Effects and Measurements of Current Differential Protection for Transmission Line with Transformer Type Controllable Shunt Reactor

Controllable shunt reactors are categorized into the following two types: magnetically saturation controlled shunt reactors (MCSR) and transfonner type controllable shunt reactors (TCSR), EHV transmission lines generally employ TCSRs that feature smaller harmonic currents, faster response and less power losses. Adjusting the capacity of TCSR causes differential current changes. This poses challenges to protection setting values, capacitive current compensation, and compensation parameters checking in line current differential protection. Through the study of TCSR, the effect of TCSR used on transmission line for line current differential protection is studied and different solutions are proposed and compared. A new method of time domain compensation for TCSR used on transmission line is presented. The transient capacitive current compensation requirements and high sensitivity of line differential protection is satisfied by this method. High reliability of line differential protection is ensured by the configuration with compensation and without compensation in parallel while CT (Current Transfonner) installed on TCSR is abnormal. To address the above challenges, the feasibility for the method above is verified by an engineering application. The current differential protection was employed in the Shazhou-Yuqia line in northwest China so as to verify the feasibility of the new methods.