A. Circuit Breakers

A Circuit Breaker is a mechanical switchgear device used to protect electrical circuits from damage caused by overload or short circuit. They can interrupt current flow and isolate a faulty section of the circuit.

i) LT (Low Tension) Air Circuit Breaker (ACB)

  • Description: An air circuit breaker is a type of circuit breaker where the arc generated when the contacts separate is extinguished by air.
  • Application: Used in low voltage applications (typically below 1000V), such as in residential or industrial power systems.
  • Working: When an overcurrent occurs, the contacts of the breaker open, and the air is used to extinguish the arc formed due to the interruption of the current.

ii) Minimum Oil Circuit Breaker (MOCB)

  • Description: This type of breaker uses a small quantity of oil to quench the arc during the opening process.
  • Application: Used for medium voltage applications.
  • Working: The contacts open in a chamber filled with oil, and the oil cools and extinguishes the arc. The oil is sometimes pressurized to improve arc-quenching properties.

iii) Air Blast Circuit Breaker

  • Description: This circuit breaker uses high-pressure air to extinguish the arc when the contacts open.
  • Application: Typically used in medium voltage systems (11kV to 33kV).
  • Working: A blast of compressed air is directed around the arc when the contacts separate, rapidly cooling and extinguishing the arc.

iv) SF6 Circuit Breaker

  • Description: SF6 (sulfur hexafluoride) circuit breakers use SF6 gas to extinguish the arc. SF6 is an inert gas with superior arc-quenching properties.
  • Application: Often used in high voltage systems (66kV and above), especially in substations and transmission lines.
  • Working: The arc is extinguished by the SF6 gas, which is an excellent dielectric material, allowing for quick isolation of faults.

v) Vacuum Circuit Breaker (VCB)

  • Description: A vacuum circuit breaker uses vacuum to extinguish the arc during operation.
  • Application: Commonly used for medium voltage systems (up to 33kV).
  • Working: When the contacts separate, the arc is extinguished in a vacuum chamber, preventing the formation of an arc and allowing for quick interruption of the fault current.

B. Isolators

An Isolator is a device used to isolate a section of the circuit or electrical equipment for maintenance. It is not meant for load switching, and only used when the circuit is de-energized.

i) Vertical Break Isolator

  • Description: In a vertical break isolator, the contacts are designed to separate in a vertical direction.
  • Application: Typically used in high voltage transmission systems where space is less and vertical separation is preferred.
  • Working: The contacts move vertically apart to isolate the circuit.

ii) Horizontal Break Isolator

  • Description: In a horizontal break isolator, the contacts separate in a horizontal direction.
  • Application: Commonly used in distribution networks and overhead transmission lines.
  • Working: The isolator operates by moving the contacts horizontally to open or close the circuit.

C. Current Transformers (CTs) and Potential Transformers (PTs)

i) Current Transformers (CTs)

  • Description: A CT is a type of transformer that measures the current flowing through a conductor by producing a reduced, proportional current.
  • Application: Used to measure or monitor the current and to provide input to protection relays.
  • Working: The primary winding is the conductor carrying the current, and the secondary winding provides a scaled-down version of the current for measurement or protection.

ii) Potential Transformers (PTs)

  • Description: A PT is a type of transformer that steps down the voltage in a circuit to a lower, measurable value, typically used for voltage measurement.
  • Application: Used in high voltage systems for voltage monitoring, and protection of equipment.
  • Working: Like a step-down transformer, the PT reduces the high voltage to a lower voltage suitable for metering and protection relays.

D. Power and Distribution Transformers

i) Power Transformer

  • Description: A power transformer is used to step up or step down voltage in large power transmission systems. These transformers are designed to handle large power loads.
  • Application: Used in high voltage transmission lines and power stations.
  • Working: Power transformers typically operate at high efficiency to transfer electrical power over long distances with minimal losses.

ii) Distribution Transformer

  • Description: A distribution transformer is used to step down the voltage from the high voltage power lines to a lower voltage that is suitable for use in homes or businesses.
  • Application: Used in local electrical distribution systems to provide power to residential or commercial buildings.
  • Working: The distribution transformer reduces the voltage from transmission levels to usable levels for end-users (e.g., from 11kV to 230V or 400V).

Conclusion

Each of these switchgear components has a specific role in ensuring the safe and reliable operation of electrical power systems. From protecting circuits with circuit breakers to isolating sections with isolators, and measuring electrical parameters with CTs and PTs, these components are crucial for maintaining the integrity and safety of electrical networks.