Powerpoint Engineering Limited recently installed an Energy Metering System (monitoring Gas and Electricity usage on site) at a metal fabrication factory in Cork. The electrical energy meters were retrofitted on existing switchgear, using any existing infrastructure available (Measure-Voltage fused signals and current transformers). The factory is Ireland’s only independently owned manufacturer of extruded aluminium profiles. They specialise in aluminium extrusion, powder coated aluminium and sheet metal fabrication as well as providing many other services from their vast 250,000 sq. ft. facility.
The installed system consists of:
- 30 Electrical energy meters and 10 gas meters, capturing total site consumption and significant energy users (SEU’s);
- Modbus data communication over ethernet for all meters;
- Energy metering software (Powerstudio Scada) with real-time meter reading, historical data trending and automated periodic reporting;
After the system installation was complete, the installed meters were accuracy tested and validated. For electrical energy meters, this is generally achieved by using a calibrated portable power analyser and comparing the installed panel mounted energy meter reading against the reading on the portable analyser. This process ensures that each sub meter reading can be deemed to be valid.
Once the meters had been validated for electrical accuracy, then the communications between the meters and the software system were configured.
In the Energy Metering software, all electrical and gas meters were set up in a hierarchical grouped fashion.
The metering system was now started recording and allowed to log for a time period. After this time period the site was re-visited for final validation.
On this system, there were 3 electrical switch-rooms and one main ESB supply. The were 10 gas meters, including the main incoming gas supply.
As part of system validation, the total energy consumption at the main electrical meters at each switch-room was summed and compared to the total main supply energy consumption (ESB meter). This validation was also performed for all gas sub-meters against the total incoming gas supply meter.
This validation proved successful, where the total of the sub-meters equalled the total main meter for both electricity and gas.
The next level of validation was performed at each individual switch-room. The main meter reading was compared to the sum of the sub-meters at that location. For two out of three of these areas this validation was successful. At one switch-room, it was found that the main meter reading was less than the total of the sub-metered total. On investigation, it was found that the main meter was measuring correctly. This pointed to an issue with one or more of the sub-meters. All sub-meters were found to be reading correctly, with the exception of one meter.
This meter of concern was found to have been configured incorrectly. This was a retrofit project, where some existing wiring was utilised and old meters were replaced with new meters. The assumption was made that the original wiring was correct. It was found that the phase sequence of the meter voltage signal wiring did not match that of the meter current signals. It was also found that the connected load being metered was unusually, highly inductive (75kW, 150kVAr lag, 170kVA, 0.43 power factor). This actual load was validated using a portable power analyser. The panel meter was incorrectly reading 163kW, 170kVA @ 0.96 power factor. This reading would appear to be ‘normal’. It was also noted that the Power Factor Correction equipment was connected to the same busbar with 4 x 50kVAr stages connected (200kVAr total). The meter wiring was corrected and the meter was re-configured. The following table shows the before and after, meter readings:
|Meter readings – Before remedial works
|Power Factor Correction
|Meter readings – After remedial works
|Power Factor Correction
The remedial works now showed that all sub-metered loads were now summing to approximately 98% of the total supply at this switch-room. It was also found that the sum of the switch-rooms main meters summed to the main ESB meter reading (Total site supply).
This validation process in summary should consist of a number of stages:
- individual meter validation against a calibrated portable power analyser;
- logging data for a period of time and then compared to utility bills;
- with reconciliation of sub-metered loads versus main meters;