Having the basic knowledge about electrical insulation testing can go a long way in helping to safeguard your electronic equipment against power faults. If systems were functioning correctly, the electrical current sent over a conductive wire would reach the destination point without any loss. However, this is not the case.
Conductors are coated with a layer of insulation and contain aluminium or copper cores to try to achieve perfection, but some current still manages to escape from the wires. Any faults in the insulation system allow some current to get out which isn’t good to electrical circuits and machinery. Conducting a test can help you ascertain whether the insulation layer is performing an effective function or not. Developing a habit of carrying out routine tests can help you to notice electrical faults before they cause damage to equipment or cause injury. Many elements such as excessive heat or cold, oil, dirt, and corrosive vapours may cause the insulation to fail. Routine insulation testing is, therefore, a necessity.
What is tested?
The insulation testers check the integrity of the insulation by measuring its resistance and comparing it to the current flow across the insulation. If the resistance level is high, then it indicates that little current is getting out through the insulation. Contrary, if the resistance is found to be low, then it shows that a more significant amount of electric current is leaking out via the insulation material.
To determine the resistance level, the conductor is pressurised with high voltage. Applying this pressure allows one to apply Ohm’s law applying a numerical value to the measurements of the resistance. Resistance can be determined by taking the value of voltage and dividing it by the value of current. i.e., Resistance, R = (Voltage, V)/ (Current, I). Take the amount of voltage and divide it by the amount of current that leaks through the insulation and is reversed back to the source (metre). During this testing, the total amount of current that passes through the insulation is determined by three parameters namely capacitive current, absorbed current and leaked current.
The capacitive current is usually the first burst of current that happens when a voltage is first made to pass through the conductor. Look at it as a rush of water through a hosepipe. Typically, the water will flow out at a very high pressure at the start, but with time the pressure comes down. The same thing happens to the conductor. The initial voltage is very high but it undergoes gradual drop once the conductor becomes fully charged.
The amount of current that leaks is usually referred to as the conduction current, and it is the small but steady amount of current that is passing via the insulation. When the insulation undergoes deterioration, the leakage current increases. This is recorded on the insulation test metre as a negative deviation in resistance.
The amount of current absorbed just like the capacitive current starts out high and undergoes a significant drop after some time, but unlike the capacitive current, absorption current falls at a lower rate. The absorption levels in the insulation tend to go down as the amount of voltage build-up. This gradual change reflects the storage of energy in and along the insulation. The absorption current is a crucial aspect of time resistance method of measuring the hindrance to current flow.
It is important to conduct insulation resistance testing when carrying out the installation of unused electrical gadgets. The test helps in determining whether the insulation is sufficient to protect the equipment and whether it is operational. The initial testing which serves as a proof test provides an important benchmark for any future tests that may be conducted. Insulation testing recorded as relative measurements due to the presence of fluctuating factors such as temperature and moisture. The values obtained are rather absurd if we don’t have previous values to carry out a comparison between the two. As conditions vary, the measurements taken during routine measurements start to provide valuable information.
The tips outlined above explain explicitly what insulation testers test. With these ideas, you will be well familiarised with the way insulation testers work.