Source: Fundamentals of Electricity
Operation of high-voltage switchgear
There are four main voltage levels of high-voltage switchgear 500kV, 220kV, 35kV and 10kV, and there are also voltage levels of 6kV in power plants. Among them, 500kV and 220kV circuit breakers are basically SF6 circuit breakers (including GIS); Most of the 110kV circuit breakers are SF6 circuit breakers (including GIS), and a few are less oil circuit breakers; Most of the 35kV circuit breakers are SF6 circuit breakers (including GIS), and a few are less oil circuit breakers; 10kV and 6kV circuit breakers are mainly vacuum circuit breakers.
Insulation resistance measurement
Instruments required for this job
Test preparation: Before the test, it is necessary to confirm that the auxiliary circuit and the control circuit have indeed been cut to the power supply.
Test requirements
1) Primary part: According to the requirements of relevant regulations, use the corresponding gear to measure the insulation resistance of the opening break, closing whole and insulation rod of the circuit breaker, connect the wire correctly during measurement, and pay attention to the operation sequence to prevent burning out the insulation resistance tester. The measured insulation resistance should be compared with the factory value, and there should be no obvious change.
When there is no factory reference value, the insulation resistance can be referred to the following table:
Measurement method: The method of measuring the insulation resistance between the fractures is that the switch is in a state of maintenance, in the opening position, the switch ground knife is opened, the L termination of the insulation shake meter is connected to one end of the tested fracture, the E termination is connected to the other end, and the gear is selected to be 2500V for measurement.
The method of measuring the insulation resistance of the insulating tie rod is that the switch is in the overhaul state, in the opening position, the switch ground knife is opened, the L termination of the insulated rocker meter is connected to the moving contact side of the breaker, the E terminal is grounded, and the gear is selected to be 2500V for measurement.
2) For the secondary circuit test of the circuit breaker, a 1000V or 500V megohmmeter is used to measure the insulation resistance of the secondary circuit to the ground. Connect the L end of the megohmmeter to the assessment end of the measured insulation, connect the E terminal to the ground, and the measured insulation resistance should not be less than 2 megaohms. When measuring, disconnect the grounding wire of the secondary circuit, short all secondary circuits, and if it cannot be shorted, it can be measured separately or by point contact.
3) For the opening and closing coil of the circuit breaker, the insulation resistance of its separate should be measured, the secondary wiring should be disconnected, and the 1000V or 500V megohmmeter should be used for measurement, the L end of the megohmmeter should be connected to the coil, and the E terminal should be grounded, and the measured insulation resistance should not be less than 10 megaohms.
Resistance measurement of each phase of the conductive loop
Instrumentation required for this test
Test requirements
1) The wiring diagram of the test principle is as follows:
Because the contact resistance of the conductive loop is very small, it is of the order of magnitude of microohms, so the internal resistance of the voltmeter is much greater than this value, so the resistance value of the conductive loop
2) The wiring diagram of the test site is as follows:
The test will rise the current to 100A, measure the voltage at both ends of the circuit breaker in the closed state, and use the voltage drop principle to calculate the conductive loop resistance R=U/I, the specific test method is determined by the test instrument, generally speaking, according to the wiring method of the instrument, the wire can be measured
Mechanical property test
The mechanical characteristics test of circuit breaker mainly includes time characteristic test and speed characteristic test, and relevant project tests are mainly carried out according to the specific needs of manufacturers and customers. At present, there are many instruments for this kind of test, and its principle is basically the same, mainly through the current parameter to measure the time, synchronousity, bounce and other parameters of the circuit breaker, through the stroke input of the stroke gear can measure its speed characteristics, and the specific test method is determined according to the structural characteristics of the equipment.
Test requirements
1) Test schematic diagram
2) Test requirements:
Unless otherwise specified by the manufacturer, the simultaneity of the opening and closing of the circuit breaker shall meet the following requirements:
The different phases of interphase closing are not more than 5ms
The different phases of interphase opening are not more than 3ms
The different periods of closing between each fracture in the same phase are not more than 3ms
The opening period between each fracture in the same phase is not more than 2ms
3) The measurement principle of the speed characteristic test of the circuit breaker is basically the same as the speed characteristic, generally speaking, the action stroke of the circuit breaker is transmitted to the measuring instrument through the transmission of the stroke gear, and the time characteristics are easily obtained through the calculation formula of V=S/t.
AC withstand voltage test
Instruments required for this test
The AC withstand voltage test is the most important insulation test in the circuit breaker handover test, and the test should be carried out only after the other insulation tests are completed and confirmed.
35kV and below circuit breaker withstand voltage test
Due to the low test voltage and small capacity of the circuit breaker in this voltage level, the test can be carried out using a transformer direct step-up
Withstand voltage test of circuit breaker of 110kV and above
Due to the high test voltage and large capacity of the circuit breaker of this voltage level, the test transformer capacity is insufficient and difficult to carry if the transformer is used for direct step-up test. Therefore, the test was carried out using a series resonant withstand voltage set that can be used in combination. It is required that the test voltage must be the power frequency.
Serial resonance knowledge points: tuning, conditions for resonance generation: the sum of inductive reactance and capacitive reactance in the series loop is 0 is the ideal resonance state (i.e., ωL=1/ωC).
For example, in a circuit that combines a 50Hz power supply, resistor R, capacitor C and reactor Z in series, and the supply voltage is 50V, the resistance is 3Ω, and the capacitance of the capacitor is 1000pF.
To form a resonant (xiézhèn) loop, it is necessary to let ωL = 1/(ωC), i.e
The insulation level of the circuit breaker to the ground shall comply with the provisions of GB311.1 "Insulation Coordination of High-voltage Power Transmission and Transformation Equipment" (the 1min power frequency dry test voltage of 10kV and 35kV products shall be 42kV and 95kV respectively). Corresponding requirements should also be put forward for the level of insulation between phases. The effect of the highest voltage of the inverted phase should be considered for the withstand voltage level between the fractures.
To sum up, the power frequency withstand voltage of the circuit breaker should include all parts of the ground, phase and fracture, and should be carried out in the closed and open states respectively. For specific tests, the pressurized parts and wiring methods should be carried out in order according to the following table. If the insulation of the high-voltage switchgear is mainly made of solid organic materials, it is necessary to carry out the power frequency withstand voltage test for 5min.
The power frequency AC withstand voltage test standard of circuit breaker is:
1 When the air pressure of SF6 is the rated value. The test voltage is 80% of the factory test voltage;
2. The voltage level below 110kV should be tested for closing to the ground and between fractures;
3. The tank circuit breaker should be closed to the ground and the withstand voltage test between the fractures;
4 500kV fixed opening distance porcelain pillar circuit breaker only carries out fracture withstand voltage test.
The amplitude and frequency of the test voltage should be consistent with the requirements of the electrical equipment connected to the circuit breaker, and the test should be disconnected if necessary
Test items and specification requirements
1. SF6 circuit breaker and GIS test project
2. Test items of oil circuit breaker
3. Air circuit breaker, vacuum circuit breaker and disconnector