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Electrical Code - CANADIAN 2002 Version - Commercial or Residential for CANADA

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  #1   IP: 70.28.63.64
Old February 19th, 2012, 06:14 PM
poutinepete poutinepete is offline
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Default 309A exam prep. question

Here's the 309A prep question and answer:
1. A four-pole 60hz SCIM has a full load speed of 1770 RPM at full load. Calculate the % slip of the motor at full-load.
Answer: 1.67%
Can someone explain to me how to figure this out because I have no idea.
Thanks.
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  #2   IP: 50.135.128.55
Old February 19th, 2012, 08:32 PM
suemarkp suemarkp is offline
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60 cycles per second = 120 peaks per second if you look at the plus and minus voltage cycles. 120 cycles per second * 60 seconds = 7200 RPM if the motor had one pole.

7200 / 4 poles = 1800 RPM calculated RPM.

Actual RPM was 1770 / 1800 = 98.333% of theoretical speed. So slip is 100% - 98.33% = 1.67%.
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