A megometeris a measuring instrument commonly used by electricians. It is mainly used to check the insulation resistance of electrical equipment, household appliances or power lines to ground and between phases. Ensure that these electrical equipment, devices and circuits operate under normal conditions to avoid accidents such as electric shock, casualties and damage to equipment.
The megometer is a commonly used and indispensable instrument in the sectors of energy, posts and telecommunications, communications, mechanical and electrical installation and maintenance, and industrial companies that use electricity as energy or industrial energy. It is suitable for measuring the resistance value of various insulating materials and the insulation resistance of transformers, motorss, cables and electrical equipment.
The case of this watch is made of high-strength aluminum alloy. It is equipped with an equipotential protection ring and a fourth-order active low-pass filter, which can effectively shield external power frequencies and strong electromagnetic fields. effect of fields. When measuring capacitive samples, since the output short circuit current is greater than 1.6mA, it is easy for the test voltage to quickly reach the rated value of the output voltage. For low resistance measurement, voltage drop does not affect the test accuracy due to the proportional method design.
Operating principle and selection of meggers
Digital meggers are composed of medium and large scale integrated circuits. This meter has large output power, short circuit current valuehigh uit and multiple output voltage levels (there are four voltage levels). The working principle is that the high DC voltage generated by the internal battery as a power source through DC/DC conversion flows from the E pole through the test product to the L pole, thereby generating a current from the E pole to the pole L, which is completed by the divider after the I/V conversion. The calculation directly displays the measured insulation resistance value on the LCD screen.
It is stipulated that the voltage level of the megger must be higher than the insulation voltage level of the object under test. Therefore, when measuring the insulation resistance of equipment or lines with a rated voltage less than 500 V, a 500 V or 1000 V megometer can be used; When measuring the insulation resistance of equipment or lines with a rated voltage above 500V, a 1000~2500V megometer should be used; used ; lors of measuring insulators, a 2500~5000V megger should be used. Under normal circumstances, when measuring the insulation resistance of low-voltage electrical equipment, a megger with a range of 0 to 200 MΩ can be used.
Reference for the above content: Baidu Encyclopedia-Megger (megger)
How does megger measure engine quality?
The motor insulation voltage specified in the national standard is >50 MΩ, and generally the higher the better. But if what you measure is between phases U, V and W, it means the motor is defective. the winding is in open circuit.
Megohm meter, also known as megohm resistance meter, is a megohm resistance meter used to measure the insulation resistance of various electrical equipment to prevent accidents. It is practical and reliable.
The toggle counter consists of a generatorcrank, one vote and three terminals (i.e. L: line end, E: earth end, G: shield end). It is widely used in the installation and maintenance of coal mines). . For checking motors, electrical devices and circuits. Insulation condition and high value resistance measurement.
How to use
1. Before measurement, the megger should be held in a horizontal position, hold the meter body with your left hand, and shake the megger rocker with your right hand. at around 120 rpm the pointer should point to infinity (∞), otherwise the megger is faulty.
2. Before measurement, the power supply to the electrical apparatus and the circuit under test should be cut off, and the relevant components should be temporarily grounded and discharged to ensure the safety of people, the megger and the accuracy. measurement results.
3. The wiringmust be correct when measuring. The megger has three terminals (L, E, G). When measuring the resistance of the loop to ground, the L end is connected to the exposed conductor of the loop and the E end is connected to the ground wire or metal shell when measuring the resistance d 'loop isolation, the first and; the last ends of the loop are connected to L and E respectively; cable insulation is measured when measuring resistance, in order to prevent leakage current on the cable surface from affecting the measurement accuracy, the cable shielding layer should be connected to the terminal G.
4. The flexible measuring wire coming from the megger terminal should be well insulated and a proper distance should be maintained between the two wires and between the wire and the ground to avoid affecting the measurement accuracy.
5. When shaking the megger, do not touch the megger terminals and circuittested with your hands to avoid electric shock.
6. After shaking the megger, do not short the terminals to avoid damage.
7. Do not shake the megger for too long.
The steps for measuring the motor with the megometer are as follows:
1 Before use, the megometer should be placed away from the magnetic field and placed on a horizontal surface. surface without being too inclined. Attach the megger measuring leads to the two terminals of the megger. The two measuring leads are both positive and negative, then tighten the screws. If the rated operating voltage of the motor under test is 380 volts, you can choose a 500 V megger.
2. Place the meter flat and perform a short circuit test. If both test leads are shorted and the handle pointer is near 0, it's good.
3. When measuring, it is best to remove the connecting part from the motorr three-phase and ground the hull.
4. Separate the two test leads and shake the handle. If the pointer is close to infinity, it's good.