Microcontroller-Based Overcurrent Protection Relay - Electrical Engineering Guide
1. Introduction
Overcurrent protection is essential for electrical safety. A microcontroller-based overcurrent protection relay monitors current levels and disconnects the load during overcurrent conditions.
2. Objectives
• To monitor load current in real-time
• To trip the relay when current exceeds a preset threshold
• To ensure system protection and prevent damage
3. Working Principle
The system continuously measures current through a sensor. If the current exceeds a threshold, the microcontroller sends a signal to activate the relay and disconnect the load.
4. System Overview
The system consists of a current sensor, microcontroller, relay driver, relay, and power supply. It operates autonomously to detect and react to overcurrent.
5. Hardware Components Required
• Microcontroller (e.g., Arduino Uno, ATmega328P)
• Current sensor (e.g., ACS712)
• Relay module
• Relay driver transistor (e.g., BC547)
• Diode (e.g., 1N4007 for flyback protection)
• Power supply (5V regulated)
• Resistors, capacitors, and LEDs for indication
6. Current Sensing Circuit Design
ACS712 current sensor outputs an analog voltage proportional to current. The output is fed to the microcontroller's ADC for processing.
7. Microcontroller Interface
The microcontroller samples the analog voltage from the current sensor and compares it with a set threshold to determine if an overcurrent condition exists.
8. Relay Driver Circuit
A transistor is used to drive the relay. The base is connected to a digital output pin of the microcontroller through a resistor, and a flyback diode is placed across the relay coil.
9. Overcurrent Detection Logic
If the ADC reading exceeds the threshold, the microcontroller sends a HIGH signal to the transistor base, energizing the relay and disconnecting the load.
10. Software Implementation
The microcontroller code is written in embedded C or Arduino IDE. It reads ADC values, compares them to a threshold, and controls the relay accordingly.
11. Power Supply Design
A 5V regulated power supply is used. Voltage regulators (e.g., 7805) and filtering capacitors ensure a clean power source for the circuit.
12. PCB Layout and Assembly
The circuit is designed on PCB using tools like KiCAD or EasyEDA. Proper spacing and isolation are maintained, especially around high-current paths.
13. Testing and Calibration
Test the system by varying load current and adjusting the threshold value. Use a multimeter and oscilloscope to verify current readings and relay operation.
14. Cost Estimation
Estimated cost: $15–$30 depending on components and relay type.
15. Challenges and Safety Measures
• Accurate calibration required
• Protect sensitive electronics from relay switching noise
• Include fuses and isolation for safety
16. Conclusion
This project demonstrates a simple yet effective overcurrent protection system using microcontrollers. It can be scaled and integrated into larger power management systems.