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Topic Title: motor tripping breaker in delta
Topic Summary: star delta problem
Created On: 25 November 2010 09:21 PM
Status: Read Only
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 25 November 2010 09:21 PM
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Posts: 8
Joined: 25 November 2010

We have inherited a 3 phase AEI Startrite 7.5 HP motor which is marked as 440V 50Hz with a FLC 19A. The terminal markings are made using Dyno tape as A1, B1, Z1 & A2, B2, Z2 which I have never come across on a 3 phase machine.
However, we have checked that the motor has a satisfactor insulation resistance and found each pair of windings (these being 2.2 ohms).
We have connected the motor to a new Moeller Star/ Delta starter which we have done many many times, only to find that (off load) in Star the motor draws about 7-8Amps on each line, but when it changes to Delta it draws 70-80A on two lines and virtually no current on the third line.
Thinking that there may be a situation where one winding is working in opposition to the others we went through a reconnection of all possible permutations, but to no avail.
Any ideas on what may be causing this situation.
 02 December 2010 08:37 PM
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Posts: 64
Joined: 25 July 2008

A, B and Z usually refer to servo motors, re-check the rating plate in case it's a 2 phase (A, B) with reference (Z)

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