Protective relay | Wikipedia audio article
Channel: wikipedia tts
Date: 02/10/2019

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Protective_relay


00:02:21 1 Operation principles
00:05:36 2 Types according to construction
00:05:46 2.1 Electromechanical
00:07:22 2.2 Induction disc overcurrent relay
00:11:34 2.3 Static
00:13:05 2.4 Digital
00:15:19 2.5 Numerical
00:16:20 3 Relays by functions
00:16:45 3.1 Overcurrent relay
00:17:50 3.1.1 Definite time over-current relay
00:18:16 3.1.2 Instantaneous over-current relay
00:19:06 3.1.3 Inverse-time over-current relay
00:19:40 3.1.4 Inverse definite minimum time relay
00:23:49 3.2 Distance relay
00:25:24 3.3 Current differential protection scheme
00:27:16 3.4 Directional relay
00:27:52 3.5 Synchronism check
00:28:28 4 Power source



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SUMMARY
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In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected.:4 The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current, over-voltage, reverse power flow, over-frequency, and under-frequency.Microprocessor-based digital protection relays now emulate the original devices, as well as providing types of protection and supervision impractical with electromechanical relays. Electromechanical relays provide only rudimentary indication of the location and origin of a fault.  In many cases a single microprocessor relay provides functions that would take two or more electromechanical devices. By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays. However, due to their very long life span, tens of thousands of these "silent sentinels" are still protecting transmission lines and electrical apparatus all over the world. Important transmission lines and generators have cubicles dedicated to protection, with many individual electromechanical devices, or one or two microprocessor relays.
The theory and application of these protective devices is an important part of the education of a power engineer who specializes in power system protection. The need to act quickly to protect circuits and equipment often requires protective relays to respond and trip a breaker within a few thousandths of a second. In some instances these clearance times are prescribed in legislation or operating rules. A maintenance or testing program is used to determine the performance and availability of protection systems.Based on the end application and applicable legislation, various standards such as ANSI C37.90, IEC255-4, IEC60255-3, and IAC govern the response time of the relay to the fault conditions that may occur.