First, the purpose and method of measurement
The purpose of measuring the insulation resistance of the stator winding of the generator is mainly to judge the insulation condition and find insulation defects of moisture, dirt and penetration of the insulation. Measuring the absorption ratio is mainly to judge the degree of insulation moisture. For units of 200 MW and above, the Pre-Regulation recommends measuring the polarization index. This is because the polarization index not only judges the insulation performance more effectively, but also has a large range irrespective of the stator winding temperature.
Second, the stator winding insulation resistance test
    The methods of measurement are divided into two types: air-cooled generators and water-cooled generators. For air-cooled generators, the stator winding rated voltage is above 1000 V, using 2500V megger, the range is generally not less than 10 000MΩ, the rotor winding is 1000V megohmmeter ; for water-cooled generator, the stator winding is dedicated megohmmeter measuring.
    The wiring during measurement is shown in Figure 4-1 and Figure 4-2.
    In the wiring of Figure 4-1, each phase winding must be shorted between the tail and tail phases to prevent the winding from being affected by the distributed capacitance between the turns. When measuring phase A, the B and C phases are also short-circuited to ground at the respective ends, so that the rotation resistance and the absorption ratio are relatively large for each phase and each phase. Windings with parallel branches must measure the insulation resistance between the branches of the same phase during overhaul or accident repair. The measuring leads should have sufficient insulation levels, and the ends of the windings A and X should be shielded from the insulating surface to eliminate the effect of edge leakage on the measurement. When measuring, the ground wire and the generator casing should be in good contact. After the megohmmeter is turned to the rated speed, when the needle indicates “00â€, the phase wire and the measured winding A and X are contacted, and the insulation of 15 and 60s is read. resistance. After the measurement is completed, disconnect the phase line at the rated speed of the megohmmeter, and then disconnect the ground wire to prevent the megohmmeter from being damaged by the reverse charging and discharging of the megohmmeter.
    After the measurement is completed, the generator should be fully discharged, and the discharge time should be greater than 5 min. When the phase is measured, each winding should be discharged for more than 5 minutes.
    In the case of different temperatures, the insulation resistance should be temperature-converted, and the conversion formula is
R C =K T R T
K T =0.5 (40-T)/10
    R C in the formula - the insulation resistance corrected to 40 ° C, MΩ;
           K T - temperature correction factor;
           R T - the insulation resistance at the time of measurement.
    When comparing, you should use the same temperature and the same voltage, model of the megohmmeter.
    For water-cooled generators, the wiring of Figure 4-2 should be used when using a dedicated megohmmeter. In order to measure the insulation resistance of the true water-cooled stator winding when passing water or not, the water pipe must be connected to the shield terminal of the megger. When the water is not measured, it is the same as the air-cooled generator, but it must be dried after the water in the generator is blown dry. When passing water measurement, due to the supply of a large current flowing through the water, a megohmmeter with sufficient capacity is needed, and the influence of the DC-polarized electromotive force in the waterway can be compensated and the sample capacitor can be prevented from being discharged to the parallel water resistance after the measurement is completed. And the header is damaged.
    In order to ensure that the output voltage of the tester is rated, the water resistance between the water pipe and the stator winding water pipe is required to be about 100kΩ; the insulation resistance of the water pipe (in parallel with the inlet and outlet pipes) should be above 30kΩ.
Third, the rotor winding insulation resistance measurement
    The insulation resistance measurement of the rotor winding is divided into static and dynamic conditions, and the dynamics are divided into two types: idling and load.
    Static measurement
    The generator is at a standstill. At this time, the brush is lifted up and measured with a 1000v megger (500V or less megger for water cooling). The "L" end of the megger is connected to the collector ring, "L "Terminate on the shaft. Before the measurement, the positive and negative collector rings should be short-circuited.
    2. Dynamic measurement
    (1) No-load measurement. At this time, the excitation circuit is in the demagnetization state, the brush is lifted, and the insulation resistance is measured point by point during the speed increase process, and the relationship between the insulation resistance and the rotation speed is plotted.
    (2) Load measurement. Using a voltmeter method, a multimeter with a internal resistance of 20000 Ω/V or a DC voltmeter (internal resistance of 5000 Ω or more) is used to measure the voltage Uk between the positive and negative collector rings and the voltage u + , u - of the opposite axis , respectively, and the rotor winding The value of the shaft insulation resistance
R=R V [u k /(u + +u - )-1]*10 -6 (MΩ)
    Where R V - the internal resistance of the multimeter, Ω.
    This measurement wiring includes the total insulation resistance including the excitation circuit, so the excitation circuit should be well insulated.
    For the water-cooled rotor, when measuring the insulation resistance, it is measured together with the water resistance in the case of water, and its insulation resistance is low.
Fourth, the analysis and judgment of measurement results
    (1) If the insulation resistance of the stator winding is reduced to less than 1/3 of the normal value over the years under similar test conditions (temperature, humidity), the cause should be ascertained.
    (2) The difference between the insulation resistance values ​​of each phase and each branch of the stator winding shall not exceed 100% of the minimum value.
    (3) The absorption ratio or polarization index of the stator winding, the absorption ratio of asphalt dipping and baking mica insulation should not be less than 1.3 or the polarization index should not be less than 1.5; the absorption ratio of epoxy powder mica insulation should not be less than 1.6 or polarization The index should not be less than 2.0. The water-cooled stator windings are self-regulated.
(4) The insulation resistance value of the rotor winding is generally not less than 0.5 m at room temperature; the insulation resistance value of the water-cooled rotor winding is generally not less than 5 kΩ at room temperature.
Feed Through Terminal Block Section
Feed Through Terminal Block.
In the electrotechnics, the terminal refers to the terminal and is designed to run through the terminal production. The type is divided into single hole, double hole, socket, hook, etc. from the material, copper silver plating, copper zinc plating, copper, aluminum, iron, etc. their functions are mainly to transmit electrical signals or conduct electricity. The unit of terminal block is "bit", and one wiring bit is "bit". Usually the so-called table is the serial number of the terminal, which has different definitions in different applications. "Jie" and "bit" have the same meaning, but they are called differently. Groups are made up of sections.
Feed Through Terminal Block
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