Electrical submetering means installing power analysers in distribution boards to know the consumption of each line, machine or section, not just the meter total. The data travels over a bus such as Modbus to a dashboard showing consumption, power and peaks. It is used to allocate costs, detect out-of-shift consumption and justify investments.
What should be measured first?
There is no need to measure everything from day one. The incomer and the four or five biggest consumers already explain most of the bill.
- The main incomer, to check against the bill.
- The big consumers: compressors, HVAC, ovens and industrial refrigeration.
- Each production line or section, if costs are to be allocated.
- Lighting, separately.
- Base load: what stays on at night and at weekends.
Which equipment is used?
For internal use an analyser of a suitable class is enough. If the measurement is used to bill a third party, such as a tenant, a MID-certified meter is required.
| Equipment | Function | Bear in mind |
|---|---|---|
| Power analyser | Measures energy, power, voltage, current and power factor | DIN-rail or panel-door mounted |
| Current transformers | Adapt the line current to the analyser | Split-core types fit without disconnecting the cable |
| Communication bus | Carries the data (Modbus RTU or TCP) | One cable runs through the boards; network and radio units also exist |
| Gateway or data logger | Collects and sends the data | Stores data if the connection is lost |
| Dashboard | Shows consumption, peaks, comparisons and reports | With threshold alerts |
What decisions does it enable?
- Switching off what consumes without producing: idling compressors, HVAC at night, lines on standby.
- Staggering start-ups to lower power peaks.
- Watching reactive energy and demand overruns, which are charged separately on the bill.
- Comparing shifts, lines or sites against one reference, such as consumption per unit produced.
- Checking with data whether an investment delivered the expected saving.
- Providing records for an energy management system such as ISO 50001.
How is it installed without stopping the plant?
Split-core transformers clamp around the cable without disconnecting it, and the analyser fits in a free space in the board. The analyser’s voltage connection does require electrical work with the corresponding safety measures, planned board by board. Where running the bus is not worthwhile, radio-linked units are used.