The invention belongs to the field of 
relay protection of a power 
system, and relates to a split-phase 
differential protection method based on scalar product 
brake criterion normalization. The method comprises the following steps of: acquiring the currents on the two sides of a 
transmission line by utilizing current transformers (CTs) on the two sides of the 
transmission line; calculating the amplitude values, the phase angles and the 
phase angle difference between the currents on the two sides by utilizing a full-wave Fourier 
algorithm; if the 
phase angle difference between the currents on the two sides is less than 120 degrees, determining that an internal fault exists, performing the protection action of 
tripping; and if the 
phase angle difference between the currents on the two sides is more than 120 degrees, turning to the amplitude value judgment below: first, judging whether the amplitude values of the currents on the two sides are both greater than three times the rated current of the primary side of the CT, wherein if the amplitude values are both greater than three times the rated current of the primary side of the CT, the 
proportionality factor K=2, and if the amplitude values are not greater than three times the rated current of the primary side of the CT, the 
proportionality factor K=0.8; and then calculating the ratio of the smaller amplitude value to the greater amplitude value of the currents on the two sides, wherein if the ratio is less than the K, determining that an internal fault exists, and performing the protection action of 
tripping. According to the split-phase current 
differential protection method of the 
transmission line provided by the invention, the sensitivity of the internal fault and the selectivity of an external fault are taken into consideration.