no load at starting a single phase motocompressor

[pardal]

Hi all Refrigeration people:

Due a lack of power suplyed by the gen set I can only start the second unit.
System is as follow:
Gen set , 16 hp brigstraton with a 8 KVA generator at 220 V 50 Hz.
Two semihermetic compressor 1 3/4 HP with a Full load ampere 9 to 11 A
Starting system by a voltimetric relay , 160 mF start capacitor and 65 mF run capacitor.
A lot of tryal and all error was done on this array .
It is mounted on a truck to transport freezed goods at
-30 °C .
The main problem is that the second unit can not be started
because the inrush current is so high that it do the gen set to low voltage and the termic switch is triped.

My thoug is to do a temporaly by pass from discharge to suction on the runing compressor and on the to start one.

I had seen a system like it , but used to control a chiller compressor.

The only and main constraint is that not the gen set or any of the compressor should be changed.

Only it can be done changes on electrical or refrigeration circuits.

Any comments and help will be aprecciated.
thanks in advance.




















Pardal

 

[mdonner]

Yes, you may use a suction-discharge bypass solenoid valve for compressor starting.
Make sure the controlls energizes the solenoid 3-5 seconds before compressor start, and de-energizes the solenoid about 5 secs after compressor start (check starting time to fine tune the time delay). Stagger the compressors starting: do not start both compressors simultanuously.

If compressors are constantly running (no on/off control), and the generator excitation voltage regulator has a constant V/Hz start mode, you may connect compressors directly to supply and let it start with the generator. The starting torque will be very low due to ramping speed (with frequency)from zero to nominal.

If this is not the case, and you will find that you have too many start cycles, you may include in the refrigeration system a hot gas bypass valve with liquid quench, and keep compressors running practically between zero to nominal cooling capacity. This is done on many military mobile air conditioners to avoid starting peaks on generator.