Jianjun Yao

A new axial magnetic field contact for 126kV single break vacuum interrupters

We proposed a new kind of coil type axial magnetic field (AMF) contact for 126 kV single break vacuum interrupters (VIs). The objective of this paper is to analyze and optimize AMF characteristics of the new contact. Compared with a former coil type AMF contact with 2 segments we developed, the new AMF contact is advantage with stronger AMF and lower electrode resistance. Its AMF characteristics were analyzed by finite element method (FEM) and we optimized AMF characteristics of the new contact by quadratic orthogonal regressive analysis. The optimization design results show that 1) the maximum axial magnetic flux density is 8.84 m T/kA on intermediate plane of contact gap 30 mm at current peak; 2) the maximum axial magnetic flux density is 1.18 m T/kA on intermediate plane of contact gap 30 mm at current zero; 3) the minimum electrode resistance is 7.8 muOmega.

Development of a 126kV single-break vacuum circuit breaker and type test

High-voltage vacuum circuit breakers in transmission voltage, as their environmental friendly characteristics, are drawing more and more interests all over the world. The objective of this paper is to present experimental results of type-test for a 126kV/40kA-2500A single-break vacuum circuit breaker based on a standard of IEC 62271-100. Two kinds of test circuits were adopted in type tests for the 126kV/40kA-2500A single-break vacuum circuit breaker. One is direct test circuit for test duties such as out of phase making and breaking test duties OP1 and OP2. The other is synthetic circuit for test duties, such as terminal fault test, capacitive current switching test, short-line fault test, out-of -phase test, double earth test and electrical endurance test. Type-test results, for the 126kV vacuum circuit breaker, presented in this paper are as follows: Dielectric test, 230kV 1min power frequency voltage withstand test and lightning impulse voltage withstand test, with 15 times 550kV in both of polarities; Short time withstand current with 4s duration and peak withstand current test with 100kA; Terminal fault test, including test duties: T10, T30, T60, T100s, T100a; Out of phase making and breaking test, including OP1 and OP2; Short-line fault test L90 and L75; Double-earth fault test as well as capacitive current switching tests of class C1 with test duties of LC1, CC1 and LC2, CC2; Electrical endurance tests; And assessment of condition after test with a 80%of dielectric test voltage; Temperature rise test under rated current of 2500A; Mechanical endurance test of class M1. In summary, the 126kV/40kA-2500A single-break circuit breaker passed the type tests.

Development and Type Test of a Single-Break 126-kV/40-kA–2500-A Vacuum Circuit Breaker

The objective of this paper is to present a 126-kV/40-kA-2500-A single-break vacuum circuit breaker (VCB) and its type test results based on the IEC 62271-100: 2006 and GB1984-2003 standards. A single-break 126-kV vacuum interrupter (VI), with a pair of 2/3 coil-type contacts, is used in the 126-kV VCB. The external insulation of the VI is provided by SF6 at 0.1 MPa. A spring-type operating mechanism is used to provide a closing velocity of 1.15 m/s, which is an average velocity for 4 mm before the moving contact mates with the stationary contact. The opening velocity within 20 mm, which is 1/3 of a full contact stroke of 60 mm, is 3.5 m/s. Two kinds of test circuits are used in the type tests to verify the making and breaking capabilities of this 126-kV VCB prototype. One is a direct test circuit for test duty cycles, such as out-of-phase making and breaking test duties, that is, OP1 and OP2; capacitive current switching test of class C1, that is, CC1/LC1 and CC2/LC2. The other is a synthetic circuit, used for tests, such as the terminal fault test, the short-line fault test, the double earth fault test, and the electrical endurance test of class E2. The dielectric tests of a 230-kV/1 min power frequency voltage withstand test and a 550-kV lightning impulse voltage withstand test were used to verify the dielectric withstand performance of the VCB. Experiment results presented in this paper showed that the 126-kV/40 kA-2500 A single-break VCB passed the type tests according to IEC 62271-100 and GB1984-2003.

Relationship between displacement characteristics of a 126kV vacuum circuit breaker and spring type operating mechanism

Spring type operating mechanism is widely used in high voltage circuit breakers. We investigated displacement characteristics of moving contact in opening and closing operation and how it is influenced by design of the spring type operating mechanism. Dynamics models were set up to demonstrate the relationship between displacement characteristics including initial opening speed, average opening speed, average closing speed and design parameters of operating mechanism including contact spring, over-travel, opening spring, cam and damper etc. Our simulation results show that the initial velocity increased significantly as over-travel and preload of contact spring increased. The damper and the cam can be designed to get a suitable displacement characteristic of movable contact.

Experimental characterization of current chop in 126kV vacuum interrupters

Because of great harmfulness of greenhouse effect, SF6 gas has to be limited, and it is necessary to develop high voltage vacuum circuit breakers to replace SF6 circuit breakers. Current chop is a well-known phenomenon for vacuum interrupters and results in high overvoltage. The chopping current depends not only on material parameters and gap parameters, but also on the parameters of the electrical network. In this paper, current chop phenomena of 126kV single break vacuum interrupters have been researched in an experimental circuit where current is limited either by a resistor or an inductance. In the experiment, contact gap is 20mm or 30mm and arcing current is 32A or 66A. A serial of experiment has been carried out for two 126kV vacuum interrupters with CuCr55 and CuCrTa contact material. It has been found that the current chop phenomenon shows a significant dependence on contact materials, arc current and the capacitance parallel to the switching gap. The results showed that the chopping current of CuCrTa contact material is lower than that of CuCr55 contact material for 126kV vacuum interrupters.