Which relay is used for protection of long lines ?

<div dir="ltr" style="text-align: left;" trbidi="on"> As reactance relays are affected by power surges more than impedance relays and mho relays, they are not suitable for longer lines. The effect of power surges stay for a longer period in case of long lines and hence, a relay which is least affected by a power surge is preferred for the protection of long lines. The MHO relay is less affected by power surges than the impedance and reactance relay and hence, it is best suited for the protection of long lines against phase faults.</div>

Electrical Engineering Interview Questions Which relay is used for protection of long lines ?

As reactance relays are affected by power surges more than impedance relays and mho relays, they are not suitable for longer lines. The eff...

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What are the advantages of star-delta starter with induction motor

<div dir="ltr" style="text-align: left;" trbidi="on"> <b data-iceapc="270" data-iceapw="811" style="background-color: white; color: #333333; font-family: Verdana; font-size: 12px;"><table border="0" cellpadding="0" cellspacing="10" data-iceapc="269" data-iceapw="811" style="width: 100%px;"><tbody data-iceapc="268" data-iceapw="811"> <tr data-iceapc="267" data-iceapw="811"><td data-iceapc="266" data-iceapw="811"><table bgcolor="#E6F2FF" border="0" cellpadding="5" cellspacing="1" data-iceapc="101" data-iceapw="642" style="width: 100%px;"><tbody data-iceapc="100" data-iceapw="642"> <tr data-iceapc="99" data-iceapw="642"><td bgcolor="#FFFFFF" data-iceapc="93" data-iceapw="642" valign="top" width="80%"><div style="text-align: center;"> <b data-iceapc="270" data-iceapw="811" style="color: #333333; font-size: 12px;"><table border="0" cellpadding="0" cellspacing="10" data-iceapc="269" data-iceapw="811" style="display: inline !important; width: 100%px;"><tbody data-iceapc="268" data-iceapw="811" style="display: inline !important;"> <tr data-iceapc="267" data-iceapw="811" style="display: inline !important;"><td data-iceapc="266" data-iceapw="811" style="display: inline !important;"><table bgcolor="#E6F2FF" border="0" cellpadding="5" cellspacing="1" data-iceapc="101" data-iceapw="642" style="display: inline !important; width: 100%px;"><tbody data-iceapc="100" data-iceapw="642" style="display: inline !important;"> <tr data-iceapc="99" data-iceapw="642" style="display: inline !important;"><td bgcolor="#FFFFFF" data-iceapc="93" data-iceapw="642" style="display: inline !important; text-align: center;" valign="top" width="80%"><img height="141" src="http://3.bp.blogspot.com/-_5oSxD8dgWA/TezXb22B6WI/AAAAAAAAAH4/4V9MrlRC2TM/s1600/Star+Volts+Amp+Relation.jpg" width="200" />    <img height="141" src="http://4.bp.blogspot.com/-tVdE2LKQZ2E/TezWnFYAUeI/AAAAAAAAAH0/IQl-0NBVbBM/s200/Delta+Volts+Amp+Relation.jpg" width="200" /> </td></tr> </tbody></table> </td></tr> </tbody></table> </b></div> <span style="font-family: Trebuchet MS, sans-serif;"><br />The main advantage of using the star delta starter is reduction of<br />current during the starting of the motor. Starting current is reduced to 3-4 times Of current of Direct online starting. Hence the starting current is reduced; the voltage drops during the starting of motor in systems are reduced.</span></td></tr> </tbody></table> </td></tr> </tbody></table> </b></div>

Electrical Engineering Interview Questions What are the advantages of star-delta starter with induction motor

      The main advantage of using the star delta starter is reduction of current during the starting of the motor. Starting curre...

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Difference between synchronous and asynchronous motors

<div dir="ltr" style="text-align: left;" trbidi="on"> <b>Synchronous machines:</b><br /> <div> <b><br /></b> <br /> <div class="separator" style="clear: both; text-align: center;"> <img border="0" height="342" src="http://1.bp.blogspot.com/-f0UNslo_KyU/UDJgn9OaxAI/AAAAAAAABOc/8nunM0BXnZY/s640/syn.png" width="595" /></div> <div> <b><br /></b> <br /> <ol> <li>Wound-rotor or permanent magnet to generate the rotor magnetic field.</li> <li>Rotor magnetic field is stationary with respect to the rotor. </li> <li>Always turn at synchronous speed.</li> <li>Require some form of control to operate. </li> <li>More expensive to produce than squirrel cage induction machines.</li> <li>Not self-starting.</li> <li>More efficient than induction machines.</li> </ol> <b>Induction Machines:</b></div> <div class="separator" style="clear: both; text-align: center;"> <img border="0" height="410" src="http://3.bp.blogspot.com/-WIqGWlBe8hE/UDJi2kWsFaI/AAAAAAAABOk/bucW_6piiIc/s640/im.png" width="595" /></div> <div> <b><br /></b> <br /> <ol> <li>Wound-rotor or squirrel cage to generate the rotor magnetic field.</li> <li>Rotor magnetic field rotates with respect to the rotor. </li> <li>Always turn at less than synchronous speed.</li> <li>Do not require control. </li> <li>Much cheaper to produce (true for squirrel cage machines).</li> <li>Self-starting.</li> <li>Less efficient than synchronous machines.</li> <li>More suitable for explosive environments.</li> <li>No maintenance (for squirrel cage machines).</li> </ol> </div> </div> </div>

Electrical Engineering Interview Questions Difference between synchronous and asynchronous motors

Synchronous machines: Wound-rotor or permanent magnet to generate the rotor magnetic field. Rotor magnetic field is stationary w...

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What cause electrical earth fault on a rotor?

<div dir="ltr" style="text-align: left;" trbidi="on"> <span style="font-family: Trebuchet MS, sans-serif;">The Rotor Protection relay is used in synchronous motors and generators to identify the presence of an earth fault in the rotor winding. While the winding in the rotor is insulated from the ground during normal operation, the Rotor is subjected to stresses due to vibration, heat, etc. These stresses can cause the winding to give way in a particular place and the winding can get earthed. <br /><br /><br />While a single earthing in the winding is not immediately damaging. It sets the stage for damage if a second failure should occur. The second earthing can cause a short-circuit through the rotor causing extensive damage to the rotor and the winding. <br /><br />The currents produced during a rotor earth fault can cause excessive vibration and disturb the magnetic balance inside the alternator. These forces can cause the rotor shaft to become eccentric and in extreme cases cause bearing failure. <br /><br />Hence, it is necessary that any earthing in the rotor is detected at the earliest. <br /><br />In slip ring rotors, carbon deposits on the slip rings may compromise the insulation resistance of the rotor. Hence, the slip rings need to be inspected for any deposits. <br /><br />The Rotor Earth Fault Protection Device consists of a current injection device which applies an AC voltage to the rotor winding by means of a slip ring fitted on the rotor. The current is applied to the rotor through a coupling capacitor. In the normal condition, the system is floating and the current flowing through the device is zero as the resistance is high. <br /><br />When a fault occurs, the current increases causing the relay to operate. The relay can be configured for alarm or trip depending on the criticality. </span><div style="text-align: right;"> <span style="color: red; font-family: Trebuchet MS, sans-serif; font-size: xx-small;">Source: wiki.answers</span></div> </div>

Electrical Engineering Interview Questions What cause electrical earth fault on a rotor?

The Rotor Protection relay is used in synchronous motors and generators to identify the presence of an earth fault in the rotor winding. Wh...

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