9/18/2021
Series Motor
Characteristic
Prepared By:
Engr. Renante D Junto REE,MTM
Technological University of the Philippines Taguig
Instructor
What is a DC Series Motor
Series DC motors are a group of self-excited
DC motors in which the field coil is connected
in series to the armature winding and thus a
higher current passes through it.
The field coils of such motors are made of
thick wires with low resistance, and few
turns to be able to carry that heavy load of
current.
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
2
9/18/2021
SERIES MOTOR CHARATERISTIC
have a relatively high starting torques
have a good accelerating torques
have low speed at high loads and dangerously
high speed at low loads.
Due to his high starting torque Series
Motor can be used in
Cranes, Air compressor, Lifts, Elevators,
Winching system, Electric traction, Hair
drier, Vacuum cleaner and in speed
regulation application
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
DC Series MOTOR
𝑉 - SUPPLY VOLTAGE
𝐸 - BACK EMF OR COUNTER emf
𝐼 - CURRENT DRAWN FROM SUPPLY VOLTAGE IN AMPERE
𝐼 - ARMATURE CURRENT
𝑅 - series field resistance
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
4
9/18/2021
Torque & Speed Characteristic of DC Motor
In a series motor the torque is directly proportional to the square of the
armature current.
In a series motor if not specified, flux is directly proportional to the
armature current.
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
Speed Regulation of DC Motor
The speed regulation of a DC Motor is defined as the change in
speed from no load to full load. It is expressed as a fraction or a
percentage of the full load speed.
𝑁 −𝑁
% 𝑆𝑝𝑒𝑒𝑑 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = 𝑥 100%
𝑁
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
6
9/18/2021
Sample Problem 1
A 100 volts series motor is used to drive a load through a pulley. This
machine has an armature resistance of 0.2 ohm and a series field
resistance of 0.25 ohms. When a torque of 25 N-m is applied to the
pulley, the speed is 600 rpm. If the stray losses at this load is 300 W,
Calculate the armature current?
Ans; I=20.62 Amp
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
8
9/18/2021
Sample Problem 2
Determine developed torque and shaft torque of 220-V, 4-pole series
motor with 800 conductors wave-connected supplying a load of 8.2 kW by
taking 45 A from the mains. The flux per pole is 25 mWb and its armature
circuit resistance is 0.6 Ω
Ans; TA = 286.2 N-m
Tshaft= 270.5 N-m
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
10
9/18/2021
Sample Problem 3
A d.c. series motor takes 40 A at 220 V and runs at 800 r.p.m. If the
armature and field resistance are 0.2 Ω and 0.1 Ω respectively and the
iron and friction losses are 0.5 kW, find the torque developed in the
armature. What will be the output power of the motor ?
Ans; TA = 99.3 N-m
Pshaft= 7.82 kW
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
11
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
12
9/18/2021
Sample Problem 4
A 230 V series motor is taking 50 A. Resistance of armature and series field
windings is 0.2 Ω and 0.1 Ω respectively. Calculate : (a) Eb (b) power wasted
in armature (c) mechanical power developed
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
13
Problem Exercises
1. A d.c. series motor operates at 800 r.p.m. with a line current of 100 A from
230-V mains. Its armature circuit resistance is 0.15 Ω and its field resistance
0.1 Ω. Find the speed at which the motor runs at a line current of 25 A,
assuming that the flux at this current is 45 per cent of the flux at 100 A.
2. The armature circuit resistance of a 18.65 kW 250-V series motor is 0.1 Ω, the
brush voltage drop is 3V, and the series field resistance is 0.05. When the motor
takes 80 A, speed is 600 r.p.m. Calculate the speed when the current is 100 A.
3. A 230 V series motor is taking 50 A. Resistance of armature and series field
windings is 0.2 Ω and 0.1 Ω respectively. Calculate : (a) Eb( (b) power wasted in
armature (c) mechanical power developed
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
14
9/18/2021
Problem Exercises
4. A 200 V series motor takes 15 amp and runs at 700 rpm. The armature
resistance including the resistance of the series winding is 0.8 ohms. At what
speed will it run if a 2 ohms resistance is connected in series with supply voltage?
Assume the motor is taking the same current?
5. A 20 HP 220 volts 540 rpm shunt motor has an armature and a field resistance
of 0.24 ohm and 157 ohms, respectively. If the starter resistance is 1.7 ohms,
what current does the motor take at instant of starting?( Assume 2 volts brush
drop)
Technological University of the
Engr. Renante D. Junto REE DC MOTOR Characteristic
Phils. Taguig
15
