climaveneta screw problems

[goshen]

we have encounterd a bitzer compressor burnout, on a big screw unit,r-134a, air cooled,none of the saftey fetures seemed to work ,compressor heated to a point, where it melted all the surroundings!!and shorted out!the compressor is started with a soft starter,
has anyone seen this before ?or heard of it happening?

[NoNickName]

It failed to start and the windings behaved as heaters. Probably the softstarter didn't give enough current to overcome the starting torque. But when this happens generally the SS should stop trying after few seconds and signal a fault status.

[goshen]

It failed to start and the windings behaved as heaters. Probably the softstarter didn't give enough current to overcome the starting torque. But when this happens generally the SS should stop trying after few seconds and signal a fault status.

Hi
interesting idea ,however the entire comp changed color !! the high side was extremley hot and melted all the surroundings,and as you mentioned the ss should of stopped or warned,or even the kriwan!!
none of these protection fetures worked!
a real mind bender!

[NoNickName]

Hi
interesting idea ,however the entire comp changed color !! the high side was extremley hot and melted all the surroundings,and as you mentioned the ss should of stopped or warned,or even the kriwan!!
none of these protection fetures worked!
a real mind bender!

The kriwan doesn't stop the soft start unless it's interlocked with it.
Maybe an arsonist?

[binti]

i saw a mcquay fr4 screw do similar. we found a contactor welded in.It was a two contactor star delta setup, once the star contac welded there was no way to stop it until the building breaker tripped(600amp)
The comp had melted EVERYTHING, anything plastic was a blob.

[goshen]

i saw a mcquay fr4 screw do similar. we found a contactor welded in.It was a two contactor star delta setup, once the star contac welded there was no way to stop it until the building breaker tripped(600amp)
The comp had melted EVERYTHING, anything plastic was a blob.

Hi
now this sounds familiar!
we have the site monitered ,no arsonist!
thx

[DTLarca]

I was asked to investigate the source of disagreement on a chiller issue that had existed between supplier, main contractor, consultant and end user.

The chiller was a Climaveneta Bitzer Screw application.

The soft starters were tripping frequently - whenever both compressors were available one soft starter would trip and then the other compressor would be fine. They didn't realise this - I studied the full history of alarms and came up with this pattern myself - I realised the soft starters could really only manage starting the compressors half as often as the compressors without soft starters could manage.

3 years of hassle on their part was solved with me simply asking them to reduce the number of compressor starts somewhat

Winding heat = I²RT

Assume R of 1

If the normal starting amps are 10 for a duration of 0.5 seconds then the normal heat is 10² x 0.5 = 50W

A soft starter reduces the inrush current to about 50% but the start takes maybe 8 times as long (4 seconds). So the heat produced in the windings is then

5² x 4 = 100W

So the soft starter halves the current in-rush but it can in fact increase the motor heat produced at start up requiring that the compressor be started only half as often.

It sounds like on your screw the winding thermistor module was faulty or disabled. The thermal overload underneath the contactor will not know that the motor winding is getting too hot. The soft starter will not necessarily know there is a winding overheat problem either - that is for the embedded thermistors to detect.

[goshen]

I was asked to investigate the source of disagreement on a chiller issue that had existed between supplier, main contractor, consultant and end user.

The chiller was a Climaveneta Bitzer Screw application.

The soft starters were tripping frequently - whenever both compressors were available one soft starter would trip and then the other compressor would be fine. They didn't realise this - I studied the full history of alarms and came up with this pattern myself - I realised the soft starters could really only manage starting the compressors half as often as the compressors without soft starters could manage.

3 years of hassle on their part was solved with me simply asking them to reduce the number of compressor starts somewhat

Winding heat = I²RT

Assume R of 1

If the normal starting amps are 10 for a duration of 0.5 seconds then the normal heat is 10² x 0.5 = 50W

A soft starter reduces the inrush current to about 50% but the start takes maybe 8 times as long (4 seconds). So the heat produced in the windings is then

5² x 4 = 100W

So the soft starter halves the current in-rush but it can in fact increase the motor heat produced at start up requiring that the compressor be started only half as often.

It sounds like on your screw the winding thermistor module was faulty or disabled. The thermal overload underneath the contactor will not know that the motor winding is getting too hot. The soft starter will not necessarily know there is a winding overheat problem either - that is for the embedded thermistors to detect.

Hi
i have actully encounterd the same problem on a diffrent unit as you discribed ,and we came up with the same solution!
as for the burnt comp ,when i examined what was left from the kriwan it seemed ok and after checking the units black box history it seemed to have given a warning,but the comp just kept on working!
untill it shorted the main breaker!
i must tell you this one is a real mind bender!
my thought is that the softstarter for some ungodly reason kept the comp in running mode even after it recieved a stop command and workef the compressor to its death! why it did this is beyond me ,perhapse a power surge??lighting strike?
anyhow thanks for the response