The benefits of Numerical relays are. A Relay is electromagnetic switch. You can use a safety relay of that type in category B, 1 and 2 circuits too. Relay will monitor Current and Voltage in the feeder line (PT and CT secondary), and from these values, the relay will calculate Impedance value Z. Its important to note that damp, wet, and dusty environments require extra diligence in design and maintenance. This results in a heavy current flow through the relay coil, causing the relay to operate by closing its contacts. How does a Relay works! But now a day we are using Numerical relays for all protections. Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. Supplied with TecQuipment’s Protection and Relay Test Set (PSL50), the relay enables investigations into the protection and monitoring of overhead lines and underground cables. The working of an electrical relay based on the above diagram is explained below. The settings typically are more sensitive than the fuses or circuit breakers. Once these limits are exceeded, the protection relay will operate an internal switch (relay contacts). Your email address will not be published. Disconnect the abnormally operating part so as to avoid the damage or interference within the effective operation of the rest of the system. They work on the following two main operating principles : Electromagnetic attraction relays operate by virtue of an armature being attracted to the poles of an electromagnet or a plunger being drawn into a solenoid. Switching and isolating the circuits for maintenance: Switching is also an important function of substations. Bottom: The same relay photographed from the front.Suppose you want to build an electronically operated coolingsystem that switches a fan on or off as your room temperaturechanges. Such relays may be actuated by d.c. or a.c. quantities. In normal load condition the impedance values on line will be high. The principal function of protective relaying is to cause the prompt removal front service of any element of the power system when it starts to operate in an abnormal manner or interfere with the effective operation of the rest of the system. As against this, if it is disconnected quickly then only a few coils may get damaged instead of the entire winding. They are not used with dc quantities owing to the principle of operation. fuses. Also asked, how does a feeder protection relay work? In graph there are 4 quadrants of operation. Good explain but give more diagrams please, Your email address will not be published. The relay operating characteristic must be set to coordinate with other protection devices, such as fuses, ‘downstream’ from the supply station. For Distance protection now a day Quadrilateral characteristics is used. The abnormal behavior of an element might cause damage or interference within the effective operation of the rest of the system. The working principle of distance relay or impedance relay is very simple. Now if IDIFF> 0.15A relay operation results. Engineered from the ground up, the relay has been guided by the IEC 61850 standard for communication and interoperability of substation automation devices. Difference between Diesel Engine and Petrol Engine, 7 FE Electrical and Computer Practice Problems with Solutions, 2 Important Distribution Transformer Testing Methods. The relay setting must be sensitive enough for the relay to operate and clear faults at the very end of the feeder. A protection relay is a switching device that detects or fails and starts switching operation to isolate the defective element from the rest of the system. If voltage drops, the coil can no longer hold the armature and the relay contacts will open. Prevent the subsequent faults by disconnecting the abnormally operating part. The main inputs needed for distance protection is Voltage and Current from corresponding feeder PT and CT. They are compact and self-contained devices which can detect abnormal conditions. We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. Thus we will get a parallelogram graph and the protection zone is inside the parallelogram. For feeder protection, there would be more than one overcurrent relay to protect different sections of the feeder. Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? A common mistake technicians make is they hear a "click" and assume the relay is good. But when fault comes on the feeder line, the impedance will decrease and becomes less than the impedance setting in the relay, then the distance relay will trip with in 40 ms in zone 1 (different zones are there and that will be explained later) and isolate power equipments from fault. 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