Electromechanical relays and microprocessor-based relays are two types of protective relays used in electrical systems to detect abnormal conditions such as overcurrent, overvoltage, and faults, and to initiate appropriate actions to isolate the faulty section of the system. Here are the key differences between electromechanical and microprocessor-based relays:

1. Operating Principle:

   • Electromechanical Relay: Electromechanical relays operate based on the movement of mechanical components, such as coils, armatures, and contacts. When a fault or abnormal condition is detected, the relay's electromechanical components physically move to open or close contacts, initiating a trip or control action.
   • Microprocessor-Based Relay: Microprocessor-based relays use digital electronics and software algorithms to analyze electrical signals and make protective decisions. They typically include digital signal processing (DSP) capabilities, microcontrollers, and programmable logic, allowing for sophisticated protection functions, coordination, and communication capabilities.

2. Flexibility and Programmability:

   • Electromechanical Relay: Electromechanical relays have fixed operating characteristics determined by their mechanical design and construction. They are not programmable and cannot be easily customized to adapt to different protection requirements or system configurations.
   • Microprocessor-Based Relay: Microprocessor-based relays offer greater flexibility and programmability compared to electromechanical relays. They can be programmed to perform a wide range of protection functions, including overcurrent, distance, differential, and synchrocheck protection, among others. Additionally, microprocessor-based relays can be easily configured and customized through software settings or programming to suit specific application needs.

3. Accuracy and Sensitivity:

   • Electromechanical Relay: Electromechanical relays typically have lower accuracy and sensitivity compared to microprocessor-based relays. Their response time may be slower, and they may have larger hysteresis and tolerance levels, leading to less precise protective coordination and control.
   • Microprocessor-Based Relay: Microprocessor-based relays offer higher accuracy, sensitivity, and precision in protective functions. They can accurately measure and analyze electrical signals in real-time, allowing for faster and more reliable detection of faults and abnormal conditions. Additionally, microprocessor-based relays can provide advanced features such as adaptive protection settings, event recording, and waveform capture for detailed analysis.

4. Maintenance and Diagnostics:

   • Electromechanical Relay: Electromechanical relays require periodic maintenance, including inspection, cleaning, and testing of mechanical components such as contacts and springs. Troubleshooting and diagnosing faults may be more challenging due to the limited diagnostic capabilities of electromechanical relays.
   • Microprocessor-Based Relay: Microprocessor-based relays offer advanced diagnostic features and self-testing capabilities, allowing for proactive maintenance and condition monitoring. They can perform internal diagnostics, detect internal faults, and provide detailed event records and fault records for analysis and troubleshooting.

In summary, while electromechanical relays have been widely used for many years and offer simplicity and reliability, microprocessor-based relays provide advanced functionality, flexibility, accuracy, and diagnostic capabilities required for modern electrical protection systems. The choice between the two types of relays depends on factors such as the application requirements, system complexity, performance expectations, and budget considerations.