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

A new approach is proposed to solve the directional overcurrent relay coordination problem, which arises from installing distributed generation (DG) in looped power delivery systems (PDS). This approach involves the implementation of a fault current limiter (FCL) to locally limit the DG fault current, and thus restore the original relay coordination. The proposed restoration approach is carried out without altering the original relay settings or disconnecting DGs from PDSs during fault. Therefore, it is applicable to both the current practice of disconnecting DGs from PDSs, and the emergent trend of keeping DGs in PDSs during fault. The process of selecting FCL impedance type (inductive or resistive) and its minimum value is illustrated. Three scenarios are discussed: no DG, the implementation of DG with FCL and without FCL. Various simulations are carried out for both single- and multi-DG existence, and different DG and fault locations. The obtained results are reported and discussed.

Restoration of Directional Overcurrent Relay Coordination in Distributed Generation Systems Utilizing Fault Current Limiter

This paper presents a comparative survey of research activities and emerging technologies of solid-state fault current limiters for power distribution systems.

Survey of Solid-State Fault Current Limiters

Two approaches are proposed to solve the directional overcurrent relay coordination problem associated with the installation of distributed renewable generation (DRG) in interconnected power delivery systems (IPDS), depending on the existing system protection capability (adaptive or non-adaptive). For adaptive protection systems, the first proposed approach introduces a procedure to select the optimal minimum number of relays, their locations and new settings. This procedure is restricted by the available relay setting groups. For non-adaptive protection systems, the second proposed approach implements a practice to obtain optimal minimum fault current limiter values (FCL) to limit DRG fault currents and restore relay coordination status without altering the original relay settings. An integration of the proposed two approaches is evaluated for IPDSs possessing both protection systems. Three scenarios are assessed for different numbers of DRGs, and DRG and fault locations using an optimisation model implemented in GAMS software and a developed MatLab code. The obtained results are reported and discussed.

Resolving the impact of distributed renewable generation on directional overcurrent relay coordination: a case study

The design and application requirements for solid state distribution current limiters and circuit breakers are described and compared to those for the electromechanical switchgear used in present day distribution systems. Control strategies are provided for current limiting application in the power transformer main circuit and for current limiting and interruption for the bus tie location. >

Solid-state distribution current limiter and circuit breaker: application requirements and control strategies

The need for a distribution current limiting device (DCLD) by the utility industry is addressed. An evaluation was made of what specifications would be acceptable and what DCLD technique would fill the utilities' needs. Using this survey and a distribution system analysis, a DCLD that could limit a 20 kA fault to 10 kA in a 15 kV circuit was shown to be the primary candidate for further development. The study showed that gate turn-off thyristors (GTOs) are the best technology available that could be developed into a practical DCLD. A recommendation was made to develop a DCLD using GTOs. >

L. Hong

Papers

The utility requirements for a distribution fault current limiter