Starters

Starter or known as starter motor is an electric motor that initiates the rotational of an internal-
combustion engine under its own power which commonly used on gasoline engines or small diesel
engines. Modern starter is either a permanent magnet or a series-parallel wound direct current electric
motor.

Operation: Current is applied to the solenoid by turning on the key-operated switch. The solenoid
engages a lever that pushes out the drive pinion on the starter drive shaft and meshes with the starter ring
gear on the flywheel of the engines.

Figure: Engine starter diagram

Types of starter – DOL, SD, AT, RR and etc.

Direct-On-Line (DOL) starter

DOL starter is one of the induction motor starters. Due to high startup currents were draw at the beginning;
motor starters were designed to prevent windings damage. DOL starter consist a MCCB (Molded Case Circuit
Breaker), Contactor, and an overload relay for protection [6w]. Typically, contactor will be controlled by
separate “Start” and “Stop” buttons whereby the auxiliary contact (Located across the “Start” button) as a hold
in contact. Since DOL starter has a maximum start current and start torque starting, it may cause electrical
problem with the supply or mechanical problem with the driven load. Therefore, it is normal to experience a
voltage drop during start up. But, motor with high power doesn’t affect much by these factors; motor with
0.75 ¿ 3 kW ∨¿ 5.5 kW . DOL starter power circuit can be referred to Appendix 1.

Figure: MCCB (Left), Contactor (Middle), Overload relay (Right)

D.O.L Starter parts

1. Contactors & Coil

a. It is electromagnetically operated switch for connecting and interrupting branch circuits in safe
and convenient means.
b. Electromagnet consists of wire coil around the iron bar. Magnetized iron bar attracts Armature
(Another form of iron bar) to close the circuit, due to the air gap presence.
c. Contactors mainly to control machineries that use electric motors of 230 V (Single phase) or 415
V (Three phase).
d. 3 main Normally Opened (NO) contacts for Line-voltage and an auxiliary contact, a lesser power
rated contact, either in NO or NC type.

Figure: Front view of contactor (Left), Relay (Shading cooper ring attached to iron yoke & Armature) of contactor (Middle),
Contactor info (Right)

2. Overload relay
a. Comprises with current sensing unit which connected in line of motor, served directly or
indirectly to break the circuit when full-load current exceeded which preventing burnout while
ensuring operating life of motors.
b. Since motor windings/coils are deteriorating over time, operating temperature limit has
established which by mean the current drawn limit is control by an overload relay.
c. Overload relay can be categorized into three types:
i. Thermal relay: Melting Alloys or Bimetallic; Rely on rising temperature which caused
by overload current to allow motor tripping.
ii. Magnetic relay: Uses electromagnetic mechanism to open the relay circuit if overload
current happening & not affected by temperature.
iii. Electronic relay: A high-speed trip, adjustability, and easy installation type of relay.
iv. Sizing capacity is depending on rated motor amps.
1. Minimum Thermal Overload Relay setting = 70 % × Full Load Current (Phase)
[7w].
2. Maximum Thermal Overload Relay setting = 120 % × Full Load Current (Phase)
[7w].
 Figure: Thermal overload relay (Left), Overload relay info (Right)

Star Delta (SD) starter

SD starter is one of the voltage reduction starting methods for high (Normally¿ 5.5 kW ) power motors. High
powered motor required high voltage supply, normally at the beginning which could cause disturbance to power
supply. Thus, Star-Delta motor starter was introduced to lower the initial voltage supply by connecting the Main
(KM3) to Star Υ (KM1) contactor, supplying 1/3 of motor rating current which given time (Timer), after
gaining it’s speed (Nominal speed), the Delta Δ (KM2) contactor will connecting to the Main contactor (KM3)
for full load and rated motor speed. SD starter consists of MCCB (Molded Case Circuit Breaker,¿ 1000 A), 3
contactors & auxiliary contactors, a timer, and a thermal overload relay. The parts are mostly similar to DOL
starter except for high rating and an addition of secondary contactors and a timer. SD starter power circuit can
be referred to Appendix 2.

*Important – SD starter that does not have a closed transition could damage electrically and mechanically
towards the machines and motors.

1. Closed transition required a fourth set of contactor (KM4) and a set of three resistors to redirect
the generated “coasting” rotor’s current due to star-to-delta changeover, into the resistors
instead of producing surges and spikes of current.

Figure: Main & auxiliary contactors (Left), Timer & Fuse (Middle), Overload relay (Right)

S.D Starter parts

1. 3 Contactors & Auxiliary contactors

 a. Main (KM3) and Delta (KM2) contactors have 58% of motor amp rating. Star (KM1) contactor
has 33% of motor amp rating.
2. MCCB (Molded Case Circuit Breaker)
a. Has high rating of 1000A.
3. Overload relay (Thermal Relay)
a. Melting Alloys or Bimetallic; Rely on rising temperature which caused by overload current to
allow motor tripping.
b. Sizing capacity in range of ½ of the rated motor amps. i.e 30 Amps motor needed a (13-18 A, 13
A was selected = 26 Amps) overload relay rating. 6 wires (2 set of R Y B wire) connected from
KM3, KM1 and KM2 to motor, splitting the overload amp tripping value.
c. Minimum Thermal Overload Relay setting = 70 % × Full Load Current (Phase) [7w].
d. Maximum Thermal Overload Relay setting = 120 % × Full Load Current (Phase) [7w].
e. Installed after a point of contacts wiring are split into Main and Delta, known as Overload
Relay in “winding” in line in “line”. In-winding installation measures the motor winding
current.
4. Timer

Figure: Star Delta starter circuit flow

Auto Transformer (AT Forward-Reverse with timer) starter

Auto Transformer starter is another reduced voltage starting method, other than Star-Delta motor starter. In
contrast to Star-Delta timer method of switching from low KM1 rating contactor reduced current to high KM2
& KM3 motor rated current, AT starter use transformer as starting reduced current of different Auto
Transformer taps such as 75%, 60%, and 50% supply line-to-motor current ratio. Different tapping offered
suitable starting voltage. Timers switch off K2M-to-K1M star connection to K2M-to-K3M the main line supply
voltage. At the beginning, taps are selected depending on how big or low the starting reduced voltage lines are.
When the rated motor speed reached 80%-95% or in this case after timer comes up (Star – 6 seconds & Main 4
seconds), K3M (NC, with NO auxiliary contactor) connected to K2M (NC), connecting the main line supply to
the motor, under overload relay controls. This type of starter uses in range of ¿ 30 kW rated motor, i.e use Boiler
Water Feed Pump electric motor and Empty Bunch Press motor. Auto Transformer starter power circuit refer to
Appendix 3.

Figure: Auto Transformer starter circuit (Left), AT transformer information (Right)

A.T Starter parts

1. Auto Transformer
a. Consist of primary and secondary coils, same as other transformer configurations.
b. Comprise with three different taps of 75%, 60%, and 50% supply line-to-motor rated current
ratio.
2. Timers – Two timers acting as a setup for Main contact and Star contact to be circuited.
3. Overload relay (Thermal Relay)
a. Sizing of overload relay is the same as the Star-Delta starter, which is ½ of the rated motor amps.
b. Minimum Thermal Overload Relay setting = 70 % × Full Load Current (Phase) [7w].
c. Maximum Thermal Overload Relay setting = 120 % × Full Load Current (Phase) [7w].
4. MCCB (Molded Case Circuit Breaker, ¿1000A rating) – 2000A

Figure: AT starter contactor (Left), AT transformers-taps of EB press No. 1 (Middle), AT overload relay (Right)
Rotor Resistance (RR) starter – w/ 3 step rotor resistance

Rotor Resistance starter reduces the initial current line by an addition of rotor resistance circuit in form of three
phases star connected rheostat. External resistance is added in each phases of motor winding through slip ring
and carbon brushes assembly. This type of starter limit only for slip ring induction motors as in Squirrel Cage
Motor, mainly uses for high power motor, i.e Boiler’s Induced Draft (I.D) fan. It uses steps (nth) in fluctuating
fixed current between I2min and I2max of point AB, separated by point called Stud. Controlling the rheostat is
maybe using stud or contactor. RR starter fluctuate current from I2max to I2min while moving across the resistance.
For example, Beginning at point Rx1 current is at I2max then it reduces to I2min when pass across the resistance
which later increases back to I2max at beginning of Rx2 while cutting off the Rx1. Current will pass through all the
nth resistances and reach max rated current at Rn, leaving the external resistance out. Kretam mill uses 3-steps
rotor resistance starter power circuit (Refer: Appendix 4)

External resistances Rotor resistance

Current flow

Figure: Rotor Resistance motor starter circuit diagram for single phase of 3 phase motor with rheostat.
R.R Starter parts

1. Slip ring & Carbon Brushes

a. Applicable for Slip Ring Induction motor (Squirrel Cage Motor).
2. Rheostat/Resistors
a. Rheostat is a variable resistor which used to control current without interrupting the circuit
during varies are conduct.
b. The resistance can be either using rheostat or rated resistor.
3. Contactors & Auxiliary contactors
a. Three contactors of KM1, KM2, & KM3, the same configuration as Star-Delta motor starter
setup, but instead an addition of carbon rotor resistors for Star Υ (KM2-to-KM3) connection to
reduce the initial current.
4. Overload relay (Thermal Relay)
a. Sizing of overload relay is the same as the Star-Delta starter, which is ½ of the rated motor amps.
b. Minimum Thermal Overload Relay setting = 70 % × Full Load Current (Phase) [7w].
c. Maximum Thermal Overload Relay setting = 120 % × Full Load Current (Phase) [7w].
5. MCCB (Molded Case Circuit Breaker) or Circuit Breaker
a. ¿1000A rating type of Circuit Breaker – 4000A
Figure: Rotor Resistance starter circuit vie of Induced Draft fan-Boiler (Left), RR overload relay (Middle), Resistor of Boilermech
(Right)