×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Current Excitation Unstable

Current Excitation Unstable

Current Excitation Unstable

(OP)
Dear All,
Please advice me,I have problem with my generator.the current excitation hunting around 2-7 A, I 'am already inject the exciter using 12 V battery and disconected source exciter from AVR but the voltage remains unstable
help me please

RE: Current Excitation Unstable

Forget the excitation current; are there any other signs of trouble? What caused you to look at the excitation current? Depending on many things, the excitation current will be much more volatile than either output voltage or output power.

RE: Current Excitation Unstable

(OP)
Thnks David,
Because when no load& with load condition the voltage main stator/output Unstable and i see the current and voltage excitation unstable

RE: Current Excitation Unstable

What David said.
A problem with fuel flow or with a governor may cause those symptoms, even on a battery.
A generator requires much more exciter current when the generator is loaded compared to when it is unloaded.
If there is a mechanical issue causing the generator to pick up and drop the load, then the AVR will be changing the output to keep the voltage stable.
When you replace the AVR with a battery, the generator output voltage will vary as the load varies.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Current Excitation Unstable

(OP)
Thnks Waross,
I 'am Already check for the Prime mover factor
when running test without load ,the RPM Stable
AVR replace using Battery it should be stable for the output voltage,
but Not with my generator

RE: Current Excitation Unstable

So with a battery feeding the field the output voltage is still unstable with no load on the generator?

It would be useful to know whether this is a slipring machine or a rotating rectifier machine when diagnosing the problem.

RE: Current Excitation Unstable

(OP)
Thanks Scotty
I'am Already Check for the rotating dioda 6 Pcs ,all good condtion

RE: Current Excitation Unstable

Probably a defective/failing brushless exciter.
Disconnect the rotating diodes and megger the exciter windings.
Also check the field of the brushless exciter.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Current Excitation Unstable

(OP)
Thnks waross,
need to know,Winding Exciter already rewinding and insulation resistance is 100 M Ohm, whats normal value for resintance rotor winding and stator winding Exciter ?

RE: Current Excitation Unstable

That depends.
Does the generator have problems when it is started cold or do the problems develop when the generator has been working and is warmed up?
What is the maximum voltage output of the AVR and what voltage did you megger at?
I have seen installations pass a 250 Volt megger test but fail a 500 Volt megger test.
Was the test done hot or cold?
I had an exciter that would fail when it got hot in service. It would not fail when heated in an oven.
Have you checked the main field winding?
Normally 100 M Ohms is adequate if the test is at a sufficiently high voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Current Excitation Unstable

(OP)
Thanks waross,
every start up the current exciter up down 2-7 A samotimes until maxium current 10 A,but after running maybe around 10 Minutes the hunting Slowly up down,
i megger winding using voltage 500 V,

Thnks

RE: Current Excitation Unstable

What is the load on the generator?
Is this set islanded or paralleled with other sources?
Is there a surge suppressor of some type on the rotating diode plate and have you checked or replaced it?
Did you megger both the stator and the rotor of the brushless exciter?
Does the current output of the main generator carry with the field excitation?
Does the kW output of the main generator vary with the excitation?
What size is this generator?
What type of prime mover?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Current Excitation Unstable

(OP)
Thanks Waross,
These my generator nameplat
Marine Generator Type,Varistor and Rotating dioda has not been replace because already check and good condition,
any 3 Unit Generator same type,parralel operation.

Thnks for Your information

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources