Sheet 4
1- A 500V, 1800rpm, 165A separately excited DC motor has armature resistance of 0.0874Ω and total inertia
of 0.5kg.m2.if the motor is running at rated speed and delivering rated torque and required to be stopped,
determine:
a- the required braking resistor to limit the initial current to one and half the rated current, and the braking
time in case of dynamic braking, the initial braking torque and the initial dissipated power in braking
resistor.
b- the required braking resistor to limit the initial current to double the rated current and the braking time
in case of plugging braking, the initial braking torque and the initial dissipated power in the braking
resistor.
c- The initial and final supply voltage values to ensure constant braking torque at rated torque and the
braking time in case of regenerative braking, the initial braking torque, and the initial power
transferred back to the supply.
2- A 300V, 1500rpm, 150A DC separately excited motor has armature resistance of 0.1Ω and total inertia of
0.25kg.m2. If a 1.2Ω resistor is used to limit the initial braking current to the rated current in dynamic
braking, determine
a- The motor speed before braking, the braking time, and the initial braking torque.
b- The energy dissipated during braking at no load.
3- A 300V, 1500rpm, 150A DC separately excited motor has armature resistance of 0.1Ω. The motor was
operating at half-load when dynamic brake is applied using 2Ω resistor, which took the motor 0.31s to
stop. Determine
a- The motor inertia, the initial braking current, and the initial braking torque.
b- The consumed energy during braking at no load.
4- A 300V, 1500rpm, 150A DC separately excited motor has armature resistance of 0.1Ω. The motor was
operating at quarter full-load when plugging brake is applied with initial braking current at 1.5 the rated
current, which took the motor 0.14s to stop. Determine
a- The braking resistor, the motor inertia, and the initial braking torque.
b- The energy dissipated during braking at no load.
