electrical engineering

Insulation Resistance Value Required For Operation

<h3 class="post-title entry-title"><span style="color: #351c75; font-size: medium;"><span style="font-weight: normal;">This post is the third part of </span></span></h3><h3 class="post-title entry-title"><a href="http://hayatei.blogspot.com/2010/12/coil-and-insulation-in-high-voltage_17.html">COIL AND INSULATION IN HIGH VOLTAGE MOTORS</a></h3><h3 class="post-title entry-title"><span style="color: #351c75; font-size: large;"><span style="font-weight: normal;"> The second part  </span></span></h3><h3 class="post-title entry-title" style="font-weight: normal;"><span style="font-size: large;"><a href="http://hayatei.blogspot.com/2010/12/measurement-of-insulation-resistance.html">Measurement Of Insulation Resistance</a></span></h3><h3 class="post-title entry-title" style="font-weight: normal;"><span style="font-size: large;"> </span></h3><h3 class="post-title entry-title" style="background-color: cyan; color: red; font-weight: normal; text-align: center;"><u><span style="font-size: large;"> Insulation Resistance Value Required For Operation</span></u></h3><br />
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<div style="text-align: justify;">In general, it is difficult to give a minimum of permis¬sible insulation resistance value for starting since it varies with the type, rating and size of the motor. However, as a simple standard for daily maintenance, the following equation may be considered for the minimum value.</div><br />
Rm = E + 1<br />
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<span style="background-color: cyan; color: red;">where, </span><br />
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<span style="background-color: yellow; color: red;">Rm </span>: recommended minimum insulation resistance at 40ºC of the machine winding, in MΩ</div><div style="text-align: justify;"><br />
<span style="background-color: yellow; color: red;">E </span>: Motor rated voltage, in KV</div><br />
<div style="text-align: justify;">When applying the Rm as given by above equation, the temperature correction of measured insulation resistance should be made by use of the following equation if the winding is not at a temperature of 40ºC.</div><div style="text-align: justify;"></div><div class="separator" style="clear: both; text-align: center;"><a href="http://hayatei.blogspot.com/2010/12/insulation-resistance-value-required.html"><img alt="http://img101.herosh.com/2010/12/18/319898224.png" border="0" src="http://img101.herosh.com/2010/12/18/319898224.png" /><span id="goog_1476959027"></span></a><span id="goog_1476959028"></span></div><div style="text-align: center;"></div><div style="text-align: justify;"></div><div style="background-color: yellow; color: red; text-align: center;">where, </div><div style="text-align: justify;"><br />
<span style="background-color: yellow; color: red;">Rc </span>; insulation resistance corrected to 40ºC, in MΩ<br />
<span style="background-color: yellow; color: red;">Rt </span>. measured insulation resistance at a temp. t ,in MΩ <br />
<span style="background-color: yellow; color: red;">A¬0 </span>: insulation resistance correction factor</div><div style="text-align: justify;"><br />
(See Fig. 1-2 Temperature Correction Curve)</div><div style="text-align: justify;"></div><div style="text-align: justify;"></div><div style="text-align: justify;"><br />
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</div><div style="text-align: center;"><a href="http://hayatei.blogspot.com/2010/12/insulation-resistance-value-required.html"><img alt="http://img101.herosh.com/2010/12/18/815714691.jpg" src="http://img101.herosh.com/2010/12/18/815714691.jpg" /></a></div><div style="text-align: justify;"><br />
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</div><div style="background-color: yellow; color: red; text-align: center;"><span style="font-size: large;">Fig.1.2-a Temperature correction curve </span></div><div style="text-align: justify;"><br />
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</div><div style="text-align: center;"><span style="font-size: large;"><a href="http://hayatei.blogspot.com/2010/12/prevention-of-megger-reduction-and.html"><span style="color: black; font-family: Arial;"><span style="background-color: yellow; color: red;"> The 4th part  Prevention Of Megger Reduction .</span></span><span style="background-color: yellow; color: red;"><span style="font-family: Arial;">avaible now</span></span></a></span><br />
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Insulation Resistance Value Required For Operation

This post is the third part of COIL AND INSULATION IN HIGH VOLTAGE MOTORS The second part Measurement Of Insulation Resistance Insulati...

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Measurement Of Insulation Resistance

<div style="text-align: justify;"><h3 class="post-title entry-title"><span style="color: #351c75; font-size: large;"><span style="font-weight: normal;">This post is the second part of </span></span></h3><h3 class="post-title entry-title"><a href="http://hayatei.blogspot.com/2010/12/coil-and-insulation-in-high-voltage_17.html">COIL AND INSULATION IN HIGH VOLTAGE MOTORS</a>  </h3><div style="background-color: magenta; color: yellow; text-align: center;"><u><span style="font-size: large;">Measurement Of Insulation Resistance</span></u></div><div style="color: red;"><br />
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</div><div style="color: red;"><span style="font-size: small;">Insulation resistance is the direct current resistance of the insulation which corresponds to leakage current flowing inside and on the surface of the insulation. Decrease in insulation resistance is caused by deterioration or absorption of moisture of the insulation, adhesion of dirt, and temperature rise. The values of insulation resistance obtained by measurement decreases as the test voltage increases and as the duration of the test voltage application is shortened. Since insulation resistance is a useful measure for determining the condition of insulation, it should be measured periodically, while the motor is not in operation, and records of the measuring apparatus used, coil temperature, ambient temperature, relative humidity, and other conditions (for example, the time elapse after motor stoppage) are to be kept.</span></div><div style="color: red;"><span style="font-size: small;"><br />
</span><span style="font-size: small;">The motor, if contaminated, is to be cleaned in the aforementioned manner, the insulating resistance before and after cleaning is to be recorded. Either 500V rotary megger or the-electron tube megger may be used. With a rotary megger, rotate it continuously for at least one minute. With an electron tube megger, apply voltage for 10 minutes. Record insulation resistance values for 30 seconds, 1 minute, and 10 minutes. Recording of time is necessary since insulation resistance varies with the duration of the test because of charge current or absorbed current. Insulation resistance varies with changes in temperature and humidity, but the pressure of salty substance affects the value greatly. If this -happened, consult Mitsubishi Electric Corporation.</span></div><div style="color: red;"><br />
</div><div style="color: red; text-align: center;"><span style="font-size: small;"><span style="font-size: large;"><span style="background-color: yellow; color: red;">To be continued ..... soon</span></span></span></div><div style="color: red;"><br />
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Measurement Of Insulation Resistance

This post is the second part of COIL AND INSULATION IN HIGH VOLTAGE MOTORS Measurement Of Insulation Resistance Insulation resistance is...

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