NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Language
NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Author: Noyafa–CCTV Monitor Tester
How to use a megohmmeter and measure insulation resistance A megohmmeter is commonly known as a shaker. It is used to measure large resistance and insulation resistance. . There are many types of megohmmeters, but their functions are roughly how to use megohmmeters and how to use megohmmeters to measure insulation resistance The service organization, our company has been engaged in cable fault detection, cable fault finding, cable fault location, high-voltage cable fault detection, etc. For measuring large resistance and insulation resistance, its unit of measurement is megohm (MΩ), so it is called a megohmmeter. There are many types of megohmmeters, but their functions are roughly the same.
Measurement method of insulation resistance The megohmmeter has three binding posts, and the two larger binding posts at the upper end are marked with“ground”(E) and“line”(L), marked on the lower one of the smaller binding posts“guard ring”(or“shield”) (G). 1. Measure the insulation resistance of the motor. Connect the E terminal of the megohmmeter to the casing (ie, ground), and the L terminal to the winding of a certain phase of the motor. As shown in Figure b above, the measured insulation resistance value is a certain Phase-to-ground insulation resistance value. 2. The insulation resistance of the line to ground will be the value of the megohmmeter“ground”The terminal (ie, the E terminal) is reliably grounded (generally connected to a grounding body), and the“line”The terminal (ie, the L terminal) is connected to the circuit under test, as shown in the figure below.
After the connection is complete, shake the megohmmeter clockwise, the speed gradually increases, keep at about 120 rpm and then shake at a constant speed. When the speed is stable and the pointer of the meter is also stable, the value indicated by the pointer is the insulation resistance of the object to be measured. value. In actual use, the two terminals E and L can also be connected arbitrarily, that is, E can be connected to the object to be measured, and L can be connected to the grounding body (ie, grounding), but the G terminal must not be wrongly connected. 3. Measure the insulation resistance of the cable When measuring the insulation resistance of the conductive wire core of the cable and the cable shell, connect the terminal E to the cable casing, the terminal L to the wire core, and connect the terminal G to the cable casing and the core. The insulating layers between them are connected, as shown in Figure c above.
Insulation resistance is a characteristic of a given time, due to the influence of external conditions, insulation resistance may change, because it depends on many factors, the main influencing factors are the temperature and humidity of the insulation at the time of measurement. Specifications for minimum allowable insulation resistance are not standardized because there is no absolute standard for minimum allowable insulation resistance. If measurements are made at different winding temperatures, usually set in the standard for a particular type of machine or in the product or material specification, these parameters force an indication of the temperature at which the measurement should be made, as well as reducing the measurement resistance to standard conditions method of recalculating the measured resistance.
By measuring the insulation resistance of windings, insulation tests can be performed at high voltages without the danger of electrical breakdown in good condition, but with increased insulation humidity. Measure with a digital megohmmeter, whose test voltage depends on the rated working voltage of the insulation under test. For devices rated up to 500V (660) V, use a 500 V megohmmeter; for devices rated up to 3000 V-1000 V with a megohmmeter; for devices rated 3000V and higher, 2500 V and higher Megohmmeter.
Shenzhen Noyafa Electronic Technology Co., Ltd.
Copyright © 2022 SHENZHEN NOYAFA ELECTRONIC CO.,LIMITED - www.noyafa.net All Rights Reserved.