Meridian Energy Ltd had a PSI Quad 4+ based revenue metering platform at its hydro power stations in the South Island of New Zealand. Purchased in the early 1990s, the PSI Quad 4 revenue meters were once ‘state of the art’ but, while still providing reliable service, had become obsolete. New meters offered significant advantages with additional functionality, far superior communications capability and reduced routine maintenance.
PSC had previously carried out a detailed meter upgrade investigation for Meridian followed by a trial installation at the Tekapo A power station (project Phoenix). This was highly successful, and set the standard design and configuration pattern to be used at Meridian’s remaining power stations in the Waitaki Valley plus Manapouri. By this revenue metering upgrade, Meridian ensured full compliance with the mandatory requirements of New Zealand’s electricity market.
The new metering installation was based around the Schneider Electric (formerly Power Measure-ment Limited) PowerLogic ION 8600 meters. These meters provided all of the required recording and storage capabilities, and separate data recorders were no longer required. All data connections were made directly to these meters via their serial and LAN ports.
A separate aggregation meter was provided where aggregation to a station total is required. The meter LAN connection, using Modbus over TCP/IP protocol, is used by the aggregation meter to extract unit data for the station total.
Revenue data was extracted from the meters by STARK at half hourly intervals and also by ION Enterprise software at 1 second intervals, both via the LAN connection to the meters. Measurements to be displayed on SCADA and archived in PI Historian are extracted via RS485 links to station PLCs.
Project Outline
PSC was appointed by Meridian to carry out the detailed design of the metering installations, including supply of installation drawing sets, provision of meter setting parameters to the meter supplier (Quasar), commissioning plans, and QA inspection of the completed installation.
The meters provide compensation calculations for the transformer and line losses between the metering installation and the point of connection to the national grid. Unlike the existing Quad 4+ meters, the ION 8600 meters have the facility to enter the transformer and line losses separately. The ION meters also provide correction for both ratio and phase errors in CTs and VTs. Both corrections use a piecewise linear interpolation from the input data.
Outcome
The project was successfully carried out in 2010-2011.
PSC’s engagement was extended in 2011 to modify the existing design of the Benmore installation to take account of generator circuit breaker and transformer equipment changes, and to bring the Benmore installation into line with the standard of the rest of the Waitaki valley.
