GENERATOR AND ELECTRICAL INFORIiIATION
An e l e c t r i c a l generator is a machine s o constructed t h a t when its r o t o r i s revolved a voltage i s b u i l t up, which causes current t o flow. Generators a r e
divided i n t o two classes: Direct current, i n which the current always flm
in the same direction, and Alternating Current, i n which the current reverses
its d i r e c t i o n 60 times a second i n a 60 cycle generator or 50 times a second i n
a 50 cycle generator, etc.
Voltage i s the force o r pressure which causes a flow of current through the
conductor. Voltage can be compared t o pressure i n a pipe of water system.
Amperage i s a measure of the r a t e of current f l o w through t h e conductor.
can be compared t o the number of gallons per minute i n a water system.
It
An ohm i s a measure of the resistance i n a conductor t o the flow of current,
If one v o l t can cause one ampere t o flow through a conductor the resistance of
the conductor i s one ohm. This can be compared t o the manner i n which the resistance of a water pipe limits the flow of water a t a given pressure,
CHANGING ROTATION OF GENERATORS
To change the r o t a t i o n of Belt-Drive Generators, interchange the leads t o the
DC brushes. I n other words, there a r e Cwo DC Brushes o r two airs of DC &shes.
Take the lead or' leads from the f i r s t brush and fasten them t o the second brush
and take the lead o r leads from the second brush and f a s t e n them t o the first
brush,
I n a d i r e c t current generator the current always f l m s i n the same direction.
This i s accomplished by means of the commutator and brushes which a c t t o keep
the current flowing i n a constant direction. The commutator and brushes a c t
a s a group of double throw switches, reversing a c o i l ' s connection t o the l i n e
j u s t a s it i s star.ting t o pass under a f i e l d pole of opposite polarity.
The commutator and brushes of a D.C. rrachine carry a l l of the current generated
within the machine. These a r e subject, therefore, t o a l l overloads. If overload continues t o eldst, the generator may become daxnaged. The commutator
becomes hot and then arcing develops, v:hich, i n turn, continues t o r u i n the
commutator. Therefore, never subject a D.C. generator t o overload a s it shortens
t h e life of the unit.
D.C. Generators a r e a l s o divided i n t o two types, namely, shunt and compound
wound, The shunt wound type has only the shunt f i e l d coils. Therefore, the
voltage of this type of machine w i l l drop a s load i s increased. The shunt
wound generator is used most often f o r b a t t e r y charging plants. The compound
wound machine, i n addition t o shunt f i e l d c o i l s , a l s o has the s e r i e s f i e l d
coils. These c o i l s a r e i n s e r i e s with the load. A s the load increases, so
does the current through the s e r i e s coils, automatically supplying e x c i t a t i o n
and e i t h e r boosting the voltage s l i g h t l y o r maintaining it more o r l e s s constant.
Therefore, ~ 5 t h
a compound DeC, machine you can overload excessively *thou%
causing voltage t o drop, T h i s c h a r a c t e r i s t i c of the compound wound D.c.
generator makes it e a s i e r t o unknowingly overload the engine, It is, themfore, advisable t o carefully check the load a t regular i n t e r v a l s t o gather
assurance t h a t overload does not e x i s t ,
GENERATOR TROUBLES
- DeCo
The most common source of D,C, generator trouble is overloading, Overloading, i n turn, causes commutator and brush troubles which can be very bothersome and costly. Overloading a machine beyond i t s rated capacity r e s u l t s
i n sparking o r arcing brushes, accompanied possibly by heating and discolorat i o n of the commutator due t o the excessive current which they a r e carrying.
!Chis sparking i s of such a nature a s t o damage both the brushes and commut a t o r whose surface w i l l be burned and discolored due t o overheating, espec i a l l y if the overload is.allowed t o continue. A healthy commutator w l l l
acqilire a good polish and chocolate brown color, Black deposits on t h e
commutator often indicate bad c o r n t a t i o n ,
Another source of commutator trouble is o i l and grease, If o i l o r grease gets
on the commutator, the mica insulation of the commutator w l l l become o i l soaked
r e s u l t i n g eventually i n ruined c o r n t a t o r , Ring f i r e is a v i s i b l e sympton of
this condition; therefore, never lubricate the commutator,
Arcing brushes may a l s o be caused by improper adjustnent of the brush ring,
thus placing a l l the brushes i n wrong position with respect t o the f i e l d
poles. Brush rings a r e adjustable, It is, of course, first necessary t o
b o s e n the s e t screw, Then adjust the brush r i n g t o a position where l e a s t
sparking e x i s t s , I n t h e case of some D,C. generators, individual adjustment
of each brush may reduce arcing, Brushes should be equally spaced around
the commutator, T h i s spacing should not vary more than 1/32 inch,
Brush troubles which continually p e r s i s t due t o atmospheric conditions can
usually be solved by some l o c a l e l e c t r i c a l expert, However, should the
services of such an expert not be available, it i s possible t h a t the dealer,
through suggestions received from the factory, can correct the trouble,
Consistent overload, which overheats the insulation, exposure t o o i l y o r
moist atmosphere, and a number of other causes dl1 eventually r u i n the insulation of the machine's windings. This w i l l cause short c i r c u i t s and
grounds t o appear, These conditions must be eliminated a s f a u l t s of this
type i n an e l e c t r i c a l machine a r e accumulative,
When the commutator of a generator s h m bad condition from wear and improper
operation, it should immediately be repaired, It never pays to wait, Bg
having the commutator machined and brushes replaced a t the first signs of improper condition, considerable service costs can be avoided,
Sanding the commutator with a f i n e grade of sandpaper (never use emery cloth)
w i l l often stop sparking and r i n g f i r e , i f the damage is not already too
great. Sometimes a d i r t y commutator is the primary source of sparking, and
t h e removal of the blackening by sandpaper w i l l cure the trouble, Therefore, inspect the generator about once or twice a week and considerable
trouble and expense w i l l be avoided,
An exceptional hot commutator w i l l throw solder, and therefore connection
between commutator bar and c o i l is broken. Should such a condition ever
develop within the machine, it could be a d i r e c t r e s u l t of overload, Therefore, never averload a D.C, generator. It my r u i n t h e generator and a l s o
shorten the l i f e of the engine.
ALTERNATING CURRENT GENWATORS
'1
'
A,C. generators, commonly called alternators, a r e b u i l t ' t o generate a voltage which periodically varies from a given positive t o the same negative
value, T h i s i n turn w i l l cause the current t o reverse i t s direction a t the
same frequency a s the voltage change, The number of these alternations o r
cycles depends upon the s p e d of the machine and the number of oles, A
s i x t y cycle alternator, having a speed of the 1800 R,P.K. is a -pole machine, while an a l t e r n a t o r of the same frequency operating a t 1200 R.F.M.
is
a 6-pole machineo
E
A self-exc'!ited generator has the D.C, e x c i t e r winding on the same armature
with the A,C. winding. The D.C, and A,C. windings are, of course, f u l l y
insulated from each other, The D.C, current generated i n the e x c i t e r windings supplies the current f o r the f i e l d poles. T h i s current i n the f i e l d
poles builds up a magnetic flux, which causes voltage t o be generated by the
The amount of current flcwing through the f i e l d may be conA.C, winding.
t r o l l e d by a rheostat. More o r l e s s current i n the f i e l d c i r c u i t causes the
A,C, voltage t o r i s e or d r o ~ . Variation i n e i t h e r t h e f i e l d resistance
(rheostat) o r speed of the machine will cause a voltage drop, Reactance i n
the load cikcuit causes a lagging current, T h i s current must come from the
generator but t h i s lagging current tends t o oprose the magnetic f i e l d thus
reducing the output voltage of the generator.
Lagging current i s a subject t h a t is r a t h e r d i f f i c u l t t o conceive by the
average u s e r of small power plants, It is, however, something t h a t must be
considered. It should be remembered t h a t lagging current i s due e n t i r e l y
t o e l e c t r i c a l equipment of t h e induction type, such a s induction motors,
transformers, neon sign transformers, radio equipment, e t c o
The mst common s i g n of a lagging current i n generator s e t s i s a condition
where t h e engine does not seem t o be overloaded (engine does not smoke o r
slaw down, but the ammeter shows a high current reading and t h e voltmeter
s h m l e s s than rated voltage,
Another point t o be considered i s t h a t of s t a r t i n g an e l e c t r i c motor, The
reactance of an e l e c t r i c motor is bad while s t a r t i n g and i f the motor i s of
o l d construction, it may stall, due t o the voltage drop caused by excessive
s t a r t i n g current of the motor.
The user should carefully read the above paragraphs and should he have any
reason t o ' believe t h a t the capacity of his plant is being reduced by t h e
reactance of h i s motors, should immediately comunicate with the dealer,
Correcting capacitors a r e available a t reasonable cost and t h i s i n s t a l l a t i o n
w i l l i n many cases prove t o be a n i d e a l solution. Prices on capacitors m y
be obtained through your dealer.
A capacitor a f f e c t s an a l t e r n a t i n g current c i r c u i t i n j u s t the opposite manner
t h a t reactance does. A capacitor tends t o make t h e current "lead" t h e volt.age r a t h e r than make it ftlagtt. Therefore, if enough capacitors a r e i n s t a l l e d
they w i l l n e u t r a i l i z e the bad e f f e c t s of lagging current, Remember, it is
the reactance of t h e load (not the a l t e r n a t o r , which has i t s own e x c i t e r ) t h a t
i s being corrected. Old and underloaded motors and transformers a r e the main
cause of reactance. -
GENERATOR TROUBLES
- A.C.
Most A.C. generator troubles a r e confined t o the e x c i t e r , which, a s s t a t e d
previously, i s a d i r e c t current generator with commutator and brushes. Brush
and commutator troubles a r e caused by any number of conditions, such a s dusty
and sandy a i r , o i l y or moist atmosphere, grease g e t t i n g on commutator, improper brush spring tension, brushes of improper composition, excessive vib r a t i o n of the machine, running the machine too f a s t , e t c o
Brush troubles which continually p e r s i s t due t o atnospheric conditions can
usually be solved by some l o c a l e l e c t r i c a l expert. However, should the services of such an expert not be available, i t i s possible t h a t t h e dealer,
through suggesti-ons received from the factory, can correct the trouble.
Consistent overload, which overheats the insulation, exposure t o o i l y o r
moist atmosphere, and a number of other causes, w i l l eventually r u i n t h e ins u l a t i o n of t h e machine's windings, T h i s w i l l cause short c i r c u i t s and
grounds t o appear, These conditions must be eliminated a s f a u l t s of t h i s
type a n e l e c t r i c a l machine a r e accumulative.
GENEUTOR SERVICE
The most common cause of a generator f a i l i n g t o produce current i s an extern a l s h o r t somewhere on t h e main like. I f it i s suspected t h a t t h i s is the ,
cause of f a i l u r e , t h e main l i n e c i r c u i t should be disconnected by throwing
t h e main l i n e switch, and a t e s t lamp
across the output of the generat o r , If the p l a n t f a i l s t o generate with the A,C, main l i n e d i s c m e c t e d
from the plant, then t h e trouble l i e s i n t h e generator, With t h e trouble
traced t o the generator, the following t e s t s w i l l indicate whether o r not
the d i f f i c u l t y is due t o a s h o r t or a grounded f i e l d o r armature.
COMMUTATOR: Mica is used f o r i n s u l a t i o n between the commutator bars, After
t h e r e is machined, the mica i s cut away from 1/32" below the surface
of t h e bars. The surface of the bars w i l l wear d m t o t h e l e v e l of t h e mica
eventually. Mica i s harder than copper and it forms ridges which cause t h e
brushes t o 'jump and make poor contact. High q i c a should be under-cut caref u l l y , and the commutator turned and cleaned. Loose brush wires can cause
f a i l u r e of t h e generator t o produce current. Brushes in which t h e leads have
become loosened should be replaced.
.
TESTING D.C. BPINDITJG OR ARllfiTURE FOR GROUNDS: First, disconnect b a t t e r y and
A,C, l i n e wires from plant, RAISE ALL BRUSfBiS FROM COldMUTAT0R AND COLLECTOR
RINGS, Place one end of t e s t lamp orire on comrrmtator, Touch other end of
t e s t lamp w i r e on clean surface of armature shaft, If t e s t lamp burns, the
commutator or D.C, winding is grounded. NOTE: A shorted o r grounded D,C,
armature c i r c u i t P v i l l generally be indicated by overheating of the armature
o r burned windings,, The p l a n t will run, but no current P v i l l be generated,
TESTING A,C. WINDING OR ARMATURE FOR OPEN CIRCUITS: First, disconnect batAND
t e r y and A.C. l i n e Poires from plant. RAISE ALL BRUSHES FROM C-ATOR
If the generator i s single phase, 2 or 3 ring, place o m
C O ~ ~ C T ORINGS.
R
t e s t lamp wire on the center r i n g then touch the other w i r e t o each other
ring, The lamp should b u n when any tPro r i n g s a r e touched, If t e s t lamp
does not burn an open c i r c u i t is indicated.
On a t-fing s i n g l e phase generator t h e lamp should burn w h n r i n g No. 1and
Ring No, 2, o r when r i n g No, 3 and No, 4 a r e touched. With any other combination, t h e lamp should not burn,
On a 3-phase, b r i n g generator with one test lamp Kire on ring N, lamp should
burn when touching any other rlng, Check a l l rings,
On a 3 9 h a s e , 3-ring generator touching any combination of two rlngs should
cause the lamp t o burn. If lamp f a i l s t o burn i n any of these cases an open
c i r c u i t has developed. Check a l l combinations, Note: An open c i r c u i t in
t h e A,C, armature winding w i l l r e s u l t i n the plant f a i l i n g to generate voltage.
Placing one end of t e s t lamp wire on shaft, t h e lamp should not burn when
other end of t e s t lamp are i s placed on any collector ring, If l i g h t burns,
it indicates a ground i n A.C. winding, Any s h o r t o r ground i n the a r m a t m
mans t h a t it must be rewound,
-
TESTING FIELDS FDR OPEN CIRCUITSa Disconnect b a t t e r y and A,C, l i n e wlres
From plant, Raise a11 brushes from conmmtator and c o l l e c t o r rings, Disconnect D,C. f i e l d wires. Connect one t e s t Lamp wire t o f i e l d Prire leading t o
brush holder, Connect other t e s t lamp wire t o wire i n o u t l e t box leading
d i r e c t t o f i e l d coil. If t e s t lamp does not bum, D,C, f i e l d c i r c u i t is
open, NOTE: Broken wires or loose connections between generator f i e l d and
corrtrol panel should be checked f i r s t , An open c i r c u i t i n t h e f i e l d winding
would prevent the plant from generating.
SERVICE DIAGNOSIS
POOR COMMUTATION_: Indication of poor commutation is excessive sparMng and/
- o r overheating of commutator, blackened o r p i t t e d commutator bars.
CAUSES OF POOR COMMUTATIONt
1. The brushes not s e t c o r r e c t l y i n respect t o the f i e l d poles.
2.
3.
Brushes may not be f i t t e d t o the surface of the c o r n t a t o r e
Brushes binding i n t h e holders.
4.
6.
7,
8,
9.
10.
Brushes may not be equally spaced around t h e commutator.
Brushes may have reached t h e i r l i m i t of wear, with the r e s u l t t h a t there
w i l l be a n i n s u f f i c i e n t amount of briish spring tension.
Some brushes may have excessive pressure, thereby taking more than t h e i r
share of t h e current.
The car5on brushes, if replaced, may be of an unsuitable grade, Metal
graphite brushes generally a r e not used on D O C * voltages higher than 30
t o 40 volts. Great care must be taken t o be sure t h a t the proper grade
i s being used on the generator when replacements a r e made.
Some commutator bars m y be loose o r projecting above the other.
High mica, t h i s prevents a proper contacting surface between t h e brush
and the commutator.
A v a r i a t i o n i n the a i r gap of t h e machine o r strength of the f i e l d poles.
This w i l l a l s o cause severe sparking a t the commutator.
FAILURE OF GENERATOR TO BUIJ;D UP VOLTAGE:
lo The speed of the s e t may be below normal.
2. Field c o i l s not connected i n proper sequence. T h i s could only occur if
the wiring has been changed since leaving the factory.
30 A reversed shunt f i e l d , Switch wires leading t o DeC, brush holders.
'be Brushes i n c o r r e c t l y spaced, and not located on a n e u t r a l position,
5. An e x t e r n a l s h o r t c i r c u i t ,
6, An open c i r c u i t i n the shunt f i e l d , .
7. Loss of r e s i d u a l magnetism. The process of building up voltage i n a l l
types of generators requires t h a t there be a small amount of r e s i d u a l
magnetism i n the i r o n p a r t s of t h e f i e l d e x c i t e r s t r u c t u r e when the machi n e i s standing s t i l l , This r e s i d u a l magnetism produces t h e i n i t i a l
voltages i n the a r m t u r e c o i l s a s soon a s the armature i s rotated, which
a r e b u i l t up u n t i l the f u l l magnetic f i e l d i s developed, and the mchine
d e l i v e r s f u l l voltage, A l l generators leave the f a c t o r y with s u f f i c i e n t
r e s i d u a l magnetism t o build up when s t a r t e d o However, through long
periods of storage, and sometimes due t o rough handling i n t r a n s i t , a n
occasional generator w i l l l o s e a l l or p a r t of i t s r e s i d u a l magnetism,
and s o f a i l t o b u i l d up voltage, The following procedures w i l l usually
c o r r e c t t h e trouble:
(a)
Carefully check t h a t . all brushes a r e free i n th brush holders, and
a r e seated on the commutator, and t h a t no oSjectiona5le film has
collected on the c o r n t a t o r , See t h a t brush shunts a r e not binding
on adjacent p a r t s o r shorted t o ground.
(b) With the generator running, apply l i g h t pressure t o the top of one
o r two D O C . brushes with a wooden s t i c k , t o p o l i s h the c o r n t a t o r
and break through commutator film. Often t h i s w i l l permit the
generator t o build up when the r e s i d u a l f i e l d is weak,
(c)
If the machine s t i l l refuses t o build up, t h e r e s i d u a l magnetism
can be restored by applying d i r e c t current t o the f i e l d s , Lift a l l
t h e brushes c l e a r of t h e commutator. T i t h the generator a t stands t i l l , connect t h e positive terminal of a 6-volt storage b a t t e r y
o r !'Hot Shotu dry b a t t e r y t o a p o s i t i v e brush holder, I n generators
where one brush holder i s grounded this will be t h e grounded cormnut a t o r brush. Touch the negative connection from the battery t o t h e
adjacent commutator brush holder. T h i s w i l l be a negative brush,
Hold. the connection a few seconds, Remove battery connections,
lower brushes and s t a r t generator.
(d)
Should the generator build up with reversed polarity, t h a t is, should
the positive connection becorhe negative, or i n an A.C. machine s t i l l
f a i l t o produce current, this can be overcome by reversing the connections b e w e n the b a t t e r y used t o build up the residual magnetism
and repeating the process described above.
I n e l e c t r i c a l l y cranked plants, where the generator serves a s t h e
s t a r t i n g motor, r e s i d u a l magnetism is automatically restored when
t h e s t a r t i n g windmg i s energized,
NOISES I N THE BRUSHES: Noise i n brushes i s generally due t o a rough o r outof-round commutator, caused by high and lorn bars, This d i f f i c u l t y may only
be corrected by machining t h e commutator i n a l a t h e o
COMlUTATOR: Mica i s used f o r insulation between the commutator bars. After
%he a m t u r e i s machined, the mica i s cut away about 1/32" beluw the surface
of the bars. The surface of the bars w i l l wear down t o the l e v e l of the mica
eventually, The mica i s harder than the copper, and it forms ridges which
cause the brushes t o jump and make poor contact. High mica should be under
cut carefully, and the c o r n t a t o r re-machined and polished.
The commutator should maintain a polished surface. Blackening of all t h e bars
indicates incorrect brush positions. Blaclcening of groups of bars a t regular
i n t e r v a l s indicates rough, eccentric commutator. A s l i g h t , even discoloration
of the commutator i s a normal condition*
A severelyburned bar o r number of bars, indicates an open c i r c u i t i n the armature, which w i l l a P s o be noted by excessive f l a s h i n g when t h e machine i s operat i n g with load. This type of d i f f i c u l t y can only be corrected by competent
armature r e p a i r senrice men.
Ordinarily the commutator w i l l require only an occasional wiping with a nonl i n t i n g cloth, but i f blackening appears and grows worse, the cause must be
determined and corrected.
Use no lubricant on the commutator. The use of any lubricant w i l l only cause
sparking and increase the commutation d i f f i c u l t i e s .
BRUSHES: See t h a t the brushes move f r e e l y i n the holders and a t the same
efirm even contact with the commutator. The brushes should a l l have
t h e same spring tension t o prevent one from carrying more than its share of
the load, An extra s e t of brushes should always be kept on hand,
See t h a t both t h e i n t e r i o r and the e x t e r i o r of the machine a r e kept f'me from
metal dust, d i r t of any description, o r water,
GENFJRATOR HEATING:
May be due t o one of t h e following causes:
1, Overload on the l i n e ,
2, Short c i r c u i t of a c o i l o r number of c o i l s i n the winding,
3, Grounds i n the armature winding o r commutator,
Lo Poor commutation,
5. Overheating of t h e e n t i r e u n i t , may be caused by:
(a) Unequal a i r gap.
(b) A shorted out o r grounded f i e l d winding,
(c) A reversed f i e l d c o i l wtnding,
NOTE: A n y of these troubles cause a large circulating current i n the e x c i t e r
armature windings of the commutator, the brushes and brush connections, which,
w i l l cause a r t i f i c i a l overloading of the armature. The a i r gap should not
vary over a few percent e i t h e r way from the average value, A l l f i e l d c o i l s
of the shunt type should have within 10%
of t h e same resistance, a higher value
than this indicates shorted turns i n the winding,
F'IELD COIL HEATING:
1, Too high an operating s p e d of the plant, with a r e s u l t a n t high output
voltage
20 A p a r t i a l short c i r c u i t of one coil.
MAINTENANCE:
A l l Generators a r e equipped with b a l l bearings.
These bearings w i l l last f o r
It i s very important t o keep the generator clean and f r e e from
accumulations of d i r t and grease, It i s not necessary t o take the generator
apart t o clean it, a s i n most cases the dust accwrmlations can be r e a d i l y
blown out with an a i r hose and the h n g s and commutator be wiped with a clean
cloth. The grooves between the commutator bars should be occasionally cleaned out and kept f r e e from accumulations of carbon, dust o r other foreign
a very t h i n hack saw blade ground t o a
matter. This can best be done ~ 5 t h
hook shape o r a large needle o r h a t pin.
maw years.
MAINTENANCE SERVICE INSTRUCTIONS
FOP DC Generators and Ekeiters
AC Alternators
build up rated
~ h e o s t a t ,f i e l d
l i g h t up on f l e l d coils with
many turns; consequently, DC
should be used for testing.)
A bank of b a t t e r i e s connected
i n s e r i e s t o give 12 t o 24
storage battery f o r j u s t an
20 See t h a t brushes move f r e e l y
holder tension springs which
actuate t h e brush holder
tension arms have beenaljusted
a t t h e f a c t o r y f o r proper
tension. However, a f t e r t h e
brushes have been worn down
t o half of t h e i r o r i g i n a l
length, t h e spring tension may
be increased one notch. Bushes
should be cheeked periodically
so when brushes have worn t o
the point where brush holder
tension arm i s almost a t t h e
end of travel, the brush may
be replaced, On small machines
using fixed brush holders and
f i b e r caps, the brush sprFng
tension i s not adjustable, and
when the brush has worn t o
about 1/2 its original length
it should be replaced, Care
should be taken, however,
see t h a t t h e shunt does n o t
become pinched betwee
of the b m h spring.
MAINTENANCE smVICE INSTRUr3TIONS
For DC Generators and Exciters
AC Alternators
Trouble
Generator f a i l s t o
b u i l d up r a t e d
voltage (cont 'd)
Cause
Poor Brush contact
(cont 'd)
Armature shorted o r
grounded.
Remedy
*
4, Replacigg brushes,, It is
important t 5 a t a l l brushes be
of t h e sane g~ade, preferzbly,
t h e same kind and type a s
s~zpplledwith t h e o r i g i n a l U t e
A T t e r bruslies have been i n s t a l l e d
i n 'c3e holde~?s,I t is necessary
t h a t the br- shes be f ittec! t o
the conmta-'ml: w c o n ec-tono
ring, (See note 2,)
~ e r n o zazns.'~=c and t e s t on
groxla-, If Lest shows short,
o r o?en, a m , i a i ~ r ek i l l have
--
F2) f r o n brxihes and armature
l e a d s a i d c h c k f o r continui.ty
and r e s i s t a n c e t o ground with
cormect Lng generator to l i n e ,
Check f o r shorted f i l t e r con-
due t o comuta-kzthrowing sol.der
from riser, Due t o
turned, a ~ 1-mderc~lt;
d
h a ~ i n ga ci ji:,s table
plact*s the p o s i t i o n of -tihe
brushes is f i x e d by desF,g,
On the 12 and. 1Lim f i e l d frames
t h e a d j n s t a b l e r i n g may be
re?osi.tior.ed s o e l a t the brushes
MAINTENANCE SERVICE INSTRUCTIONS
For DC Generators and Exciters
AC Alternators
Trouble
Generator f a i l s t o
b u i l d up r a t e d
voltage (cont td)
Cause
Wrong r o t a t i o n
(cont Id)
F a u l t y voltage regul a t o r operatlon,
Low output voltage
Excessive load
Ensufficient excitat i o n due t o t o o
much r e s i s t a n c e
i n the f i e l d .
High r e s i s t a n c e
High Line Losses
Low speed
1 0 Belt slipping
2, Defective governor
30 Defective bearing
46 Excessive
load
Remedv
r o t a t e clockwise; engine driven
p l a t s r o t a t e counter-clockwise,
Tf it is desired t o run t h e
machine i n the opposite direction
to t h e way i t was ,adjusted a t
t h e factory, t h e i n t e r n a l connections of t h e generator w i l l
have t o be changed, and t h e
commutating plane of t h e brushes
readjusted, The sure way is t o
take all the wires off t h e
p o s i t i v e brushholder and place
them on the negative brushholder
and place a l l t h e wires which
o r i g i n a l l y connected to the
negative brushholder on t h e
p o s i t i v e brushholder, On a
st r a i ght shunt-wound machine,
r o t a t i o n can be changed simply
by interchanging t h e f i e l d leads,
To a d j u s t the commutating plane
of the brushes, s h i f t t h e brush
spider or ring i n t h e direction
which r e s u l t s i n the highest
D.C, armature voltage w i t h
minimum sparking a t the brushes
when the f i e l d r h e o s t a t o r
r e s i s t o r is a t minimum r e s i s t ance s e t t i n g ,
Try operating t h e plant without
voitage r e G a t o r . See t h e
i n s t r u c t i o n manual f o r t h e
p a r t i c u l a r voltage regulator
US ed.,
Reduce l o a d
Reduce the amount of f i e l d
resistance,
Connections w i l l be warm o r
hot t o t h e touch. Make b e t t e r
e l e c t r i c a l and mechanical j o i n t s
and connections,
Increase s i z e of l i n e wires
1, Tighten Belt,
2, Adjust, repair, o r replace
governor,,
3* Replace bearings,
4, Reduce load.
PIAINTEXANCE SERVICE INS!l!RUCTIONS
FOP DC Generators and Excite~s
AC A l t e m t s ~ s
ower-factors less
(see nameplate data
MAINTENANCE SERVICE INSTRUCTIONS
For DC Generators and h c i t e r s
AC Alternators
Mote 3 0 ) A l l micas should be
l a t h e ; however, when doing s o
a competent machinist must be
employed, Make a b s o l u t e l y sure
t h a t the armature s h a f t i s
centered concentric with t h e
bearing s u r f ace. Dontt machine
commutator u n t i l you have
checked t o s e e t h a t s h a f t
center is concentric with
bearing, The surface of the
commutator should be machined
a s l i t t l e as possible and
2, A very e f f e c t i v e p o l i s h e r may
be constructed by f o l d i n g
s e v e r a l l a y e r s of canvas o r
duck over t h e end of a s t r o n g
piece of wood and tacking it
Ln place, The canvas pad may
be held on the commutator o r
c o l l e c t o r rings, T h i s w i l l give
a high p o l i s h without c u t t i n g
t h e surface, however, if t h e
commutator i s p i t t e d , it w i l l
be necessary t o f i r s t p o l i s h
with a f i n e grade of sandpapero
(oo), following it with t h e
canvas polisher, NEVER USE
EMERY CLOTH TO POLISH, s i n c e it
contains m e t a l l i c p a r t i c l e s
which w i l l s h o r t o u t t h e commuta-
MAINTENANCE SERVICE INSmCTIaNS
For DC Generators and Exciters
AC A l t erna t o r s
w
.
Trouble
Excessive sparking
(cont f d )
Cause
Brushes not i n
commutating plane .Brushes s t i c k i n g
i n brushholde~s
berload
Grounded, open, o r
shorted f i e l d c o i l
windings.
Open Armature
Eoose b m h h o l d e r
irregular speed of
engine.
'tinstable voltage
regulator.
'nuttua t i n g DC
voltage
Remedy
(See Page 20)
Clean brushes and brushholders
and a d j u s t b n ~ s h e s .
Check ammeter readings w i t h
~ a m e p l a t er a t i n g , Reduce load.
Replace o r r e p a i r defective
coil,
Repair o r replace armature.
Re-slim and t i g h t e n holder.
Adjust governing device*
Try operating without voltage
regulator, See voltage regulator
i n s tr-JC
ti on manual
S t a b i l i z e load.
F l u c t u a t i n g load
(See Pages 19 & 20)
Poor brush contact
Ihke b e t t e r connections
Loose terminal
mechanically & e l e c t r i c a l l y .
come c'Gions
Generator overlosding Reiruce load
Replace worn b e a r i n ~ s
b e f e c t i v e bearing
Raise UC brushes and contact
P30lari+y-5,-fgenerato2 Long i n a c t i v i t y ,
positive and negative terminals
short circuit,
revorsod
lightening s t d k i n g with 6 t o 12 v o l t s t o produce
c m e c t polarity.
system, etc.
Connect .5 mfd condensers fron
RadAo I~tarf'eronoe Kadio P'requency
a l l brushes t o frame. Voltage
interference due
r a t i n g should be a t l e a s t
ta sparking of
donble t h e r a t e d voltage on
brushes
the c i r c u f t to which they are
cor,iected.
If condensers are
already connected t o t h e s e
points, replace with new
condensers,
I n s t a l l s h a f t grounding b d h
Radio frequency
interference caused assembly.
by leakage of s t a t i c
charge from
generator s h a f t *
Radio i n t e r f e r e n c e -SuppSs s radio in€erf erence
caused by electrical. i n usual manner. It is suggested t h a t competent radio
system of engine
mar, o r e l e c t r i c i a n be consulted.
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