A solid state fault current limiter control algorithm

The fault current limiter (FCL) is considered as the ideal solution to limit the fault current in integrated electrical power systems with distributed energy resources because of its speed of response. However, there are some practical application issues for FCL in commercial industrial deployments. In this paper, the coordination issue of FCL with the other protective devices is discussed making use of simulation and experimental results. The fundamental point of operating a FCL is that it introduces an additional equivalent impedance into the power system and thus influencing the operation of the other protective devices, sometimes, leading to malfunction. A formula is proposed in this paper to estimate the impedance range of the equivalent FCL in order to maintain the coordination with the other protective devices. An example is used to demonstrate that the fault current can be limited by controlling the switching position of a solid state fault current limiter (SSFCL) while maintaining system coordination.

I. Introduction

To satisfy the increase of power demand and growth of distributed energy resources while maintaining or even increasing system reliability, researchers have addressed the need for fault current limiters in transmission and distribution power systems [1]–[4]. There are some practical application issues when deploying FCLs into electric power systems [5], in particular, coordination, product life and maintenance, performance, cost and size. From a technical point of view, the coordination of the FCL with pre-installed protective devices has to be studied to understand the impact of the FCL to the distribution system [6]. The impact of a FCL on circuit breakers has been reported in [7], which concluded that the best position for placing a FCL is downstream from the circuit breakers. The authors of [8]–[9] studied the coordination between protective devices in a power distribution system with a FCL and determined that the resistance or impedance of the FCL should be selected within a limited range to maintain protection coordination. The authors of [10]–[11] identified that deploying the FCLs in electrical power systems would delay the initiation of a tripping event in over current relays (OCR) and possibly make previously well-coordinated relays becoming miss-coordinated. The author in [12] designed an experiment to study the impact of a solid-state fault current limiter (SSFCL) to an impedance relay in a scale-down distribution system, and observed that the operation of the relay was delayed when a grounding fault occurred. In this paper, an example was given to illustrate that the impedance introduced by the SSFCL caused the OCR to lost coordination and a formula was proposed to estimate the correct range of the FCL impedance. Finally, it provided an example to demonstrate that the equivalent impedance of the SSFCL can be regulated by controlling the firing angle of the switching position, and thus, limiting the fault current and maintaining coordination with relays. SSFCLs operate by either inserting an impedance (mainly an inductor) [13]–[15] or voltage control by controlling the triggering angle of the semiconductor devices [12], [16]. The latter is considered in this work.