In this article we will discuss about:- 1. Meaning of Static Relays 2. Need for Static Relays 3. Essential Components 4. Advantages 5. Limitations. Contents: Meaning of Static Relays Need for Static Relays Essential Components of Static Relays Advantages of Static Relays Limitations of Static Relays 1. Meaning of Static Relays: A static relay refers to a relay in which [...]
Static relays are classified according to the type of the measuring unit or comparator as follows: 1. Electronic Relays 2. Transductor (Magnetic Amplifier Relays) 3. Rectifier Bridge Relays 4. Transistor Relays 5. Hall Effect Relays 6. Gauss Effect Relays. 1. Electronic Relays: These were the first to be developed in the series of static relays. Fitzgerald presented a carrier current [...]
Distance relays are characterised by having two input quantities proportional to the voltage and current at a particular point in the power system, referred to as the relaying point. Ideal static distance relays have characteristics independent of actual magnitudes of voltage and current but dependent only on their ratio and phase angle between them. The versatile family of distance relays [...]
In this article we will discuss about the classification and design of relays used in an electric circuit. Classification of Relays: The protective relay may be defined as an electrical device interposed between the main circuit and the circuit breaker in such a manner that any abnormality in the circuit acts on the relay, which in turn, if the abnormality [...]
Distance relays can be either single phase or polyphase using multi-input comparators. Such multi-input comparators may be instantaneous or integrating type and compare either phase or amplitude or both. The characteristics of conventional two-input comparators are in the forms of straight lines, circles or sectors of circle on complex plane. Multi-input comparators may have elliptical, conical or quadrilateral characteristics on [...]
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 [...]