Question

Two dc machines of the following rating are required:

DC Machine 1: 120 V, 1500 rpm, four poles
DC machine 2: 240 V, 1500 rpm, four poles
Coils are available that are rated at 4 volts and 5 amperes. For the same number of coils to be used for both machines, find the following:
a) Type of armature for each machine
b) Number of coils required for each machine
c) kW rating of each machine
A. a) Lap (120 V), wave (120V) b) 120 v, 120 V c) 2.4 kW
B. a) Lap (120V), wave (240 V) b) 120 V, 240 V c) 2.7 kW
C. a) Lap (460 V), wave (120V) b) 460 V, 120 V c) 2.4 kW
D. a) Lap (208V), wave (120V) b) 208 V, 120 V c) 5.4 kW

Answer 1

To determine the type of armature, number of coils, and kW rating for two DC machines with different voltage and speed ratings, we can calculate the requirements for each machine separately. For the given specifications, the answers are: a) Wave type for Machine 1 and Lap type for Machine 2, b) 30 coils for Machine 1 and 60 coils for Machine 2, and c) 18 kW for Machine 1 and 72 kW for Machine 2.

Step-by-step explanation:

For both machines, in order to have the same number of coils, we need to choose a type of armature that can accommodate the available coils and the required voltage. The type of armature chosen will determine the voltage rating of each machine. We can calculate the number of coils required for each machine by dividing the total voltage rating of each machine by the voltage rating of each coil. Finally, the kW rating of each machine can be calculated by multiplying the voltage rating, current rating, and number of coils of each machine.

a) For DC Machine 1 (120 V), the type of armature that can accommodate the available coils (4 volts and 5 amperes) is the wave type. For DC Machine 2 (240 V), the type of armature that can accommodate the available coils is the lap type.

b) The number of coils required for each machine can be calculated by dividing the total voltage rating of each machine by the voltage rating of each coil. For DC Machine 1, the number of coils required is 120 V / 4 V = 30 coils. For DC Machine 2, the number of coils required is 240 V / 4 V = 60 coils.

c) The kW rating of each machine can be calculated by multiplying the voltage rating, current rating, and number of coils of each machine. For DC Machine 1, the kW rating is 120 V * 5 A * 30 coils = 18,000 W = 18 kW. For DC Machine 2, the kW rating is 240 V * 5 A * 60 coils = 72,000 W = 72 kW.