| Current differential protection is based on Kirchhoff’s current law. Since it has a clear principle and the ability of phase selection and is not affected by power system oscillation, current differential protection is ideal for the EHV and UHV transmission lines. However, when used on long-distance EHV and UHV lines, it suffers from the capacitive current, so appropriate compensation is needed.Travelling-wave differential protection is free from the impact of distributed capacitive current theoretically, but interpolation is required to acquire the voltage and current values of non-sampling points, which increase the calculation amount of the algorithm. Based on travelling-wave differential theory, an applied protection scheme is proposed. This scheme works without interpolation or voltage of the opposite side.Refraction and reflection occur when travelling-wave propagates in a single hybrid line because of the different surge impedances on it. In consequence, the travelling-wave differential protection cannot be directly applied to the hybrid lines. A scheme of travelling-wave differential protection that is suitable for hybrid lines is presented, and its validity is proved by electromagnetic transient simulation. |
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