Voltage regulator monitoring reduces costs

Jeff Loven

Electrical Engineer

French Broad Electric Membership Cooperative

Jack Trainor

Product Manager

Siemens Power Transmission & Distribution

One of the major expenses for rural electric cooperatives is the cost associated with the purchase of power from larger utility companies.

Using equipment and strategies that reduce these expenses can pay for themselves very quickly and then continue to save money over the long run.

This is the situation at the French Broad Electric Membership Cooperative (FBEMC), Marshall, N.C. FBEMC provides approximately 70 MW of power to its customers along the French Broad River and in the Appalachian Mountains in western North Carolina. FBEMC generates approximately 3 percent of this power with its own hydro equipment. It purchases the remaining 97 percent from Carolina Power and Light (CP&L), Raleigh, N.C. There are nine delivery points between CP&L and FBEMC. CP&L meters the demand at each of these nine delivery points. Billing to FBEMC is determined by “coincident peak” metering-when CP&L delivers peak power to all of its customers, it meters FBEMC demand at that time and bases billing on these demand figures.

One way to reduce the cost of purchased power is to anticipate when these peak periods will occur, then, just prior to that time, reduce voltage on the lines so that the actual demand is less. This strategy requires two major components: a strategy for estimating when the peaks will occur, and a means of quickly reducing voltage on the lines. The reduction timing depends upon carefully studied contemporary and historical data. The communications ability of Siemens` MJ-X regulator control panels and MJXplorer remote monitoring and control system provides quick voltage reduction.

FBEMC`s equipment setup is as follows: the data port of each MJ-X regulator control panel connects via a communications cable to a port on the multiplexer. The multiplexer is connected through a surge protector to a modem. The PC with the MJXplorer software is connected to a modem that communicates with other modems in the system over dial-up telephone lines.

FBEMC`s system consists of approximately 45 MJ-X regulator control panels, 15 multiplexers, and 15 modems connected to one “master” PC and modem.

When connected in this manner, the MJXplorer retrieves operating and logging data from MJ-X control panels and can also be used to send Voltage Reduction Control (VRC) commands to MJ-X control panels.

FBEMC estimated savings of up to $50,000 per month using reduction timing strategy and Siemens control equipment. Voltage reduction timing is described as an educated guess, since it is sometimes difficult to predict when CP&L demand will peak relative to when FBEMC demand peaks.

In North Carolina, predicting winter low temperatures is generally easier than predicting summer high temperatures. For this reason, FBEMC gets more benefits from wintertime voltage reductions.

The capability and reliability of the Siemens equipment is very easy to predict. The data logging capability of the equipment makes it easy to monitor FBEMC demand at all times. Event Log and Interval Logging capabilities of the MJ-X regulator control panel provide powerful tools for analyzing operation of the power distribution system.

FBEMC estimated it shaved about 3 percent off its peak kW demand during the winter months. With an average system demand of 75 MW, the savings is 2.25 MW. The cost of power from CP&L is slightly over $16 per kWh, so the average cost savings is just over $36,000 per month. FBEMC estimated it made the right call about 6 out of the 8 winter months, resulting in total average savings of about $216,000 per year.

In addition to yearly savings in operating costs, installation expense was considerably less with Siemens equipment than it would have been with a comparable SCADA system. FBEMC considered several SCADA systems at a cost of approximately $30,000 to $50,000 per station. Siemens equipment cost was approximately $4,500 per station. This included about $2,000 per station for communications equipment, multiplexer, and wiring, and about $2,400 for MJ-X control panels. The co-op also incurred a phone-line expense of about $42.50 per month per station.

Installation and operation were more flexible than for a SCADA system, which works well when the same types of devices are used at each station. However, FBEMC has a mix of regulators and needed a system to control not only Siemens regulators, but other types as well.

Siemens MJ-X regulator control panels and MJXplorer software allow FBEMC to closely monitor its own system. One FBEMC customer is a ski resort whose snow-making equipment instantly doubles the system load when it turns on. FBEMC`s agreement with the ski resort states that the snow-making equipment must be turned off between 6 and 10 a.m. Using the MJ-X Interval Log, FBEMC can accurately track the ski resort`s power usage.

FBEMC personnel use the system`s collected data for many tracking, monitoring and analysis functions. The built-in communications capability of the MJ-X regulator control panel and the data- gathering capability of the software provide powerful cost-saving tools for rural electric cooperatives.

Siemens Power Transmission & Distribution

Inquire R.S. 101

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