Design of Low-Frequency Quasi-dc GIC Voltage Stability Laboratory Protocol

Low-frequency currents in electrical power systems driven by a geomagnetic disturbance (GMD) are known as geomagnetically induced currents (GIC). These have several effects on transformers and power systems. The main concern for power system operators is the voltage stability of the networks in presence of GIC. There are several reports on GIC and system voltage collapse during significant GMDs. However, very little information is available on the dynamic analysis of the resultant voltage instability. This paper presents a laboratory protocol that can be used to study voltage stability under GIC conditions. The testing protocol uses frequency-dependent transmission lines with both resistive and inductive elements. While almost all GIC studies use a straight direct current for steady-state analysis, this study proposes a special “quasi-dc” injection circuit which oscillates at a very low frequency - necessary to emulate better the dynamic behaviour of a real GIC. The design, fabrication, and characterization of each scaled down power system component is presented. To test the veracity of the protocol, simulations were carried out in PSCAD/EMTP. The simulation results showed that an increase in the quasi-dc injection drove the power system to voltage instability. The dynamic analysis which compared the conventional dc injection response to the low-frequency injection indicates the response to the latter is more representative of the real power system response reported in the literature. The implication of this study is an improved approach to modelling GIC for voltage stability studies.