Electrical wiring requires high performing insulation to prevent hazards, such as electrocution and damage to expensive equipment. Yet, with time, insulation can succumb to wear tear and lose its efficiency.
Preventive maintenance, primarily through regular insulation testing can help mitigate electrical hazards, prevent equipment downtime, and provide a safe working environment.
Plant managers can benefit from learning about electrical insulation in order to take the necessary steps to prevent costly insulation failure. Below is what you need to know about electrical insulation, causes of failure, and the benefits of preventive care.
Electrical Insulation Basics
Insulation is a protective sheathing that works to prevent leaking of electrical currents passing through copper or aluminum wires. This sheathing ensures that a certain amount of current reaches the desired destination.
The three categories of insulation are solid, liquid, and gas insulators. Examples of solid insulators are rubber, mica, Teflon, clay, plastics, paper, and glass.
The most common liquid insulator is transformer oil. The electrical industry uses a special type of non-conductive gas to prevent hazardous electrical problems, such as arcing.
Each application requires its own type of insulation. Some applications, such as high-voltage wiring, call for the use of more than one type of insulation.
Causes of Electrical Insulation Failure
Other than normal wear and tear, certain factors can accelerate insulation failure.
Moisture presents a significant threat to electrical insulation. With time, small cracks appear on the insulation and let in moisture from the surrounding environment. Moisture inside the wires accelerates short-circuiting, which can affect the performance of equipment.
Heat is a reality of life in industrial settings. However, prolonged exposure to high temperatures can result in thermal aging. Thermal aging is when insulation becomes increasingly brittle due to exposure to intense heat.
Transient currents are powerful, short-lived voltage spikes commonly known as surges. Operating equipment, such as motors or transformers, can result in excessive current flow.
Frequent voltage spikes not only cause mechanical damage to the core wire but also to the insulator. Transient currents can also generate localized heating, further destroying the surrounding insulation.
Other types of electrical stresses that can damage insulation include partial discharges, corona, and spikes.
Testing of Electrical Insulation
Testing insulation entails measuring the degree of resistance to the current flow of a particular type of insulation. An insulator with a high resistance rating is doing a good job of preventing current leakages.
Electricians use special equipment to test the capacitive current, absorptive current, and the leakage current to determine the resistance of an insulator. The capacitive current is the total current that flows along the insulator.
The absorptive current is the amount of current the insulator captures and directs along the core wiring, while the leakage current is the amount of current that seeps through the insulation. An increasing amount of leakage current over time is an indication of faulty insulation.
Electrical contractors use several tests to evaluate insulation resistance. The most common tests include:
- Proof Test: Proof testing entails checking the electrical system for incorrect installations.
- Spot Test: This test measures voltage flow within a specific period, typically sixty seconds. Electricians usually perform several spot tests to identify trends that may indicate current leakages.
- Time Resistance Test: This test involves taking successive readings of current flows within fixed periods and plotting these readings to identify trends.
- Step Test: A step test entails obtaining two or more voltage readings and comparing the results to determine the insulation's level of resistance.
Some applications may require the use of more than one test to accurately measure insulation resistance.
Regular preventative testing can help to identify and eliminate the causes of insulation failure. If you are looking for complete preventative electrical care in Battle Creek, Michigan, call the experts at Motor Shop Electrical Construction Company.