Mineral insulating oil, also known as transformer oil, is commonly used in oil circuit breakers (OCBs). The insulating oil in the Oil circuit breakers (OCBs) performs two critical functions: arc extinction (quenching) and electrical insulation. The oil acts as a cooling medium and deionizes the arc generated when the circuit breaker operates. The oil also provides insulation between live parts and the grounded components of the system. The most commonly used types of oil in OCBs are:
1. Mineral Oil
- Composition: Mineral oil is derived from refined petroleum. It consists mainly of hydrocarbon compounds and is chosen for its insulating properties.
- Characteristics:
- High Insulating Strength: Mineral oil provides excellent insulation, preventing the breakdown of the dielectric strength of the air or the surrounding material.
- Arc-Quenching Ability: An arc is formed between the contacts of the circuit breaker during the circuit breaker opening during the fault. Mineral oil helps quench this arc by cooling and deionizing the ionized gases produced during the arc. The oil absorbs the heat generated, vaporizes, and forms hydrogen gas. The gas suppresses the arc and reduces the temperature.
- Heat Dissipation: Mineral oil acts as a coolant by absorbing heat produced during the arc formation and dissipating it, and prevents overheating of the circuit breaker components.
- Widely Used: OCBs use this oil most commonly because of its availability, cost-effectiveness, and reliable performance under various operating conditions.
- Applications: Mineral oil is primarily used in medium- to high-voltage OCBs in transmission and distribution systems.
2. Synthetic Oil
- Composition: Synthetic oils are custom-made using chemical compounds to provide better thermal stability and fire resistance than natural oils. Their tailored composition ensures improved thermal stability, durability, and safety in high-temperature or demanding conditions.
- Characteristics:
- Improved Performance: Synthetic oils has enhanced performance characteristics compared to mineral oils, such as better fire resistance and reduced oxidation over time. This makes them more stable under extreme operating conditions.
- Environmental and Safety Benefits: Some synthetic oils are less environmentally hazardous and have higher biodegradability than mineral oils. They also offer reduced toxicity, making them preferable for environmentally sensitive areas.
- Longevity: Synthetic oils tend to last longer and degrade more slowly than mineral oils, which may reduce maintenance intervals and enhance the overall reliability of the circuit breaker.
- Applications: Synthetic oils are more expensive and are typically used in specialized applications, where higher performance and environmental concerns are critical, such as in high-voltage or heavy-duty circuit breakers.
What is the main purpose of oil in OCB?
The oil in OCBs performs two primary functions:
When a circuit breaker operates to interrupt a fault or open a circuit, an electric arc forms between the contacts of the breaker, this arc is extremely hot and needs t
- Arc Extinction (Quenching):
- When a circuit breaker operates to open a circuit to interrupt a fault, an electric arc forms between the contacts of the breaker. This arc is extremely hot and needs to be extinguished to prevent damage to the system.
- As the arc forms, the oil surrounding the contacts absorbs the heat, vaporizes, and forms hydrogen gas. This gas has a high cooling effect and quickly reduces the arc temperature.
- The oil vaporization also produces a bubble of high-pressure gas around the arc, which pushes the arc away from the contacts and eventually extinguishes it.
- Insulation:
- The oil also acts as an insulating medium and it prevents electrical discharges between live parts of the breaker and grounded metal components. It ensures that the circuit breaker maintains its dielectric strength, allowing it to function safely even under high-voltage conditions.
- The insulating oil also prevents short circuits and breakdowns by ensuring that the dielectric strength between the breaker’s contacts and the ground remains intact.
In summary, mineral oil is the most widely used oil in oil circuit breakers because of its excellent insulating and arc-quenching properties. Synthetic oils, while less common, are used in specialized applications where higher performance, environmental concerns, and safety are priorities. Both types of oils are critical in ensuring the reliable operation of oil circuit breakers in electrical systems.
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