In the world of electrical motors, insulation to ground plays a crucial role in ensuring safety, durability, and efficient performance.
One would assume that a motor with zero insulation to ground would be prone to malfunctions or, at worst, pose a significant safety risk. Surprisingly, this isn't always the case.
There are instances where motors with zero insulation to ground not only start but also operate in what appears to be a normal manner. This article aims to delve into this perplexing phenomenon by exploring the underlying factors that allow such motors to start and the inherent risks involved.
We'll also discuss precautionary measures to consider if you find yourself dealing with a motor that has zero insulation to ground. Keep reading to understand this seemingly contradictory occurrence better.
Electric Motor voltage 380V triangular connection, each time after the shutdown, before the start with 500V megohmmeter according to the rules of the routine shaking sub winding insulation level to ground, the resistance value is 0, but can start normally, and there is no abnormality in the operation!
The motor itself has no damage, and the ambient temperature and humidity are within normal allowable range! This phenomenon is not unique to a single device. There are four motors with the same phenomenon. The on-site staff have been working for many years and have only shaken out normal values once, but he said that he himself did not know how it was shaken out… But it can be certain that the real ground insulation of the four motors is normal, but conventional shaking measurement methods can only shake out 0 value! What could be causing this phenomenon?
The Electric motor itself is not damp, there are no problems with the shaking meter, and all shaking measurement processes are operated according to regulations… It can now be confirmed that the cause of this phenomenon is not a single situation but rather a result of multiple factors acting together. However, each factor alone is not a fault or defect!
Electrician A: It is possible for an electric motor to have failed insulation but still be usable.
Electrician B: When using a shake meter to test the insulation, it may show zero, but in reality, the resistance is not actually zero. If you don't believe it, use a multimeter to measure the resistance and you will find that it is at least several tens of kilohms! If the resistance were really zero, wouldn't there be a short circuit when electricity flows through it?!
Electrician C: Why does this happen? Generally speaking, it's because the environment is humid and the insulation material of the motor contains too much moisture.
Electrician D: Why does it start up and run normally then? In fact, in this situation, the leakage current of the motor is initially quite large. As soon as heat builds up in the motor, gradually drying out any moisture. Don't believe me? Stop running your motor after a few hours and try shaking testing its insulation again to see if its value has increased.
Electrician E: Another possibility could be that your motors are all normal but there might be some issues with your 500V megohmmeter during routine shake tests. Before using a megohmmeter properly check whether both probes are separated by turning them 120 times per minute; their resistance should be infinite. Then short-circuit both probes together while shaking them at 120 turns per minute; their resistance should read zero. Check carefully how you connect three terminals on your shake meter; maybe they're connected incorrectly.
