Star/Delta, but not as I know it.

[Tayters]

Hoping someone could shed some light here please.
This is a copy of a Carrier water chiller condenser fan schematic. The motor is a star/delta which I understand.
Well I thought I did...

On this one the delta part is as normal. Note how L3 however is switched through the delta contactor KM12.
When in star this means no feed to W1 of the motor from this phase. Instead it comes from L1, through the main contactor KM11, through the star contactor KM11A and through capacitor C11.
In simple terms it's using 2 phases and the third phase is one of the others through a capacitor.

Why?

I suppose that has the effect of shifting the phase round a bit like in single phase motors. My guess is so it starts with less current? Or would it take more and there is some other reason - I've seen much bigger motors with bigger fans wired up as normal so that theory not quite sound anyway.



3703

Many thanks,

Andy.

[Magoo]

Seems like a two speed configuration. One says 0.5 Kw the other says 0.9 kw.

[nike123]

Give us control circuit diagram (sheet 8 and 9).

This is star delta:
http://i52.tinypic.com/1432iq.jpg

In your diagram we do not have star part at all of star/delta.
Also, for delta, beginning of one winding must be connected with end of other winding, witch is not case in your diagram.
This doesn't have anything to do with star/delta.
It looks like 2speed 3phase motor internally connected in star.
Your setup is probably for getting one additional (third) speed.

[Gibbo]

Yes its a 2 speed fan, high and low speed.
Carrier don't use star delta fan motors.

[Tayters]

Thanks for the quick replies.



Give us control circuit diagram (sheet 8 and 9).

In your diagram we do not have star part at all of star/delta.
Also, for delta, beginning of one winding must be connected with end of other winding, witch is not case in your diagram.
This doesn't have anything to do with star/delta.
It looks like 2speed 3phase motor internally connected in star.
Your setup is probably for getting one additional (third) speed.


If I get to go back and do the repairs (H.P. fault alarm) then I'll grab the other sheets.

I did note the delta seemed to connect each winding to the same phase (i.e. no voltage across it), so assumed U1 wasn't connected to U2 but either V2 or W2, same for V1 and W1.

Which bit of the star bit is missing?
I see U2, V2, W2 connected together on pins 3, 4, 5 and 6 on KM11A. Missing part seems to be the L3 phase to W1.

Makes more sense when you all say not a star/delta motor in the first place. The signs are always there, sometimes I just don't see them.:)

Cheers,

Andy.

[nike123]

Thanks for the quick replies.





If I get to go back and do the repairs (H.P. fault alarm) then I'll grab the other sheets.

I did note the delta seemed to connect each winding to the same phase (i.e. no voltage across it), so assumed U1 wasn't connected to U2 but either V2 or W2, same for V1 and W1.

Which bit of the star bit is missing?
I see U2, V2, W2 connected together on pins 3, 4, 5 and 6 on KM11A. Missing part seems to be the L3 phase to W1.

Makes more sense when you all say not a star/delta motor in the first place. The signs are always there, sometimes I just don't see them.:)

Cheers,

Andy.


Ok, I see that U2 V2 W2 are connected together when K11A is energized. That could be star connection if windings are 1 speed and their ends are not internally connected.
Since K11A and K12 could not be energized in same time (it will be all 3 phase short circuit) it appears that in one moment K11 and K11A could be energized in same time.
That brigs all 3 end of windings at star and L1 phase at U1 beginning of U winding and at same time L1 phase shifted for 90° to W1 start of W winding.

I could not see any benefit of that connection.

[ref717]

Hi Tayter, your motor is definitely a Wye-start/Delta-run wound motor, and your motor has a reduced voltage starter configuration. During start-up the windings are connected in the Wye configuration which results in reduced line voltage applied across each winding. (Your guess is right, the motor starts with less inrush current, approx. 33% reduced current than normal across the line Delta connection):). After a certain time delay, the motor leads are switched to the Delta connection in full voltage normal operation.
You can never change the speed of any 3-phase motors unless you vary the line voltage frequency or the no. of poles of the motor.
Hope this helps.;'

[nike123]

Hi Tayter, your motor is definitely a Wye-start/Delta-run wound motor, and your motor has a reduced voltage starter configuration.

Please, where did you see delta connection.


You can never change the speed of any 3-phase motors unless you vary the line voltage frequency or the no. of poles of the motor.
This is not true.
http://www.electrocontrols.co.uk/datasheets/F05.pdf

[chemi-cool]

We miss the control for these two condenser motors, there is also a capacitor there which bring me to thought that it is not 3 phase but only 2 phase motor widely used by American manufacturers.

Looks to more like a motor with two windings for two speeds.

Can you get the control drawings?

[ref717]

Nike, I think there is a "typo error" on the drawing within the motor's symbol. U2 should be W2, V2 should be U2 and W2 should be V2. In the Delta connection, as you can see L1 voltage is on the same motor winding leads(U1 & U2) w/c is abnormal in any 3 phase motor configuration,likewise with L2 and L3 line voltages.
For a constant supply line voltage, you can never alter the speed of a 3-phase motor unless we have a VFD control or dual voltage motor.

[Yuri B.]

Clear, all 6 intputs of the motor belong to interconnected windings inside of it (and U2 is not - just the - ending of U1, and so on).
Also the purpose here is rather 2 speeds - not soft starting (0.9kW motor is not too big deal), let alone 3-speeds.
(I would like to know what quantity of windings' copper has saved the motor designer by providing the cap into the schematics.) Very strange schematics.

[nike123]

For configuration with 2 phase and condenser Google "Steinmetz circuit".


Operation of three-phase Motors in single-phase supply
Induction motors with a three-phase stator winding can
either be driven from a three-phase supply or from a
single-phase supply when suitably connected with a
capacitor (Steinmetz circuit, Fig. 2a and fig. 2b).
A three-phase induction motor with its stator connected
in star for a 380V three-phase supply has 220V as phase
voltage. The motor can therefore also run on a 220V threephase
supply when delta connected. If the motor is designed
for 125/220V then its phase voltage is only 125V and
the motor must be connected in star for a three-phase supply
of 220V.
The Steinmetz circuit gives similar characteristics to threephase
operation but with a single-phase supply.The motor
runs as a three-phase machine, if the capacitor voltage
causes a symmetrical voltage star at the rotor windings as
with a three-phase supply. A symmetrical voltage
distribution can however only be obtained with a certain
capacitor at a certain load. For all other loads an asymmetrical
voltage star is formed at the rotor, so that the
motor can no longer operate under optimum conditions.
The starting torque is reduced and the heat
generation in the motor can become higher at no load
than at full load.
Experience has shown that with a voltage supply of
220V, 50 Hz, a capacitance of 70 mF/kW of motor power
is necessary in order to give a starting torque of 30% of
rated torque and in operation about 80% of the rated
three-phase power.
In order to obtain a higher starting torque, a starting
capacitor with about double the capacitance must be
connected in parallel. This must be switched off during
run up to avoid overloading the motor. The direction of
rotation can be reversed by connecting the capacitor to
the other supply connection.
The voltage across the capacitor terminals in the
“Steinmetz” circuits is, at the rated power of the motor, about
the value of the supply voltage, and under no load about
15% higher.
If the “open star circuit” should be used for a special
application please state this when ordering in order that
the correct capacitor can be supplied. This circuit can
be used when 125/220V three-phase motors are to
operated from a 220V single-phase supply.
http://i54.tinypic.com/2jg42ds.jpg

I would say this setup is for 3 speed
1 - Steinmetz (KM11 and KM11A energized)
2 - one winding in star (KM12 energized)
3 - both winding energized in star (KM11 and KM12 energized)

[nike123]

For a constant supply line voltage, you can never alter the speed of a 3-phase motor unless we have a VFD control or dual voltage motor.
That is different than what you said here:

You can never change the speed of any 3-phase motors unless you vary the line voltage frequency or the no. of poles of the motor.

Any asynchronous motor have slip. That slip varies with motor power and required power for synchronous speed. If we aply power regulation to motor(by varying voltage or by pulse with modulation) we vary actual speed of rotation of fan no matter if it is 3 phase or single phase.

[Tayters]

Thanks again chaps for your input.

I'll try and get hold of the control diagram also but there may be some delay on this.

Didn't mention before so as not to add unnessesary info but the first chiller I looked at would start with star contactor first then delta (thats what made me assume star/delta).
The second chiller would start on the delta for a few seconds, then star for about 20secs then back to delta. Now there could be a fault but after turning the unit on/off to put the electric panel back on (which had the isolator on the front of it, hence all the on/off) it would do the same thing. Note the HP alarm was on a this chiller but another circuit which wouldn't run due to the alarm.
Why the first one worked different, beats me.
It's a not a massive fan by any means, no bigger than DOL ones I've seen.
Mr Steinmetz is a new one on me which I'll look into.

That'll please the wife.:D

Cheers,

Andy

[Yuri B.]

By Nike

2 - one winding in star (KM12 energized)The position of the thermorelay (FR11) makes me think all motor currents always pass through the KM11, that is, no other contactor runs without it.

[ref717]

Clear and agreed.,thanx Nike for the input. I was confused with the strange power diagram.:rolleyes:

[nike123]

I think this setup is some form of Dahlander. Y/YY would be most suitable for fans.


http://i53.tinypic.com/2we9j0n.jpg

This is diagram for Dahlander. It is simmilar as original one. Only difference is addition of Steinmetz and lack of second thermal relay in original diagram.

http://i53.tinypic.com/qqwbit.jpg
http://i52.tinypic.com/20sb1h2.jpg

[Magoo]

Dahlander seems more like planet Crypton to me, Carrier France have done it again. Totally confused me.

[Tayters]

Agreed, the French seem to have a habit of doing things a bit different. Working on their cars was never straight forward.

I showed the circuit to a couple of engineers responsible for Rolls Royce power systems on ships. They were as baffled as me.
For a motor that size a star/delta start wasn't really required. One of them raised the point that if the motor is spinning the wrong way due to the wind blowing it, then extra power is drawn on start up. Some systems have a braking circuit that comes in first and possibly that is what the capacitor is used for. I don't think that is the case here.

I've given a copy to a friend of mine who is an electrical engineer. I'll let you know what he makes of it.

Many thanks to Nike for enlightening me. There's me thinking Dahlander was that Tibetan bloke who didn't like fighting.

[r.bartlett]

What is the function of C31 the 6uf cap?

[nike123]

What is the function of C31 the 6uf cap?

That is mystery, since if it is Steinmetz, than capacity is too low.

[TRASH101]

What is the function of C31 the 6uf cap?




That is mystery, since if it is Steinmetz, than capacity is too low.


I think it is just an phase inversion capacitor and the value may be determined by matching the reactance to the motor winding resistance.

[NoNickName]

I think the capacitor is to avoid arcing when switching the two speeds while controlling condensation.
Remember coil ignition of the 50s?

[shieldcracker]

I am baffled as well, but with out the control diagram and assuming there are no typing errors on the drawing we can draw these conclusions.

1. KM11 must be closed at all times since the motor thermal overload is in that branch.
2. This is not a wye-delta start: A) motor is too small; B) When starting in wye (KM11A Closed & KM12 open) line 3 does not reach the motor instead the capacitor is connected across line 1 and 3; C) When transitioning to delta (KM11A opens first and the KM12 closes) this would bring Line 1 voltage to U1&U2 bringing the current to zero for that coil group, the same would apply to the other phases as well and the motor would stop
3. This is not Steinmetz connection we have three phase power present to begin with!
4. Everything points that this is Dahlander but then we have to forgo our initial assumption about typos and even if we did we still have the capacitor and a modified connection to deal with.
CONCLUSION: TAYTERS get the control diagram or the motor diagram, though I think the key lies with the motor.

[chilliwilly]

Like some of the other posters say, its configured for a dual voltage operation. KM 11 and KM 11a would be energised for single phase operation at a reduced running torque, KM 11 would switch L1 and L2. L1 would be connected to live/hot direct to U1, and W1 via Km11a and through the cap for an artificial phase. Also when KA 11a is energised, it will provide a star point for U2 and W2 connecting back through V2 leaving L2 to be connected to the neutral via V1.

When connected to three phase KM 11 and KM 12 would be energised switching all windings direct on line in delta, but the UVW2 connections should be connected so that they all see three phase. In the drawing they will see a null voltage across the windings. I don't know about anyone else but since they've let cad operators loose on electrical drawings, who might I add don't know much about elctrical controls. This kind of thing happens all the time. Bring back draughts men, at least they understood what they were doing.