| Tellegen’s quasi-power theorem states that for two circuits with identical topology,the sum of the cross product of voltage and current on each branch is zero,regardless of whether the content of the branch is the same or not.If two circuits with the same topological structure are considered to operate in different working conditions,the two circuits have the same topological structure without internal failure,which satisfies the Tellegen’s quasi-power theorem.If an internal failure occurs,the circuit topology changes before and after the failure,and this theorem is no longer satisfied.Based on this characteristic,the internal faults of the power network can be reflected sensitively by using the Tellegen’s quasi-power theorem.In this paper.the Tellegen’s quasi-power theorem and its application in fault detection and line protection are studied.First,the Tellegen’s quasi-power theorem is generalized.Two sets of voltage and current measured by the same circuit network under different operating conditions are used as the voltage and current measured by two circuits with the same topology.Because of the same topology,the Tellegen’s quasi-power theorem is satisfied.The Tellegen’s quasi-power theorem is further extended to circuits with multiple operating conditions and individual topologies.For a circuit with a certain topology,the similar power calculation can be performed separately with other circuits.The Tellegen’s quasi-power theorem can only be satisfied if the two circuits have the same topology.Based on this,the Tellegen’s quasi-power theorem is extended to LCC converter,and the thyristors in the converter are turned on in turn.which is equivalent to the switching circuits of different topologies.A detection method of commutation failure based on the Tellegen’s quasi-power theorem is proposed.The scheme can detect the internal thyristor conduction state only by measuring the external port electrical quantity of the converter.Finally,the effectiveness of the method is verified by simulation.A further extension of the Tellegen’s quasi-power theorem is given.If the two power networks are not only topologically identical,but also the impedances of their internal branches are equal,the similar power of each branch in the two circuits can be canceled out.Based on this characteristic,the Tellegen’s quasi-power theorem is extended to transmission lines.The positive sequence network before and after the failure of transmission lines is treated as two equivalent circuits which conform to the Tellegen’s quasi-power theorem.A longitudinal protection of transmission lines based on the similar power theorem is proposed.The internal failure is determined by calculating the similar power difference between the two circuits.Since internal branches such as distributed capacitance branch and shunt reactor branch also meet similar power requirements,they are eliminated in the calculation process without affecting the discrimination and sensitivity of protection.Similar power calculation can be carried out by using only the electrical quantity at the ends of the lines.No precise line parameters are required,and the protection scheme is not affected by the system load state and distributed capacitive current.This provides a new protection scheme choice for dual protection configuration of UHV/UHV transmission lines.In addition,based on the zero difference of line similar power under normal load,a synchronization method based on Tellegen’s quasi-power theorem is proposed,which can calculate the synchronization errors at both ends of the line,so that the sampling time at both ends of the line can be corrected and synchronized under normal load.This method does not require equal communication delay and has good versatility.Finally,through the MATLB/Simulink simulation system,a large number of simulation models of 1000kV UHV transmission demonstration project are established,which verifies that the proposed protection scheme has good resistance to transition,high sensitivity and reliability for various fault types,and the validity of the proposed synchronization scheme.Based on the principle of Tellegen’s quasi-power protection,the Tellegen’s quasi-power theorem of lines with mutual inductance is deduced and verified.It is proved that the mutual inductance branch and the coupling capacitance branch inside the line are also full of Tellegen’s quasi-power theorem,and the protection principle is extended to double-circuit transmission lines.This paper presents a Tellegen’s quasi-power protection longitudinal protection method for high-voltage double-circuit transmission lines with the same tower.power calculation is done directly using the end voltage-current phasor,which is not affected by the internal coupling of the lines.It does not require complex compensation capacitive current calculation and decoupling calculation.Therefore,it can also be used for Multi-circuit Transmission Lines with insufficient or no transposition,which makes up for the drawback of traditional protection which is greatly affected by the accuracy of line parameters.Finally,the MATLB/Simulink simulation system is used to establish the model of the double-circuit transmission project with UHV transmission towers from Anhui to East China,which verifies the applicability and validity of the proposed Tellegen’s quasi-power protection scheme and the protection timing scheme for double-circuit transmission lines. |
