The federal government has been driving the process to develop an interconnected standard to establish the criteria and requirements of distributed generation (also called distributed resources or dispersed generation) to be connected into the utility-owned electric power grid. With the weight of the Department of Energy (DOE), Federal Energy Regulatory Commission (FERC), and National Renewable Energy Lab (NREL) behind it, an IEEE standards group has been working at a furious pace to develop the standard for such. The committee consists of a balanced group of 150+ members from the categories of “user,” “producer,” and “general interest,” translated as utilities, manufacturers of DG and the curious.
Begun in April 1999, IEEE P1547 Draft Standard for Interconnecting Distributed Resources with Electric Power Systems had its first ballot in October 2001. After a number of revisions and re-balloting, it is just about ready to go. The document provides a uniform standard for the interconnection of distributed resources with electric power systems. It provides requirements relevant to the performance, operation, testing, safety considerations and maintenance of the interconnection. There is additional work ongoing for additional documents:
- IEEE P1547.1 Draft Standard for Conformance Tests Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems
- IEEE P1547.2 Draft Application Guide for IEEE P1547 Draft Standard For Interconnecting Distributed Resources with Electric Power Systems
- IEEE P1547.3 Draft Guide For Monitoring, Information Exchange, and Control of Distributed Resources Interconnected with Electric Power Systems
- IEEE P1589 Draft Standard for Conformance Test Procedures for Equipment Interconnecting Distributed Resources with Electric Power Systems—specifies the type, product, and commissioning tests that shall be performed to demonstrate that the interconnection functions and equipment of a distributed resource conform to IEEE Std 1547.
The connection between electrical contractors and the world of DG is that it may be affecting your facility from both the inside and the outside in the very near future —particularly in the world of power quality and demand management. Distributed generation has been around for some time, especially in Europe. More often, the DG in the United States was used in a load shedding, off-line mode. The facility would remove loads from the grid and power them from their own DG equipment in their facility. With the energy crisis in California that occurred a couple of years ago, it rose to the forefront of the headlines of magazines and newspapers. Some of the companies that produced DG equipment saw their stock prices go through the roof. It also was a wake-up call to many facility electricians, who would find out when they switched over to backup generation, interesting things began to happen. Sometimes the generators failed to start, or produced much lower-than-rated capacity. In other facilities, areas that were suppose to be powered by such found themselves in the dark, and areas that were “wired” to be shed were burning brightly. Disconnect and system protection equipment didn’t always work as was thought.
The standards groups are striving to maintain the quality of the supply that one expects from the grid, even when the DG is interconnected onto the grid and helping to power loads throughout the grid. But knowledge of what the capacity and performance of the DG equipment that is in a facility and the compatibility of the loads that it will be powering is key information to have before it is called to be switched on. Some DG devices may not have the “electrical inertia” to keep a stiff regulated voltage during changing loads. For example, a generator may have a higher source impedance and less capacity to stay centered on the frequency and voltage levels when a large current drawing load is switched on. This may affect other loads on the circuit, as not only will there be a voltage sag, but the frequency may shift lower until the generator gets back into regulation.
In addition, there may be some involvement with the installation, testing and commissioning of DG infrastructure and equipment. One critical aspect of DG equipment that will be interconnected onto the grid is how it operates and recovers when there is a disturbance on the grid itself. Suppose lightning brings down a conductor, and that feeder is isolated from the grid either by the operation of a system protection breaker or a fuse. The generator will still try to backfeed into the grid which it can’t possibly support, unless its own system protection equipment operates. And then there is the sequence to bring things back on line. The loads are usually still there when the power goes out. If the same demands are on the system that required the activation of the DG are still there when the utility system is brought back on line, this will require the coordinated re-connection of all of the DG throughout the area.
As the Boy Scout motto says “Be Prepared.” In these days of increasing demands on raising productivity, waiting until the lights go out may not be in the best interest of you and your customers. EC
BINGHAM, a contributing editor for power quality, can be reached at 732.287.3680.