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'''Blocked rotor test''' is conducted on an [[induction motor]]. It is also known as [[short circuit test]] or locked rotor test or stalled torque test.<ref>{{cite web|url =http://www.eswtesters.com/motor_testing_methods.php|title =Motor testing methods|publisher =Electronic Systems of Wisconsin, Inc.}}</ref> From this test [[short circuit current]] at [[Voltage|normal voltage]], [[power factor]] on short circuit, total [[Electrical reactance|leakage reactance]], [[Torque|starting torque]] of the motor can be found.<ref>{{cite web|url =http://iitg.vlab.co.in/?sub=61&brch=168&sim=916&cnt=1712|title =Blocked rotor test|publisher =Sakshat virtual labs}}</ref><ref>{{cite journal|last=de Swardt|first=Henk |url=http://www.mandc.co.za/pdfs/Locked_rotor_test_explained.pdf|title =The Locked rotor test explained|publisher =Marthinusen & Coutts (Pty.) Ltd}}</ref> The test is conducted at low voltage because if the applied voltage was normal voltage then the current flowing through the stator windings were high enough to over heat the winding and damage them.<ref>{{cite web|url =http://www.eswtesters.com/motor_testing_methods.php|title =Motor testing methods|publisher =Electronic Systems of Wisconsin, Inc.}}</ref> The ''blocked rotor torque test'' is not performed on a wound rotor motors because the starting torque can be varied as desired. However, ''blocked rotor current test'' is conducted on squirrel cage rotor motors.<ref>{{cite book|url =http://books.google.co.in/books?id=V1pepm-1m-cC&pg=PA263&dq=Locked+rotor+test&hl=en&sa=X&ei=_vDqT7-NMoizrAfE1uTVBQ&ved=0CFwQuwUwBw#v=onepage&q=Locked%20rotor%20test&f=false|title =Industrial Power Engineering and Applications Handbook|publisher =Newnes}}</ref>

==Method==
In the blocked rotor test, the [[Rotor (electric)|rotor]] is locked.<ref>{{cite web|url =http://iitg.vlab.co.in/?sub=61&brch=168&sim=916&cnt=1712|title =Blocked rotor test|publisher =Sakshat virtual labs}}</ref> A low voltage is applied on the stator terminals so that [[full load current]] flows in the stator winding. The current, voltage and power input are measured at this point. When the rotor is stationary the [[slip (motors)|slip]], <math> s = 1 </math>.<ref>{{cite book|last =B.L. Theraja|first=A.K. Theraja| title = Electrical Technology volume 2|publisher= S. Chand|edition=Twenty third revised multicolour|year=2010|page=1317|isbn=81-219-2437-5}}</ref> The test is conducted at <math> 1/4 ^{th} </math> the rated frequency as recommended by IEEE. This is because the rotor's effective resistance at low frequency may differ at high frequency.<ref>{{cite web|last =Knight|first =Dr Andy|url =http://www.ece.ualberta.ca/~knight/electrical_machines/induction/parameters/params.html|title =Electrical Machines|publisher =Department of Electrical and Computer engineering, University of Alberta}}</ref><ref>{{cite journal|last=Pitis|first=CD |https://docs.google.com/viewer?a=v&q=cache:dqMYx9A7SR8J:www.eepublishers.co.za/images/upload/femco%2520squirrel.doc+&hl=en&gl=in&pid=bl&srcid=ADGEESg5Rz7fWQUOsorcMSEdx-w1qmBvd52ATrYU2Txc0O4MlIJOxcGYmiX1l6o_Yrwg3LwlChi83gSKgv8iEgHIr7f5mN5cxiXDvpJWo3HJx_ksx1uwqnECdBs_Dib77K8JPqhUu4T2&sig=AHIEtbQMHjRqDCfrS9x7QA8klVs3r2mHEA|title =femco squirrel.doc|publisher =Femco mining motors}}</ref> The test can be repeated for different values of voltage to ensure the values obtained are consistent. As the current flowing through the stator may exceed the rated current, the test should be conducted quickly.<ref>{{cite web|url =http://www.eswtesters.com/motor_testing_methods.php|title =Motor testing methods|publisher =Electronic Systems of Wisconsin, Inc.}}</ref> By using the parameters found by this test, the motor circle diagram can be constructed.<ref>{{cite book|last =Deshpande|first =M.V.|url =http://books.google.co.in/books?id=7rwh4cw4C5gC&pg=PA254&dq=Locked+rotor+test&hl=en&sa=X&ei=_vDqT7-NMoizrAfE1uTVBQ&ved=0CEAQuwUwAg#v=onepage&q=Locked%20rotor%20test&f=false|title =Electrical Machines|publisher =PHI Learning Pvt. Ltd}}</ref>

==Calculations involved==

===Short circuit current at normal voltage===
<math> I_{S} </math> is the short circuit current at voltage <math> V_{S} </math><br>
<math> I_{SN} </math> is the short circuit current at normal voltage <math> V </math><br>
<math> I_{SN} = I_{S} \times \frac {V} {V_{S}}</math>

===Short circuit power factor===
<math> W_{S} </math> is the total input power on short circuit<br>
<math> V_{SL} </math> is the line voltage on short circuit<br>
<math> I_{SL} </math> is the line current on short circuit<br>
<math> cos \phi_{S} </math> is the short circuit power factor<br>
<math> cos \phi_{S} = \frac {W_{S}} {{\sqrt{3}} {V_{SL}} {I_{SL}}} </math><ref>{{cite book|last =Deshpande|first =M.V.|url =http://books.google.co.in/books?id=7rwh4cw4C5gC&pg=PA254&dq=Locked+rotor+test&hl=en&sa=X&ei=_vDqT7-NMoizrAfE1uTVBQ&ved=0CEAQuwUwAg#v=onepage&q=Locked%20rotor%20test&f=false|title =Electrical Machines|publisher =PHI Learning Pvt. Ltd}}</ref>

===Leakage reactance===
<math> Z_{01} </math> is the short circuit impedance as referred to stator<br>
<math> X_{01} </math> is the leakage reactance per phase as referred to stator<br>
<math> Z_{01} = \frac \text {short circuit voltage per phase} \text {short circuit current} = \frac {V_{S}} {I_{S}} </math>

<math> W_{cu} </math> is the total copper loss<br>
<math> W_{c} </math> is the core loss

<math> W_{cu} = W_{S} - W_{c}</math><br>
<math> W_{cu} = {3} \times{{I_{S}}^{2} {R_{01}}}</math>

<math> R_{01} = \frac {W_{cu}} {3{I_{S}}^{2}}</math>

<math> X_{01} = \sqrt {{Z_{01}}^{2} - {R_{01}^{2}}}</math>

==See also==
*[[Open circuit test]]
*[[Circle diagram]]

==References==
{{reflist}}

[[Category:Electrical circuits]]