ECE 3614
HW # 3
1. A four pole, 800-rpm, DC generator has 36 armature slots with four conductors per slot. The flux
per pole is 22 mWb, and each armature conductor has a maximum current capacity of 40 A.
a. Compute Ea, Ia, and power rating for lap winding configuration.
b. Compute Ea, Ia, and power rating for wave winding configuration.
2. A 25 kW, 400 V DC shunt generator has an armature resistance of 0.22 Ω, field coil resistance of
600 Ω, and total brush voltage drop of 1.8 V. The generator delivers rated current at rated speed
and rated voltage (rated load). From this information calculate the following:
a. Load current.
b. Field current.
c. Armature current.
d. Armature induced voltage.
3. A 50 kW, 180 V, DC generator is configured with series and shunt field coils. The shunt field
coil requires 2.5 A for no load, and 3.5 A for full load in order to get zero voltage regulation. The
shunt field coil has 2000 turns. The cumulative compound configuration is intended, for flat
compounding at the terminals.
a. Calculate the series turns required (nearest integer) for a long-shunt configuration.
b. Calculate the series turns required (nearest integer) for a short-shunt configuration.
4. An 80 V DC machine, has the parameters listed below. When the machine is connected as a
shunt motor, it will draw 3 A under no-load condition. When the mechanical load is attached, the
constant voltage source delivers 5 kW to the motor.
Armature Winding Resistance = 0.12 Ω
Series Field Winding Resistance = 0.06 Ω
Series Field Winding = 3 turns
Shunt Field Winding Resistance = 32 Ω
Shunt Field Winding = 1200 turns
No Load Speed = 800 rpm
a.
b.
c.
d.
e.
Calculate the speed regulation for this load.
Calculate the torque developed at the load.
Calculate the copper loss of this motor configuration.
Calculate the rotational loss of this motor configuration.
Calculate the efficiency of this motor configuration.
5. The 80 V DC machine of problem 4 is configured as short-shunt cumulative compound generator,
and delivers 5 kW at rated voltage. The machine has the magnetization curve:
100
90
80
70
Ea
60
50
40
30
20
10
0
0
0.5
1
1.5
2
2.5
If
a.
b.
c.
d.
e.
Find the terminal current for a rated load.
Considering brush contact drop of 1 V, find the armature voltage for a rated load.
If rotational loss is 50 W, find the efficiency of the generator for a rated load.
Considering armature reaction of 268.5 A-t, find the effective mmf for a rated load.
For the no-load case, if the field current If,NL reduces to 92% of If,FL find the %VR.
3
6. A 10 hp, 180 V, 900 rpm, four pole, DC shunt motor has a total of 596 conductors arranged in a
wave winding, two parallel paths. The armature circuit resistance is 0.18 Ω. When the motor
delivers rated output power at rated speed, the motor draws a line current of 45 A and a field
current of 2 A. Do not consider effects of armature reaction.
a. Compute the flux per pole.
b. Compute the developed torque.
7. A 20 hp, 220 V DC motor with shunt configuration delivers rated power to a mechanical load, at
a speed of 1150 rpm. Efficiency at full load is 85%. The armature and field winding resistances
are 0.15 Ω and 110 Ω, respectively.
a. Calculate a starting resistance such that the Ia,start ≤ 2Ia (Rext,start in series with armature).
b. Calculate the starting torque with Rext,start added in the circuit.