Regarding transformer equipment, the differential protection of a dry-type transformer is the main protection of the transformer, which is installed according to the principle of circulating current. The transformer differential protection is mainly used to protect the short-circuit shortcomings of various phases that occur inside the windings of the double-winding or three-winding transformer and its lead wires. It can also be used to protect the short-circuit shortcomings of single-phase transformers.

  A current transformer is installed at both ends of the winding transformer, and its secondary side is connected according to the circulating current method, that is, assuming that the same-level ends of the current transformers at both ends are facing the bus side, the same-level terminals are connected, and the two terminals are connected. Connect current relays in parallel between. The current flowing in the relay coil is the difference between the secondary currents of the currWhen the short circuit between phases occurs in the transformer, in the differential circuit, because I2 changes the direction or is equal to zero (no power supply side), this is the current flowing through the relay is the sum of I1 and I2, that is, Ik=I1 I2=Iumb. The relay operates reliably. The planning of the transformer differential protection is the electrical equipment between the current transformers that constitute the transformer differential protection, and the wires connecting these equipment.ent transformers at both ends, that is to say, the differential relay is connected to the differential circuit.

  In theory, the differential loop current is zero during normal operation and external shortcomings. In fact, due to the fact that the characteristics of the current transformers at the two ends cannot be completely consistent, etc., during normal operation and external short circuit, there is still an unbalanced current Iumb flowing in the differential circuit. At this time, the current IK flowing through the relay is Ik=I1- I2=Iumb requires that the unbalanced point flow should be as small as possible to ensure that the relay will not malfunction.