OP
Knobhead
Sod it, I can’t get to sleep!
View attachment 9100
There are two types of autotransformer starters and to add to the confusion they are wired the same. The sequence and the transformer construction are different.
The standard starter is open transition where at the change over from start to run there is a brief moment when no power is supplied to the motor. This can cause mechanical stress to the motor and load.
The Korndorfer starter is closed transition, so no loss of power at change over. Because of this the transformer has to be a bit more “beefy”. But because there is no break in the supply to the motor there is no mechanical stress.
Standard starter, open transition:
contactors 1 and 3 close. Giving a reduced voltage to the motor
time delay
contactors 1 and 3 open
small time delay (no power to motor)
contactor 2 closes. Giving full power to the motor
Korndorfer starter, closed transition:
contactor 3 closes
small time delay
contactor 3 closes. Giving a reduced voltage to the motor
time delay
contactor 3 opens. The transformer is now acting as a choke
small time delay
contactor 2 closes. The transformer is now shorted between it’s incoming and % tappings. But as it's the same potential bewteen the two points there is no current flow
small time delay
contactor 1 opens.
As can you see the sequence for the Korndorfer puts stress on the transformer where it has to withstand acting as a choke. So for small motors it’s uneconomical.
View attachment 9100
There are two types of autotransformer starters and to add to the confusion they are wired the same. The sequence and the transformer construction are different.
The standard starter is open transition where at the change over from start to run there is a brief moment when no power is supplied to the motor. This can cause mechanical stress to the motor and load.
The Korndorfer starter is closed transition, so no loss of power at change over. Because of this the transformer has to be a bit more “beefy”. But because there is no break in the supply to the motor there is no mechanical stress.
Standard starter, open transition:
contactors 1 and 3 close. Giving a reduced voltage to the motor
time delay
contactors 1 and 3 open
small time delay (no power to motor)
contactor 2 closes. Giving full power to the motor
Korndorfer starter, closed transition:
contactor 3 closes
small time delay
contactor 3 closes. Giving a reduced voltage to the motor
time delay
contactor 3 opens. The transformer is now acting as a choke
small time delay
contactor 2 closes. The transformer is now shorted between it’s incoming and % tappings. But as it's the same potential bewteen the two points there is no current flow
small time delay
contactor 1 opens.
As can you see the sequence for the Korndorfer puts stress on the transformer where it has to withstand acting as a choke. So for small motors it’s uneconomical.
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