basic exciter question 1

[rmiell]

I am troubleshooting the controls for an AC generator (vintage 1940) in our light plant. I need some info on the actual wiring of the exciter, which has 3 conductors, indentified on prints as EN, EF, & EP. Can anyone explaing how this exciter works, and/or any troubleshooting tips?

TIA

Rick Miell

 

[ccjersey]

With that vintage, I suggest you try posting as much information as possible such as make, model, voltage and size of light plant and type of exciter ie DC generator (common)or static type (uncommon in that age set) to the following website for more specific information.

http://www.smokstak.com/forum/forumdisplay.php?f=6

Most common problems with old generators involve brushes and commutator and or sliprings. If no problems there, you should check for residual AC voltage output from the stator and DC output from the exciter. If no output, the set may need flashing to restore the residual magnetic field. In some cases this is automatic when the engine is cranked, but in others the set depends upon residual magnetism to build up voltage in the exciter and or alternator.

If you flash it and there is a defect in the insulation, it may burn things when the voltage builds up, so a priliminary check on the condition of the windings would be a good idea prior to running the set. It may need drying or a trip to a repair shop first.

 

[waross]

Would this be a DC exciter with brushes, actually a DC generator, with the output from the brushes fed to a pair of slip-rings? That was a common arrangement in that era. The voltage regulator often controlled the field of the DC exciter. Over the years, many of these were changed to brushless. The comutator and slip rings would often but not always be removed. Three spots on the armature winding 120 deg. apart would be tapped and fed to the rotating diodes that were installed as part of the conversion. The diode output was connected directly to the main field leads. Often the same voltage regulator would still serve.
Then there were as many variations as there were competent designers.
Post more info. please.

 

[ccjersey]

EP exciter positive
EN exciter negative
EF exciter field

Regulator technology of that era was either a manual field rheostat or a "finger" regulator that closes and opens a series of contacts, adding or removing resistance to the exciter shunt field circuit. As waross says, the positive and negative exciter terminals were paralleled to the main alternator field by way of the sliprings and brushes. The field terminal is probably to an exciter shunt field. There may be an exciter series field in the circuit with the main field and the exciter armature.

Lots of brushes and contacts to be dirty, stuck and corroded and prevent excitation of the main field.

I have a 1944 Century 37.5 kVA alternator in a BUDA Dieselight set that is setup with selectable manual rheostat control or automatic control by GE finger type AVR. All of 33 hrs on the clock. This set needs flashing whenever it has been inactive for a year or so. It does seem to help to select manual control and turn the manual voltage adjust all the way up to get it going and then once it builds up, adjust to correct line voltage before connecting the load.

This Century alternator has a wound rotor with slots and windings instead of the common wound poles. It also has a squirrel cage winding on the outside. I saw some mention of armotisseur windings on some old Onan literature and wondered what advantage it was supposed to confer in a generator.