PART 2

Question 1

-change in the terminal voltage with the change in load current
when it is running at a constant speed
– if change in voltage between no-load and full load is small, the
generator is said to have a GOOD regulation, otherwise it is said to have
a POOR regulation
– is the change in voltage when the load is reduced from
rated to zero, expressed as percentage of the rated load voltage

Answer 1

VOLTAGE REGULATION (VR)

Question 2

– occurs in the different parts of the DC machine
– causes heating of the machine

Answer 2

POWER LOSSES in DC Generators

Question 3

EFFECTS IN POWER LOSSES

Answer 3

Effects:
– increases the temperature inside the machine which affects the
performance and life of the machine, particularly insulation
– machine rating is directly affected by the losses
– losses are waste of energy and waste of money
– increases the operating cost of the machine

Question 4

– also known as electrical losses or 𝐼
2𝑅 losses
or ohmic losses
– resistive losses in the armature and field
windings
– varies with the variation of load on the machine
(variable losses)
– for SHUNT machine, the field copper loss will
be constant if field resistance is not varied
– about 20% − 30% of full load losses

Answer 4

COPPER LOSSES

Question 5

– is due to the presence of circulating current in the
core material
– as the armature rotates and cuts the magnetic flux,
EMF is induced
– This EMF is very small but it sets up a large current in the
body of the core
– this circulating current is wasted and produces heat
– to counter act eddy current losses, the core is made up of
thin laminations, stacked and riveted at right angles to the path
of the eddy currents
– these laminations are insulated by thin coats of varnish.

Answer 5

IRON LOSSES
a. Eddy Current Loss (𝑷𝒆)

Question 6

– due to the reversal of magnetization of
the armature core as it passes under the
north and south pole alternately
– depends on the volume and grade of iron,
maximum value of flux density, and frequency of
magnetic reversal

Answer 6

b. Hysteresis Loss (𝑷𝒉)

Question 7

– is due to the rotation of the armature
Bearing Friction Loss – depends on the type of bearing
used and on the viscosity of the lubricant
Brush Friction Loss – proportional to the contact
area and the brush pressure
– also depends on other factors like material of the
brush and commutator, their polish condition, and
the temperature at the contact surface

Answer 7

III.MECHANICAL LOSSES
a. Friction Loss

Question 8

– Is due to the rotation of the armature in air
– proportional to the cube of the speed

Answer 8

III. MECHANICAL LOSSES
b. Air Friction or windage Loss

Question 9

– also known as magnetic and mechanical losses
– also known as rotational losses
– produced when machine is loaded
– very small in value and difficult to calculate
– generally considered to be 1% of the output power in total

Answer 9

STRAY LOAD LOSSES

Question 10

– field copper loss is constant for shunt and compound
generators
– stray losses and shunt copper loss (𝑊𝑐)

Answer 10

❖ CONSTANT or STANDING LOSSES

Question 11

– known as variable loss
– varies with the load current

Answer 11

❖ Armature Copper Loss