1145 Operational Concerns

As discussed previously, operational concerns are minor whenever just a few small distributed generator units are installed on a distribution feeder and the penetration, in terms of the ratio of the capacity of the generators to the minimum load demand on the feeder, is very small (typically less than 10%). This scenario is already commonplace in the U.S. and Canada on some rural distribution feeders where small wind and PV systems are in operation at widely-spaced farms and ranches. DG operational concerns are expected to move to the forefront on highly-loaded urban feeders, where the scenario of many distributed generators (high density) and much higher penetration is expected to become the norm.

It is argued that without centralized control of the distributed resources (and possibly some of the loads), network stability and reliability will be greatly compromised. Ironically, this will require the design and implementation of control and dispatch approaches on a small scale that, on a larger scale, are now a necessary and vital part of the of the conventional centralized generation paradigm. This system of many distributed generators on a given feeder or feeders, along with the necessary monitoring and control system able to dispatch the generators individually, has been termed the virtual utility. The concept includes not only the ability to dispatch specific generators to supply the network, but also the ability, through remote and centralized control, to dispatch specific generators to serve loads that are being disconnected from the network feeder (i.e., shed) to mitigate peaks, for example. The disconnected loads go into intentional islanded operation but are returned to the network supply when conditions warrant. Inherent in this approach is the assumption that individual generators will start, connect to the network (if required), and operate reliably when called upon. In addition, the transfer switches and protective relays must also operate reliably. To some degree, each generator will operate intermittently.

While renewable power sources such as wind turbine generators and PV power generators can be connected and disconnected from the network at will, their power output varies continuously (albeit less so for PV). Therefore, more careful planning is required for the use of these resources in the high density, virtual utility generating mix. Nevertheless, their value can be substantial in situations where the wind and solar flux are substantial and predictable.

Most utilities require performance verification testing of larger distributed generating units. The rationale is quite simple — the larger the generating unit, the greater the impact it can have on network reliability and stability. Verification testing is, of necessity, site specific. To ensure reliable performance, the tests must be repeated periodically over the life of the installation. Until now, test procedures for interconnected generators have focused on the components and subsystems critical to protecting the network. In the new paradigm of DG, where effective utilization of the distributed resources is vital, the reliability of the distributed generators and their control and protection systems is of equal importance and they must also be periodically tested.

All critical interconnection, control, and protection components and subsystems should have type approval based on type testing carried out by independent testing laboratories. Typically, these components and sub-systems are required to meet the requirements of relevant UL, CSA, IEEE, ANSI, and other established and relevant standards as an integral part of the approval process for interconnecting and operating the distributed power plant.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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