Introduction to Circuit Breaker
A circuit breaker serves as a device to interrupt abnormal or fault currents and also functions as a switch. The role, rating, and testing of circuit breakers were covered in the previous chapter. In this chapter, we will explore the classification of circuit breakers, focusing on the different types.
“A circuit breaker is the device that interrupts abnormal currents and acts as a switch.”
Classification of Circuit Breakers
Circuit breakers can be classified in several ways. One classification is based on the type of current, which differentiates between AC circuit breakers and DC circuit breakers.
1. AC Circuit Breakers: Further classified on the basis of rated voltage, those below 1,000 V are called low-voltage circuit breakers and those above 1,000 V are called high-voltage circuit breakers. Common classifications are based on the medium of arc extinction, including air break circuit breaker, oil circuit breaker (tank type or bulk oil), minimum oil circuit breaker, air blast circuit breaker, sulfur hexafluoride circuit breaker, and vacuum circuit breaker. High-voltage circuit breakers fall into two main categories: oil circuit breakers and oil-free circuit breakers.
2. Oil Circuit Breakers: Using dielectric oil (transformer oil) for arc extinction, bulk oil circuit breakers use the oil filled in them to extinguish the arc during contact opening. Oil also acts as an insulator for parts that conduct electrical current. Ratings range from 25 MVA at 2.5 KV to 5,000 MVA at 230 KV.
3. Low oil content or minimal oil circuit breakers: These use oil to cause arc extinction by burst action, the oil filled arc chambers are located within a porcelain insulator, insulating live parts from earth. Let’s insulate. Suitable for voltage from 33 KV to 220 KV and breaking capacity of 1,500 MVA to 7,500 MVA.
4. Oil impulse breaker: Using a piston pump to create an arc-extinguishing oil jet, similar to an air blast circuit breaker.
Oilless Circuit Breaker:
1. Air circuit breaker: Arc initiation and extinction occurs in still air, typically for low voltages up to 15 kV and breaking capacity of 500 MVA.
2. Air blast circuit breaker: A blast of air extinguishes the arc, in which compressed air stored in a tank generates a high-velocity jet. Used for medium-high voltage indoor services with capacities up to 15 kV and 2,500 MVA.
3. Sulfur hexafluoride circuit breaker: SF6 gas under pressure extinguishes the arc, which has excellent dielectric and arc-quenching properties.
4. Vacuum circuit breaker: The contacts are placed inside a sealed vacuum interrupter, with the arc extinguished in high vacuum. Efficient, compact, cost-effective, requiring minimum maintenance and long-lasting.
BRIEF SUMMARY
• A circuit breaker functions as both a switch and a device to interrupt abnormal currents.
Classification of Circuit Breakers:
1. AC Circuit Breaker:
• Classification based on current type (AC/DC).
• Distinguishes between low-voltage (<1,000 V) and high-voltage (≥1,000 V).
• High-voltage categories include oil and oil-free circuit breakers.
2. Oil Circuit Breaker:
• Use dielectric oil for arc extinction.
• Bulk oil circuit breakers use oil to extinguish the arc during contact opening.
• Ratings range from 25 MVA at 2.5 KV to 5,000 MVA at 230 KV.
3. Circuit breakers with low oil content:
• Use oil to eliminate the arc through a blast action.
• The arc chambers are housed within porcelain insulators.
• Suitable for voltages ranging from 33 KV to 220 KV with breaking capacity ranging from 1,500 MVA to 7,500 MVA.
4. Oil Impulse Breaker:
• The arc-extinguisher deploys a piston pump to create an oil jet.
Oil less Circuit Breaker:
1. Air Circuit Breaker:
• The initiation and extinction of the arc occurs in calm air.
• Designed for low voltage up to 15 KV with breaking capacity of 500 MVA.
2. Air Blast Circuit Breaker:
• Arc extinction occurs through a blast of air, generated by compressed air in a tank.
• Applied in medium-high voltage indoor services with capacities up to 15 KV and 2,500 MVA.
3. Sulfur Hexafluoride Circuit Breaker:
• To extinguish the arc uses SF6 gas under pressure, which has excellent dielectric and arc-quenching properties.
4. Vacuum Circuit Breaker:
• The contacts are housed inside a sealed vacuum interrupter, which extinguishes the arc in a high vacuum environment.
• Known for efficiency, compact design, cost-effectiveness, minimum maintenance required and long-lasting performance.