Analytical Model of Capacitive Voltage Transformers for the Calculation of Voltage Collapse Transients

Protection relays monitor system voltage through Capacitive Voltage Transformers (CVTs), which scale voltages to safe levels. However, during voltage collapse, CVTs lag in transmitting the event due to their internal capacitors, impairing protection performance. Because of this, manufacturers and relay operators need an accessible, simple and reliable model to design and predict CVT behavior under collapse conditions. This paper presents an analytical model of CVT transient response during voltage collapse. The proposed model is validated against an established Electromagnetic Transient (EMT) simulation tool. Our model predicts the output voltage under sustained short circuits at the input without simulations, eliminating the need for specialized software or extensive training. Derived from an accepted equivalent circuit, it depends only on CVT parameters and construction. The model applies across wide burden ranges, accuracy classes, and several ferroresonance suppression circuit types (resistive, electronic, or non-linear). Compared with EMT simulations, the model achieves over 90% accuracy and dependability across all tested cases. The model can be readily integrated into CVT design workflows using standard software, enabling faster and more economical modeling of CVT behavior during voltage collapse tests as required by industry standards.