In this article we will discuss about:- 1. Construction of SF6 Circuit Breakers 2. Properties of Sulphur Hexafluoride Gas 3. Arc Extinction 4. Advantages 5. Problems Associated. Contents: Construction of SF6 Circuit Breakers Properties of Sulphur Hexafluoride Gas Arc Extinction in SF6 Circuit Breakers Advantages of SF6 Circuit Breakers Problems Associated With SF6 Circuit Breakers 1. Construction of SF6 Circuit [...]
In this article we will discuss about:- 1. Meaning of Circuit Breakers 2. Operating Principle of Circuit Breakers 3. Arc Phenomena 4. Arc Extinction 5. Resistance Switching 6. Ratings. Meaning of Circuit Breakers: Circuit breakers are mechanical devices designed to close or open contact members, thus closing or opening of an electrical circuit under normal or abnormal conditions. Automatic circuit [...]
In this article we will discuss about:- 1. Principle of Arc Extinction in Air-Blast Circuit Breakers 2. Types of Air-Blast Circuit Breakers 3. Features 4. Drawbacks. Principle of Arc Extinction in Air-Blast Circuit Breakers: The air-blast circuit breaker requires an auxiliary compressed air system which supplies air to the breaker air receiver. When opening is required, compressed air is admitted [...]
There are two methods of arc extinction in circuit breakers. They are: 1. High Resistance Method 2. Low Resistance or Current Zero Interruption. 1. High Resistance Method: In this case the arc is controlled in such a way that its effective resistance increases with the time so that the current is reduced to such a value that the heat produced [...]
The circuit breakers may be subjected to widely varying stresses under different operating conditions. The current may vary from a few amperes due to no-load magnetizing current of a transformer to the heaviest short-circuit currents amounting to a hundred kilo-amperes. The circuit impedance may also change within the first 10–4 to 10–3 second because open lines or cables connected to [...]
In this article we will discus about:- 1. Introduction to Re-Striking Voltage Transient 2. Expression for Re-Striking Voltage Transient 3. Classification 4. Characteristics 5. Factors Affecting. Introduction to Re-Striking Voltage Transient: Electrically a power system is an oscillatory network so that it is logical to expect that the interruption of fault current will give rise to a transient whose frequency [...]
Generator faults can be considered under the following heads: 1. Stator Winding Faults 2. Field Winding or Rotor Circuit Faults 3. Abnormal Operating Conditions. 1. Stator Winding Faults: Such faults occur mainly due to the insulation failure of the stator coils. The main types of stator winding faults are: (i) Phase-to-earth faults (ii) Phase-to-phase faults and (iii) Inter-turn faults involving [...]
In this article we will discuss about:- 1. Stator Protection of Generators 2. Overload or Overcurrent Protection of Generators 3. Over-Voltage Protection 4. Over-Speed Protection 5. Protection against Motoring 6. Negative Sequence Protection 7. Protection against Vibration 8. Bearing Overheating Protection 9. External Fault Backup Protection 10. Direct Connected Protection. Stator Protection of Generators: The earth fault current is usually [...]
The following points highlight the top seven systems employed for stator protection of generators. The systems are: 1. Differential Protection for Generators 2. Modified Differential Protection for Generators 3. Biased Circulating Current Protection (Percentage Differential Relay Protection) 4. Self-Balance Protection System 5. Balanced Earth-Fault Protection 6. Stator Inter-Turn Protection 7. Stator Overheating Protection. System # 1. Differential Protection for Generators: [...]
In this article we will discuss about:- 1. Protection of Low-Voltage (Below 1,000 V) 3-Phase Induction Motors 2. Protection of Large Sized Motors 3. Protection for Exclusively Synchronous Motors. Protection of Low-Voltage (Below 1,000 V) 3-Phase Induction Motors: These are the most widely used industrial motors. Circuit diagram for a magnetic contactor starter for a low-voltage 3-phase induction motor is [...]