The need and safety of circuit breakers is important in the field of electrical engineering and power distribution. Circuit breakers are used to avoid overload, short circuit and earth fault. Circuit breakers protect appliances, prevent fire hazards, and prevent the entire electrical system from blacking out. Oil circuit breaker are known to be the oldest type of breaker. In this article, we will discuss in detail about the construction, working principle, types, maintenance, application, advantages and disadvantages of this device.
What is Oil Circuit Breaker?
In case of system failure or overload, oil circuit breaker is a mechanical device whose purpose is to stop the flow of electric current.
As the name suggests, insulating oil is used in oil breakers to break the circuit safely. Actually mineral oil (transformer oil) is used as insulating oil whose dielectric strength is better than air. This oil quickly extinguishes the arc caused by a fault condition while providing insulation between the contacts during normal operation.
Construction of Oil Ckt Breaker
This is a simple type of breaker which has an metal tank. The transformer oil is filled inside the tank, that is why it is called oil breaker. The oil used in the breaker is also called breaker oil Inside this tank, contacts are made through insulators which are immersed in transformer oil.
There is a lot of vibration during high current interrupting. To absorb this vibration the oil tank is bolted to the pad.
Parts of Oil Circuit Breaker
Oil Circuit Breakers (OCB) use several parts to sense faults and close-open the circuit, stopping the flow of electricity in case of any fault. The major parts of oil breaker are used.
Contacts
- The contacts of OCB are made of metallic material which is used to open and close the electric circuit.
- In addition, auxiliary contacts are used for signaling and control purpose.
Insulating Oil Reservoir
- In oil circuit breaker, insulating oil used for functions as an arc extinguishing as well as a dielectric medium.
- There is enough oil in the insulating oil reservoir to function as insulation between contacts and to help extinguish arcs under fault circumstances.
Arc Chute
- A room or tunnel created to direct and regulate the arc created during fault conditions is called an arc chute.
- By quickly cooling and putting an end to the arc, it aids in directing the flow of insulating oil and promotes effective arc quenching.
Operating Mechanism
- In reaction to control signals, the working mechanism is in charge of opening and closing the breaker connections.
- There are several kinds of operating mechanisms that can be employed, including spring-, hydraulic-, motor-, pneumatic-, and electromagnetic-operated mechanisms.
Tank
- The circuit breaker's internal parts are kept in the tank, which also offers mechanical support and security.
- To endure mechanical and environmental loads, steel or other strong materials are usually used in its construction.
Oil Filling and Draining Valves
- The circuit breaker's insulating oil can be replaced or refilled thanks to oil filling and drainage valves.
- These valves are employed in maintenance procedures to guarantee that the breaker's insulating oil is at the right level and quality.
Seals and Gaskets
- To stop oil leaks and preserve the integrity of the breaker enclosure, seals and gaskets are utilized.
- They are located at various points throughout the breaker assembly, including around the contacts, operating mechanism, and oil reservoir.
Bushing
- Electrical wires entering and leaving a structure are connected by insulated bushings.
- They guarantee that the circuit breaker and any external circuits or equipment are properly insulated and electrically isolated.
Trip and Close Coils
- The electromagnetic devices known as trip and close coils are employed to regulate the opening and closing of the breaker connections.
- When trip coils are powered, they produce a magnetic field that causes the contacts to open, whereas close coils cause the connections to close.
Monitoring and Control Devices
- For safety, monitoring, and control purposes, the circuit breaker may incorporate sensors, relays, and auxiliary switches among other monitoring and control devices.
- When necessary, these devices trigger tripping or closing actions and offer feedback on the state of the breakers. They also detect fault conditions.
Cooling Systems
- To dissipate heat produced during operation and maintain ideal operating temperatures, cooling devices like fans, radiators, or heat exchangers may be included in some OCB designs.
These are special components of oil circuit breaker that are usually present in oil; which is essential to prevent every abnormal electrical currents and protect the electrical equipment from malfunctioning.
Working Principle of OCB
OCB is a device for switching and interrupting current. Detailed descriptions of how they work:
Normal Operation
- There are fixed and moving contacts inside its tank which remain closed during normal operation. During this time current keeps flowing through the circuit.
- In normal operation the substation operator closes and opens the breaker for switching and maintenance. For this purpose the operator uses the remote switch fitted in the panel.
Fault Condition
- The current flowing through the contacts beyond the circuit's rated capacity when an electrical problem, such as an overload or short circuit, occurs.
- In this condition the trip coil of the breaker gets activated and the moving contact gets separated from the fixed contact and the circuit gets opened.
- An arc is created between the contacts by the high current. This arc is extremely hot and can be a serious risk to the electrical system's integrity if it isn't put out quickly.
Arc Extinction
- The insulating oil around the contacts evaporates as the arc forms between them because of the intense heat it produces.
- The oil expands quickly and blasts through the arc chute as a result of the vaporization of the oil, creating a high-pressure condition inside the chute.
- The quick expansion of the oil cools and extinguishes the arc, so stopping the circuit's current flow.
Contact Separation
- The breaker mechanism physically stops the flow of current in the circuit by causing the contacts to separate as soon as the arc is extinguished.
- The personnel and equipment are kept secure and additional damage is prevented by isolating the malfunctioning portion of the circuit from the remainder of the system.
Recovery and Resetting
- Depending on the kind of breakers, the contacts can be reset manually or automatically once the problem has been fixed.
- In the event that the insulating oil evaporates during the fault, it returns to liquid state and becomes ready to offer insulation and arc extinction properties in the event of another fault.
Types of Oil Circuit Breaker
Oil breakers can be divided into several varieties according to a number of criteria, including structure, insulation type, and arc control technique. Here we will discuss about two main types of oil circuit breakers:
Bulk Oil Circuit Breaker (BOCBs)
Due to excessive use of oil it is called bulk oil circuit breaker(BOCB) or dead tank type. The contacts are immersed in oil so that the arc generated during a fault is extinguished by this oil.
Quantity of Oil is used in this type of breaker according to the system voltage. BOCBs, which are the earliest type of oil circuit breaker, are popular for their reliability and simplicity.
Minimum Oil Circuit Breaker (MOCB)
Comparatively speaking, MOCBs require less amount of insulating oil than BOCBs. MOCBs use specialized chambers or containers with a regulated amount of oil inside of them, rather than completely submerging the contacts in it.
This design still provides good insulation and arc quenching, but it uses less oil for arc extinction. That is why this breaker is also called low oil circuit breaker. MOCB occupies less space, weight less and uses less oil as compared to BOCB
Vacuum Circuit Breakers (VCBs) with Oil Interrupter
The arc extinguishing medium in vacuum circuit breakers is a vacuum. Nonetheless, some designs include a tiny amount of insulating oil in the vacuum interrupter to improve its ability to interrupt arcs.
When compared to pure vacuum interrupters, these VCBs incorporating oil interrupters perform better, especially in high-current applications.
Dual Pressure Circuit Breakers
The features of both BOCBs and ABCBs are combined in dual pressure circuit breakers. In order to improve arc quenching, they combine a compressed air system with insulating oil for arc extinction.
Dual pressure circuit breakers offer faster arc extinction and higher interrupting capacities by employing both mediums.
Oil-Immersed Circuit Breakers (OICBs)
OICBs are intended for use in situations where insulating oil is submerged around the entire breaker unit. Because of their improved cooling and insulating capabilities, OICBs can be used in high-voltage and high-current applications where effective heat dissipation is essential.
These are a few popular varieties of oil circuit breakers, each with unique benefits and applications in mind. A number of variables, including voltage level, interrupting capacity, operating requirements, and environmental circumstances, influence the choice of oil ckt breaker type.
Operation of Oil Circuit Breaker
From fault identification to current flow interruption and system restoration, there are multiple phases involved in operating an oil circuit breaker (OCB). The workings of an oil breakers are explained in depth here.
Detection of Fault
- An overload, short circuit, or ground fault in the electrical system triggers the activation of an oil circuit breaker.
- Relays and sensors are two examples of protective devices that identify anomalous conditions in the system and communicate with the circuit breaker to start the interruption process.
Trip Signal
- The circuit breaker mechanism opens contacts to stop current flow when it receives a trip signal from the safety devices.
- Protective relays have the ability to trigger the trip signal automatically, but in certain situations, an operator must do it manually.
Contact Separation
- The functioning mechanism of the circuit breaker initiates the separation of the contacts in response to the trip signal.
- The circuit breaker's contacts, which are normally submerged in an insulating oil pool, start to separate and open up a gap.
Arc Formation
- The ongoing current flow causes an electric arc to emerge between the contacts as they separate.
- If the arc is not put out quickly, it could cause damage to nearby equipment and contacts due to its high heat output.
Arc Extinction
- For the arc to be extinguished, the insulating oil around the contacts is essential. There is considerable pressure in the area as the heat from the arc causes the insulating oil to evaporate.
- The oil is forced to burst through the arc quickly by the pressure created by its vaporization, cooling and extinguishing it in the process.
- The arc chute's design, which helps control the flow of oil and promote effective arc quenching, aids in the arc extinction process.
Current Interruption
- The circuit's current flow is essentially stopped after the arc is extinguished.
- By separating the contacts, the defective portion of the circuit is kept apart from the remainder of the system, preventing additional damage and guaranteeing the security of both people and equipment.
Restoration of System
- The circuit breaker can be reset to return the system to normal operation once the fault has been fixed.
- The procedure of resetting a circuit breaker can be either manual or automatic, and it usually entails shutting the contacts in order to restore the electrical circuit.
In conclusion, an oil circuit breaker’s functions include fault detection, starting the interruption procedure, putting out the arc, stopping the current flow, and returning the system to normal. An essential component of oil ckt breakers is their use of insulating oil as an arc extinguishing medium, which enables them to offer dependable protection against electrical faults in a range of applications.
How Arc Control of Oil Circuit Breaker
Arc management is essential for effectively stopping electrical arcs produced during fault circumstances in oil circuit breakers (OCBs). The following describes how oil breakers perform arc control:
Insulating Oil as Arc Extinguishing Medium
- Insulating oil functions as an arc extinguishing agent and a dielectric medium in oil circuit breakers.
- When a circuit breaker opens under fault conditions, the continuous current flow between the contacts causes an arc to occur.
- The arc's extreme heat causes the insulating oil around it to evaporate, producing a high-pressure atmosphere that puts an end to the arc.
Arc Chute Design
- The arc chute, which guides and controls the arc during extinguishing, is an essential part of an oil circuit breaker.
- Effective arc extinction is ensured by the arc chute's design, which also affects the direction of the arc blast and the flow of insulating oil.
- Arc chute designs might differ according to requirements for the application, voltage level, and current rating, among other things.
Splitter Plates and Cooling Fins
- To improve arc control and cooling, certain oil circuit breakers have splitter plates and cooling fins inside the arc chute.
- Arc interruption is facilitated by the placement of splitter plates inside the arc chute, which split the arc into smaller segments.
- Cooling fins help to cool the arc gases and lower the chance of re-ignition by increasing the surface area available for heat dissipation.
Gas Formation and Pressure Build-Up
- Hydrogen and methane are released as the insulating oil vaporizes as a result of the arc heat.
- The oil is forced to blast through the arc, extinguishing it, by the high-pressure zone created by the fast production of gases within the arc chute.
Quenching Grids and Magnetic Blowout Coils
- Quenching grids and magnetic blowout coils are used in some oil circuit breaker designs in order to improve arc control.
- Quenching grids, which are made of metallic plates positioned in the arc's path, dissipate the arc's energy to cool and disrupt it.
- In order to help in arc extinction, magnetic blowout coils provide a magnetic field that interacts with the arc, causing it to lengthen and cool more quickly.
Optimization of Oil Properties
- To enable effective arc control and extinction, the viscosity and dielectric strength of the insulating oil used in oil circuit breakers are tuned.
- To increase the oil's capacity to quench arcs and boost overall breaker performance, certain additives may be added.
Maintenance of Oil Circuit Breaker
Oil breakers (OCBs) require maintenance in order to function dependably and have a longer service life. Below is a summary of the common maintenance procedures for oil circuit breakers:
Visual Inspection
- Visually inspect the breaker housing, contacts, insulating oil reservoir, and related components on a regular basis for indications of wear, corrosion, or leaks.
- Keep an eye out for signs of overheating, such as melting or browning of the insulation.
Oil Quality Assessment
- Regular oil tests can be used to keep an eye on the insulating oil's quality and state. Moisture content, acidity, dielectric strength, and dissolved gas analysis (DGA) are often used tests to find any anomalies or contamination.
- If the insulating oil is found to be significantly deteriorated or does not satisfy the required quality standards, replace it.
Contact Inspection and Maintenance
- Look for wear, erosion, pitting, or uneven surfaces on the contacts; these conditions might reduce the contacts' ability to interrupt and resist contact.
- For optimal electrical conductivity, use appropriate techniques to clean the contacts and get rid of any carbon deposits or other impurities.
Mechanism Lubrication
- To reduce friction and guarantee smooth performance, lubricate the circuit breaker mechanism's moving elements, including the hinges, linkages, and operating rods.
- When it comes to lubrication intervals and processes, use the required lubricants and adhere to manufacturer specifications.
Tightening and Alignment
- To ensure they are firmly fixed and retain appropriate mechanical and electrical contact, check and tighten all bolts, connections, and fasteners.
- To avoid misalignment problems that could reduce the performance of the breaker, check the alignment of the contact assemblies and moving parts.
Arc Chute Inspection
- Check for wear, deterioration, or deformation brought on by frequent arcing on the arc chute and related parts.
- Clear the arc chute of any dirt or debris that might interfere with the operation of the interrupter and arc extinction.
Cooling System Maintenance
- To guarantee effective heat dissipation, check and clean the cooling components on the OCB if it has a cooling system, such as fans or radiators.
- To ensure ideal cooling performance, check coolant levels, pressure, and flow rates. Replace coolant as necessary.
Functional Testing
- To ensure that the OCB responds to control signals and fault circumstances correctly, perform routine operational checks and functional tests.
- Make sure protection relays, trip circuits, and auxiliary systems operate as intended in fault scenarios by testing them.
Documentation and Record-Keeping
- For every OCB, keep thorough records of all maintenance operations, test outcomes, and inspection conclusions.
- Maintaining a record of equipment history, including dates of repairs and replacements, will help with maintenance planning and troubleshooting in the future.
Advantages of Oil Circuit Breaker
Because of their many benefits, oil circuit breakers (OCBs) are a popular option for a number of applications in electrical distribution and transmission systems. The following are a few main benefits of oil breakers:
High Interruption Capacity
- Oil circuit breakers are appropriate for situations where fault currents might be significant, including high-voltage transmission networks, because they can interrupt high fault currents.
- Oil circuit breakers are appropriate for situations where fault currents might be significant, including high-voltage transmission networks, because they can interrupt high fault currents.
Effective Arc Extinction
- The insulating oil found in OCBs is a great arc extinguishing medium because it quickly cools and puts out any electric arc that develops between the contacts when a fault occurs.
- As the oil vaporizes, a high-pressure blast is produced that pushes the oil into the arc, effectively quenching it and guaranteeing a consistent stoppage of current flow.
Self-Healing Properties
- Because OCB insulating oil has self-healing qualities, it may tolerate small malfunctions and eventually regain its insulating qualities.
- In the event of minor errors, this self-healing property helps preserve the integrity of the insulation system and lowers the possibility of sustained arcing or insulation failures.
Reliability and Longevity
- When properly maintained, OCBs have a long service life and are renowned for their dependability. They require less maintenance and are less prone to mechanical failures than other types of circuit breakers because they have fewer moving parts.
- For tough settings and applications where dependability is crucial, they are suited due to their sturdy structure and long-lasting materials.
Low Maintenance Requirements
- When compared to certain other types of circuit breakers, oil circuit breakers require comparatively less maintenance.
- Cleaning and lubricating the breaker on occasion, keeping an eye on the insulating oil's state, and testing and checking its parts are the key responsibilities of routine maintenance.
Adaptability to High-Voltage Applications
- Because OCBs can tolerate high voltage levels and manage high interrupting capacity, they are ideal for high-voltage applications.
- Under high voltage transmission and distribution systems, they are frequently utilized in substations, power plants, and industrial sites.
Cost-Effectiveness
- Because of their dependability, durability, and low maintenance needs, oil circuit breakers can save money over time even after they are initially installed.
- Over time, their capacity to successfully interrupt high fault currents lowers operating expenses by lowering the chance of equipment damage and downtime.
Disadvantages of Oil Circuit Breaker
Although oil breakers (OCBs) provide many benefits, there are certain drawbacks that need to be taken into account as well. Oil circuit breakers have the following significant drawbacks:
Environmental Impact
- The possible environmental effects of using insulating oil are one of the main disadvantages of oil circuit breakers. An oil leak or spill can pose a harm to the environment by contaminating land and water supplies.
- Hazardous materials like PCBs (polychlorinated biphenyls), which can have negative effects on both human health and the environment if not handled and disposed of correctly, may be present in insulating oil.
Fire Hazard
- Because the insulating oil used in OCBs is flammable, it presents a risk of fire if it is lit on fire by sparks, overheating, or electrical problems.
- In enclosed areas or indoor facilities, where the buildup of oil vapors can produce explosive atmospheres, the risk of fire is especially significant.
Maintenance Requirements
- Compared to some other types of circuit breakers, OCBs often require less maintenance; nonetheless, in order to ensure appropriate operation, they still need to be periodically inspected, tested, and maintained.
- Maintenance procedures like oil testing, filtering, and cleaning can take a lot of time and may need for certain tools and knowledge.
Oil Handling and Disposal
- Because of its dangerous nature and the regulations surrounding it, handling and disposing of insulating oil can be difficult and expensive.
- Operating expenses may increase if used or polluted oil is not appropriately recycled, disposed of, or treated in compliance with environmental standards.
Space and Weight
- When it comes to greater voltage and current ratings, OCBs are typically heavier and bulkier than some other types of circuit breakers.
- Particularly in situations that are small or have limited space, the larger size and weight of OCBs may present difficulties for installation, transportation, and space needs.
Limited Operating Positions
- Certain OCB designs may only be appropriate for particular mounting orientations due to their operating position limits.
- This restriction may limit installation flexibility and necessitate more engineering considerations in order to accommodate the chosen operating position.
Risk of Oil Leakage and Contamination
- Over time, oil leaks and contamination can cause oil circuit breakers to lose their dependability and function.
- Reduced insulating qualities and possible operational problems might result from external sources such mechanical stress, temperature swings, and climatic conditions that can cause seal degradation and oil leaks.
Oil Circuit Breaker Operating Mechanism
An oil breaker’s (OCB) working mechanism is in charge of starting the breaker contacts’ opening and shutting in response to control signals, stopping or restarting the circuit’s electrical current flow. An outline of the common working mechanisms found in oil circuit breakers is provided below:
Spring Operated Mechanism
- The force needed to open and close the contacts in oil circuit breakers is often provided by spring-operated mechanisms.
- When the breaker is in the closed position, a strong spring or several springs that are compressed or charged make up the mechanism.
- The mechanism operates and opens the contacts quickly when it receives a trip signal from control circuits or protective devices. This release of energy from the springs causes the mechanism to work.
- To put manual reset oil circuit breakers back in the closed position after tripping, the springs need to be manually reset or refilled.
Hydraulic Operated Mechanism
- The movement of the breaker contacts is controlled by hydraulic pressure in hydraulic-operated systems.
- The contacts are opened or closed by applying hydraulic pressure that is generated and stored by a hydraulic pump or accumulator.
- Precise control over the contact movement is provided by hydraulic-operated mechanisms, which can also be linked with auxiliary systems to provide increased functionality, including tripping delays or closing speed adjustments.
Motor Operated Mechanism
- The breaker connections are opened and closed by electric motors in motor-operated systems.
- The gearbox or transmission system that the motor is attached to transforms the rotational motion of the motor into linear motion in order to activate the contacts.
- Larger oil circuit breakers frequently use motor-operated mechanisms, since manual or spring-operated mechanisms might not be feasible given the enormous forces involved.
Pneumatic Operated Mechanism
- Compressed air or gas is used by pneumatically powered machinery to operate the breaker contacts.
- The compressed air or gas's energy is transformed into mechanical motion by a pneumatic cylinder or piston, which then opens or closes the contacts.
- Because pneumatic-operated systems are comparatively simple and dependable, they can be used in situations where electrical power is scarce or nonexistent.
Electromagnetic Operated Mechanism
- The breaker contacts are operated by electromagnetic forces in machines that use them.
- Electromagnetic coils, when powered, produce magnetic fields that either attract or repel moving parts, which is how the opening or closing movement starts.
- Applications needing quick tripping or closing actions can benefit from the responsiveness and fine control that electromagnetic-operated mechanisms provide over the movement of the contact.
Oil Circuit Breaker Testing
For proper functioning of power distribution and transmission systems, Oil Circuit Breaker (OCB) should be tested regularly. This ensures dependability and security. Routine required tests that are often performed on oil breakers are:
Insulation Resistance Test
- In order to confirm the integrity of the insulating materials and find any indications of contamination or deterioration, this test gauges the breaker's insulation resistance.
- A high-voltage DC test voltage is applied between the contacts and the grounded enclosure using a megger or insulation resistance tester, and the insulation resistance is measured.
Contact Resistance Test
- To guarantee a good electrical connection and little voltage drop across the contacts, the contact resistance test assesses the electrical conductivity of the breaker contacts.
- The resistance between the main contacts and the auxiliary contacts or grounding connections is measured using a low-resistance ohmmeter.
Dielectric Strength Test
- The purpose of this test is to evaluate the insulating oil's dielectric strength, or its capacity to sustain high voltages without failing.
- To verify that the insulating resistance or leakage current complies with the required criteria, a high-voltage AC or DC test voltage is provided between the live elements and ground.
Oil Quality Analysis
- To evaluate the moisture content, acidity, dielectric strength, and dissolved gas concentration of the insulating oil, routine oil sample and analysis are carried out.
- To assess the qualities of oil and find any anomalous circumstances or contamination, testing techniques such the Karl Fischer titration, acidity test, dielectric breakdown test, and dissolved gas analysis (DGA) are employed.
Mechanical Operation Test
- The mechanical operation test assesses the breaker's overall mechanical performance, taking into account the functioning of the interlocks, moving parts, and operating mechanism.
- To ensure correct operation, smooth operation, and alignment of the contacts and moving parts, the breaker is run several times under both fault and normal circumstances.
Tripping and Closing Tests
- Tests of the breaker's tripping and closing systems evaluate its responsiveness and dependability in a range of operational scenarios.
- The timing and order of tripping or closing activities are recorded and examined when the breaker is exposed to control signals or simulated fault events.
Overcurrent and Short-Circuit Testing
- To ensure that the breaker can interrupt high-current faults and works in tandem with protective devices, overcurrent and short-circuit tests assess how well the breaker performs under these situations.
- The breaker's capacity to stop the current and endure thermal and mechanical stresses is evaluated by subjecting it to simulated short circuits or controlled fault currents.
Auxiliary System Testing
- To guarantee correct integration and operation with the breaker, auxiliary systems including signaling devices, trip coils, protective relays, and control circuits are checked.
- Calibration and verification of trip and alarm signals under both fault and normal conditions are among the tests that are performed.
Visual Inspection and Maintenance
- Visual inspections are carried out on a regular basis to look for indications of deterioration, corrosion, or leaks in the contacts, insulating oil reservoir, breaker housing, and related parts.
- Maintaining optimal performance and reliability requires performing maintenance tasks including cleaning, lubricating, tightening connections, and replacing worn or damaged parts as needed.
Conclusion
The arc quenching of oil circuit breaker is the best, that is why this breaker is used in high voltage. However, currently due to advancement in technology, oil circuit breakers have been replaced by vacuum breakers as they require less maintenance and environmental friendly. Proper maintenance and monitoring is required for longevity and optimal functioning of OCB.
I am an engineer in a government department and also a blogger. I write posts on topics related to electrical and electronics engineering.
