Screw Compressors, help & advice

[jtt]

can anybody give me there opion on power cuts and screws, so far I have blown 4 mcquay compressors up due to sudden power loss

[NoNickName]

No way. Power loss is in no way related to compressor failure. In fact, stopping a compressor involves cutting the power.

[US Iceman]

Hi jtt,

I would be more concerned about the power quality and service. By this I mean true three phase power with voltage variations less than 5% or so between phases and minimum voltage loss from the supply.

If the compressor problem has occurred in a relatively short time frame I would suspect the power quality or service.

What actually happened? Have you checked the motors to be sure it is due to electrical problems?

Another item to be aware of is anti-recycle time or hot starts per hour. If the motor is short cycling for some reason, this could also present a similar problem. The motor may burnout, but it would not be due to an electrical problem. In this case this would be system operation related.

By the way... Welcome to the RE forum.

[NoNickName]

Recently I'm also experiencing multiple deaths on various brands and types of compressors, and any time this happens, the plant where they are installed is rephased with capacitor banks.
Rephasing sometimes induces harmonic distortion, when SCRs or other rectifiers/triacs are installed in the same line. This in turns results in fuse burning or tripping with no apparent reason.
If this is the case, the resonant circuit must be detuned, and an expert must be called.

[Peter_1]

Were those open or semi-hermetic screws?

[guapo]

Hi,
I have the same experience, I had a low voltage before the power is totaly off. another is single phase of the power supply.

Guapo

[jtt]

cheers for the replies guy's, I'm getting a bit more infor from McQuay and I'll update you all, thanks

[Andy]

Hi

we fit phase failure relays to all our systems, this monitors voltage (under/over) phase rotation and phase loss.

This will go a long way to protecting any motor.

Kind Regards. Andy

[protect]

Hi Anday,

what are your eperiance with pahse failure relays due to power qulaity problems. In my opinion in certain countries you will get much probelms due to teh voltage spectrum.

[jamcool]

This part of the world we call them Phase Monitors, can be installed on the phases coming into the unit or on the line side of the compressor contactor.The most popular type has a digital display with the ability to set and change alot of variables,such as %, time delays,alarm types also has a memory feature.Its a USA make monitor

[Chris Burton]

Hi andy, i used to work for mcquay & have seen a fair few of their screws buy the farm. Firstly are you sure it's not the compressor going down thats taking the power out ? What type of screw is it ? Frame 2 which has 4 capaity stages either liquid or oil injected, frame 4 two discharge pipes & continous capacity, or frame 3200 which has inbuilt oil seperator. Nearly all mcquay screws have inbuilt phase monitors so i doubt it's that. Frame 2 had problems with liquid starts & allegedly there was a batch of dodgy windings. If you could give me a few more details i might be able to help. Cheers

[md.tanwir]

Dear,
$ compressors in a go or took time. Any way there a single phase failure relays,motor protection device, contactors, over load relays for any compressor to run. These devices make sure your compressor does not get burn. If still there is problem, check the control wires after that make sure that the power connection specially for three phase the connection should be made as per the diagram provided by the supplier.
Hpe this will solve your problem.
Have nice day

[Tejbir Singh]

can anybody give me there opion on power cuts and screws, so far I have blown 4 mcquay compressors up due to sudden power loss

can you give details of starter/winding type of the motor/compressor.

incase of the screws its mainly partwind but again question arises which one double star or double delta?

Tejbir singh

[Superheat6k]

Star wheel or Gate rotor screws such as the McQuay are prone to gate wheel failure when situations of excessive backspin occur.

If the compressor stops suddenly (as in the case of a power cut) then the backspin which is quite usual in screws can become excessive.

Also if the discharge NRVv is stuck or passing then the backspin can last an excessive period as the entire pressure build up from the condenser equalises through the compressor to the suction side.

The lubrication to the gate rotor is provided solely by the normal forward motion so if the backspin lasts too long the rotor surface can become dry and can 'stick' tot he screw rotor. Also the support for the partially flexible gate rotor (a complex plastic material) is provided by a backer star wheel. In normal operation the stress is down into this wheel, but in reverse rotation the gate rotor is being pulled up and away from the backer and this may explain the tendency for the gate rotor tips to break off.

I have observed this effect on several makes of Gate rotor compressor.

We have overcome this upon one McQuay installtion by replacing the original compressor with a parallel shaft compressor, which although prone to backspin has a totally different mode of construction and too my knowledge is not affected by backspin, even at high loading sudden stops.

Superheat6k