown in
the connection diagrams in Section 5.2.10 “Connection diagrams for all PQC types”.
Phases L1, L2 and L3 must be connected in correct phase sequence.
For 3-phase measurement, it is advisable to connect the N terminal as well. This
enables the high measurement accuracy of the PQC to be achieved when measuring
phase – neutral voltages and the parameters derived from these. If no neutral conduc-
tor is present, the N terminal can be left unconnected. However, this is only advisable
when the phases are symmetrically loaded.
Note
If an instrument type designed for three-phase measuring is used to meas-
ure only one phase, the terminals L1 and N must be used. The terminals
L2 und L3 must then be commoned with the terminal N to prevent incor-
rect measurements being made.