Insulation resistance testing involves applying a voltage across a dielectric, and measuring the resulting current and resistance. However, in order to get a proper reading, any electrical charge still within the system needs to be taken out, so as not to mess with the readings.
To prevent, reduce electrical noise, cross-talk.
dc insulation test = 2 * operating voltage +1000V ac insulation test = 2* operating voltage impedance of long wires or cables make ac testing sort of impractical dc test will never be lower than 1000V
for the insulation purpose.
There is no single 'formula' for this, as the maximum current a circuit can handle depends on the temperature the various components within that circuit can operate at, without deterioration. There are so many factors involved, such as the type of component, the type of insulation, whether it can cool naturally or whether it must be force cooled, etc. Every circuit must be considered on an individual basis.
The Megger MFT 1552 is a combined electrical circuit tester which includes test features for Insulation testing, Earth loop impedance tests, RCD Testing and Continuity testing. It comes supplies with full Calibration Certificate.
Megger testOn the whole megger testing is non destructive. What happens is a DC voltage is applied to the device or winding under test. It is an insulation test to see is the insulation has been injured in any way to cause a short circuit when normal power is applied to it. On my megger there are 3 ranges 300V, 750V, and 1000 volts. Applying the proper voltage is essential to not damaging the device you are testing. Working voltages up to 240 volts should use the 300 range. Working voltages up to 600 volts use the 750 volt range and working voltages above 600 use the 1000 volt range. As you can see if you used the 1000 volt range on a device that had a working voltage of say 24 volts you could damage the insulation just by testing it. So meggering a device is non destructive if you use the tester as its instructions tell you to.
explain why all the load must be removed when to conduct the insulation and resistance testing
Insulation.
insulation
The current is determined by the load. So if the conductors are designed to carry the resulting load current, then the high-voltage supply will have no effect. If not, then the conductors will overheat, their insulation will fail, and a short-circuit will result. However, the conductor's insulation must also be capable of withstanding the high voltage; if not, then the insulation will break down and a short circuit will result.
dc insulation test = 2 * operating voltage +1000V ac insulation test = 2* operating voltage impedance of long wires or cables make ac testing sort of impractical dc test will never be lower than 1000V
By definition a short circuit is the path of least resistance of current flowing through a circuit be it three phase or single phase. The main cause of this condition in electrical circuits is an insulation break down. This break down can be caused by overheating of the insulation to a point where the insulation disintegrates from the conductor that it is supposed to be protect. With the insulation missing from the wire there is the possibility of a short circuit to surrounding grounded material. The other cause of insulation break down is from vibration. Unsupported conductors can vibrate against their metallic enclosures to a point where the insulation is just worn away. Once the insulation becomes thin enough the voltage will bridge the insulation threshold and take the path of least resistance to ground and a short circuit will occur.
for the insulation purpose.
in order to avoid unwanted short circuit break downs.... short circuit can burn the transformer and motor winding.... Megger is the device used to check the insulation .
By providing high insulation.....
There is no single 'formula' for this, as the maximum current a circuit can handle depends on the temperature the various components within that circuit can operate at, without deterioration. There are so many factors involved, such as the type of component, the type of insulation, whether it can cool naturally or whether it must be force cooled, etc. Every circuit must be considered on an individual basis.
By testing capacitor tolerance
We have to protect them to avoid damage due high voltage generated by the isolation tester.