Summary The paper presents integrated impedance-based intelligent relaying for thyristor-controlled series capacitor-compensated transmission lines on Real Time Digital Simulator platform. Integrated impedance is defined as the ratio of sum of the voltage phasors across two ends of the transmission line to the sum of the current phasors through two ends of the same transmission line. The imaginary part of integrated impedance of the transmission line is used as input to a data-mining model known as decision tree that determines whether the fault is within the protected zone or not. Critical issues such as power swing and fault during power swing are also included during validation of the relay on Real time digital simulator platform. The test results obtained indicate that the proposed integrated impedance-based intelligent relaying is highly dependable and secure for protection of extra high voltage transmission lines including thyristor-controlled series capacitor. © 2014 John Wiley & Sons, Ltd.