Conventional power distribution system is radial in nature, characterized by a single source feeding a network of downstream feeders. Protection scheme for distribution system, primarily consisting of fuses and reclosers and, in some cases, relays, has traditionally been designed assuming the system to be radial. After connecting distributed generation (DG), part of the system may no longer be radial, which means the coordination might not hold. The effect of DG on coordination will depend on size, type, and placement of DG. This paper explores the effect of high DG penetration on protective device coordination and suggests an adaptive protection scheme as a solution to the problems identified. Results of implementation of this scheme on a simulated actual distribution feeder are reported.

Development of adaptive protection scheme for distribution systems with high penetration of distributed generation

In today's distribution grids the number of distributed generation (DG) units is increasing rapidly. Combined heat and power (CHP) plants and wind turbines are most often installed. Integration of these DG units into the distribution grid leads to planning as well as operational challenges. Based on the experience of a Dutch distribution system operators (DSO), this paper addresses several possibilities to handle grid planning issues. Effects on voltage control, grid protection, and fault levels are investigated and described. These aspects are illustrated with the aid of simulations on an existing distribution grid. It is demonstrated that in compact distribution grids voltage control problems and blinding of protection are not likely to occur and that false tripping and fault level have to be considered carefully.

Integration Issues of Distributed Generation in Distribution Grids

Microgrids can be operated either grid-connected to reduce system losses and for peak shaving or islanded to increase reliability and provide backup power during utility outage. Such dual configuration capability imposes challenges on the design of the protection system. Fault current magnitudes will vary depending on the microgrid operating mode. In this paper, a microgrid protection scheme that relies on optimally sizing fault current limiters and optimally setting directional overcurrent relays is proposed. The protection scheme is optimally designed taking into account both modes of operation (grid-connected and islanded). The problem has been formulated as a constrained nonlinear programming problem and is solved using the genetic algorithm with the static penalty constraint-handling technique. The proposed approach is tested on two medium-voltage networks: a typical radial distribution system and on the IEEE 30-bus looped power distribution system equipped with directly connected conventional synchronous generators.

Optimal Protection Coordination for Microgrids With Grid-Connected and Islanded Capability

Among different sources of alternate energy, wind and solar are two prominent and promising alternatives to meet the future electricity needs for mankind. Generally, these sources are integrated at the distribution utilities to supply the local distribution customers. If the power generated by these sources is bulk, then they are either integrated at the distribution/transmission level or may be operated in an island mode if feasible. The integration of these renewables in the power network will change the fault level and network topologies. These fault levels are intermittent in nature and existing protection schemes may fail to operate because of their pre-set condition. Therefore, the design and selection of a proper protection scheme is very much essential for reliable control and operation of renewable integrated power systems. Depending upon the level of infeed and location of the renewable integration, the protection requirements are different. For low renewable infeed at the distribution level, the existing relay settings are immune from any small change in the network fault current from new incoming renewables. However, bulk renewable infeed requires modification in the existing protection schemes to accommodate the fault current variation from the incoming renewables. For bulk penetration of the renewable, the requirement of modified/additional protection schemes is unavoidable. Adaptive relaying and non-adaptive relaying schemes are discussed in the literature for protection of power networks, which are experiencing dynamic fault currents and frequent changing network topologies. This article presents a detailed review of protection schemes for renewable integrated power networks which includes distribution, transmission and microgrid systems. The merits and demerits of these protection schemes are also identified in this article for the added interest of the readers. The visible scope of advance protection schemes which may be suitable for providing reliable protection for dynamic fault current networks is also explored.

Protection challenges under bulk penetration of renewable energy resources in power systems: A review

The paper aims at providing an overview of the impact that distributed generation (DG) might have on the operation of distributed networks. Issues like impact of DG on losses, voltage control, power quality, short circuit power, and system protection are discussed. Based on the discussion, it can be concluded that the impact of DG depends on the penetration level of DG in the distribution network as well as on the DG technology. Furthermore, critical issues, for example the impact of DG on the protection system, can be solved by using the right technology and detailed studies beforehand. Also, new operation approaches, using IT technologies, might help to integrate DG into the distribution network operation.

Interaction between distributed generation and the distribution network: operation aspects

Protection of a power system is an extremely important aspect as the duality and scheme of protection decides system reliability, controllability and stability. This paper concentrates on the protection of a distribution system in the light of developments in distributed generation (DG). The conventional distribution system is radial in nature, characterized by a single source feeding a network of down-stream feeders. The protection system has traditionally been designed assuming the system to be radial. After connecting DG, part of the system may no longer be radial, which means the coordination might not hold. The effect of DG on coordination will depend on size, type and placement of DG. This paper explores the effect of DG on protective device coordination such as fuse-fuse, fuse-recloser and relay-relay. In each case, depending on size and placement of DG, there are some margins in which the coordination may hold and certain cases, where no margin is available. These conditions are identified for each case through coordination graphs.

Effect of distributed generation on protective device coordination in distribution system

Conventional power distribution system is radial in nature, characterized by a single source feeding a network of down-stream feeders. Protection scheme for distribution system, primarily consisting of fuses and reclosers and in some cases, relays, has traditionally been designed assuming the system to be radial. After connecting distributed generation (DG), part of the system may no longer be radial, which means the coordination might not hold. The effect of DG on coordination will depend on size, type and placement of DG. This paper explores the effect of high DG penetration on protective device coordination and suggests an adaptive protection scheme as a solution to the problems identified. Results of implementation of this scheme on a simulated actual distribution feeder are reported.

A.A. Girgis

Papers

Development of adaptive protection scheme for distribution systems with high penetration of distributed generation

Effect of distributed generation on protective device coordination in distribution system

Development of adaptive protection scheme for distribution systems with high penetration of distributed generation