Overload protecter

[ismayil59@yahoo]

Hello members
I am working on a 20tons/day flake ice machine. It has 4 nos of Bitzer 6G 30.2 compressors. Each compressor takes 30 amps current at full load. Now the manufacturer has instaled 48 to 60 amps overload protecter. I feel, it is bit high. The manufacturer is adement that they are right. One more importent thing the ambiant at
the place where the machine made is around +12*c
but here in OMAN the temp will be btween +25 to 40*c. Now a valuble Advice inthis regard is much apriciated. thank you. (I willbe traveling to a remorte place so i will not be available to chek posted reply till sunday )

[NoNickName]

Bitzer compressore 6G30.2 has a MRA of 53, therefore am adjustable protection 48-60A is fine.
The ambient temperature has no influence on the compressor itself, but on the condenser. Please make sure that
1) the room where the compressor is installed is properly ventilated.
2) the condenser is sized for the appropriate summer max temperature and the resulting condensing temperature is still within the operational envelope of the compressor.

[chemi-cool]

i do not agree with you,
motor protection should be set in the middle third for optimum protection, i.e. if your amp draw is 53 than you need a unit with a set range 40 > 80.

Otherwise, it will be hot all the time and will have a much shorter life span.

In Muscat, in the summer, ambient can easily reach 45°C

[NoNickName]

53A is in the middle third of 48-60. And if you read, it doesn't draw 53A. That's the MRA, not the actual current input.

[nike123]

What is protection model#?
Is it thermal or electronic type?

[Electrocoolman]

What is motor starting method?

Assuming that its Star/Delta then overload will need to be 0.58 * FLA

[NoNickName]

What is motor starting method?

Assuming that its Star/Delta then overload will need to be 0.58 * FLA

If you've got two of them, yes.

[ismayil59@yahoo]

Hello, frends thanks for all the repply.
sorry iwas out, for more than aweek .
For no nikname the FLA is 60 and RLA is 30 at +12*c. and in Muscat it willbe +45 t peak . in this case ther can be an increase of 10 amps at the the actual working conditions. Doyou think it willbe ok to have a 48-60 amps thermal overload relay
To Chemicool . asuming the ambiant
i expect the over load protector to trip the compressor btween 40-50 amps.in case of any troble in the system. may be i am wrong correct me if iam wrong.
to Nike 123. it is Telemechanic thermal type .
To Eletroman. it is direct on line starting .
The machine is going to be commissioned in a week are so . I respect all your valuble in put in this regard . thak you all once agin.

[NoNickName]

Yes 48-60 is fine with a FLA of 60

[nike123]

to Nike 123. it is Telemechanic thermal type .

For such big compressors I would choose electronic overload relay.
http://www.schneider-electric.co.uk/electricity.nsf/automation-control/power-control-protection/lr9d-lr9f-electronic-overload-relays

[ismayil59@yahoo]

Thank you NoNickName, It is reassuring
Thank you nike123, we here in Muscat, normaly use Thermal over load only. and thanks for the referance. Sorry idont have a skype in may system . Iwill try down load it
Thanks for all .

[nike123]

Some readings from Siemens

Electronic overload relays are another option for motor
protection. The features and benefits of electronic overload
relays vary, but there are a few common traits. One advantage
offered by electronic overload relays is a heaterless design,
reducing installation cost and the need to stock a variety
of heaters to match motor ratings. Heaterless design also
allows the electronic relay to be insensitive to the ambient
temperature, minimizing nuisance tripping.
Electronic relays also offer phase loss protection. If a power
phase is lost, motor windings can burn out very quickly.
Electronic overload relays can detect a phase loss and
disconnect the motor from the power source. Phase loss
protection is not available on mechanical types of overload
relays.
Class 48 ESP100 A single ESP100 electronic overload relay replaces at least six size ranges of heaters. Instead of installing heaters, the fullload
amperes (FLA) rating of the motor is set with a dial.
The ESP100 overload relay illustrated below, for example, is
adjustable from 9 to 18 amperes. NEMA Class 10, 20, and 30
trip curves are available for a variety of applications, in either
manual or self-resetting versions. A manual test button is
provided to test the operation of the overload relay contacts.
One normally closed auxiliary contact is included as a standard
feature.

Siemens 3RB10/20 SIRIUS 3RB10/20 electronic overload relays come with a Class 10 or Class 20 trip and feature manual or automatic
reset, adjustable current settings, and ambient compensation. A
normally closed auxiliary contact for de-energizing the contactor
and a normally open auxiliary contact for signaling an overload
trip are included. Pressing the STOP button momentarily opens
the normally closed contact without affecting the normally
open contact. The switch-position indicator incorporates a test
function which, when activated, simulates a tripped overload
relay by actuating both auxiliary contacts and displaying the
switch position.
Siemens 3RB12/22 SIRIUS 3RB12/22 electronic overload relays provide trip class adjustments from Class 5 to Class 30 and ground fault,
phase imbalance, and phase loss protection. Motor current is
continuously monitored in each phase. Two auxiliary contacts,
one normally open and one normally closed, are switched in
the event of an overload, phase imbalance, or phase loss. One
additional set of auxiliary contacts, one normally open and one
normally closed, are switched without time delay in the event
of a ground fault. In addition to sensing current, SIRIUS 3RB22
overload relays directly sense motor winding temperature via a
thermistor sensor.
http://www.sea.siemens.com/step/pdfs/cc_2.pdf

http://www.automation.siemens.com/cd-static/material/info/e20001-a980-p302-x-7600.pdf

[NoNickName]

For such big compressors I would choose electronic overload relay.
http://www.schneider-electric.co.uk/electricity.nsf/automation-control/power-control-protection/lr9d-lr9f-electronic-overload-relays

It's not big. It's 30hp compressor.

[nike123]

It's not big. It's 30hp compressor.

Big enough to invest in better protection and Bitzer is not cheap one.;)

[MIT]

can anyone help me on my single phase compressor:

here's the problem:

Hard restarting cycle of compressor especially after defrost cycle or sudden power interruption causing tripping of external overload protector or circuit breaker and damaging potential relay contact points.

what causing this problem?

[nike123]

can anyone help me on my single phase compressor:

here's the problem:

Hard restarting cycle of compressor especially after defrost cycle or sudden power interruption causing tripping of external overload protector or circuit breaker and damaging potential relay contact points.

what causing this problem?

Check/change capacitor!

[MIT]

Check/change capacitor!


Hi nike,

but the compressor is brand new, from the supplier. is the capacitor defective?

[nike123]

Hi nike,

but the compressor is brand new, from the supplier. is the capacitor defective?
You cannot tell that by looking in it. You need to measure it!;)
Also, if it is LST (low starting torque) you need some time after defrost and after power interruption to pressure equalize in system (10 min).

[MIT]

ok thanks nike. but if the capacitor are ok what made the "tripping of external overload protector or circuit breaker and damaging potential relay contact points".
or this is just normal?

[nike123]

ok thanks nike. but if the capacitor are ok what made the "tripping of external overload protector or circuit breaker and damaging potential relay contact points".
or this is just normal?

When you have LST motor and not equalized pressures at suction and discharge, than starting torque is insufficient to start compressor and it stall. That trips overload protector and makes other damage since compressor pulls starting current whole time.
That happens also when capacitor is faulty, since capacitor is responsible for ensuring enough torque.

[MIT]

thanks nike,

that really help. i guess i really have lots to learn. design is just design i really need to have field training.

[Magoo]

Hi MIT.
Check with manufacturer to see if a 'high torque start kit 'is available for compressor. Alternatively use an anti-cycle timer, to ensure balanced pressures as Nike 123 suggested, or else depending on size of system fit a crankcase pressure regulator so as compressor does not overload after defrost.

[MIT]

Hi magoo,

thanks on the info. i'll tell that to the supplier. coz up to they haven't give any solution for this problem. they just blame the capacitor. is possible to convert the 1 ph motor to 3 ph motor by just changing the motor winding or something?

[NoNickName]

This issue is already taking care of, and we extensively answered to the customer about this specific problem, which is not related to a faulty capacitor.
My answer was: "


Dear sir, we cannot accept the claim for those compressors, and here I explain why. It is a well known fact that single phase compressors have a starting torque which is lower than three phase compressors, and for this reason when they are restarted under heavy load they may stall and buzz. After few seconds the electrical protection trips. This is perfectly normal.
The capacitor run motor serves to shift the phase on one of thewindings so that the voltage across the winding is at 90° from the other winding, thus making the capacitor run motor a truly two-phase machine at its rated load. If theproper value of capacitance is chosen, the currents through each of the two equal stator windings(under full-load) can be made such that the power factor is close to 100%. However, the startingtorque is rather low and the capacitor run motor is not recommended for severe starting conditions.We are working on a solution, because we have other inputs from the market about problems of start at heavy load or severe conditions @50 and @60Hz, therefore we kindly ask you to keep the compressors and we will revert back to you in three or four weeks with a test solution to increase the starting torque in your off-boundary conditions.The answer was



I have read your email to sir xxxx. And we are a little confuse, kindly take note: please inform me if i'm wrong.

1. We are claiming for compressor replacement from single phase to three phase connection.

2. You said that single phase compressor may stall and buzz when restarted under heavy load then how come are other brand of compressor don't have any problem like this? Hermetic and semihermetic compressor.

3. I know the fact that capacitor run motor is the one improving the efficiency of the compressor motor. And you said "if proper value of capacitance is chosen...", Isn't the capacitor are "built in" in the compressor where in the selection is made by xxxxx? Because we didn't replace any capacitor that may affect the value of capacitance that the compressor can withstand.

4. And here's the big question, you said that the problem of single phase compressor are normal even in other market. Then how come you don't have any solution that you can give to us, we still need to wait three to four weeks for you to come up for a recommendation. Which is by design you should have anticipated this problem.

I'm writing this comment as an individual customer would think and employee of xxxx. Please take note we have other brand of compressor which are using single phase connection, so it's a little hard to accept single phase have problem.My answer was:


Ok, let me summarise and answer your pertinent questions:

1) There is no need to replace single phase to three phase compressors, unless it is your request to do so, but there is really no need for that, at this time.
2) I can't answer for other brands. Surely there is space for improvements also for us. Please bear with us in the meantime.
3) The capacitor is selected with no load condition. The angle between the main winding and auxiliary winding depends on the value of the capacitor, which in turn depends on the actual load. So, our selection is a blind selection, which can be improved against different refrigerants and working conditions.
4) See above. It is not a design fault, but clearly it can be improved, and that's what we are doing. Again, please bear with us in the meantime.

And for the claim of warranty, since we would be delivering the same compressors with the same windings and capacitors, that will not solve your problem, and that is why we are not advising for returning the compressors.


Would anybody here think we have been blaiming the capacitor?
We are working on this problem, which is very specific, and we asked some patience to develop a solution, which he will benefit from.

[grahamgfm]

It sounds to me that you may have a voltage drop on that circuit. Worth checking volts before start and during start. It has happened to me b4. Another machine starting at the same time on the same circuit where wrong size cables used (to small) could be another reason. Ideas for thought :-)