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The problem
On rural agricultural feeders, phase faults are daily life: a blown fuse, a snapped line or a loose joint can kill one phase while the other two keep going. A 3-phase pump motor running on two phases - single-phasing - draws heavy overcurrent in the healthy windings and can burn out in minutes while the farmer is away. Standard MCBs and fuses do not protect against this; they see only slightly elevated current and stay closed. The classical answer is a single-phase preventer: sense all three phases continuously and disconnect the motor the moment one fails or voltage drifts out of safe bounds. The next problem is the restart: after a transient fault, the farmer must walk to the panel, and hasty restarts on an unstable supply harm the motor. Auto-reclosure with a safe delay solves both - the contactor re-closes only after the supply has stayed healthy through the countdown. This project builds that protection chain as a working prototype: isolated phase sensing, threshold comparison, contactor trip and timed auto-reclosure, with a calibration procedure the student performs and documents.
R, Y, B phases plus neutral feeding the pump panel.
Follow the working sequence
How it works
- Each supply phase (R, Y, B to neutral) feeds a small 230/12 V sensing transformer, producing an isolated low-voltage AC replica of that phase.
- The three secondaries are rectified, filtered and divided to DC levels proportional to each phase voltage, feeding three ADC channels of an Arduino Nano.
- Firmware compares each reading against the potentiometer-set undervoltage and overvoltage thresholds; a reading below the design loss level on any channel is treated as a lost phase.
- On any fault, the controller de-energizes the relay driver, the contactor coil drops and the pump motor is disconnected; the FAULT LED lights and the phase LEDs show which phase failed.
- The controller watches the supply continuously; when all three phases stay within tolerance, the reclosure countdown starts (design range 30–300 s, set by the delay potentiometer) with the RECLOSING LED lit.
- If a fault reappears during the countdown, the timer aborts and restarts only after the supply is healthy again - no reclosure onto a sick supply.
- When the countdown completes, the relay driver re-energizes the contactor and the pump restarts automatically; in manual mode the system instead waits for the reset button.
- The test push-button forces a simulated phase loss, so the examiner can watch the full trip-and-reclose cycle in under a minute at a short delay setting.
Tech stack:
- Arduino Nano (ATmega328P, 10-bit ADC)
- Three 230/12 V isolation sensing transformers
- Bridge rectifier + RC filter + divider conditioning stage
- 4-channel electromechanical relay module with driver stage
- 3-pole AC-3 power contactor as trip actuator
- Potentiometers for threshold and delay adjustment
- Panel LEDs (phase, fault, reclosing) + selector switch
- Arduino IDE (C/C++ firmware)
| Parameter | Value |
|---|---|
| Supply sensed | 415 V AC, 3-phase, 50 Hz (design) |
| Sensing | Three 230/12 V isolation transformers, phase-to-neutral |
| Phase-loss detection | Any phase below ~50% of nominal (design threshold, buyer-calibrated) |
| Undervoltage cutoff | Adjustable design range ~300–380 V line, potentiometer-set |
| Overvoltage cutoff | Adjustable design range ~430–480 V line, potentiometer-set |
| Reclosure delay | Adjustable design range 30–300 s, potentiometer-set |
| Output | 3-pole contactor, AC-3 duty, 400 V class (rating selected to the pump in the build) |
| Controller | Arduino Nano (ATmega328P), firmware in C/C++ |
| Indication | 3 phase LEDs + red FAULT LED + green RECLOSING LED |
| Modes | Auto-reclosure / manual-reset, panel selector switch |
| Power | Control supply derived from sensing transformers + 12 V / 5 V regulation (design) |
Project features
- [Three-phase voltage sensing] Three 230/12 V isolation transformers sense each phase-to-neutral voltage independently, giving safe, galvanically isolated replicas of the supply phases.
- [Phase-loss detection] The controller trips the contactor when any single phase collapses below the design loss threshold, disconnecting the pump before single-phasing can overheat the motor windings.
- [Undervoltage/overvoltage cutoffs] Separate adjustable thresholds for low and high voltage; sustained undervoltage or overvoltage on any phase trips the output just like a lost phase.
- [Adjustable auto-reclosure delay] After the supply returns to tolerance, a countdown (design range 30–300 s, potentiometer-set) runs before reclosure, letting the motor cool and the supply stabilize.
- [Contactor trip output] A relay driver stage drops a 3-pole AC-3 contactor coil to disconnect the pump - the same trip-chain architecture used in real motor-control panels.
- [LED fault indication] Per-phase LEDs show which phase failed, plus a red FAULT LED and a green RECLOSING LED during the countdown, giving the examiner a readable demo.
- [Manual/auto selector] A panel switch chooses automatic reclosure or manual-reset lockout, so the student can demonstrate both protection philosophies.
- [Test push-button] Simulates a phase loss on demand, letting the trip and reclosure sequence be demonstrated repeatedly without touching the real supply.
What is included
- Working single-phase preventer prototype (sensing stage, control board, relay module, contactor, LED panel)
- Complete firmware source code (sensing, thresholds, trip logic, reclosure timer, mode select)
- Circuit and wiring documentation with transformer and divider sizing notes
- Component list with ratings and contactor selection guidance
- Threshold and delay calibration procedure (buyer-run: set and verify trip levels)
- Project report PDF (protection background, single-phasing theory, methodology, test procedure)
- PPT presentation for final review
- Viva Q&A preparation document (single-phasing, protection coordination, contactor duty classes)
- Setup and demonstration guide
Limitations & prerequisites
- An academic demonstration prototype, not utility-grade protection equipment; it must not be installed on a real farm supply without a licensed electrician's panel work.
- Trip thresholds and the reclosure delay are design settings verified by the buyer's own calibration procedure - the prototype ships uncalibrated and final values depend on the transformers and potentiometers used.
- This protects the motor against SUPPLY faults (phase loss, under/overvoltage); it does not provide motor overload or short-circuit protection - a thermal overload relay belongs in series in any real installation.
- The contactor rating must be selected for the pump motor it will switch; the prototype ships with a demonstration-class contactor and the selection procedure is in the docs.
- Auto-reclosure does not diagnose why the fault happened; on a persistent fault the timer simply keeps waiting, which protects the motor but needs the farmer to investigate.
- Correct phase-to-neutral wiring and proper earthing are required; mis-wired sensing gives misleading protection.
- The sensing stage assumes 50 Hz supply; other frequencies are outside the design.
Frequently Asked Questions
Why do pump motors burn out on single-phasing?
A 3-phase induction motor forced to run on two phases draws heavy overcurrent in the healthy windings to deliver its shaft power, overheating them; insulation fails and the motor burns. Ordinary fuses and MCBs see only mildly elevated current and do not trip - which is exactly why a dedicated preventer exists.
What does auto-reclosure add over a plain preventer?
A plain preventer disconnects the pump and waits for someone to reset it - a long walk to the panel for a transient fault. Auto-reclosure reconnects automatically, but only after the supply has stayed healthy through a safe countdown, so the motor is not switched onto a flickering supply.
How is the reclosure delay set?
A panel potentiometer sets it across the design range of 30–300 seconds; the calibration procedure shows how to verify the delay and the trip thresholds on your own build before the demo.
Can this be installed on a real farm pump?
Not as shipped. It is an academic prototype demonstrating protection principles. A real installation needs panel-grade construction, correct contactor and overload sizing, and installation by a licensed electrician.
Which controller is used?
An Arduino Nano (ATmega328P). It samples the three conditioned phase voltages on its 10-bit ADC, applies the threshold logic and reclosure timer, and drives the contactor through the relay stage.
Is this project suitable for a final-year project?
Yes - for Electrical engineering programs. It demonstrates voltage sensing, protection thresholds, contactor trip chains and timer logic, with a calibration procedure and protection theory that make strong viva material. Suitable for B.E./B.Tech final-year projects in Electrical engineering.
Components & software requirements
- Arduino Nano (ATmega328P, 10-bit ADC)
- Three 230/12 V isolation sensing transformers
- Bridge rectifier + RC filter + divider conditioning stage
- 4-channel electromechanical relay module with driver stage
- 3-pole AC-3 power contactor as trip actuator
- Potentiometers for threshold and delay adjustment
- Panel LEDs (phase, fault, reclosing) + selector switch
- Arduino IDE (C/C++ firmware)
Delivery information
Built-to-order project. Delivery timeline is shared after order confirmation based on current queue.
Support terms
Complete documentation, setup guide, and viva preparation included. Support for setup and explanation provided.
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