DC machine

Yarn!!!!

A series machine has it's Field and Armature windings connected in series

A shunt has it's field and Armature windings connected in Parellel

And a compound is a mixture of both, Hench the name compound!!

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Thank you And good night!!

IN SERIES MOTOR ARMATURE AND FIELD WINDING ARE SERIES TO THE LOAD WHEREAS IN SHUNT MOTOR ARMATURE AND FIELD WINDING ARE PARALLEL TO LOAD. IN COMPOUND MOTOR BOTH SERIES AND SHUNT WINDING ARE PRESENT.

Series machines are used in traction motors and in things like a car's starter. They slow down significantly when loaded, but produce lots of torque. As the load is removed they REALLY SPEED UP (your starter motor doesn't engage and it really overspeeds).

Shunt are used for controled speed, and may be staight shunt (no additional windings), a compensated shunt means there are a few series windings along with the shunt field to ensure stable speed regulation with load (some straight shunt machines will increase in speed with increasing load due to armature reaction), and your compound wound is a little of both and usually shows significant droop with increasing load ( valuable when trying to load share 2 motors on a common dc armature supply).
Straight shunt machines with 4 to 1 field ranges are often used for unwind stands on paper or steel processing lines.

Then there are pole face compensated motors, expensive, but good high performance speed regulators.

There are also dual compensated windings ( 2 seperate series fields compound wound) for reversing duty on SCR controls. Provides superior torque for stopping.

The combinations and percent compounding combinations are endless and application specific.

All answers are excellent, but I would like to stress that a series DC motor can overspeed to possible complete destruction (and of anyone or anything near it!) if run completely unloaded for more than a few seconds!!!

It will just keep on accelerating provided the supply can maintain the current needed of course!!

I have been there, done that and got the T-shirt....(It was a controlled and planned experiment!!) (The motor actually held together far longer than we thought it would too!!!)

I have the awards for flashing coms, twisting shafts, smoking armatures, and destroying drives, but never managed to overspeed a series machine to destruction, but then the only experience with the attempt was a 1Hp motor with a small diameter. It topped out somewhere near 10,000 rpm and then the residual pole magnetism (and windage?) saved it.

So, what was your demonstration setup? I have heard of several incidents with large machines being tested for stalled (with locked rotor which wasn't) IR drop and Te measurement with shunt field removed and technician not realizing there was still a small stabilizing series field that had sufficient torque to get the motor rolling. Some motors I have been told came right out of the frame. I haven't seen photos, so I am not sure it wasn't exaggerated.

Royal Navy, 220volt DC Fan motor, about 40HP, we simply removed the fan completely.

We did not monitor either rpm or current, just stood well back and waited. The motor just kept accelerating at a slower and slower rate though.

Suddenly, after about 10 minutes or so, though I did not time it, there was a massive shower of sparks and the motor came to a rapid stop, blowing out black clouds of carbon dust....a short inspection showed fresh solder tracks and the rotor had shed some windings, which were now jammed between rotor and stator (armature & fields).....the brushes were well worn before we started....most were broken, god knows why....the rotor was impossible to move by hand, even after dropping off the end plates and bearings. It had to cool for a few hours before we could touch it though.....it was still warm a few hours later....

Opinions were that the commutator got very hot (flash-over) and the soldering of the armature windings eventually gave out....as did the laquer that held some of the windings together...some segments of the commutator were also missing if I remember correctly!.....

We scrapped it!

Cool.

That could be a classic "Myth Busters" video!

Why not let them do it? Write them.....

"Can some one please tell me the difference between a

• series
• shunt
• compound

D.c machine"

Series has armature and field coils wired in series.

Shunt has armature and field coils wired in parallel.

Compound has armature wire in series with a portion of the field coils and in parallel with the balance.

In short notes.....with respect to speed,

1. Shunt Motor:

Its speed regulation is much better then that of the series or compound motor, and is suitable for constant speed application, though its speed does decrease slightly with an increase in load. That is, shunt motor speed is inversely proportional to the field flux.

2. Series Motor:

Series motor speed depends entirely on the flied flux; an increase in load current, the stronger the field flux, the lower the speed. A decrease in load current and therefore in the field current and field flux, causes an increase in speed.

Thus speed varies from very high speed at light load and low speed at full load.

3. Compound Motor:

Compound motor has a definite no – load speed and may be operated safely at no load. As load is increased, the amount of field flux increases causing the speed to decrease more than that of the shunt motor. Hence, the speed regulation of the compound motor is poorer than that of the shunt motor.

Regards,

Ron

Compound motor can also be designed so that it will speed up on increasing load.

These were fitted to escalators,at busy times they would move faster!

Not likely.

Wound this way the motor becomes unstable and runs away.

Thats true,special starting arrangements needed,they were used for all sorts of drives though, back in the 20s,you dont see any now,but they are well documented in books.

They do not run away,becuse of the shunt winding,in fact very constant speed,slightly increasing with heavy load.