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This is the first time I have dealt with a BITZER compressor and the concept of part winding start. I have searched for meaning of all the information on the nameplate of a compressor motor. I want to make sure my information are correct

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Nominal voltage = 380-420.

Frequency = 50.

Maximal operating current = 37.

A(Y) = 97 is starting current using the connexion part winding start Y/YY.

A(YY) = 158 is starting current using the connexion direct on line start YY.

The thing that confuses me the most is :

In nameplate of the compressor, the part winding start connexion it is indicated by (Y) but in cover of the motor terminal board by (Y/YY), while the direct on line start connexion it is indicated by (YY) and the same in the motor terminal board.

According to what I understood, the indication to Part winding start is Y=Y/YY while YY refers to direct on line start.

Correct to me if I am wrong

Thanks in advance

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    \$\begingroup\$ Too dangerous to guess so contact the supplier. \$\endgroup\$
    – Andy aka
    Aug 26, 2020 at 9:18

1 Answer 1

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A motor designed for part-winding start has two identical windings. To start the motor, one winding is connected directly to mains power. After a short delay, the second winding is also connected directly to mains power so that the two parallel winding act as a single winding.

The starting current for the first winding is less than the current would be if the two parallel windings were connected at the same time.

When the first winding is connected, the initial immediately increases to some value and then decreases somewhat. When the second winding is connected, the total current immediately increases, and then ultimately decreases to the normal operating current value. I suspect that the 97 and 158 amp markings represent initial starting current values for the connection of the first winding and the addition of the second. If that is true, the initial current for connecting both winding simultaneously would be significantly higher than 158 amps.

It seems to me that the symbolism makes more sense as Y designates one Y connection winding and YY designates two Y connected windings connected in parallel with each other. Then Y/YY would mean one Y - time delay - YY or part winding start. For a motor with two Y windings direct on line start would be YY.

Unless the manufacturer describes in in more detail or their is a detailed description in a published standard, we can not know for certain what the nameplate means. Even then, there is the possibility that standards have not been followed.

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