Video: Nexus 1450 – Technical guide

Video transcript

How the Nexus 1450 goes into a switchboard: the base and its displays, the wiring in star and in delta, the supply, the 6 ports and the checks before service. This is work on live circuits, for qualified staff only: terminals, C Ts and P Ts can all carry lethal voltages. Voltage leads and supply are fused, the C Ts go through a shorting block, and a switch next to the meter acts as its disconnect. And never open a CT secondary with current flowing.

The installation has two parts. The transducer base mounts behind the panel, and occupies the same place as a 125x base. The display goes on the door: the LED display in an old analogue meter opening, or the 4.3 inch colour touchscreen. External modules clip onto a mounting bracket, and the inputs are sealed for billing. Along the top edge: port one, RS-485 or RS-232, ports two to 4 in RS-485,

the IRIGB input, two pulse outputs and 8 digital inputs. Then the two Ethernet ports: port 5 on RJ 45 and port 6 in fibre. Along the bottom: the supply terminals and the earth, then the voltage inputs, V aux, V ref, V a, V b and V c. To the right, under the cover, the 4 current inputs. And on the front of the base, the test pulse lights used to check accuracy. In a four-wire star the meter works with 3 elements, 3 P Ts and up to 4 C Ts. The current circuits come first:

the common of the CT secondaries to earth, then each CT through the shorting block, polarity mark to HI, the other side to LO. The 4th CT, on the neutral, gives the neutral current. Now the voltage. The PT secondary common is earthed and taken to V ref, the reference input. Each phase feeds its PT, whose primary returns to the neutral, and the secondaries reach V a, V b and V c through their fuses. The inputs accept up to 720 volts between any two of them.

In a three-wire delta two elements are enough: C Ts on phases A and C, and two P Ts in open delta, between A and B and between C and B. Their secondary common is earthed and goes to V b, with V ref tied to the same point; V a and V c complete the connection. The meter has its own supply: D two, universal, from 96 to 276 volts AC or DC, or D, from 18 to 60 volts DC.

Earth first, to the GND terminal. Then neutral or negative to N minus, and line or positive to L plus, through a fuse and with a disconnect switch nearby. Six ports work at once. The 4 serial ports take SCADA, the displays and the external modules; port one can also work as RS-232 and as a Modbus master. The two Ethernet ports have separate IP addresses, so the utility network and the plant network can stay apart.

RS-485 is a daisy chain, never a star or a tee, in shielded twisted pair. The shield is earthed at one point only; then plus to plus, minus to minus and shield to shield, device after device, with termination only at the two ends of a long line. When the standard inputs and outputs are not enough, external modules add them: analogue outputs for old transducers or a PLC, analogue inputs, digital inputs, relays and pulse outputs. Up to 4 modules of each type, on their mounting bracket,

with an extra power supply when there are several. Before service: check the wiring and power up, connect the PC software, program the CT and PT ratios and the hookup, check the phasors on the display, and set the time source. Then create the administrator and the users with your own passwords, and seal the meter. Power network analysers, from Amperis.