A three-phase supply fails in ways a single-phase one cannot: one phase can disappear while the others stay live, the phases can arrive in the wrong sequence after a maintenance reconnection, and the three voltages can drift apart under unbalanced loading. Each of those damages three-phase motors in a different way. This project monitors all three phases, trips a contactor on phase failure, reversal or excessive unbalance, and for single-phase loads fed from a three-phase board it transfers the load to whichever phase is healthy, with an interlock that makes cross-connection impossible.
Not just the parts. Teams budget from a component list, then run out in week six on wire, connectors and the driver board they destroyed. These are the lines that catch them.
| Line | Cost |
|---|---|
Components and materials From the bill of materials | Rs 4,566 to Rs 11,135 |
Spares and replacements 15 % — you will destroy something | Rs 685 to Rs 1,670 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 548 to Rs 1,336 |
Perfboard and assembly | Rs 150 to Rs 400 |
Report, printing and binding Two or three bound copies, plots and the plagiarism check | Rs 400 to Rs 1,200 |
| Total | Rs 6,349 to Rs 15,741 |
| Each, split 3 ways | Rs 2,116 to Rs 5,247 |
Indicative bands last checked in August 2026 — a guide, not a quotation. Prices move and vary by seller, and anything you can borrow from the lab comes straight off the total. The 4.3 week figure assumes 10 person-weeks of work shared between 3; students past 4 add coordination rather than output, so the estimate stops improving there.
The same chain in words
Each phase is sensed to neutral and its RMS value computed the same way as in a single-phase monitor. A phase reading near zero while the others are healthy is single phasing.
Phase sequence comes from the order of the zero crossings. In a healthy 50 Hz supply the crossings are 6.67 ms apart. If the order is R then B then Y instead of R then Y then B, the sequence is reversed and any three-phase motor will run backwards.
Percentage unbalance is the largest deviation of any phase from the average, divided by that average. Above a couple of percent, motor derating becomes significant.
On any fault the three-phase contactor drops out. For the single-phase load, the controller opens the contactor on the failed phase, waits out a dead time, and only then closes the contactor on a healthy phase.
The three changeover contactors are wired with both electrical and mechanical interlocks, so no software fault can close two of them at once and short two phases together.
This is the chapter that separates an engineering project from an assembly job. Every value below carries the formula that produced it and the assumptions it rests on — check them against your own ratings before you use them, because your motor is not this motor.
unbalance % = (maximum deviation from the average) / average x 100
Average = 673 / 3 = 224.33 V. The largest deviation is 224.33 - 210 = 14.33 V. 14.33 / 224.33 = 6.39 %. NEMA MG-1 wants motors derated above one percent and does not recommend running above five.
Current unbalance is several times the voltage unbalance
The negative sequence component sees a very low impedance in an induction motor, so a small voltage asymmetry produces a large circulating current and extra heating in the rotor.
t = T / 3, with T = 1 / f
This is the number the sequence detection is built on. Measuring 13.3 ms instead means the sequence is reversed.
Break before make, longer than the contactor's release time
A contactor takes tens of milliseconds to physically release and its arc takes longer still to clear. Closing the next contactor early shorts two phases through the load path, which is a line-to-line fault.
I = P / V
2000 / 230 = 8.7 A. Three contactors are needed, one per phase, all identically rated.
| Item | Qty | Unit cost |
|---|---|---|
Microcontroller board Arduino Mega or ESP32 (needs several ADC channels) | 1 | Rs 350 to Rs 750 |
Voltage sensor modules ZMPT101B, one per phase | 3 | Rs 120 to Rs 260 |
Optocouplers PC817 with series resistors, for zero-crossing detection | 3 | Rs 12 to Rs 35 |
Changeover contactors 16 A, 230 V AC coil, with auxiliary contacts | 3 | Rs 420 to Rs 1,100 |
Mechanical interlock Interlock kit for the contactor pair | 1 | Rs 250 to Rs 700 |
Relay module 4 channel, opto-isolated | 1 | Rs 180 to Rs 400 |
MCB 16 A four pole | 1 | Rs 600 to Rs 1,500 |
LCD display 20x4 with I2C backpack | 1 | Rs 250 to Rs 500 |
SMPS power supply 5 V, 2 A, enclosed | 1 | Rs 180 to Rs 400 |
Enclosure and DIN rail Metal or ABS panel box, 300 x 400 mm | 1 | Rs 700 to Rs 1,800 |
Wiring and terminals 2.5 sq mm wire, ferrules, terminal blocks, lugs | 1 | Rs 400 to Rs 900 |
Specifications are written as ratings rather than brands, so any equivalent part works. Where a line says to borrow from the lab, do — it is usually the largest number on the page, and the total drops to Rs 6,349 at the low end without them.
None of these blocks you — they are learnable inside a semester. Each one you do not have costs a couple of weeks, so count them into your plan.
Anything marked required is a blocker, not a difficulty. Arrange the access before you commit to the project, not after.
Use these when your guide says the scope is too small, or when you want something in the results chapter that nobody else in your batch will have.
The structure below is what a project report is marked against, with the mistake that costs marks in each chapter. There is no template to download and there will not be one: the writing is your work, and a site that did it for you would be helping you cheat rather than helping you pass.
A diploma report is typically 40 to 60 pages. The design and results chapters carry the marks; the literature survey can be short. A mini project report runs to about 40 to 50 pages, and the literature survey is usually brief. Guides expect one clear objective, met and measured. A final year report is normally 60 to 90 pages with a substantial literature survey, and many departments expect a paper submission alongside it.
The full report guide — front matter, conventions and page countsOne paragraph covering what the problem is, what you built, and what the result was. Written last, even though it appears first.
Loses marks: Describing the problem and the method but never stating a result. If there is no number in your abstract, it is not finished.
Why the problem matters, the context it sits in, and a clear statement of the objectives your project set out to meet.
Loses marks: Objectives written so vaguely that nobody can tell at the end whether they were met. Write objectives you can tick off in the conclusion.
What has already been done, what each approach achieved, and the specific gap your work addresses.
Loses marks: A list of paper summaries with no comparison and no gap. The survey exists to justify your design choice, so end it by saying what you chose and why.
The system as a whole: the block diagram, what each block does, and the signal or power path between them.
Loses marks: A block diagram copied from a datasheet or another report. Draw yours to match what you actually built, including the parts that are inconvenient.
Every component value and rating, with the formula, the assumptions and the arithmetic that produced it. This is the chapter that distinguishes an engineering project from an assembly job.
Loses marks: Component values with no justification. If a resistor is 10 kOhm, the report must say why it is not 1 kOhm.
The circuit as built, the PCB or wiring, the flowchart, and the parts of the code that carry the actual logic.
Loses marks: Twenty pages of pasted source listing. Include the flowchart and the few functions that matter, and put the full listing in an appendix.
What you measured, in tables and graphs, compared against what you predicted in the design chapter — including where they disagreed.
Loses marks: Photographs of the working model presented as results. A photograph is evidence that it exists, not evidence that it works. Results are measurements.
Whether each objective was met, what the measured performance was, and what the honest next step would be.
Loses marks: Future scope written as a wish list of unrelated features. It should follow from a limitation you actually hit.
Every source in a consistent style, plus datasheets, full code listings and the complete bill of materials.
Loses marks: Citing a blog or a video where a datasheet or a standard exists. Cite the primary source for anything you relied on.
The demonstration is half the assessment. These are the questions this project invites, and the answers are written the way you would give them out loud.
Single phasing is the loss of one phase while the other two remain live, usually from a blown fuse or a broken conductor. A running three-phase motor keeps turning on the remaining two phases but now delivers the same mechanical power through two windings instead of three, so their current rises by roughly the square root of three and they overheat. Worse, the motor still runs, so nothing obvious signals the fault until the winding fails.
By the order in which the three phase voltages cross zero going positive. In a balanced 50 Hz supply those crossings are 6.67 milliseconds apart, so timing the gaps and noting which phase leads which gives the sequence. A reversed sequence means any three-phase motor connected downstream will rotate the wrong way.
An unbalanced set of voltages can be resolved into a positive sequence set and a negative sequence set. The negative sequence set produces a field rotating against the rotor, and the motor presents a very low impedance to it, close to its locked-rotor impedance. So a one or two percent voltage unbalance produces a current unbalance six to ten times larger, and that current is almost entirely heat.
Because the two contactors are fed from different phases. If both are closed at the same instant, the load path connects two phases together, which is a line-to-line short at 415 V. Break before make with a dead time longer than the contactor release and arc-clearing time is the only safe order.
Because software fails in ways that mechanics do not — a latched output, a brownout during a write, a welded relay contact. The mechanical interlock is a physical bar that makes the dangerous state impossible regardless of what the controller does. Protection design assumes the controller can be wrong.
Normally taken as a Diploma project (C-20, 6th sem) or B.E. mini project (5th/6th sem) or B.E. final year project (7th/8th sem) project. If yours is a different course, the extensions above scope it up and the simpler half of the design scopes it down — the arithmetic does not change. Back to all projects.