Synchronization method for current differential protection

1. A synchronization method for current differential protection, the method comprising:

selecting a point on a transmission line protected by a current differential protection;

measuring a current and a voltage of each of multiple terminals of said transmission line;

calculating a compensating voltage at a selected point respectively according to the measured current and the voltage of each of the multiple terminals;

detecting and calculating a synchronization error by comparing all the compensating voltages.

2. The method according to claim 1 , wherein said current and voltage of each of the multiple terminals are measured before a fault or after a fault.

3. The method according to claim 1 , wherein said current and voltage of each of the multiple terminals are vectors or sampling values.

4. The method according to claim 1 , wherein the current and the voltage of each of the multiple terminals are phase quantities or sequence quantities.

5. The method according to claim 1 , wherein said point is selected from one of any points of transmission line or a T connected point of the multi-terminal transmission lines.

6. The method according to claim 5 , wherein for a two-terminal transmission line, said point is selected from any points of transmission line, preferably from the middle or the end of the transmission line;

for a three-terminal transmission line, said point is selected from one of the T connected point or an end of the transmission line;

for a transmission line with more than three-terminals, the transmission line is divided into one of two-terminal transmission lines, three-terminal transmission lines or their combination; said points are selected according to a method of two terminal transmission line or three terminal transmission line.

7. The method according to claim 1 , wherein a startup element method, echo method or improved echo method is used for a preliminary synchronization.

8. The method according to claim 1 , further comprising:

distinguishing a calculated synchronization error caused by a serious line parameter change or an asymmetrical channel switching by calculating a changing speed of a phase angle difference or a wave shift of said compensating voltage.

9. The method according to claim 2 , wherein if the current and voltage of each of the multiple terminals are measured after a fault, the current and voltage are fault positive sequence components, negative sequence components, zero sequence components or a combination of some of them.