Overspeed testing of HV DFIG generator using LV VFD and transformer 1

[LENELEC]

Hi all,

Long time lurker, first time poster.

I work for a motor/generator overhaul facility in Australia.
As part of a refit on a ~2.5MW DFIG machine we are required to do a 150% overspeed test. This test only needs to be conducted once and only for 90 seconds.

To do this we would be looking at using our LV S150 drive (around 800kw from memory, will need to check the spec in the office tomorrow) with a 415/6.6kV tx.
Im expecting around 200kW load at 75hz (windage, bearings and losses). The transformer would likely be bought second hand and used exclusively for this test before its sent to the big substation in the sky.

Has anyone done anything like this before? Any thoughts?

Currently focused on if we could, not if we should, for now.

Cheers,

LEN

 

[edison123]

A DFIG has a rotor winding rated at a much lower voltage than the stator. Since this is an open shaft test condition not requiring much torque to run, you can use the LV VFD on the rotor winding and set the frequency to 75 Hz at 415V without a 415V/6.6 KV trafo.

I doubt windage and bearing loss would be anywhere near 200 KW since the machines have an efficiency over 90%.



Muthu

http://www.edison.co.in

 

[Gr8blu]

A DFIG might have a rotor voltage that is lower when compared to the stator - or maybe not. Most wind generators (which are DFIGs) are either roughly equal (stator vs rotor) or the rotor is considerably higher. In this power range, a wind generator would typically have either a 690 V stator and a 400-1000 V rotor, a 3300 V stator and 1000 V rotor, or a 690 V stator and a 6000 V rotor - depending on which company owned the base design.

Sounds like you're trying to complete a mechanical "it won't fail and kill someone" kind of overspeed test, in an unloaded condition. Our shop has done similar testing both ways - variable frequency on the stator winding with a shorted rotor, and variable frequency on the rotor and an unpowered stator.

Converting energy to motion for more than half a century

 

[edison123]

I have rewound many slipring motors and the maximum I have seen is 2.5 KV rotor voltage. HV insulation for rotors and sliprings are a big pita due to clearances and hence are never used in my experience.

In OP's case, he could even apply 415 V VFD to the 6.6 KV stator with rotor shorted (or use rotor resistance start) and could get away with 150% overspeed due to open shaft condition.

Muthu

http://www.edison.co.in

 

[waross]

How about a belt drive from a pony motor?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[LENELEC]

Hi all,

I did think about running from the rotor (600v for reference) but I was not sure if our drive would find it agreeable. Unfortunately I wouldn't get time to do a dry run before the big show. Ill see if we have another machine in the workshop I can use. Certainly the most simple option if it works.

@Waross - pony motor with a shaft (belt drive is a bit sketchy at that speed) was considered but unfortunately the customer vetoed that ¯\_(ツ)_/¯

 

[edison123]

Assuming the worst case of 1% windage loss, at 150% overspeed would be 4% max. i.e. 100 KW. Your 800 KW drive should handle it.

Muthu

http://www.edison.co.in