AVR circuit 2

[MahendraLohitaksh]

This Avr circuit consist of Choke,Radio noise supressor, protection transformer and static CT.
Kindly assist in how the circuit works.

 

[ScottyUK]

How do you think it works? Put your ideas forward, we'll assist you and correct them if necessary.

Hint: I would begin my explanation at the exciter field.

 

[MahendraLohitaksh]

Hi Scotty,
Well noted. Pls find below my idea,
This is a shaft generator.
W10 is connected to choke via terminal 2( purpose not understood) and sorted to Radio

noise suppressor capacitor. Further
it is connected to stationary rectifier and current transformer. The purpose of CT (pos 6) to

sense load current.
Not understood how protection transformer (pos 12) and static transformer (pos 11) works.

.CT produces a current in its secondary which is proportional to the current in its primary.
Sensing load current will fed to AVR, where it will be compare with input/set data,

generator error signal to fire SCR, genertaed cuurrent in AVR will cuased Excitation field

current feed to stator winding of excitor through F1 and F2.

There are many transformer in series which unable to understand.

 

[ScottyUK]

OK, here's my effort:

The AVR (9) is powered from a DC source which is supplied by the stationary rectifier. (8)
DC from the AVR output is applied to F1 & F2 at the exciter field (stator) winding. (4)
3-phase AC is generated on the exciter rotor (3) and is rectified by a shaft-mounted rectifier (5) to feed DC to the main field. (2)
The rotation of the main field within the alternator stator (1) develops 3-phase AC on the main terminals of the alternator.

The interesting component here is the stationary rectifier (8) which is dual-fed from both a set of power CT's (7) on each phase of the alternator stator and from the alternator main terminals via a choke (6). The purpose of the choke is to decouple the inputs to the stationary rectifier from the alternator terminals, so the CT's aren't directly connected to the output of the alternator. The input to the stationary rectifier is therefore a factor of both the alternator terminal voltage and the alternator phase currents.

Under normal conditions stationary rectifier (8) is principally fed from the alternator terminals via choke (6), and the contribution from the power CT's (7) is negligible. Under fault conditions the alternator terminal voltage will collapse and the phase current will increase, with the result that the power CT's will feed into the rectifier making up for the shortfall due to the reduced terminal voltage during the fault, and ensuring that a source of power is available to the AVR during the fault.

The AVR (9) itself looks fairly standard, with single-phase voltage sensing between lines U-V and a quadrature droop CT (11) to aid reactive load sharing.

RF suppressor (10) shunts any high-frequency noise on the generator terminals to earth.


Hope this helps, if anyone spots any errors please feel free to correct me.

 

[itsmoked]

RF suppressor (10) shunts any high-frequency noise on the generator terminals to earth.

From loads like VFDs or any other supplied rectifier loads.

I like it Scotty!

Very interesting dual feed. Must've taken them a bunch of trial and error to settle on the specifics.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Either they have some outstandingly good models of the magnetic components or they did as you suggest. Given magnetic components are tricky to model I rather suspect the latter! It's a real old-school piece of design but quite elegant too. I suspect it's on a relatively small set - I haven't come across AVR booster CT's on large utility-class generators, although that might just be me living in ignorance of them.

 

[MahendraLohitaksh]

Dear Scotty,
Many thanks for your effort in clearing doubt of fundamental principle.
Until now, this shaft generator was giving trouble as out put voltage found 125 volt /60Hz instead
of 440v/60Hz.
We checked all in according to troubleshooting list:
- Rotary rectifier diodes replaced.
- AVR swapped with port side alternator.
- Stationary rectifier checked.
- All cable connection checked.
- Choke connection checked.
And we still have same result: output voltage 125V
Not understanding where could go wrong and struggling what could be the reason for output voltage only can be generated 125V instead of 440 volt.

 

[edison123]

If you have the means, do a surge comparison test of the exciter armature winding to check for interturn shorts. Check the varistor for any failures.

Long time ago, I used to see this of stationary bridge rectifier arrangement called self-exciting, self-regulating choke + capacitor AVR in small diesels, which I believe was a Brush design, which was neat. First time, I am seeing this in combination with a rotating rectifier arrangement.

Muthu

http://www.edison.co.in

 

[ScottyUK]

Possibly a phasing error between the power CT's and the supply derived from the main terminals via the choke?

If you have a small laboratory-type variable power supply then disconnect the exciter field from the AVR and drive the field directly with the PSU. You should be able to raise full terminal volts with a modest input to the exciter. With this type of AVR I think you'll need to provide some sort of load to ensure that the CT's have somewhere to drive current: a tungsten lamp would be a reasonable choice of load.

 

[MahendraLohitaksh]

Dear Scotty and Edison,

Many thanks for assistance provided.
This afternoon was found the fault,
One cable from main terminal box to choke in excitation system, that was broken inside holding only by the plastic insulation. Wire replaced, shaft tested with load and all ok.

 

[itsmoked]

Thank you MahendraLohitaksh for sharing that with us as we can all learn something.

Glad you have it back in service too.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Glad you fixed the problem.

Muthu

http://www.edison.co.in