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The problem
Most distribution transformers in the field are checked only when a patrol team visits, which can be weeks apart. Between visits, three slow-developing faults can quietly escalate: the top-oil temperature climbs under sustained overload, oil level drops through gasket seepage or a failed breather, and the load creeps past the rated current. By the time any of these becomes visible to a patrol, the transformer may already have damaged insulation or tripped a feeder. Continuous condition monitoring is the standard utility-side answer — sensors on temperature, oil level and load, with alarms routed to staff who can act. This project demonstrates that exact loop at model scale: a small demo transformer tank instrumented with a DS18B20 temperature probe, a float-switch level sensor and an ACS712 current sensor, an Arduino reading all three channels, a 16x2 LCD showing live values, and a SIM800L GSM module sending SMS alerts when temperature, level or current cross user-set thresholds. Everything is built on accessible parts with firmware written for explanation, so the student can describe every measurement chain in the viva.
Waterproof DS18B20 probe sampling top-oil temperature about once per second at 12-bit resolution.
Follow the working sequence
How it works
- The DS18B20 probe samples the top-oil temperature about once per second (750 ms conversion at 12-bit, datasheet), the float switch reports oil level as a digital OK/LOW state, and the ACS712 channel is sampled hundreds of times per cycle to compute true RMS load current.
- The Arduino averages the temperature and current readings over a rolling window of a few seconds to reject noise, then refreshes the 16x2 LCD with temperature in °C, level state and current in amperes.
- Each averaged reading is compared against its firmware threshold: high oil temperature, low oil level, and load current above the overload mark.
- On any breach, the controller sounds the buzzer and closes the relay output for a local alarm, and the event is latched so a brief flicker cannot clear it.
- After a debounce delay, the SIM800L sends an SMS naming the fault and its measured value to the configured number; a periodic status SMS is also sent at a configurable interval, and replying "STATUS" returns the live readings on demand.
- The model transformer's secondary is loaded with resistive bulbs to demonstrate overload behavior, and all thresholds can be adjusted in firmware to suit the demonstration.
Tech stack:
- Arduino UNO (ATmega328P)
- Embedded C (Arduino IDE)
- DS18B20 digital temperature sensor (1-Wire)
- ACS712 Hall-effect current sensor module
- SIM800L GSM module (AT commands)
- Float / reed level switch
- 16x2 LCD with I2C backpack
- LM2596 buck converter (GSM supply)
| Parameter | Value |
|---|---|
| Controller | Arduino UNO, ATmega328P at 16 MHz (datasheet) |
| Temperature sensor | DS18B20: −55 to +125 °C range, ±0.5 °C (−10 to +85 °C), 12-bit / 0.0625 °C (datasheet) |
| Temperature sampling | Approximately 1 reading/s (750 ms conversion at 12-bit, datasheet); LCD refresh approximately 2 s (expected) |
| Oil-level sensing | Reed float switch, digital OK/LOW; model level column approximately 25 mm of travel (prototype dimension) |
| Current sensor | ACS712-05B: ±5 A range, 185 mV/A sensitivity, ±1.5% at 25 °C (datasheet) |
| RMS current accuracy | ±5% (design target after buyer-performed calibration; not a measured claim) |
| GSM module | SIM800L, quad-band 850/900/1800/1900 MHz; 3.4–4.4 V supply, ≈2 A peak transmit bursts (datasheet) |
| Temperature-rise reference | IEC 60076 ONAN limits — 60 K top-oil rise, 65 K winding rise — used as design reference for thresholds |
| Local outputs | 16×2 LCD (I2C); buzzer ≈85 dB at 10 cm (design target); relay with 5 A rated contact (datasheet) |
| Power supplies | Arduino: 5 V USB or 7–12 V barrel jack (datasheet); SIM800L: LM2596 buck set to ≈4.0 V, 2 A peak capable (expected) |
Project features
- [Top-oil temperature sensing] A waterproof DS18B20 digital probe is mounted on the model tank and reads temperature over −55 to +125 °C at 12-bit resolution with ±0.5 °C accuracy in the −10 to +85 °C band (datasheet values), giving the controller a trustworthy oil-temperature channel.
- [Oil-level monitoring] A reed float switch fitted in the tank's level column closes or opens at the low-level mark, so the controller detects a drop in oil level and can raise an alert before the windings are exposed.
- [Load current sensing] An ACS712-05B Hall-effect module (±5 A range, 185 mV/A per datasheet) sits in series with the model transformer's secondary, and the firmware computes RMS current from fast ADC sampling for the overload channel.
- [GSM SMS alerts] The SIM800L module sends a text message to a configured phone number whenever temperature, oil level or load current crosses its threshold, and also answers a "STATUS" text with the current readings, so monitoring reaches staff without internet.
- [Live 16x2 LCD readout] An I2C 16x2 LCD continuously shows temperature, oil-level state and load current in amperes, so the rig is fully demonstrable at a bench with no phone needed.
- [Local alarm outputs] A buzzer sounds on any threshold breach and a relay output switches an external lamp or contactor circuit, demonstrating how a protection output would behave in a real installation.
- [Configurable alert thresholds] Temperature, low-level and overload limits are set through named constants at the top of the firmware, so the student can tune them to the model or re-derive them from IEC 60076 rise limits and explain the choice in the viva.
What is included
- Working prototype: sensorized model transformer tank with DS18B20 probe, float level switch, ACS712 module, Arduino, SIM800L with antenna, 16x2 LCD, buzzer and relay
- Complete firmware source code with configurable threshold constants
- Wiring diagram and breadboard layout document
- Component list with datasheet references
- Threshold derivation note (IEC 60076 rise limits as design reference)
- Calibration guide for the current channel (buyer-performed procedure)
- Project report PDF (background, sensor theory, methodology, results)
- PPT presentation for final review
- Viva Q&A preparation document (sensors, GSM AT commands, RMS measurement, protection concepts)
Limitations & prerequisites
- The build is a model-scale demonstration rig, not utility switchyard equipment — it must never be connected to a live 11 kV or 230 V distribution network.
- SMS alerts depend on an active 2G SIM with balance; GSM coverage and the recipient network determine alert latency, typically seconds but not guaranteed.
- The float switch reports OK/LOW only, not a continuous level in millimeters.
- The ±5% RMS accuracy figure is a design target after buyer calibration — the report records the actual measured figure from the calibration procedure.
- The SIM800L must be fed 3.4–4.4 V with ≈2 A peak capability (a dedicated buck); powering it from the Arduino 5 V rail causes resets and is documented as a wiring error, not a supported mode.
- DS18B20 reads oil temperature at its mounting point; thermal gradients mean this is an approximation of true top-oil temperature.
Frequently Asked Questions
Which controller is used and can it be swapped for an ESP32?
The build uses an Arduino UNO because the project is a GSM/SMS-based monitor rather than a Wi-Fi one, and the UNO's 5 V ADC matches the ACS712 output directly. An ESP32 variant is offered as an optional customization, but it needs an external ADC or divider for the 5 V sensor and adds Wi-Fi logging scope to the project.
How do the GSM alerts work and do they cost anything?
The SIM800L holds a standard 2G SIM and sends SMS on threshold breaches, periodic status, and "STATUS" replies. SMS costs follow the SIM's plan (typically a few paise per message on Indian prepaid plans); the firmware keeps messages short and the status interval is configurable to control cost.
Can this be fitted to a real transformer at a substation?
Not as shipped — the model rig operates on a low-voltage bench transformer and the enclosure has no HT insulation or certification. The sensing and alert logic transfers directly, but a real installation needs an HT-rated instrumented design and utility approval, which is listed as future scope.
What power supply does the rig need?
The Arduino runs from a 5 V USB adapter or 7–12 V barrel supply, while the SIM800L gets its own LM2596 buck converter set to about 4.0 V with 2 A peak capability, because the GSM transmit bursts reset the module on weak supplies. The bench load bulbs draw from a separate low-voltage source.
How is the current reading calibrated?
The firmware includes named constants for the ACS712 zero-current offset and sensitivity (185 mV/A nominal). The calibration guide has the student measure a known resistive load, record the raw ADC values, and derive the corrected constants, documenting the actual achieved accuracy in the report.
Is this project suitable for a final-year project?
Yes — for Electrical Engineering (and related instrumentation programs). It demonstrates sensor interfacing, RMS measurement, embedded decision logic, GSM communication with AT commands, and protection-style alarm outputs, all tied to a genuine utility problem the student can explain end to end.
Components & software requirements
- Arduino UNO (ATmega328P)
- Embedded C (Arduino IDE)
- DS18B20 digital temperature sensor (1-Wire)
- ACS712 Hall-effect current sensor module
- SIM800L GSM module (AT commands)
- Float / reed level switch
- 16x2 LCD with I2C backpack
- LM2596 buck converter (GSM supply)
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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