POWER PLANTS

Have you ever wondered what causes the mechanical load on a
generator? Even a big generator turns over really easy by hand, but
bring it up to speed and start using electricity and you’ll
notice that the more current you use the harder the engine
pulls.

This had me curious, so I set out to find why. In one
experiment, I took a small heater blower motor from a junked car.
First I connected it to a battery to see if it would run, which it
did and by running, it would leave a residual magnetism in the
field core. I next hooked it to an electric motor, and turned it in
the opposite direction that it turned as a motor. The electric
motor turned it like nothing, until I touched both of the heater
motors wires together and it created such a load, the HP electric
motor had a job running it.

That little experiment proved that it’s the currents flow
that produces the load. No current flowing in the generator, and no
load on the motor.

I took the heater motor apart to see if I could find what causes
that big load when it worked as a generator. I used a couple of
wires, which I hooked to a battery, and used it as a prod. I
touched it on the field windings and found that current flowing
through it caused the core to turn into a strong magnet. Next I
touched the prods on the commutator in the same position that the
brushes contacted it. This turned the armature into a powerful
electromagnet.

Now I was on the road to understanding what causes that load. It
was magnetism. In order for a generator to produce current, the
field windings have to be energized, which creates a magnetic field
having a north and a south pole.

When the armature revolves, the field windings induce magnetism
into the cores of the armature. Being wire is wound around the
armatures cores, this moving magnetism through the core causes
current to flow in the windings. This current being generated in
the windings and flowing does what an electromagnet would do: its
core would become magnetized.

Really it is simple what causes that load. With the field cores
producing a magnetic field, and the armature producing a magnetic
field of its own, that load is caused by pulling the armature away
from the attracting field pole, then turning it towards the other
pole, which would repel it. The generator producing current is like
a magnetic coupling, as the outside housing would revolve too, if
it is not tightly secured.

I read in a manual later on that this load on a generator is
called ‘Armature Reaction.’ And due to this armature
reaction, the brushes on a generator are turned in the same
direction of rotation, to reduce sparking at the commutator. The
more current that flows the more the brushes should be shifted in
the direction of rotation, due to armature reaction.

An electric motor has to have the brushes shifted in the
opposite direction of rotation to reduce sparking at the
commutator.

To reduce the sparking at the brushes, some generators and
motors have interpoles and compensating winding. This doesn’t
reduce the load any, it just reduces sparking.

With the aid of a manual on electricity, armature reaction and
the mechanical load placed upon a generator, can be explained more
thoroughly.

It will be noted with the armature rotating in a clockwise
direction (Fig. 1) that the magnetic lines of force rotate around
the wires in a clockwise direction on the left side, and a
counter-clockwise direction on the right side.

On the left side, with the magnetic lines of force rotating in a
clockwise direction around the wires, it will be noted that it
produces a positive charge of electricity. This produces a south
pole polarity on the left side of the armature.

Whereas on the right side of the armature, the magnetic lines of
force rotate around the wires in a counterclockwise direction, thus
producing a negative charge of electricity and a north pole
polarity.

Looking at Fig. 2, it will be noted that from line A to B, there
is going to be a repulsion felt in the movement of the armature, as
alike poles repel, and opposite poles attract. The field magnets
have to demagnetize the armatures core, and remagnetize it into an
attracting polarity. In doing so, this moving magnetic field,
induces or generates electricity to flow in the windings.

When this electricity flows in the armatures windings, this
produces an electro-magnetic effect of its own, which so happens to
be in the same polarity as to which the field magnets induced into
the core, thus producing a strong magnet out of the armatures
core.

The more current generated, the stronger these magnetic fields
are, and the harder the load is placed upon whatever is driving
it.

Also, the more current generated, the slower it is to leave the
armature, due to the magnetic field in the cores. Thus the brushes
are shifted in the same direction of rotation to compensate for
this as a repelling field will speed things up at this point.

Being magnetism and electro-magnetism is very much used in
generating electricity, it is important to look at an electromagnet
and see what it does.

Any time current flows in a wire, it sets up a magnetic field
around the wire. Should the wire be coiled up, this magnetic field
adds up thus producing more lines of force.

Looking at the illustration, it will be noted an iron core
inserted into a coil increases the inductance, as it provides a
better path for magnetic lines of force than air. An iron core will
collect and concentrate magnetic lines of force, thus it will
produce a magnetic field about 280 times stronger than the air
core.

The copper core has the opposite effect, as copper opposes lines
of force more than air. The copper core will diminish the magnetic
lines of force.

Magnetism is like electricity; both like to flow more on the
outside of a conductor, than on the inside. Therefore, a laminated
iron core will collect and concentrate magnetic lines of force more
so than the solid iron one. Thus producing a stronger magnetic
field.

Looking at the armature of an electric motor, or generator,
you’ll notice that the core is made out of laminated iron. This
laminated core is used to reduce eddy currents, which exist in an
alternating magnetic field. Eddy currents is current induced into
the core from the alternating magnetic field created by the current
flowing through the winding. Even though eddy currents have a small
current value, it is wasted current, which turns into heat in the
core. By using laminations which are thin plates insulated from one
another, these eddy currents are reduced.

By having this knowledge of how the core material affects the
inductance of a coil, it will be noted that this laminated iron
core in the generator’s armature will produce a very strong
magnetic field, which adds to the load placed upon whatever is
driving it.

Next I want to point out how this laminated iron core will place
a resistance on the current flowing in the windings. A laminated
iron core increases inductance, and an increase of inductance will
increase resistance on the current flowing in the coil or
winding.

I also want to point out that inductance holds back AC current
more than DC current, as AC current drops to zero value and builds
up and DC builds up and stays constant.

A DC generator produces AC current in the armature, and is
converted to DC current at the commutator and brushes.

A coil of wire is used which is connected in series with a light
bulb. When the circuit is energized from a 115-volt AC line, the
lamp’s brilliance is noted.

With the circuit still energized the iron core is carefully
inserted. Note the decrease in the lamp’s brilliance resulting
from the increased inductance of the coil. A good part of the
current is now dropped across the coil.

Next the copper core is carefully removed and the laminated core
is inserted. The lamp’s brilliance has dropped greatly, and is
barely lit, as the laminated core has increased the inductance of
the coil more than the solid iron one.

Pretty much the same results would have occurred if DC current
would have been used instead of the AC. The resistance would not
have been as great though, as DC current is of the same value, or
in other words, more constant. With AC current dropping to zero,
and building up, this building up current in the coil produces a
moving magnetic field which generates an opposing current in the
coil. This is called counter electromotive force, or sometimes
called self-induction.

This self-induced current in a building up electromagnetic
circuit, opposes or bucks the original current. DC current only
experiences this upon building up, and the inductive circuit then
only acts as a resistor. AC current will have this resistor effect
the coil, plus the resistance from self-induction, or counter
emf.

I hope this will be of help to those planning on building a
power plant, or those who have antique power-plants. The next time
you see a steam engine driving a generator, and a switch is closed
and current flows, you’ll know why the steam engine’s
governor opened up, and let out a few big chugs out the exhaust