How significant is insulation resistance testing? Since 80 of electrical conservation and testing involves assessing insulation integrity, the answer is" truly important."
"Electrical insulation starts to progress as soon as it's made. And, growing deteriorates its performance. Harsh installation surroundings, especially those with temperature axes and/ or chemical contamination, beget further deterioration. As a result, help safety and power responsibility can suffer. Obviously, it's important to identify this deterioration as snappily as possible so you can take the necessary corrective measures.
What is insulation resistance testing?
Basically, you're applying a voltage ( specifically a largely regulated, stabilized DC voltage) across a dielectric, measuring the amount of current flowing through that dielectric, and also calculating ( using Ohm's Law) a resistance dimension. Let's clarify our use of the term" current. "We're talking about leakage current. The resistance dimension is in megohms. You use this resistance dimension to estimate insulation integrity.
Current flux through a dielectric may feel kindly contrary, but remember, no electrical insulation is perfect. So, some current will flux.
What's the purpose of insulation resistance testing?
A quality control measure at the time a piece of the electrical outfit is produced;
An installation demand to help ensure specifications are met and to corroborate proper hook over;
A periodic precautionary conservation task; and
A troubleshooting tool.
An installation demand to help ensure specifications are met and to corroborate proper hook over;
A periodic precautionary conservation task; and
A troubleshooting tool.
How do you perform an insulation resistance test?
Generally, you connect two leads ( positive and negative) across an insulation barricade. A third lead, which connects to a guard terminal, may or may not be available with your tester. However, you may or may not have to use it, If it is. This guard terminal acts as a shunt to remove the connecting element from the dimension. In other words, it allows you to be picky in assessing certain specific factors in a large piece of an electrical outfit.
know what is supposed to be insulated from what. The outfit you're testing will determine how you hook up your megohmmeter.
After you make your connections, you apply the test voltage for 1 min. (This is a standard sedulity parameter that allows you to make fairly accurate comparisons of readings from formerly tests done by other technicians.)
During this interval, the resistance reading should drop or remain fairly steady. Larger insulation systems will show a steady drop; lower systems will remain steady because the capacitive and absorption currents drop to zero faster than on larger systems. After 1 min, you should read and record the resistance value.
When performing insulation resistance testing, you must maintain consistency. Why? Because electrical insulation will parade dynamic behavior during the course of your test; whether the dielectric is" good" or" bad. "To estimate the number of test results on the same piece of outfit, you have to conduct the test the same way and under the fairly same environmental parameters, each and every time.
Your resistance dimension readings will also change with time. This is because electrical insulation paraphernalia cortege capacitance and will charge during the course of the test. This can be kindly frustrating to a neophyte. Still, it becomes a useful tool to a seasoned technician.
As you gain further chops, you'll come familiar with this behavior and be suitable to make maximum use of it in assessing your test results. This is one factor that generates the continued popularity of analog testers.
What aspects insulation resistance readings?
Insulation resistance is temperature-sensitive. When temperature increases, insulation resistance decreases, and vice versa. A common rule of thumb is insulation resistance changes by a factor of two for each 10 DegrC change. So, to compare new readings with former bones, you'll have to correct your readings to some base temperature. For illustration, suppose you measured 100 megohms with an insulation temperature of 30 DegrC. A corrected dimension at 20 DegrC would be 200 megohms (100 megohms times two).
Also," respectable" values of insulation resistance depend upon the outfit you're testing. Historically, multitudinous field electricians use the kindly arbitrary standard of 1 megohm per kV. The inter National Electrical Testing Association (NETA) specification Conservation Testing Specifications for Electrical Power Distribution Outfit and Systems provides much more realistic and useful values.
Remember, compare your test readings with others taken in a similar outfit. Also, inquiry any values below the NETS standard minimums or unlooked-for departures from former values.
Thank You.!!!