Large-scale synchronous condenser (LSC) has a broad application prospect in China's ultra-high voltage direct current (UHVDC) to provide dynamic reactive power. Loss of excitation (LOE) is an important grid-related fault of LSC

resulting in uncontrolled reactive power consumption. However

due to the un obvious fault feature and UHVDC's diverse reactive power demands

LSC's LOE protection faces challenges in criterion and action mode configurations. Thus

this paper proposes a complete LOE protection strategy for the LSC used in UHVDC

including effective criterion and proper action mode. First

the defect of existing reverse reactive power-based protection is presented through an in-depth analysis of the LOE LSC's reactive power behavior. Then

excitation current difference between the measured value and equivalent actual value is identified as the new fault feature. Compared with existing reverse reactive power features which also appear in healthy LSC's leading phase conditions

this current difference feature only appears in the LO E process and thus is more typical. Since actual excitation current is unmeasurable in practice

an estimation model is built and validated by experiment and simulation. Moreover

the novel LOE protection strategy including current-based criterion and improved action mode is proposed. Through comparative simulation studies in PSCADIEMTDC

the novel protection exhibits superior performances compared to existing protection in LOE detection and commutation failure immunity improvement

as well as overvoltage suppression.