The Necessity of Insulation resistance testing for protecting our asset

What is insulation testing?

Insulation resistance testing is performing to ensure that motors stay operational, resulting in time and money savings. It is using to test the integrity of cables, motor and transformer windings, switchgear, and electrical installations.

The digital insulation resistance testers, also known as megger insulation testers. It gives noise-free, dependable results whether you're working on motors, generators, cables, or switchgear. A Fluke insulation tester is safe, simple to use, and gimmick-free while providing advanced performance. Insulation troubleshooting, commissioning, and preventative maintenance can all benefit from a mega ohm meter test.

Insulation resistance starts from 1MΩ, but according to the Bangladesh National Building code (BNBC), it has to start from 5MΩ. Practically GΩ range is using for proper insulation.

Figure 1: Insulation resistance tester

What makes Insulation Go Bad?

 Several effects can damage insulation; some of them are:

• Mechanical damage
• Vibration
• Moisture from process
• Dirt
• Electrical stresses
• Corrosive vapors
• Excessive heat or cold
• Oil
• Just for the humidity on a muggy day

Methods of Insulation Testing

There are four methods for Insulation testing such as:

• PI method

It shows the resistance ratio after 10 minutes and after 1 minute. The insulator's PI value must be greater than 2. The higher the PI, the better the insulating material's insulation. The PI equation is

• DAR Test

The dielectric absorption ratio shows how quickly the capacitive current decays. In a healthy insulation system, the capacitive current must degrade within one minute. It's a ratio test, similar to the PI test, used to assess the insulation's quality. It's the difference between the insulating resistance after 60 seconds and 30 seconds. The equation is  as follows

• SV Method

Two or more short-time insulation tests are performing at different test voltages in a step voltage insulation test. A modest test voltage, such as 500V, is employed in the first step. After that, a 2.5KV overvoltage is applied. Regardless of the test voltage, an ideal insulator will give the same reading. If the higher voltage measurement produces a lower resistance value than the standard voltage test, this indicates that the insulation may have cracks or voids.

Figure 2. Step voltage test

• Ramp testing

The ramp test is the method of gradually increasing voltage at a constant rate to a specified voltage. The response of insulation to a ramp test provides information about the system's condition and can help the user spot minor issues. The leakage current as a function of voltage is the plot for this test. Specific voltage-current trends can indicate ingress and localized faults.

Observations about how to interpret in general insulation resistance tests continuously and what to do with the results

Factor affecting Insulation resistance reading

The measured resistance is determined by the applied voltage and the resulting current (R = E/I) (of the insulation). The insulation temperature and humidity, for example, have an impact on current. Consider the nature of current through insulation and the effect of applying voltage for a short period. There are three elements to total current:

• Capacitance Charging Current

            After the insulation has been charged to full voltage, the current begins to drop.

• Absorption Current

            A current that is initially high but then drops

• Conduction or Leakage Current

            Through and Over the insulation, a small, essentially constant current.

Fluke 1555 10KV, 1550C 5KV Insulation resistance meter

Among many kinds of insulation resistance available in Bangladesh, Fluke is the best because it is easier to operate and accurate. Fluke Connect and Fluke's market-leading insulation testers make preventive maintenance tasks faster, easier, and safer.

Fluke Connect provides three significant advantages in data collection for preventive maintenance programs

• Simple, uncomplicated setup and operation of the

        insulation tester via remote control

• Real-time trending results in a visual graph
• Drag-and-drop report creation facilitates the creation of test result documentation

Fluke Connect also makes test configuration easier. The Fluke Connect app for smartphones guides you through the setup process for any number of tests. You can quickly and precisely set parameters like:

• Test voltage
• Time limit (duration) for the test
• Measure polarization index (PI)
• Ramp test selection                           
• Measure dielectric absorption ratio

Figure 3: Fluke 1550c Insulation resistance tester

Fluke 1507 Insulation Resistance Tester

It's a hand-held insulation tester that's versatile and compact for modern industrialized and electrical insulation testing. Because of its multiple check voltages, it's ideal for various troubleshooting, authorization, and preventative maintenance tasks.

Figure 4: Fluke 1507 Insulation resistance tester

Key Features of 1507-ohm Meter

• Performs test from 0.01MΩ to 2GΩ
• Simple to pack and use
• CAT iv 600V overvoltage category rating
• Saves battery power with auto power off
• Complete with calibration certificate

Conclusion

Digital Insulation tester, also known as digital megger, is essential in many systems. But it is vital for high-temperature systems. If a process involves a motor, generator, dryers, high and low voltage lines, proper insulation is something to monitor so that operation can run smoothly. Insulation is one of the most effective ways to save energy in the house and industry because it keeps things warm in the winter and cools in the summer. That's why a Proper insulation tester is vital for protecting our electrical assets from an accident.