INTRODUCTION

First of all, Thomas Edison introduced circuit breakers in his patent application to protect circuit wiring in case of short circuits accidentally and due to overload. But in the beginning fuse was used to implement this concept.

After that Cie, Boveri, and Brown presented a modern miniature circuit breaker in 1924. There was a need for an advanced circuit breaker when it came to grid stations with more load voltage for proper safety and protection to deal with that high voltage. By the year 1935, specially designed breakers were used to deal up to 2500 MVA. It was completed in three cycles of AC power frequency.

This electrical Circuit Breaker(CB) training course introduces basic safe operational and field diagnostics of CBS with a focus on safe operation, testing, and maintenance of the CBS normally installed in substations.

CIRCUIT BREAKERS

• Circuit breakers play an important role in the design and performance of a power system.
• The circuit breakers are the key pieces of apparatus protecting the system and thus ensure the reliability of supply.
• Hence utmost care shall be taken in the selection of the circuit breakers.
• High voltage circuit breakers are mechanical switching devices, which should be able to do the following performances under normal circuit conditions & also for a limited time under abnormal circuit conditions e.g. Short circuit, at maximum specified operating voltage & frequency.
• Switching operations of:
  • Over headlines.
  • Cable branches (Lines).
  • Power Transformers.
  • Reactors.
  • Shunt Capacitor Banks.
  • Continuously carry normally rated currents.

Operation working:

We have same operation in almost all circuit breakers and in detail they may differ with respect to voltage or current values.

First of all, the breaker detects a fault itself using a heating or magnetic effect in circuit breakers. But when we talk about large voltage or current values, breakers operate with relays to detect a fault, and then the circuit performs its protection operation. In grid system, we have relay panels separately to detect faults using timers.

When we got a fault, circuit breakers interrupt using mechanical force such as spring or compressed air to separate the breaker’s contacts. Breaker contacts must be able to carry the load current with excessive heating and stand with that heat. Usually, contact is made of copper or silver or conducting materials depending on the best performance during fault.

Difference between fuse and breakers:

Both fuses and circuit breakers work for protection in case of fault. Only the difference is the time of fuse burning or operation and breakers operation is that fuse operation time is 0.002s and breaker operation time is 0.02-0.05s.

Fuse cannot be reused after once performing operation but circuit breakers can be used again. Circuit breakers work for overloading and short circuit while fuses work only for overloading faults in home appliances.

Ars Extinction medium:

Current ties to make the circuit through which current tries to flow and to remove that arc different breakers used different mediums as mentioned below:

• Oil
• Vacuum
• Air
• SF6(Sulphur hexafluoride) gas 

Arc removal methods:

The current arc is dangerous so we need to remove that there are different methods that we can use:

Cooling of air: Arc reduces the resistance of air due to heat. So, cooling the heat will increase resistance again, and as a result, voltage will also increase and current will decrease.

Zero Current Quenching: Usually this method is applied in AC breakers. Zero currents are present in the AC waveform and we open the circuit at the exact location of zero current. So current will not increase.

Length of arc: By increasing the length of arc voltage will also increase and as a result current will not increase.

Contact size: By reducing the size of the contact cross-sectional area will be decreased

So, circuit breakers are important in case of faults and for protection purposes. We keep in mind different aspects to install breakers such as.

• AC Current
• DC Current
• Voltage level
• Location of installation

Types of circuit breakers:

There are two types of circuit breakers.

AC Circuit breakers

• High voltage and medium voltage circuit breakers
• High voltage includes Oil and Oil less circuit breakers
• Air brake, Air blast SF-6 and vacuum circuit breakers are also present in this category

DC Circuit breakers

Now we will discuss important and main circuit breakers:

Oil circuit breakers:

These circuit breakers use oil as an arc extinction medium. They include bulk and minimum oil circuit breakers.

Bulkoil circuit breakers: They use oil as an insulator between conducting parts of circuit breakers. They work for 25MVA to 5000MVA rating range at 2,5kV and at 230kV respectively.

Minimum oil circuit breakers:Its main function is to remove the arc and it does not insulate the earth part.

Air circuit breaker:

In this type of circuit breakers current arc is started and ended/extinct into static air. These are used for 15kV as minimum value. The further classification depends on breaking method of air.

Air Blast Circuit Breaker:

As name is indicating, it uses air blast to extinct the current arc to protect the main appliances. It stores the air in tank and when needed it releases the air with high speed/velocity. This circuit breaker comes under the medium voltage category and used in homes appliances. For 220kV lines they also used in outsides.

Sulphur hexafluoride Circuit Breaker:

These breakers use SF-6 gas because this gas behaves as a great agent or medium for arc extinction.

Talking about 132kV lines, circuit breaker used SF-6 gas in this breaker. This is spring charged to act as a protective agent and DC motor charge that spring by pressing the spring.  To remove flash in case of fault SF-6 gas works efficiently.

Operating media in this circuit breaker is Spring charge and quenching media is SF-6 gas. We have panels of incoming voltage lines and in incoming lines we VCB (Vacuum circuit breaker). VCB uses vacuum bottles to remove flash. In old times oil was used to remove flash.

HVDC circuit breaker:

For the interruption or protection in high voltage direct current we use HVDC circuit breakers. It works for 33kV and 2KA for voltage and current value.

There are two types of circuit breakers:

• Sold state
• Electromechanical

Other breakers:

Other breakers include:

• MCB (Miniature circuit breaker)
• RCCB (Residual current circuit breaker)
• ELCB (Earth Leakage Circuit breaker)
• Poly-switch

Advantages:

• Protection from excessive current
• Can be reset using switch
• Reliable device

Applications:

• They are used as electrification
• Used for protection of plants, transformers capacitor and generators
• Switching loads in buildings or industries etc.
• Interrupt currents.
  • Bus sectionalizes in multiple bus-bar installations so that power can be transmitted from one bus to another bus smoothly without interruption.
  • Make and break the circuit under normal conditions.
  • Make and break the circuit under abnormal conditions such as those of a maximum short circuit current.
  • Perform the specified Rated operating duty cycle satisfactorily.
  • It may also happen many times that the circuit breaker is closed on the system when the fault conditions still persist.  It should not get damaged or create conditions that may cause damage to other equipment on the system.

Points to be considered when selecting circuit breakers

• Standards.
• Principle parameters
• Technical requirements.
• Test Reports
• Auxiliary power supply.