Kalunta & Onu: Design and Construction of Star-Delta Starter for 50HP…
DESIGN AND CONSTRUCTION OF STAR-DELTA STARTER FOR 50HP
EXTRUSION COOKER MOTOR
1
*KALUNTA,1 F. O. and ONU,2 L. I.
Fabrication Technology Division, Federal Institute of Industrial Research, Oshodi, Lagos, Nigeria.
2
Works & Services Division, Federal Institute of Industrial Research, Oshodi, Lagos, Nigeria.
*Corresponding author: felka3@yahoo.co.uk
Abstract
A major component of an extrusion cooker (also known as extruder) is the electric motor which
produces the mechanical power needed to drive the main shaft of the extruder. When a highly
rated motor is involved; careful design is required for maximum protection of the electric motor.
This work is therefore all about the construction of a star delta starter panel required to power,
protect and control the operation of a 50hp extruder motor at the Federal Institute of Industrial
Research, Oshodi, Lagos, Nigeria (FIIRO). The circuit is in two parts namely – the power circuit and
the control circuit. The circuit is housed in a metallic enclosure and connected to the terminals of
the motor through a flexible power cable. Proper design of a motor starter for heavy duty
application such as these entails guided selection of control components, assembly and wiring
method. The materials used for the construction were purchased from the local market and
assembled together to form a unit. The design was carried out in such a way as to minimize cost
and increase the safety level.
Keywords: Starter, Star-Delta, Control and Extruder
Introduction
A squirrel cage induction motor is the
source of mechanical power which drives
the extrusion cooker. It is a device that
takes in electric power and converts it to
rotational motion that is transmitted to
the shaft via a belt or gear system. The
mechanical output power and electrical
input of the motor are related as follows
(Moeller, 1982).
P0 = 1.73VIcosфη
-------------------- (1)
P0 = Output power in Watts
V = supply voltage in Volts
I = supply current at full load in amperes
Cos ф = power factor
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η = efficiency
A magnetic motor starter is a connection
of button switches, contactors and
protection devices in a way that is capable
of opening and closing a set of contacts
that energise and de-energise the supply
circuit to a motor. Proper design of a
motor starter requires careful selection of
the control components, assembly, wiring
and testing. Control components are the
on-off devices that start and stop the flow
of electricity to the equipment that
consumes the electricity (Keith et al,
2002). The selection of these control
devices is based on the motor data.
Normal motor ratings are given on the
motor name plate.
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In a typical star delta starter one should
note that the motor phase current which
flows through the contactors is less than
the supply current which flows through
the circuit breaker by a factor of
. Since
all control components include exposed
terminals; they must be enclosed in such a
manner as to prevent accidental contact
and the external cables must be made to
enter the enclosure through cable glands
to avoid injuring the cable covering. Most
of the control components included in this
design are electrical actuators such as
manual switches, contactors, relays etc.
Relays are electrically operated switches
in which changing a current in one circuit
switches a current on or off in another
circuit (Moeller, 1982).
Materials and methods
Operating Principle of Star Delta Starter
Star delta starting is when the motor is
connected in STAR during starting
sequence and allowed to accelerate to the
normal running speed after which the
motor is connected in DELTA. The most
significant advantage of using star delta is
the huge reduction in the starting current
(by approximately 67%) resulting in cost
savings for cables and switchgears.
However, the disadvantage is in the huge
reduction in starting torque of the motor
(about a square of voltage reduction)
resulting in increased run up time may
lead to stall conditions which can damage
the motor very easily (Swardt, 2007).
A typical star delta starter comprises the
following power components:
1.
A back-up protective device, either
a fuse or circuit breaker.
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2.
3.
4.
5.
6.
Three contactors switch namely –
the main, star and delta contactors.
One thermal overload relay for
motor protection.
An on-delay timing relay meant to
switch on the delta contactor after a
pre-set time.
Manual switches.
Panel indicators.
The induction motor is of high inertia and
starts very slowly resulting in a high initial
current. This can be reduced by starting
the motor at a low voltage. The star delta
starting is a reduced voltage starting. At
the application of electrical supply, the
main and star contactors are energised
instantaneously to run the motor in star
connection. This applies a voltage of 240V
to the motor windings thereby lowering
the starting current.
Starting with reduced voltage decreases
the Full Load Current (FLC) at the motor
terminals in proportion to the voltage
reduction while the Full Load Torque (FLT)
is reduced by the square of the voltage
reduction (Motorpact, 2004). After the
motor has gained sufficient speed, the
supply current reduces further thereby
making it safe to run the motor at the
normal voltage of 415V. At this time, the
timing relay operates to change over from
star to delta contactor, while the main
contactor remains energised.
In the event of any problems such as
continuous overloading of the extruder,
loss of phase in the supply, low level fault,
the overload relay operates to cut off the
supply to prevent damage to the extruder
motor. One of the features of any system
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design is to minimise damage to
equipment and interruptions to the power
system when electrical faults or failure
occur (Robinson, 2007).
Wiring Diagram
The design of the motor starter and
control panel begins with circuit diagrams
which comprise the following:
i. Power circuit diagram
ii. Control circuit diagram
The schematic diagrams of these two
circuits are shown in fig. 1. The control
devices are represented with standard
symbols. There is a description legend to
assist the reader in understanding of the
symbols.
Design Calculations
The purpose of the design calculations is
to determine the ratings or specifications
of the various circuit components involved
in the project in compliance with
acceptable engineering standards. Choice
of components to the exclusion quality,
reliability and safety can also result in
motor and machine damage and possibly
catastrophic failure, human injury or
death (Rocky Mountain, 2011). The
engineering standards for the design of
motor controls can be obtained from
National Electrical Code (NEC or American
standard)
or,
and
International
Electrotechnical Commission (IEC or
European standard). The information
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available on the motor nameplate forms
the basis for the design of the starter
circuit. Table 1 describes the exact
information on the motor nameplate
utilised in this project and what each item
represents. With these information, one
can take the following steps to carry out
the design calculations.
Step 1: To determine the motor full load
supply amperage (FLA)
For an electric motor of 50hp (or 37kW), V
= 415V, Cos ф= 0.86, η = 0.9 (Moeller,
1982).
Full load supply current (FLA) = 66A
Full load motor winding current (FLW) =
66/1.73 = 38A
Equation (1) or the nameplate values can
also be applied to calculate the full load
supply current.
Step 2: To determine the size of branch
circuit conductor required
NEC 430-22 stipulates that,
Conductor amperage = FLA x 125%
48A for motor winding current
= 
83A for motor supply current

→25mm2 supply cable and 10mm2 motor
cables were therefore selected. All cables
used in this work are Nigerian made
copper cables.
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Figure 1: Schematic Diagram
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Table 1: Nameplate Data for the Low Cost Extrusion Cooker
V I K I N G
Exclusive
Interpretation
Nameplate Data
Manufacturer
VIKING exclusive
Phase
3 phase
JONCOD
TYPE Y 160L – 4
380V
38
38 kW
IP 44
Rated Voltage
380 V
50 HP
CONT ∆
Rated full load
38 A
50 Hz
B INS. CL
amperage
1460 r/min
No: 080511.30
Rated horsepower
50 hp
Frequency
50Hz
Rated full load speed
1460 rpm
Capacitor rating
-
Motor terminal
Delta- ∆
connection
Time rating
Continuous
Insulation class
B
Ambient temperature
130oC
rating
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→Also selected is contactor rating
between 40A to 60A, 220V as operation
coil voltage, AC3 as utilization category.
The contactors were wired with 10mm2
cable. Note that the size of the contactors
should carry the motor winding current.
Step 3: To determine the size of branch
circuit overcurrent device for back up
protection
Back up protection refers to protection
against short circuits and ground faults.
The most appropriate device is a time
delay fuse or inverse time circuit breaker.
These devices have both thermal and
instantaneous trip features that allow the
motor starting current flow for a short
time without blowing the fuse.
NEC 430-152 standard requires that the
size of:
→the inverse time circuit breaker should
not exceed 250% of motor full load supply
current.
→the time delay fuse should not exceed
175% of motor full load supply current.
This informed the choice of CB rating
between 68A – 170A. Therefore, a 100A
circuit breaker was selected for back-up
protection.
Step 4: To determine the size of motor
overload protection device
The choice of overload relay is based on
the value of full load motor winding
current which will flow through the
contactors i.e. 38A. This value must fall
between the chosen ranges.
→Thermal overload relay of rating 30A –
40A was selected.
NEC section 430-32 specifies the
maximum value of the overload relay
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rating as FLW x 115% for ambient
temperature of 40 oC and service factor of
1.0. Our selection complies with this
selection.
Step 4: To determine the rating of timing
relay
According to NEC standard, short circuit or
overcurrent protection devices should be
oversized to handle high inrush current
upon start up so as to prevent frequent
nuisance tripping. This is the determining
factor in the selection of a timing relay.
The recommended size of inrush current
is about 6 x full load = 6 x 66 = 396A
This is about 400% of the size of back up
fuse. Time delay fuses can hold 400% or
their amp rating for about 10 to 15
seconds. The motor run up time is
therefore 10 seconds, and a timing relay
of range 0 – 30s is acceptable.
Assembly and Wiring
The assembly of the various control
components in the metal enclosure to
form a unit was done. The components
were arranged according to the layout
diagram shown in fig. 2. The interior
layout shows how the contactors, relays,
protective devices and the cable tray and
connector block are arranged and fixed on
the base plate of the enclosure. The
exterior layout is the arrangement of
meters, pilot devices, push button
switches and rotary switches of the door
of the enclosure. The cabling process
involves the electrical connection of the
components together with the extruder
motor in accordance with the schematic
diagram in fig. 1. The cable sizes are
already indicated in the diagram.
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(i) Interior
(ii) Exterior
Figure 2: Layout Diagram
Figure 3: The Photographic Views of the Starter Panel Showing the Interior Cable Connections
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Figure 4: An Engineering Drawing of the Extruder Showing the Electric Motor Compartment
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The cable size for the control circuit is
1.5mm2 single core flex.
Testing and Evaluation
The following tests were carried out to
ascertain the functionality of the starter
panel that has been constructed. The
results are shown in Table 3.
Motor Tests
A preliminary test was first carried out on
the extruder motor before connecting the
motor cables.
1. Continuity Test on Motor Terminals
The continuity test was carried out with a
digital multimeter set to the ohms range
and connected to phase terminals of the
motor to determine the continuity of each
phase windings.
2.
Insulation Test between Motor
Phase Windings
This test was carried out with a 0 – 1kV
megger insulation tester set to the
MΩrange and connected between one
phase and another to determine the
insulation resistance between the motor
windings.
3.
Earth Leakage Test
Phase – to – earth insulation test was also
carried out with the megger connected
between the stator frame of the motor
and each of the motor terminals.
Interlocking Test
The mechanical interlock MI placed
between the star and delta contactors
was also tested by pressing down the
plunger of the two contactors one after
the other and also attempting to press the
two simultaneously. The former exercise
was possible but not the latter.
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Off – load Test
With the breaker F1 left in OFF position
and the panel switch SW in ON position,
the time delay relay KT was set to 10s and
the START button was operated. It was
observed that the two contactors KM and
KY switched instantly, but after a time lag
of 10s the contactor KY switched off while
KM and KD were on. The STOP button
was then operated to switch off the
contactors. This exercise was repeated
with the time delay adjusted to 15s, 20s
and 25s.
On – load Test
The breaker and panel switch left in ON
position. The time delay relay was set to
10s and overload relay set to 32A.
Operating the START button, the motor
began to rotate at lower speed. After 10s,
only the contactors KM and KD were on to
operate the motor at full speed. At this
time, the current at the supply terminal
was measured with digital clamp-meter at
the three phases. Some quantities of soya
beans were introduced into the extruder
barrel one after the other together with
drops of water for normal operation of
the extruder.
Observations
The test results as displayed in Table 3
were satisfactory. The winding insulations
were within the acceptable range.
According to the load current readings,
the extruder motor must be operating at
its maximum torque thereby reducing the
possibility of blocked barrel. Table 4
describes the characteristic design
features of this starter and their
comparison with acceptable standards.
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T able 2: Legend/Specifications
Symbol
Description
L1, L2, L3
415V, 3 ph supply
V
Panel Voltmeter to indicate supply voltage, range is 0 – 500V
F1
100A, ABB Power circuit breaker
F2
Telemecanique LR2-D3355 overload relay to protect motor against overload, single
phasing and low level faults.
F3
5A Control Isolator fuse
KM, KD
Contactors, Telemecanique (Square D), LC1-D40
KY
Contactors, Telemecanique LC1-D6511
MI
Functional type mechanical interlock: designed to prevent inadvertent closing of parallel
delta and star contactors which operate alternately.
KT
Timing Relay, range 0 – 30s, acts as changeover switch between contactors KM and KY.
C1 – C6
25mm2 cable Connector block for incomer and motor supply cables
S1
ON/OFF switch for control panel
H1, H2, H3
220V, Pilot lamps
S2
START button
S3
STOP button
M
Extruder motor, Viking Exclusive, 380V, 50hp
LK
Door Lock
CTR
40mm x 40mm Cable Trays
FR
Flat Rail
BP
Base Plate of 600mm x 400mm x 220mm indoor type sheet metal enclosure
CG
Cable Gland for 25mm2 x 4 armoured cable incomer
CG1, CG2
Cable glands for 16mm2 x 4 flexible cable as supply to motor terminals
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Table 3: Results Obtained from the Testing of the Extruder Motor and its Starter Panel
TESTS
RESULTS
1.Continuity test
Phase a-a
Phase b-b
Phase c-c
0Ω
0Ω
0Ω
Phase a-b
Phase b-c
Phase c-a
7MΩ
6.5MΩ
6-8MΩ
Phase a-earth
Phase b-earth
Phase c-earth
10MΩ
10MΩ
10MΩ
Switching
Timing
Interlock
Ok
Ok
Ok
5.On – Load Test
Phase a
Phase b
Phase c
(Line Currents)
25A
27A
26A
2.Insulation test
3.Earth leakage test
4.Off – Load Test
Table 4: Characteristic Features of the Constructed Starter Panel
Designed values
Standard
Rated Operational Voltage
415V
415V
Starting Voltage
240
0.58 x rated operational voltage
Contactor coil operating voltage
240V
120, 240, 415
Overload setting
32A
0.58 x rated current
Time delay setting
10s
15s as max starting time
Starting current
55A
6 x rated current as maximum.
No of starting stages
1
1 only
Back-up protection rating
100
Greater than the max. Starting current
and less than main supply cable rating
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Conclusion
Selecting the electric motor controls that
orchestrates the function of the motor is a
critical decision in creating efficient and
reliable operation. The star delta panel
designed and constructed in this work is
characterised by good finishing, optimal
cost, use of Telemecanique Square D
contactors for the continuous operation
of the motor, use of inverse time delay
circuit breaker for back up protection and
decent arrangement of internal cabling
using cable rack. Use of good and quality
conductors, standard electrical codes and
the need for structural safety has also
been observed in this work. The
constructed starter has been put to use on
many occasions without any problem. It is
now possible to design a star delta starter
with high level of professionalism and
local content. The design principles used
in this work can be extended to other
applications where the use of star delta
starter of this magnitude is involved. This
design can further be improved upon by
the inclusion of other forms of protection
such as Low Voltage Release and Phase
failure Relay.
Acknowledgement
We wish to express our sincere gratitude
to the Director General of FIIRO Dr./Mrs.
G. Elemo and FIIRO management for the
opportunity to publish this article. We
appreciate also, Engr. S. K. Adeyemi the
Head of Design and Fabrication Division in
FIIRO. This appraisal will be incomplete
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without mentioning the very industrious
electrician who assisted in carrying out
the cabling process, Mr. A. Adewumi of
Electrical Maintenance Unit.
References
Henk de Swardt (2007). Star Delta Starting
and Dual Voltage Motors Explained.
Article published in Vector: A
journal of South African Institute of
Electrical Technician
Engineer,
October & November 2007.
Klockner Moeller (1982), Power of Electric
Motors. Wiring Manual. pp. 11/63,
11/73.
Mobley Keith R. and Higgins Lindley R.
(2002). Maintenance Motor Control
Components.
Maintenance
Engineering
Handbook
(sixth
edition), McGraw-Hill, Section 6.49
& 6.53.
Motorpact Application Guide. (November,
2004). Publication from Schneider
Electric Industries SAS France.
Robinson E. (2007). Simple Protective
Relay Matrices. Proceedings of
International
Conference
and
Exhibition
on
Power
and
Telecommunications (ICEPT), Ikeja,
Lagos, Nigeria, 16th – 18th October
2007, Pg 102.
Rocky Mountain Supplier. (2011). Five
Reasons to Select Square D Electric
Motor Starter and Controls. NNT
Featured Publications, May 30,
2011.
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