Compressors of chiller trip upon starting

[Elec777]

Gentelmen,
At our project we have 2chillers 90tons cooling capcity ,i supplied it with power from 1600kva transforer 20/0.4kv,50HZ,6.4, oil type
there are another residential 1000amps
Load connected to the transformer ,according to my study the required cable size for 80m lengeth from the TR to the chiller panel is 3*150+95NYY for each chiller ,the problem is that:since each chiller has 4 compressors and it start and stop frequently it
Trips ,should i increase the cable size?the maximum current drawn by one chiller(4compressors running) is
200amps
Thanks in advance

 

[davidbeach]

"It trips." What trips? Thermal-magnetic circuit breaker? Relay controlled breaker? Chiller controls? What indications are you getting?

 

[Elec777]

Dears,
my guise is that :upon compressor starting, the protection of the compressor detect that an unacceptable voltage drop occured and it dictates the compressor contractor to trip, please find attached the alarm schedule, i always get alarms T51 AND T55
ALSO YOU WILL FIND THE ELECTRICAL SPECS OF ONE CHILLER , THE OTHER CHILLER IS IDENTICAL.

THANKS

 

[itsmoked]

Hello Elec777; You may be looking at the wrong issue. The alarm statement for T51 or T55 is that:

High-pressure or loss-of charge switch open, faulty
control relay or CPCS
board, loss of condenser
air, liquid valve closed.

These conditions force the trips of the breaker(s) not that the breakers are tripping from overloading.

Have you checked the status of:
1) High pressure switch?
2) Loss of charge low pressure switch?
3) Loss of condenser air?
4) Liquid valve closed?
5) Have you checked that the control relay is operating and that it's plugged into its socket firmly?
6) Any indicators on the CPCS board and are they showing any activity?



Keith Cress
kcress -

http://www.flaminsystems.com

 

[Elec777]

Dears,
all the above mentioned were checked and found OK, i checked with carrier engineer ,he confirmed that problem in the electric power supply, i run the chillers on the power of diesel generator 400 V stable, the chillers did not show any problem ,
any hint will be appreciated

 

[GroovyGuy]

Howdy Elec777,
Obviously the compressor OEM would find fault with the power supply. How does the OEM support this statement? Has he been to the Site?
80m of 150mm-sq conductor size should not be providing any issues wrt voltage drop.
q1) Does each compressor start in sequence? (ie They do not all start at the same time.)
q2) Did you measure the voltage-drop at the compressor panel during a start interval?
q3) How large is the generator unit? How is it connected to the compressor panels? (a 1-line would be beneficial)

GG

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[waross]

Motor currents:
43.6 Amps
43.6 Amps
46.8 Amps
65 Amps
Fans 3.4 x 6 = 20.4 Amps
Total load 219.4 Amps

Total capacity needed:
First chiller 220 Amps
Second chiller 220 Amps
Base load 1000 Amps
Total capacity = 220 Amps + 220 Amps + 1000 Amps
1440 Amps.
1440 Amps x 1.73 x 400 Volts / 1000 = 998 KVA (The generator would need more capacity.)
Have you measured the voltage drop on your feeders?
Have you measured the voltage dip or sag at the transformer terminals when a 65 Amp compressor starts?
You may have a "soft" 20 kV supply.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

I agree with GG that 80m of 150mm² cable shouldn't be the cause of a volt-drop problem with a 200A load, provided that there are no problems with the installation.

Hire a data logger. Obtain actual current and voltage data rather than speculate.

 

[unclebob]

What's the impedance of the transformer?
What are the specs of the diesel generator?
These T51 and T55 alarms must be resolved.

 

[waross]

When running on the generator, are you connected directly to the chillers or are you passing the current through the same feeders?
If you are connecting the generator at the supply panel and using the same feeders, you most likely have a soft primary supply, a fairly high impedance transformer or both.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Elec777]

Dears,
Am grateful to you all for your help in enlightening on the issue,
Dear Itsmoked,
we checked all of the six items and it found OK.
Dear GroovyGuy,
both chillers are running in parallel,the control will work on reaching the cooling degree set-point (say 9c), to achieve this goal , the control will dictate the compressors to start in sequence .
Dear Waross,
how we can solve the issue of soft 20KV, kindly what does it mean soft 20KV.
Dear ScottyUK,
i will follow your advice.
Dear Unclebob,
if we could solve the voltage drop , T51 AND T55 WILL DISAPPEAR , I NOTICED THAT THE COMPRESSORS RATED VOLTAGE MENTIONED ON THE COMPRESSORS NAME PLATE IS 400VOLTS WHILE ON THE CHILLER NAME PLATE IS 380VOLTS AND WHEN I RUN THE CHILLERS ON THE GENERATOR POWER(500KVA, 400V,50HZ) I got no problem , when on the transformer power problems show up again and i would mention that we pass power to the chillers in the same cable.

 

[waross]

Have you measured the voltage drop on your feeders?
Have you measured the voltage dip or sag at the transformer terminals when a 65 Amp compressor starts?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Elec777]

Dear Waross,
I NOTICED THAT THE COMPRESSORS RATED VOLTAGE MENTIONED ON THE COMPRESSORS NAME PLATE IS 400VOLTS WHILE ON THE CHILLER NAME PLATE itIS 380VOLTS,
and since nominal supply voltage at our site is 380v/3ph/50HZ, therefore I am already out of the voltage value required by the compressor(400V not 380V), so I try to convience the utility engineers to inncrease their voltage to 400 volts.

apriciate your concern

 

[waross]

Dear Elec777
Your first statement was very misleading and wasted a lot of time.

At our project we have 2chillers 90tons cooling capcity ,i supplied it with power from 1600kva transforer 20/0.4kv,50HZ,6.4, oil type

I suggest that it may be time to follow some suggestions and actually measure the voltages and voltage drops.
The nominal voltage may not be the actual voltage.
If the incoming voltage is low that may be the cause of the problems.
A " soft" supply or soft grid is one with more than normal source impedance.
A soft grid has more than normal voltage drop under load.
You may have a combination of low incoming voltage and a soft grid.
If the incoming voltage is low and if the utility declines to adjust the voltage, you can use an autotransformer boost the adjust the voltage on site.
If you want help sizing an autotransformer boost, we need to know the ACTUAL VOLTAGES and ACTUAL VOLTAGE DROPS.
If you have a soft grid, you may need more boost voltage than if you have only a low voltage issue.
No problem, but more boost voltage costs a little more.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Elec777]

Dear Waross,
I have taken the measurements and as I have a little experience with chillers compressors,
do you agree that we add reactive power compensating capacitors to each compressor, it may help in
in the issue of voltage drop.
best regards.

 

[unclebob]

Do you have any soft-starter to get this running? Or Star-delta transition, or autotransformer?

 

[Parchie]

Your voltages look okay for me. Even if the voltages drop to 360V (90%), no contactor will drop. If compressors tripped on overload, check the piping line up and the valves setting. My experience with compressors is that some valves don't functions as designed.

 

[Elec777]

dears,
appreciate your thoughts about the problem, compressors starting is DOL, no soft starters no autotransformeres ,
since the compressors rated voltage is 400v i believe we need to increase the supply voltage from 380v to 400-415v
and apply compensating capacitors for each compressor to compensate the drop in voltage and pf, any idea will be valuable to me.

 

[waross]

The problem looks like chronic low voltage.
The most economic solution is to install a pair of autotransformer boost transformers in open delta.
Capacitors are great for offsetting reactive voltage drops. I don't think that that is your problem.
Capacitors will raise the voltage but once the reactive current is cancelled, further increases in voltage are not great and not cost effective.
It may be possible to install enough capacitors to raise the voltage from 380 Volts to 400 volts but you will then have so much capacity installed that:
You may incur power factor penalties.
You may be overloading your service with capacitive current.
Your Chief Financial Officer may be screaming about the capital expenditure.

Best and cheapest solution is the "open delta auto transformer boost".
Cheapest but not best is to lower the under-voltage trip setting on the controls.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[GroovyGuy]

Is the transformer not equipped with taps? I have never seen a 1600kVA transformer that did not have (+/-2.5% & +/-5%)taps.
If you truly have a LV problem, why not increase the voltage by 5% (ie from 380V up to 400V). You also need to ensure that you do not go over voltage.
I don't recall what the voltage tolerance is for IEC motors, but for a standard NEMA motor it is +/-10%. (ie a 400V NEMA rated motor can provide NP power from 360V up to 440V).



"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)