15 kw compressor

[thomas-1981]

Hi All, I've got a job to install the supply to a 15kw compressor which will be fitted by an other contractor. I have no information on the compressor other than it's 15kw and 3-phase. The run of cable will be about 50 metres. My thinking was to use 10mm swa supplied by a 32amp triple pole type C mcb and into a 32amp rotary switch which the other contractor will connect into. Any thoughts on this would be appreciated. Thanks in advance.

 

[tannerselectric]

good luck 15kw 32a ?

 

[Darkwood]

15kw motor recommended mcb by Schneider is is a 40(d) to ensure no tripping but this isn't always reliable as this just cover a standard induction motor with typical duty.... you will be better having the circuit protected by HRC (Gm) fuses which allows you to meet you Zs tolerances alot easier.

 

[the pict]

What kind of of compressor pulls that, must be huge probably better driving it with a Rolls Royce Eagle diesel

 

[Knobhead]

Eh? 15KW is tiny!

 

[the pict]

15 thousand watts tiny ? god I must live a sheltered life
P

 

[jimmymac]

Eh? 15KW is tiny!

Tony probably uses that for his push bike tyres

 

[Lucien Nunes]

Tony's idea of a big compressor will be one where you can have a party inside the LP cylinder. Big synchronous motors, would use up all the 15kW just for the excitation supply.

Compressor starting loads can be very severe because the motor is up against full torque almost as soon as it starts to turn. C32 does not sound like it would survive a start, if 15kW is the steady running load.

 

[Darkwood]

Tony always bragging about size .... even i have to admit he regularly has his hands on to what i can only say is bigger than im used to :dizzy2:

 

[thomas-1981]

Cheers guys, compressor got delivered so rang manufacturer who stated a 32amp type d mcb.

- - - Updated - - -

good luck 15kw 32a ?

Why that?

 

[Darkwood]

Ok just make sure your ZS value complies to the permitted values in BS7671 as you now have a 0.8 x 0.36 ZS allowance .... as i suggested earlier HRC fuses up front.

I can't tell you that you won't comply as i don't know your incoming supplies values but im guessing i may have raised a concern here....

 

[Knobhead]

Depending on the starting method the starting loads vary wildly:

For reciprocating machines there’s a couple of options.
Unloading valves will prevent any back pressure by holding the cylinder head valves open.

Small compressors can start and stop when pressure is reached.
An outlet vent valve on the outlet to atmosphere on start up eases the load.

For screw compressors:
Restrict the inlet. This also provides proportional delivery volumes when running. VSD’s can do the same. The two VSD's I fitted didn’t last long. A screw compressor is designed for a set speed.

We used 2 stage vane compressors. Stage 1, a 300HP motor, stage two a 150HP motor. They were replaced with a 400HP screw.


Any methods of reduced load starting require non-return valves between the HP outlet and the receiver.

The compressors I worked on ranged from 150W to 650KW:

Above about 30KW they are kept running and some form of regulation used.


The bottom line is, what is the starting method?