Star delta Pump motor - Doesn't work clockwise but Works anticlockwise

[u913206]

Hi

I'm having a problem with a 20 HP pump motor from a hydraulic press to try molds.

When we energized the machine, it starts with star correctly but when it changes to delta, pump motor stops. The breaker doesn't strip and fuses were ok.

Video (clockwise rotation):

New video by Carlos Saravia Garcia

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We interchenge 2 phases, to inverse the rotation of pump motor. Starts with star and the change to delta, and works everthing fine. Obviusly, it was the wrong direction so there was no pressure in system.

Video (anticlockwise rotation):

New video by Carlos Saravia Garcia

photos.app.goo.gl

After that we try changing again 2 phases to reverse the rotation and get pressure. It works for 3 min well and we could have pressure to make movemente in the hydraulic press. After that it starts all again, every time we try to start, pump motor works with star connection but when change to delta it stopped. The breaker doesn't strip and fuses stills ok. If we chagen rotation of pomp motor, star delta works fine.

Photos and drawing:

4 new items by Carlos Saravia Garcia

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Anyone know what is happening? I'll appreciate your advice.

 

[James]

What cables are you swapping for change of direction?

 

[davesparks]

If this was working before then it could be that something is adding extra load to the motor when going the correct direction.
I would guess something is up with the hydraulics that is making the motor work harder, a sticky valve or restriction or something maybe.

As it works in reverse when the hydraulics aren't building pressure the motor is probably OK.

 

[James]

Depending upon how you have wired the windings
it is possible to have it so when in star, everything is ok, change to delta and each winding has 0v across it although there is 400v available at the motor terminals.
i.e.
Line contactor

L1 L2 L3
A1 B1 C1

star contactor joins A2 B2 C2
motor turns

delta contactor
L1 L2 L3
A2 B2 C2
motor stops, no current flows although everything is Live.

correct in this case would be
delta contactor
L1 L2 L3
B2 C2 A2

 

[u913206]

What cables are you swapping for change of direction?

Hi James,

I'm swapping cables like this:

 

[u913206]

If this was working before then it could be that something is adding extra load to the motor when going the correct direction.
I would guess something is up with the hydraulics that is making the motor work harder, a sticky valve or restriction or something maybe.

As it works in reverse when the hydraulics aren't building pressure the motor is probably OK.

Hi Dave,

I was thinking the same, but if there is an overload, why breakers or fuse doesnt't activate? When I check electric drawing the only way to turn off the motor is using emergency push buttom or the breaker (overload).

 

[u913206]

Depending upon how you have wired the windings
it is possible to have it so when in star, everything is ok, change to delta and each winding has 0v across it although there is 400v available at the motor terminals.
i.e.
Line contactor

L1 L2 L3
A1 B1 C1

star contactor joins A2 B2 C2
motor turns

delta contactor
L1 L2 L3
A2 B2 C2
motor stops, no current flows although everything is Live.

correct in this case would be
delta contactor
L1 L2 L3
B2 C2 A2

Hi James,

Thanks for reply. I'll check what you said.

As comment, we didn´t touch the wiring of windings. This machine was working fine 5 years ago, the owner left to use for financial problems and it was stoped until now. The idea of this purchashing was just plug and start to work, but we have this problem.

 

[WallaceP]

If you are swapping the cables correctly i would split the motor from the pump and test again. Will narrow down if its an elec or mech fault.

 

[Lucien Nunes]

we try changing again 2 phases to reverse the rotation and get pressure. It works for 3 min well and we could have pressure to make movemente in the hydraulic press.

As comment, we didn´t touch the wiring of windings. This machine was working fine 5 years ago

These two statements seem to rule out the otherwise plausible explanation given by James in post No.4, but I will mention another possible problem with motor connection errors. If the delta contactor is wired with incorrect sequence (rather than the correct sequence shifted around, as James showed) e.g.:
L1 L2 L3
A2 C2 B2
Then when it switches into delta two coils remain energised in parallel between two lines, while the 3rd coil is short-circuited. This causes very heavy overcurrent on two lines and should rapidly trip the overload relay.

When the motor cuts out, are the contactors releasing? If so, my suggestion is that the control circuit has been rewired so that the overload relay is also in the coil circuit, instead of just operating a warning lamp as shown in the drawing. I would test with a voltmeter across the overload relay contacts to prove whether they are opening as the machine stops.

If this is true, then anything that can trip the overload relay could be responsible. Mechanical overload, correct mechanical load but a faulty coil in the motor, one contact open-circuit in the delta contactor, even malfunction of the overload relay. The best test here is to compare the three coil currents under different conditions. Do you have a clamp ammeter you can put round each motor winding lead in turn?

Finally, is the supply voltage sagging due to a faulty connection upstream, so that the control supply is unable to hold the the contactors in when the mechanical load increases?

So those would by my tests:
1) 3 line voltages under load
2) 3 coil currents in star and delta
3) Does the overload relay operate at the moment the machine stops and does the opening of its contact release the contactors?