Are Primary Windings and Secondary Windings Interchangeable?

This terminology (primary and secondary motor windings) is unfamiliar. If you search for "star-delta starter" you should find some useful diagrams.

By Primary I mean U1 V1 W1 or (A1,B1,C1) and secondary i mean U2,V2,W2(A2,B2,C2).

Have you confirmed your motor voltage agrees with the supply voltage?

By your implication does it speed up in star connection? that does not seem correct.

r1 - r2 is one phase winding y1-y2 another and b1-b2 the third.

In delta r2 connects to y1 -- y2 to b1--- b2 to r1 , if one of these connections is reversed it will not produce a correct rotating field. This will give you a problem similar to yours. I do not know what U2v2W2 means.

If it stops in delta, does the overload device operate or does it catch fire?

Op's question rings with the lack of fundamental knowledge, so caution is urged here.

OP does seem to want to learn and has the nads to at least have a go which is truly commendable.

The motor wiring connector cover will (or should) have a wiring diagram that shows how delta and star are supposed to be wired.

Do you have a wiring diagram for the motor controller?

Well I got the connections. Motor runs in star fine but changeover to delta it slows down and stops. What do i have to do?

I had that once and it turned out to be an open phase in delta. Loose connection at the delta contactor on that occasion.

Check (with a meter) that all 3 phases are being delivered to the motor in delta.

If it stops in delta, does the overload device operate or does the motor catch fire?

You can interchange U1/V1/W1 and U2/V2/W2. But you have to interchange them all 3 together. If you only interchange U1 with U2, you will no longer have an rotating magnetical field in the motor.

--------

If motor accelerates normal in star (Wye) and slows down in delta, there is a misconnection between the motor and the star/delta switch.

In star all motor windings get powered. Power is flowing from first supply lead to U1, to star point, and from star point to V1 and/or W1, to second and/or third supply lead.

But in you case, in delta U1 and U2 are connected to the SAME power lead. Idem ditto with V1/V2 and W1/W2. There is no possible way to let flow the current , and the motor will stop. Power is trying to flow from first supply lead to U1 and through the motorwinding U1-U2 but then arrives back at the FIRST supply lead. So no power can flow, the power supply sees 3 times an open connection !!!

------------

Please check your following things

1) Motor check : Is the connection U1-U2 corresponding with one motor winding ? This must be the same for V1-V and W1-W2

2) Star/delta switch check : When switched to delta,

+ you must measure no voltage between connecting points U1 and W2

+ you must measure no voltage between connecting points V1 and U2

+ you must measure no voltage between connecting points W1 andV2

+ you must measure supply voltage between all other possible connection points

3) Check connection leads between motor and switch : if the above things are OK, then there is and error in the connection between motor and switch.

Good Luck, be care full and pay attention to the lethal voltages.

Is the motor dual voltage, or does it have Start windings? Does the motor have three, six or nine leads out of the motor?

In all probability seems to be a polarity mistake in power cable connections. Why don't you send me your mail ID thro this forum's mailbox so that I can send you a paper authored by me on the subject?