SUGGESTION BOX Intelligent Monitoring

Curragh Resources, the new owner of the Cyprus Anvil lead-zinc mine in the Yukon, has installed a permanent monitoring system in its mill control room. The company says the system will cut costs considerably by providing information needed in order to better manage its electrical power consumption.

The mine was closed in 1982 because of low zinc prices and high production costs. It was sold to Dome Petroleum and then to Curragh Resources in 1984. Reactivation began on Jan 2, 1986, and de-mothballing took six months under the direction of Kilborn Engineering of British Columbia. The mine went back into production on June 15 of last year.

Electrical equipment at the mine consumes 17.5 mW and peaks at about 24.4 mW. The synchronous motors for the grinding process alone use close to 5,000 kW while another 2,700 kW is used in the flotation circuit.

The way existing utility rates are structured in the Yukon, a demand charge (which is $16.73 per kva) is based on peak kva. The mine’s billing demand is based on the current month’s maximum kva demand or the maximum kva demand experienced during the 12-month period ending with the current billing month — whichever is greatest. This means the peak demand incurred in January, say, will also be the peak demand billed for the next 12 months.

The objective, then, is to avoid dramatic spikes in demand. By monitoring electricity consumption, Curragh can control peak demand on a continuous basis in order to minimize operating costs year-round. Instead of incurring exorbitant costs year-round, caused by a brief surge in electrical demand one month, the company can choose to activate a 2,500-kW emergency generator. The generator supplies to the mill surplus power during anticipated peak demand periods.

The expandable system which does the monitoring was engineered by the Vancouver office of Kilborn Engineering. It consists initially of two 3600- acm power monitors, manufactured by Power Measurement (Victoria, B.C.), and an ibm 5531 industrialized computer, with custom software supplied by Power Measurement.

The main incoming 13.8-kv line feeds two 13.8-kv/4.16-kv transformers which supply two separate 4.16-kv buses with an open tie-breaker. Each bus is monitored independently and the loads are totalled and recorded in the mill’s main control room.

All power data are collected by the “intelligent” 3600 acms, which are connected to the feeders to be monitored by pts and cts. The data in engineering value format are retrieved from the 3600 acms by the ibm computer via RS232C ports in serial ascii format.

The ibm scans the 3600 acm power monitors every 17 seconds and provides the following:

* Real time reports;

* History reports;

* Graphic display with values upgraded every 17 seconds;

* Daily reports.

In addition, alarm parameters for maximum and minimum voltage, power factor, frequency and kW demand are set by the operator. Should these parameters be violated, an audible and visual alarm is activated and the nature of the alarm and the time of occurrence are logged on a printer.

Continuous electrical data are stored on hard disk for one year before being overwritten.

The system also features a modem which allows Kilborn’s engineers in Vancouver to assess all power reports for peak shaving analysis. When sufficient data have been accumulated, Kilborn will use the load-shedding capabilities of the 3600 acms to systematically reduce peak demand.