Assessment of Fault Level in Power Systems with High Penetration of Non-Synchronous Generation

  • Rafat Aljarrah

Student thesis: Phd

Abstract

The main goal of this thesis is to develop efficient methods for monitoring the fault level in the power system with increased penetration of non-synchronous generations (NSGs). This includes analyzing the dynamics of the fault current, evaluating the steady-state fault calculation methods and proposing new fault level calculation (FLC) methods to accurately quantify the variable fault level in future power systems. In classical power systems, where a large number of synchronous generators (SGs) are connected, the entire power system has a high fault level (i.e. high short circuit current). This high fault level contributes to a secure and reliable operation of the power system. Particularly, a secure power system protection as protective devices can easily distinguish between a normal (small currents) and faulty (high currents) system state. This is usually aided by the steady-state fault level calculation (FLC) approaches and standards which can accurately provide an estimation of fault currents. This accuracy is a result of the well-understood fault current response of SG, which is traditionally modelled as a voltage behind a reactance in steady-state fault calculations. However, power systems start changing their dynamic properties due to the increased penetration of renewable energy sources, e.g. wind-farms, photovoltaic (PV), or battery storage systems, as well as decommissioning large SGs to reduce CO2 emission. These types of sources are also referred to as NSGs. They use the Power Electronics based interface, i.e. inverters, to be connected to the existing synchronously operated ac network. Therefore, they have low and a very different fault current contribution, compared to those fed from SGs. Consequently, the dynamic of the short circuit current will potentially change and the accuracy of the fault calculation methods will be under question as this new technology Page | 17 requires different modelling. Furthermore, the fault level becomes significantly low, directly affecting power system protection and the system strength. As a result of the changes above, a need to monitor both the system fault level and the fault calculation methods becomes critical, especially in future scenarios with high penetration of NSGs. This thesis proposes a modification of the up-to-date IEC60909 fault calculation standards to include the fault contribution of NSGs more accurately, in addition to a novel FLC method which formulates for the changing fault level as a function of the penetration level of NSGs in the system. This enables the assessment of the system fault level for large numbers of the future grid (FG) scenarios more accurately without a need for a detailed system modelling and/or time-domain simulations. The thesis also proposes innovative solutions to substitute the low fault level as well as to mitigate the negative implications of the low fault level due to the increased penetration of NSGs. The thesis also proposes representative solutions to substitute the low fault level as well as to mitigate the negative implications of the low fault level due to the increased penetration of NSGs.
Date of Award1 Aug 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorVladimir Terzija (Supervisor) & Peter Crossley (Supervisor)

Keywords

  • Renewable Energy Resources
  • Non-Synchronous Generation
  • Fault Level Monitoring
  • Future Power Systems

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