Final Project Proposal · 2026D4 Electrical Engineering Politeknik Caltex Riau

Design & Build of a Star-Delta Starting and Dynamic Braking System for a 3-Phase Induction Motor Using a PLC

A PLC-based motor control system that softens the starting current with star-delta switching, then stops the motor quickly and safely by injecting DC into the stator, all sequenced automatically with timers and interlocks.

Muhamad Hasan Ramdani · Student ID 2320305028

See how it works Schedule & budget

5–7×Direct-on-line starting current vs. rated current

1/√3Winding voltage in star, which cuts starting current and torque

28 s → 0.85 sStop time, coasting vs. DC braking in the cited reference study

Rp 6.085MEstimated total build cost, 18 line items

Background

Two weaknesses of the induction motor

Three-phase induction motors are rugged, simple and cheap to maintain, but they are hard on the grid when starting and slow to stop. Both problems are addressed here in one PLC-controlled system.

Starting

At start-up the motor can draw 5–7× its rated current. This can cause voltage dips, heat the winding insulation and shorten motor life when repeated. Star-delta starting begins in star (reduced voltage) and switches to delta once the motor is up to speed.

Stopping

Coasting relies only on friction and inertia, so stopping takes long and is uncontrolled. Injecting DC current into the stator creates a stationary magnetic field that opposes rotor rotation and converts kinetic energy into heat.

The gap

Star-delta and dynamic braking are each common in industry, but combining both under a single PLC control system is still rarely covered in educational settings.

Problem statement

How long does the motor take to stop under braking?
Which key indicators confirm a safe star-to-delta transition?
How can star-delta and dynamic braking logic be implemented in a PLC program that runs automatically and in sequence?
How can starting current, transition time and braking time be measured and analysed?

Scope limits

Star-delta starting and dynamic braking with a PLC as the central controller only
Three-phase induction motors only (no single-phase or DC motors)
DC injected into the stator through a diode rectifier circuit
Performance tests run under no-load conditions

Objectives

Explain how star-delta starting and dynamic braking work in a 3-phase induction motor
Apply a PLC as the main controller for starting, transition to delta and braking, automatically and safely

Expected benefits

More stable operation: starting and stopping run in the right order without overstressing the motor
Fewer operational faults and longer motor life through more regular, precise, easily monitored control

Operating sequence

Step through the control logic

Select a stage to see which contactors the PLC energises. KM1 = main, KM2 = star, KM3 = delta, KM4 = dynamic braking.

3-phase AC supply→MCB / MCCB→Main contactor→Star / Delta contactors→Motor

24 V DC power supply→PB Start · PB Stop · E-Stop→PLC logic / timers→Braking contactor→Rectifier→Stator (DC)

**Fig 2.1 · Three-phase induction motor**The load under control: rugged and low-maintenance, but it draws 5–7× rated current at start-up.

**Fig 2.2 · Star-delta winding connections**In star each winding sees 1/√3 of line voltage; in delta it sees full line voltage.

**Fig 2.3 · Dynamic braking principle**A diode bridge injects DC into the stator, producing a static field that opposes rotor motion.

Design

Power, control and hardware

Power circuit

Three-phase supply passes through a 3-phase MCB and MCCB to the main contactor (MC MAIN). Star (MC STAR) and delta (MC DELTA) contactors reconfigure the motor windings. A thermal overload relay sits in series with the motor, and an ammeter with a selector switch monitors the R, S and T phase currents.

Control circuit

A Schneider TM221C16R PLC, powered from a 24 V DC supply, reads the Start, Stop and Emergency Stop inputs and drives four contactor coils. Timer T1 sets the star-to-delta changeover, timer T2 sets the braking duration, and interlocks prevent contactors from overlapping.

Braking circuit

When the braking contactor closes, AC is fed to a diode bridge rectifier. The resulting DC flows into two stator terminals, creating a static magnetic field that produces braking torque. After T2 expires the contactor opens so DC does not keep heating the winding.

Mechanical layout

The inside panel has three DIN-rail tiers: MCB and PLC, four contactors with the overload relay, and MCCB with the power supply. Terminal blocks sit at the bottom. The front door carries R/S/T indicator lamps, the ammeter, ON/OFF lamps, an emergency stop and PB ON / PB OFF buttons.

**Fig 3.1 · System block diagram**AC supply, 24 V control supply, PB Start/Stop/E-Stop, PLC logic/timer, star-delta and braking contactors, rectifier and motor.

System flowchart — **Flowchart · Fig 3.2**Initialisation to motor stop.

Flowchart walk-through

Initialise: all outputs OFF, wait for Start
Start → KM1 main + KM2 star; timer T1 runs
T1 done → KM2 off, KM3 delta on; motor runs
Stop → KM3 and KM1 off; safety delay
KM4 braking + KM2 on; DC injected via diodes; timer T2 runs
T2 done → KM4 off; motor stopped; end

Power and control wiring diagram — **Wiring diagram · Fig 3.3**Power and control circuit. Tap to open full size and scroll.MCB 3-phaseMCB 1-phaseAmmeter + selector (R/S/T)TM221C16R PLC24 V DC supplyMC MAINMC STARMC DELTAMC braking + diode bridgeOLR overload relayInduction motor U1 V1 W1 / W2 V2 U2

**Fig 3.4 · Panel mechanical layout**Left: inside the panel (MCB and PLC; four contactors and overload relay; MCCB and power supply; terminal blocks). Right: front door with R/S/T lamps, ammeter, ON/OFF lamps, emergency stop, PB ON/OFF.

Components

What the system is built from

PLC

Industrial computer with CPU, memory, I/O modules, power supply and programming device. It runs the ladder logic that sequences the contactors. Chosen model: Schneider Modicon M221 TM221C16R (16 I/O, relay output).

Diode rectifier

Stud diodes (full-wave bridge) convert AC to DC for braking. Selected on forward current, peak inverse voltage and heat dissipation, with a heatsink where needed.

Protection

MCB (overcurrent and short circuit), MCCB, and a thermal overload relay whose bimetal element trips the contactor via its NC auxiliary contact.

Contactors

Four Mitsubishi SN-11 (220 V coil) contactors: main, star, delta and braking. Coil, main contacts and auxiliary contacts (NO latching, NC for indication).

Operator interface

NO green Start button, NC red Stop button, a locking emergency stop mushroom button, and pilot lamps for status and fault indication.

Component gallery

Parts used in the system

Figures from the proposal. Tap any image to enlarge.

**Fig 2.4 · Programmable Logic Controller**Schneider Modicon M221 TM221C16R: runs the ladder logic, timers T1/T2 and interlocks.

**Fig 2.5 · Stud power diode**Bridge rectifier element that converts AC to DC for braking; chosen by forward current and PIV.

**Fig 2.6 · 3-phase Miniature Circuit Breaker**Protects the supply against overcurrent and short circuits on all three phases.

**Fig 2.7 · Push buttons**Green NO for START, red NC for STOP; momentary action needs a latching rung in the ladder.

**Fig 2.8 · Magnetic contactor**Coil A1/A2, main contacts, plus NO (13-14) and NC (21-22) auxiliary contacts for latching and indication.

**Fig 2.9 · Thermal overload relay**Bimetal protection against overload; its NC contact drops the contactors when it trips.

**Fig 2.10 · Pilot lamps**Indicate supply present, running state and faults on the panel front.

Literature review

Prior research

Researchers	Study	Key finding
Kusuma et al., 2022	Design PLC on Induction Motors Using Star-Delta With Manual and Automatic Technique	Automatic PLC control gives better stability against inrush current than manual control and reduces human error in the star-to-delta change.
Hartawan & Galina, 2022	Omron CP1E PLC in an Industrial Star-Delta Motor Control System	PLC replaced conventional control with higher protection via a manual motor starter, and logic is easier to modify.
Hidayatullah & Binoto, 2022	Dynamic Braking Circuit Using Time Delay Relay	DC injection cut stopping time from 28 s (coasting) to 0.85 s.
Alfariki et al., 2024	Star-Delta Starting With HMI-Based PLC vs. Starting Current	PLC + HMI enables real-time current monitoring, remote control up to 20 m and suppresses current overshoot during transition (7.5 kW motor).

Method & testing

How the system will be validated

Methodology: literature study → design (components, PLC ladder diagram, wiring, budget) → testing → analysis of results with recommendations.

1 · Design realisation

Verify the built panel matches the mechanical, power and control design and PLC logic.

2 · Functional test

Check the start sequence from standstill, timed star-to-delta change and braking activation; each PLC output must energise the correct contactor.

3 · Star-delta starting

Measure starting current in star and after changeover to delta, confirming no excessive current spike or mechanical disturbance.

4 · Dynamic braking

Measure stopping time, braking stability and braking contactor response.

5 · PLC timing

Confirm programmed delays (T1 and T2) match design and cause no contactor overlap.

6 · Reliability & safety

Confirm safe, stable operation over a period of time, including emergency stop behaviour.

Schedule & budget

Timeline and cost estimate

Planned phases shown: guidance and proposal writing from Nov 2025, proposal defence in Jan 2026. Later phases (build, testing, report, final defence) run through 2026.

#	Item	Qty	Unit price	Total
Total estimate				Rp 6,085,000

References

Selected sources

Kusuma et al. (2022). Design PLC on Induction Motors Using Star-Delta With Manual and Automatic Technique.
Hartawan, F. Y. & Galina, M. (2022). Implementation of PLC Omron CP1E in a Star-Delta Induction Motor Control System for Industrial Needs.
Hidayatullah, A. et al. (2022). Planning of a Dynamic Braking Circuit for a 3-Phase, One-Direction AC Induction Motor Using Time Delay.
Alfariki, M. Z., Mubarok, R. & Murdiantoro, R. A. (2024). Analysis of Star-Delta Starting With HMI-Based PLC on Starting Current.
Sartika, L. et al. (2025). Comparative analysis of 3-phase induction motor starting current. Jurnal Eltek, 23(2), 46–52.
Nofiansyah et al. (2022). Operation 3 Phase Induction Motor 1 Kw Star Delta System Using Smart Phone. IJRVOCAS, 2(3), 56–60.
Kurniawan, H. (2023). Journal control system, 5–9.
Jamaaluddin, J. et al. (2021). Analysis of Overcurrent Safety in Miniature Circuit Breaker. J. Electrical Technology UMY, 5(2), 68–73.
Puspita, T. (2023). Thermal Overload Relay (TOR) as a Motor Protection System.