{"id":3860,"date":"2018-10-15T11:38:37","date_gmt":"2018-10-15T16:38:37","guid":{"rendered":"https:\/\/www.westfloridacomponents.com\/blog\/?p=3860"},"modified":"2018-03-07T11:39:42","modified_gmt":"2018-03-07T16:39:42","slug":"using-relays-detect-faults","status":"publish","type":"post","link":"https:\/\/www.westfloridacomponents.com\/blog\/using-relays-detect-faults\/","title":{"rendered":"Using Relays to Detect Faults"},"content":{"rendered":"<p class=\"p1\"><span class=\"s1\">Different types of relays are in use in every-day life. These include relays constructed from electromechanical elements such as from solenoids, induction discs, hinged armatures, or from solid-state elements such as from transistors, magnetic or operational amplifiers, silicon-controlled-rectifiers (SCRs), diodes, or digital computers using microprocessors and analog-to-digital converters<\/span><span class=\"s2\">.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">Development of protection with relays began with the electromagnetic types, and most descriptions of relay characteristics still retain the electromagnetic terms. Although the construction of a relay does not inherently alter the concept of protection, each type has its own advantages and disadvantages.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">General faults are often short circuits, where the current increases in magnitude, while the voltage goes down. Apart from the changes in magnitude, the AC field may also undergo changes in parameters such as system frequency, active\/reactive power, harmonic components, phase angles of the current and voltage phasor, and more.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">Operating principles of detection of faults with relays are based on detecting the above changes and identifying whether the changes exist within the predefined zone of protection or outside. Depending upon the operating principle of the relay, detection can be categorized based on which of the input quantities the specific relay will respond. This leads to eight major types of faults that relays can detect:<\/span><\/p>\n<ul class=\"ul1\">\n<li class=\"li2\"><span class=\"s1\">Frequency Sensing<\/span><\/li>\n<li class=\"li2\"><span class=\"s1\">Harmonic Content<\/span><\/li>\n<li class=\"li2\"><span class=\"s1\">Pilot Relaying<\/span><\/li>\n<li class=\"li2\"><span class=\"s1\">Distance Measurement<\/span><\/li>\n<li class=\"li2\"><span class=\"s1\">Phase Angle Comparison<\/span><\/li>\n<li class=\"li2\"><span class=\"s1\">Differential Comparison<\/span><\/li>\n<li class=\"li2\"><span class=\"s1\">Magnitude Comparison<\/span><\/li>\n<li class=\"li1\"><span class=\"s1\">Level Detection<\/span><\/li>\n<\/ul>\n<p class=\"p1\"><span class=\"s1\">Most power systems operate at a normal frequency of 50 or 60 Hz, depending on the country. Deviating from the normal frequency indicates an existing problem or an imminent one. Engineers use frequency-sensing relays to detect and take corrective action to bring the system frequency back to normal.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">Power systems usually operate with a sinusoidal waveform of the fundamental frequency. Abnormal system conditions create harmonics that are typically associated with heat and loss in efficiency. Electromechanical or solid-state relays can detect these harmonics, based on which control action may be required.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">Sometimes information is required from a remote location, and a pilot relay provides it in the form of contact status, open or closed. Usually, this information is carried over a channel of communication using telephone, microwave, or carrier circuits.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">An impedance relay determines the distance or length of the line based on a given spacing and diameter of the conductor. The relay compares the local voltage with the local current, and gives a measurement of the line impedance as seen from its terminals.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">A phase angle comparison relay compares the relative angle of phase between the AC voltage and the AC current, measuring the power factor angle. This comparison determines the direction of flow of the current with respect to the voltage, with the magnitude of the angle measured giving an indication of faults.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">Under normal operating conditions, current entering one end of an electrical equipment should equal the current exiting from the other end. However, in case of any fault within the equipment, this balance is no longer maintained. A differential relay detects the difference in the two currents, and provides protection.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">Relays can compare the magnitude of current in one circuit with the magnitude of current in another and detect abnormalities based on whether they should have been equal or proportional.<\/span><\/p>\n<p class=\"p1\"><span class=\"s1\">Finally, relays can be designed to trip the circuit breakers should the operating current level crosses a specific setting.<\/span><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Different types of relays are in use in every-day life. These include relays constructed from electromechanical elements such as from solenoids, induction discs, hinged armatures, or from solid-state elements such as from transistors, magnetic or operational amplifiers, silicon-controlled-rectifiers (SCRs), diodes, or digital computers using microprocessors and analog-to-digital converters. Development of protection with relays began with [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[15,26],"tags":[2036,2035,2037],"class_list":["post-3860","post","type-post","status-publish","format-standard","hentry","category-guides","category-relays","tag-fault-detection","tag-relays","tag-short-circuits"],"_links":{"self":[{"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/posts\/3860"}],"collection":[{"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/comments?post=3860"}],"version-history":[{"count":1,"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/posts\/3860\/revisions"}],"predecessor-version":[{"id":3861,"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/posts\/3860\/revisions\/3861"}],"wp:attachment":[{"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/media?parent=3860"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/categories?post=3860"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.westfloridacomponents.com\/blog\/wp-json\/wp\/v2\/tags?post=3860"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}