Buildings that cannot tolerate an outage are fed from more than one source, and something has to decide which one carries the load. This project builds an automatic transfer switch that continuously validates the mains, an inverter and a generator, transfers the load in priority order when the preferred source fails, cranks the generator after a start delay if both other sources are unavailable, and runs it through a cool-down before shutting it back down. Every transfer is break-before-make and every contactor pair is interlocked both electrically and mechanically, because paralleling two unsynchronised sources is the one failure this device exists to prevent.
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 6,840 to Rs 16,900 |
Spares and replacements 15 % — you will destroy something | Rs 1,026 to Rs 2,535 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 821 to Rs 2,028 |
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 9,237 to Rs 23,063 |
| Each, split 3 ways | Rs 3,079 to Rs 7,688 |
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 4.8 week figure assumes 11 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 source is validated continuously against a voltage window and a frequency check. A source is only declared healthy once it has been inside that window for a stable period, so a source that is flickering is not treated as available.
The controller holds a priority order — mains first, then inverter, then generator. When the live source fails, it drops that contactor, waits the dead time, and closes the contactor of the highest priority healthy source.
If no source is healthy and the generator is the next option, the controller energises the fuel solenoid and cranks in short attempts with rests between them, then waits for the generator to warm up and stabilise before transferring load to it.
When a higher priority source returns and stays healthy for the retransfer delay, the load transfers back. The generator is then run off load for a cool-down period before the fuel solenoid drops.
At no point can two contactors be closed at once: the auxiliary contacts of each are wired into the coil circuits of the others, and a mechanical interlock backs that up.
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.
I = P / V for a single-phase load
5000 / 230 = 21.7 A. All three contactors are sized identically, because each one may have to carry the whole load.
Longer than the contactor release plus arc clearing time
This is the interval where the load is unpowered. It is deliberate. Making it shorter risks the two sources overlapping, which is exactly what must never happen.
Crank in bounded attempts with rests, then warm up
Cranking continuously burns out the starter motor. Three bounded attempts then a lockout with an alarm is the standard sequence, and the lockout is what stops the battery being flattened overnight.
Delays set by machine protection, not by convenience
Retransferring the instant mains returns means the load rides every failed reclose attempt on the feeder. Stopping a hot generator immediately after unloading gives it no chance to shed heat from the head, which shortens its life.
Voltage window and frequency band, both must hold
A generator that is running up passes the voltage test long before its frequency is stable. Checking frequency as well is what prevents transferring a load onto a machine that has not settled.
| Item | Qty | Unit cost |
|---|---|---|
Microcontroller board Arduino Mega or ESP32 | 1 | Rs 350 to Rs 750 |
Voltage sensor modules ZMPT101B, one per source | 3 | Rs 120 to Rs 260 |
Contactors 32 A, 2 pole, 230 V AC coil, with auxiliary contacts | 3 | Rs 650 to Rs 1,600 |
Mechanical interlock kits Matched to the contactor series | 2 | Rs 250 to Rs 700 |
Relay module 8 channel, opto-isolated, for coils and generator control | 1 | Rs 250 to Rs 550 |
MCBs 32 A double pole, one per source | 3 | Rs 280 to Rs 700 |
LCD display 20x4 with I2C backpack | 1 | Rs 250 to Rs 500 |
Indicator lamps 22 mm panel LED indicators, three colours | 4 | Rs 60 to Rs 180 |
SMPS power supply 12 V, 3 A, plus a small backup battery | 1 | Rs 400 to Rs 900 |
Panel enclosure Metal panel box, 400 x 500 mm, with DIN rail | 1 | Rs 1,200 to Rs 3,200 |
Wiring and terminals 4 sq mm load wiring, ferrules, terminal blocks, lugs | 1 | Rs 500 to Rs 1,200 |
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 9,237 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.
Because two independent AC sources are not synchronised — their phase angles are unrelated. Closing both contactors connects them together, and the instantaneous voltage difference drives a very large circulating current limited only by the impedance of the machines and the wiring. Break before make guarantees an interval where neither is connected.
Open transition breaks before making, so the load sees a short outage during the dead time. Closed transition briefly parallels the two sources, which avoids any interruption, but it is only permissible when the sources are synchronised first by a synchroniser that matches voltage, frequency and phase angle. Without synchronising equipment, only open transition is safe.
Because a generator coming up to speed reaches rated voltage well before it reaches rated speed, and an inverter in a fault mode can hold voltage at the wrong frequency. Transferring on voltage alone can put the load onto a source that is not yet stable, and motor loads in particular are sensitive to frequency.
Under load the cylinder head and turbocharger are much hotter than the coolant. Cutting fuel immediately after removing the load stops the coolant and oil circulation while that heat is still there, which cooks the oil and shortens the machine's life. A few minutes off load lets the temperature come down evenly.
A starter motor is rated for short intermittent duty and overheats if it is cranked continuously. Bounding the attempts, with rests between, protects the starter and the battery, and a lockout after the last attempt raises an alarm rather than leaving the system trying forever with a flat battery and a genuine fault unaddressed.
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.