Megger
1. Insulation resistance measurement method between lines
① Connect the lines as shown in Figure 1. Both desks will remove the discharge tube of the tested line from the safety device from the desk and disconnect the external line plug from the incoming frame to cut off power to the line under test. The test desk then connects the wires from terminal “L” and terminal “E” of the megger to conductors L1 and L2 of the circuit under test respectively. Meggers generally use 250V rated output voltage type, because when using 500V meggers, the discharge tubes of the terminal pole protectors on both sides must be removed, otherwise the discharge tubes will discharge , causing test errors;
② Shake The rotation speed of the megger generator crank should be gradually increased from slow to fast. Once theIf the speed regulator is slipped, the rotation speed must be kept uniform and stable to avoid inaccurate measurements. Generally, when the starting speed reaches about 120 rpm, the rated output voltage can be reached for measurement;
③ The dial reading will wait until the generator speed stabilizes, and the pointer on the dial will also stabilize, and point to a certain scale value. This value is the value of the insulation resistance to be measured.
2. Line-to-ground insulation resistance measurement method
This test is usually carried out at the same time as measuring the insulation resistance between lines, so that as "E" connection Remove the single wire from the terminal block and connect the ground wire to the "E" terminal for measurement. Other methods are the same as those used to measure insulation resistance between wires. When the ground wire connected to the terminale "E" does not move after measuring L1, remove the wire from the L1 wire terminal and connect it to the L2 wire, then perform a ground insulation resistance test on this wire.
3. Method for Measuring Insulation Resistance of Cable Core Wire to Ground
Before performing this test, you must first understand the role of the ring protection. .
Due to the narrow distance between the terminals "L" and "E" of the megger, under the action of several hundred volts of direct voltage, the current leakage directly from "E" to " L" is very small. Large, see Figure 2. If it flows through the current coil La with current I1 flowing through the insulation resistor RX, then La will receive an additional rotational torque equivalent to the leakage current. This torque will make the reading indicated by the pointer incompatible with the actual RX value. Additionally, when measuring a high resistance insulator, the escaping current ibe of the insulator surface will also flow into the current coil La through terminal L, causing a certain error. With the protective ring G, since it is connected to the negative pole of the generator (note that the protective ring and terminal L are isolated from each other), as shown in Figure 3, the currents leakage ia and ib at the two locations will be directly connected by the protection ring. It returns to the negative pole of the generator without passing through the current coil La. i Therefore, ia and ib will not affect the insulation resistance reading RX, i.e. the guard ring plays a protective role.
The method of testing the insulation resistance of cable core wires to ground is the same as the above method of measuring the insulation resistance of single wires of lines aerials open to the ground. The method is the same. The difference is: sometimes, in order to make the measurement results precis, it is necessary to connect the protective ring wire "G" to the core insulating paper tape or cable paper roll, then the measurement can be carried out. For specific connection methods, see Figure 3.
The products we offer include earth resistance testers, insulation resistance testers, lightning protection component testers, DC resistance testers, loop resistance testers, micro water testers, salt density testers, transformer testers, dielectric loss testers, switching characteristics. testers, relay protection testers, test transformers, series resonance complete sets, etc. Boyu Electric Power is guided by "people-oriented technology innovation" and is dedicated to providing customers with better testing solutions!
Sanxin Electric Power is a solution providerhigh-end ns which integrates power testing, debugging and power technical services. It is based in Wuhan High Voltage Research Institute, Department of Electric Power. from Huazhong University of Science and Technology, Wuhan universities and other institutions provide technical support and are combined with the on-site experience of front-line debugging personnel in the electrical laboratories of several well-known domestic enterprises power construction, switch, transformer, generator and other manufacturing plants, we engage in high voltage power industry.
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