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Peter_1
18-06-2008, 09:07 PM
Real life situation.
Bitzer screw +/- CSH8561-125Y, part winding wound.
Two relays switching each 1 part of the motor.http://www.bitzer.de/de/etc/download.php?d=doc/s/&f=sh-170-3.pdf
Kriwan kriwan SE-E1 mounted. (page 47/48 of pdf)

This Kriwan measures continuous 6 thermistors in the windings, oil temperature and discharge temperature.
Additional at start up, phase sequence and absence of phases is monitored the first 5 seconds on 1 of the 2 motors (!)
If rotation is not correct or there's a phase failure the SE-E1 switches off the compressor.
The SE-E1 retries after 6 minutes and completely locks out after 3 failures within 18 minutes.
Bitzer strongly recommends an overcurrent relay in line with each motor (page 49, a whole page)

What with an OEM manufacturer which makes a chiller and doesn't mount this overcurrent relays.
Result, 2 burned motors in 3 months.

Second comment from the manufacturer when he was on-site Monday was that the power factor was 0.93 to 0.95 and that this wasn't good for the motors.

There's something that can be read of this on page 52 of the same pdf.
I would like to hear your comments on this please.

Electrocoolman
19-06-2008, 01:00 AM
Hello Peter,

Like you, I would not rely solely on the limited protection offered by the internal SE-E1 unit.

Any good control panel would incorporate phase reversal/failure and undervoltage protection in the control circuit.

Electronic overloads (as opposed to the older Thermal overloads) offer much 'closer' monitoring and faster protection response. Although they are more expensive, they are a lot cheaper than a new compressor!!

With regard to the power factor correction, I think they are more concerned when the protection is 'local' i.e. capacitors connected at the motor, rather than located at the main building supply point.

I have not actually come across this point before, but I can understand what they are suggesting with regards to the value of the p.f.
As the motor load will vary in operation, so will the motor p.f. - with fixed p.f. correction, if the value is too high then the situation could arise where the motor is over corrected. Switching the motor under these circumstances could result in high voltages (they mention insulation breakdown) and contactor arcing.
I suppose the contactors could be up-rated to cope with this, but better control of the pfc would be the answer to limit insulation damage.

protect
19-06-2008, 07:22 PM
Hello Peter

current relays are defenetive the fastest way to detect dynamic defects as e.g locked rotor but does teh help if the root cause is in teh external environment e.g. power quality problems?
The SE-E1 protect against phase failure only during the start period as discribed in the document. The problem seems obvious if you have a phase failure during operation? But in my opinion the SE-E1 will react over the PTC input as a result of temperature rising the module will shut off and a 2 phase start will be recognised from the module during the 5 S.

I think the bigger problem is the power factor and the transient peaks which could stress the motor so taht the prozess will be so fast and becomes desruptive. The question is if an overcurrent realy which are extrem expensive help to protect in this case if the power quality is not appropriate?

Peter_1
19-06-2008, 07:31 PM
The OC relay is not that expensive compared to the price of a compressor.

What if the machine shuts down and two contacts in one relay sticks together and remains in line while relay is de-energized?

What if one contact in the relay brakes on the not detected part of the part winding where the SE-E1 doesn't see this fault because it's connected only on one of the 2 windings?

protect
20-06-2008, 09:07 PM
The cost of overcurrent relay is depending on the quantity you order and tehrfore the price is minimum 2-3 times more than the proetction module.
Compared to a screw itīs nothing you are right and therefore the OC relay should be mandatory.
Do you have any information about the correct adjustment of OC relay - I see also some challange and necessary experiance to find the right trip point.
Are there any further information on this issues available?

NoNickName
22-07-2008, 10:17 PM
The first comment is non-sense. One overcurrent relay is more than enough to protect the whole motor, even if part wound. Sometimes two relays may be worse than one, when tripping is not interlocked the other winding will work alone, and soon will burn.

On the other hand I second the power factor correction thing. Instanteneous over correction may cause reactive power to become active power.

charlie
22-07-2008, 10:57 PM
Definitively I don't trust the operation of the SE-E1 module as a phase sequence relay.

I'm working for a company that is using lots of Bitzer compressor of the same size/family and we are always installing an external phase sequence relay that isn't allowing the unit to run if the phase sequence is wrong.

I don't think power factor is a problem.

In the past compressor manufacturers had as a limit 0,9 but in the last 4-5 years we have delivered lots of units for UK market equipped with power factor correction capacitors designed in order to reach 0,95 and I have no problems at all.

A quite critical problem could be related with the position of slide valve when compressor restarts.

If on site you have problems with power supply and there is a power failure when the compressor is working at 100% (for example) in order to allow the slide valve to move to the 25 % (unload start) Bitzer is recommending to energize the 25% solenoid valve and wait for 600/900 sec (depending on compressor size) due to the fact that there is a lot of oil in the piston that is driving the slide valve to drain.

If you aren't waiting enough time the compressor probably is restarting not at 25% but at 50-70% and this means a very high current input.

Have you seen the motor of broken compressors?

If it is "overheated" in a uniform way you have very good chances that this is due to that.....

NoNickName
23-07-2008, 07:08 AM
In the past compressor manufacturers had as a limit 0,9 but in the last 4-5 years we have delivered lots of units for UK market equipped with power factor correction capacitors designed in order to reach 0,95 and I have no problems at all.


That's because you sized the power factor correction for the unit. Which is something different than a big power factor correction cabinet for a whole industry.



A quite critical problem could be related with the position of slide valve when compressor restarts.


The slider has a spring behind it, and it takes few seconds to empty the oil chamber when the oil is warm. The design of Bitzer is such that the oil is trapped when no solenoids are energised. Other manufacturers use three way valve, that opens the straight way when not energised and drains the oil.

Finally, what they call as SE-E1 is a copy of the INT69VSY-II of Kriwan, and it is actually made in Turkey by Parteks http://www.parteks.eu/intro.html

Peter_1
23-07-2008, 12:17 PM
In a factory, they never go higher then 1 and you still have the wires which acts as a inductance (coil)

So I don't see what can cause problem when modifying power factor (< 1) at the entrance of a factory.

NoNickName
23-07-2008, 12:24 PM
In a factory, they never go higher then 1 and you still have the wires which acts as a inductance (coil)

So I don't see what can cause problem when modifying power factor (< 1) at the entrance of a factory.

Of course, but I wanted to highlight the fact that power factor correction battery(ies) sized for a whole factory may not have enough sensitivity for adapting to varying PF of a single compressor in a single chiller.