Simplicity — if the protective system is simple then it can be easily maintained. If the device is simple then the reliability will be high. Economy — Economical factors must be considered while selecting a protective system if the apparatus which needs to be protected is very important so we must not consider this. There are different types of protective relays and some of them are different in their operation method such as an electromechanical relay does its operation by either magnetic attraction or by magnetic induction.
Armature type relay has a pivoted lever supported on a hinge or knife edge pivot, which carries a moving contact. Armature relays could work in either AC or in DC. Relay works as a protective switch and they are used in power systems, but in certain cases relays are used as sensing devices such as in higher power applications, so in case of any abnormal condition the relay would sense it and sends the signal to the circuit breaker.
Protective relay senses the fault position and gives a signal to the circuit breaker, the circuit breaker will disconnect the faulty portion after receiving the signal. The above image shows the connection of the relay and we can see the primary winding of the current transformer is connected to the line which is to be protected.
The secondary winding of the current transformer is connected to the relay coil, and there is a tripping circuit it could be AC or DC and there is a circuit breaker. So in the case of a short circuit at point F, there is a huge hike in the current flow, and this current would reach the relay coil and the relay will operate due to this by closing its contact.
The system can detect and locate the defective issues and the electrical lines , and can also automatically initiate the protective measures and the actions of the control circuit.
Nowadays protective relays may consist of several different relays combined. These relays may have different kinds of actuators as well and may control different aspects of the system. The relay of a system may respond to certain specified inputs, and a combination deals with many different kinds of issues and conditions.
Different types of relays may have their specific actuating systems. They may function based on differences in impedance, voltage, current, and other aspects and parameters of an electrical system.
A protection relay mainly works as a sensor. It may find out the fault location and then signal the operation of the circuit breaker. The circuit breaker cuts off the faulty system from the rest of the system and the continuity of the electrical supply is not hampered. The faulty times are also reduced, which ensures that the system can work smoothly again in the least time.
The new combination protection relays that may include many different sensors and the protective relay varieties may sense a variety of faults and issues. No wonder these are the most common systems employed today in a variety of scenarios! A fault and undesirable change in variables including voltage and current among others may lead to the breakdown of the electrical system and other kinds of problems and issues. Protective relays ensure that such interferences and damages are prevented and the faulty circuit component and the system are entirely isolated from the main system.
The relay can minimize any damage to the electrical components and equipment in cases of electrical failure. When you want a smooth and hassle-free electrical service and consumption experience, you should ensure that the electrical system carries and includes the protective relays. Table of Contents The time relay is a helpful device that can be used for various purposes in the world of electricity. It is the perfect way. Protective relay work as a sensing device, it senses the fault, then known its position and finally, it gives the tripping command to the circuit breaker.
The circuit breaker after taking the command from the protective relay, disconnect the faulted element. By clearing the fault fast with the help of fast-acting protective relay and associated circuit breaker, the damage to the apparatus is reduced, and the resultant hazards like fire, the risk of the life are reduced, by removing the particularly faulted section. But the continuity of supply is maintained, though remaining healthy section, by clearing the fault fast, fault arising time is reduced, and therefore the system can be restored to the normal state sooner.
Hence the transient state stability limit of the system is greatly improved, permanent damage to the equipment is avoided, and the possibility of developing most simple fault such as single phase-to-ground into most severe fault such as double phase-to-ground fault is reduced.
The fault can only be reduced if the protective relay is reliable, maintainable and sensitive enough to distinguish between normal and abnormal condition. The relay must come into action whenever there is a fault and must not operate if there is no fault. Some relays are used for the protection of the power system.
Some of them are primary relay meaning that they are the first line of defence. Such relays sense the fault and send a signal to the proper circuit breaker to trip and clear the fault. The fault may not be cleared if the circuit breaker fails to open or relay maloperates.
The relay failure is because of three reasons such as wrong setting, bad contacts and open circuit in the relay coil. An example of an induction disk protective relay typical of the genre is seen here, a General Electric model AC overcurrent relay:.
This relay uses an aluminum disk approximately 4 inches in diameter to sense and time overcurrent conditions, the disk slowly rotated by the torque generated from a set of electromagnet coils energized by current received from a current transformer CT. The relay shown in the above photograph has already been drawn out of its case for inspection. Later protective relay designs used electronic circuits rather than electromagnetic mechanisms to detect and time overcurrent conditions.
The accuracy, stability, and reliability of modern microprocessor-based protective relays is such that there is no longer a need to regularly remove them for service and replacement. Another advantage of a microprocessor-based relay design is the ability to communicate digitally with other microprocessor-based systems. Additionally, the digital memory capabilities of a microprocessor-based relay allows for power instrument data voltage, current, phase shift, timestamps, etc.
An interesting footnote to modern protective relays is their persistent use of anachronistic terms. Even in the most modern protective relays such as the Schweitzer model shown previously, you will find parameters inside the relay designated torque control, time dial, pickup, and dropout : all terms designed to describe moving components inside an electromagnetic relay mechanism such as the old General Electric model AC induction-disk unit.
Protective relay controls were developed and perfected for so many years using electromagnetic relay technology that the nomenclature remains in common use even though the mechanisms inspiring these terms are obsolete.
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