An inductive load draws reactive power that does no useful work but is still carried by every cable, transformer and meter upstream of it, which is why industrial tariffs penalise a low power factor. This project measures the phase angle between the supply voltage and the load current using two zero-crossing detectors, computes the reactive power the load is drawing, and switches a binary-weighted bank of capacitors through relays until the measured power factor is inside a target window. The display shows voltage, current, real power, apparent power and power factor before and after correction, which is the demonstration an examiner is looking for.
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 2,878 to Rs 6,925 |
Spares and replacements 15 % — you will destroy something | Rs 432 to Rs 1,039 |
Consumables and hardware Wire, connectors, headers, screws, heatshrink | Rs 345 to Rs 831 |
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 4,205 to Rs 10,395 |
| Each, split 3 ways | Rs 1,402 to Rs 3,465 |
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 3.9 week figure assumes 9 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
The zero-crossing detector on the voltage waveform produces a pulse each time the mains crosses zero going positive. The detector on the current waveform does the same for the load current.
The controller times the gap between the two pulses. At 50 Hz one full cycle is 20 ms and one degree is 55.6 microseconds, so a 1 ms delay is an 18 degree lag.
Power factor is the cosine of that angle. Real power is V times I times cos(phi), apparent power is V times I, and the reactive power that has to be cancelled is V times I times sin(phi).
The controller works out the smallest combination of capacitor steps that brings the power factor into the target band and energises those relays. Because the steps are binary weighted, three relays give seven distinct correction levels instead of three.
After each switching operation it waits for the transient to settle, re-measures, and corrects again if the load has changed. A deliberate dead band stops it hunting between two adjacent steps.
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.
Qc = P x (tan(phi1) - tan(phi2))
For a 3 kW load at 0.75 lagging corrected to 0.98: tan(41.41 deg) = 0.8819 and tan(11.48 deg) = 0.2030, so Qc = 3 x 0.6789 = 2.04 kVAr. Round up to a 2.25 kVAr bank.
Binary weighting: 0.25, 0.5 and 1.0 kVAr
Three relays switching equal steps give three levels. The same three relays with binary-weighted steps give every multiple of 0.25 kVAr up to 1.75 kVAr — a better result for the same switchgear, and a point worth making in the report.
C = Q / (2 x pi x f x V^2)
500 VAr at 240 V, 50 Hz: C = 500 / (314.16 x 57600) = 27.6 uF. Buy a motor-run capacitor rated 440 V AC, not 250 V AC — the rating has to cover the peak plus switching transients.
Five time constants, sized to reach 50 V in under 60 s
A disconnected capacitor holds its charge. IEC 60831 wants residual voltage down to 50 V within 60 s on LV banks. 220 kOhm across 27.6 uF is a 6.1 s time constant, comfortably inside that.
one degree = 1 / (360 x f) seconds
An Arduino timer at 16 MHz resolves 62.5 ns, so timing is not the limit — the optocoupler turn-on delay is. Measure that delay once on a CRO and subtract it as a fixed offset, or every reading sits a few degrees high.
| Item | Qty | Unit cost |
|---|---|---|
Microcontroller board Arduino Nano / ATmega328P | 1 | Rs 250 to Rs 500 |
Voltage sensor module ZMPT101B, 250 V AC input | 1 | Rs 120 to Rs 260 |
Current sensor ACS712 20 A, or CT with burden resistor | 1 | Rs 150 to Rs 380 |
Optocoupler 4N35 or PC817, for zero-crossing detection | 2 | Rs 12 to Rs 35 |
Motor-run capacitor 440 V AC, 14 uF (approx 0.25 kVAr) | 1 | Rs 180 to Rs 420 |
Motor-run capacitor 440 V AC, 27.6 uF (approx 0.5 kVAr) | 1 | Rs 250 to Rs 550 |
Motor-run capacitor 440 V AC, 55 uF (approx 1 kVAr) | 1 | Rs 380 to Rs 850 |
Relay module 4 channel, 10 A contacts, opto-isolated | 1 | Rs 180 to Rs 400 |
Discharge resistors 220 kOhm, 2 W | 3 | Rs 8 to Rs 25 |
LCD display 16x2 with I2C backpack | 1 | Rs 140 to Rs 320 |
SMPS power supply 5 V, 2 A, enclosed | 1 | Rs 180 to Rs 400 |
MCB and enclosure 6 A DP MCB, ABS box with DIN rail | 1 | Rs 350 to Rs 900 |
Inductive test load Choke ballasts and a table-fan motor | 1 | Rs 400 to Rs 1,200 |
Wiring and terminals 2.5 sq mm wire, terminal blocks, lugs, fuse holder | 1 | Rs 250 to Rs 600 |
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 4,205 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 what the system needs is a quantity of reactive power to cancel, and that depends on supply voltage and frequency as well as capacitance. The same capacitor gives a different kVAr on a 415 V system than on a 230 V one, since Q equals 2 pi f C V squared. Rating it in kVAr states the job it does; the microfarad value is only how it is manufactured.
Current starts leading voltage, the total current rises again instead of falling, and bus voltage can rise above nominal because of the capacitive charging current. Utilities penalise leading power factor for the same reason they penalise lagging. With induction motors it can also cause self-excitation on disconnection, producing dangerous overvoltages.
One detector gives the reference instant on the voltage waveform, but power factor is the phase difference between voltage and current. The second detector gives the current's zero crossing, and it is the gap between the two that converts to an angle.
With n relays, equal steps give n correction levels; binary weighting gives two to the power n, minus one. Three relays go from three levels to seven, so resolution triples with no extra switchgear. The trade-off is that the largest step carries more inrush duty than the others.
A capacitor disconnected at the peak of the waveform stays charged to that peak, several hundred volts, with no path to bleed it, and anyone touching the terminals afterwards is across that charge. Standards require residual voltage to fall to a safe level within a set time, and a permanently connected bleed resistor is how that is guaranteed.
Static compensation switches fixed capacitor steps with contactors, so it responds in hundreds of milliseconds and suits loads that change slowly. Dynamic compensation uses thyristor switching or an active converter and responds within a cycle or two, which is what rapidly fluctuating loads such as welding sets and lifts need.
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.