carrier chillers(30GK) contactor stacking

[karimihassan]

Dear Sir.

Our plant uses CARRIER chilled water unit (model-30GK) for air conditioning that is manufactured by montluel France.

Already we have had a lot of contactor failure that it is very dangerous for compressor motors.so far more than ten compressors have been damaged.

NOTE:
-the maximum out door air temperature for air cooled chiller is 46 Celsius.
-the high pressure switch of chiller setted on 29 bar.
-the compressor motor is 45KW, 77AMPER.
-the selected contactors (SIEMENS 3RT1034) for each compressor is (2*15KW) =30KW, 64 AMPER.
-their compressors are reciprocating type and have two separateing winding and are not(Y/D).
-the compressor is started by two step (two contactor).

Therefore when the chiller works on the maximum operating pressure the ampere of compressor reaches to 77 amps. And (two contactors) of each compressor con not support the required current.
So the contactors have been damaged (stuck) and the compressor can not stop, resulting the winding of compressor to be burnt out.

Please advise us how we can solve this problem (contactor stacking).


HVAC- maintenance
Hassan karimi
E- MAIL: KARIMI1356@YAHOO.COM

[Lowrider]

ussually outdoor temperature for a Carrier is rated at 40 or 42 dgr C. But at 35 dgr C most of them are already in trouble!

If you have 2 (3) contactors per compressor (Y/D) each should have halve of the load on them, so the current of 77 amps would be apr. 39 going through each of the contacters!

High pressure would normally set at 26/27 bar.

If contacters are stuck one would usually aspect a freeze in the evaproator and not a burn out!


I'm not a big fan off Carrier srew chillers, especially not the oil system!

How old are they?

[monkey spanners]

I think these are partwind start. If the contactors are rated at less current than your compressor pulls, you need bigger contactors. Do these systems have overloads to trip if there are any power problems. Do they have any anti cycle timers fitted, if they are on and off on the hp switch alot this will burn out a contactor also.

Cheers Jon

[karimihassan]

I think these are partwind start. If the contactors are rated at less current than your compressor pulls, you need bigger contactors. Do these systems have overloads to trip if there are any power problems. Do they have any anti cycle timers fitted, if they are on and off on the hp switch alot this will burn out a contactor also.

Cheers Jon

thanks for your atention.
our compressors are part wind start,
both contactor power is 64 amper, and power of compressor 77 amper.
our system has over load protection relay when contactor stucking it can not do any think.
we do not have anti cycle timer .
the total number of on and of per hour is 6

hassan karimi

[walden]

I believe that these are Siemens 3TR type contactors, not type 3RT.

I would have calculated the size of each contactor in a 50/50% part wind starter using the formula: 0.7 x FLC. This gives us 54A for each contactor. This formula is based on my experience and compressor manufacturers’ recommendations.

The 3RT-10 44 contactor is rated at 65A. The 3TR-10 36 contactor is rated at 50A. You should have one of these two – preferably the larger one.

The 3TR10 34 contactor is rated at 32A. It is too small.

You say the compressor starts only 6 times an hour. If there is not some kind of electrical circuit to prevent it from starting too often, then you cannot guarantee this number of starts an hour and you run the risk of burning out compressors. Too many starts an hour is a compressor killer!

Your ambient is 35°C. Inside the panel it will be at least 10°C hotter. Most contactors are supposed to work at 40°C but it’s not a good idea! Ventilate the panel! But this may not help much as you will be drawing already warm air into the panel, heating it up before blowing it out again only to be drawn in again and so on! In the short term, you could leave the control panel doors open to get some air circulating inside the box.

[Lowrider]

I think these are partwind start.

Cheers Jon

oops! your right I think!

[karimihassan]

I believe that these are Siemens 3TR type contactors, not type 3RT.

I would have calculated the size of each contactor in a 50/50% part wind starter using the formula: 0.7 x FLC. This gives us 54A for each contactor. This formula is based on my experience and compressor manufacturers’ recommendations.

The 3RT-10 44 contactor is rated at 65A. The 3TR-10 36 contactor is rated at 50A. You should have one of these two – preferably the larger one.

The 3TR10 34 contactor is rated at 32A. It is too small.

You say the compressor starts only 6 times an hour. If there is not some kind of electrical circuit to prevent it from starting too often, then you cannot guarantee this number of starts an hour and you run the risk of burning out compressors. Too many starts an hour is a compressor killer!

Your ambient is 35°C. Inside the panel it will be at least 10°C hotter. Most contactors are supposed to work at 40°C but it’s not a good idea! Ventilate the panel! But this may not help much as you will be drawing already warm air into the panel, heating it up before blowing it out again only to be drawn in again and so on! In the short term, you could leave the control panel doors open to get some air circulating inside the box.
-------------------------------
Dear Sir.
thanks for your attention and recomendation.
our correct type of contactor is siemens 3RT 1034-1AF00.(AC-3, 32A)
both contactor are reated at 64amper.and compressor FLC is 77AMPER.
if it is possible send for us compressor manufacture data(dacument for calculating the contactor size).
e-mail: karimi1356@yahoo.com

[fixit]

There are two contactors on your part wind compressor motor, This is to lower the starting current load of the mains cable.there should be a time delay between the first contactor pulling in and the second one.The time between the contactors is important.

"Already we have had a lot of contactor failure"
Is this failure due to the contacts welded closed?
and on which phase
Which contactor fails, is it the first contactor or both.

[monkey spanners]

You can get overloads that cut all three phases when in a trip situation, so if a contactor sticks and the motor pulls too much current the overloads will turn off the power to the motor even if the contactor has stuck in. Have worked on some telemecanique ones on a 15hp partwind compressor.

Jon

[karimihassan]

There are two contactors on your part wind compressor motor, This is to lower the starting current load of the mains cable.there should be a time delay between the first contactor pulling in and the second one.The time between the contactors is important.

"Already we have had a lot of contactor failure"
Is this failure due to the contacts welded closed?
and on which phase
Which contactor fails, is it the first contactor or both.
----------------
thanks sir.
-it is happened on three phase .
-some time first contactor and some time secand contactor are stuck .already we have not had both contactor.

[fixit]

First Check the coil voltage and coil running amps,
The easy way is to replace both contactors with new 100 amp contactors.



what is the High Pressure on the chiller running ?

Regards