Thermal Relay Construction and Working Principle: Thermal Relay can operate on the principle of thermal effect of electric current. It consists of bimetallic strips which are used in small sizes and are heated by heating coils or strips supplied through a current transformer. An insulated lever arm carrying a contact is pivoted and is held […]
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Permanent Magnet Moving Coil Relay: The arrangement of permanent magnet moving coil relay is shown in Fig. 9.12. In this relay, the coil is free to rotate in the magnetic field of a permanent magnet. The torque is developed by the interaction between the field of the permanent magnet and the coil field developed due
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Electromagnetic Induction Relay – Structure and Working Principle: Electromagnetic induction relay operate on the principle of induction motor and are widely used for protective relaying purposes involving a.c. quantities. They are not used with d.c. quantities owing to the principle of operation. An induction relay essentially consists of a pivoted aluminium disc placed in two
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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 is of a dangerous character, causes the breaker to open and so to
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Types of Circuit Breaker Mounting: There are four types of circuit breaker mounting, which are described below: Cubicle Type or Cellular Type: In this type of mountings the circuit breakers and their ancillary equipment are mounted in individual chambers or cells made of slate marble or concrete with doors of sheet steel or in a
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HVDC Circuit Breakers – Construction and Working Principle: Light duty dc circuit breakers have been in use since long. However, there is lack of suitable circuit breakers for HVDC systems. At present most of the HVDC systems are with two terminals and in a two terminal HVDC system, HVDC circuit breakers are not required because
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Difference between Fuse and Circuit Breaker: The difference between fuse and circuit breaker is given in table below S. No. Particulars Fuse Circuit Breaker 1 Functions It performs both of functions—detection as well as interruption. It performs the function of interruption only. Fault is detected by relay system provided for this purpose. 2 Operation Inherently
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Factors to be Considered in Selection of Fuse: In order to ensure that the fuses will correctly and reliably protect any given section or element of an electrical circuit, selection of fuse characteristics and ratings must be suitable in accordance with the following requirements. Rated Voltage : Fuses and their fusible elements must be selected
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Instrument Transformers – Definition, Types and Errors: AC type protective relays are actuated by current and voltage supplied by current and potential (or voltage) transformers, known as instrument transformers. The main function of instrument transformers are: To provide insulation against the high voltage of the power circuit and to protect the apparatus and the operating
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Overlapping Zones of Protection: Overlapping Zones of Protection – In order to provide selectivity to the system it is usual practice to divide the entire system into several protection zones. When a fault occurs in a given zone, then only the circuit breakers within that zone will be opened and thus only the faulty element
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