How can you choose the best protection relay for your energy engineering project?

1 Understand the fault types

The first step is to understand the different types of faults that can occur in power systems, such as short circuits, overloads, ground faults, and arc faults. Each fault type has a different impact on the voltage, current, frequency, and impedance of the power system, and requires a different protection strategy. For example, short circuits can cause high currents and low voltages, and need fast and selective protection to isolate the faulted section. Overloads can cause thermal damage and need time-delayed and coordinated protection to avoid unnecessary tripping. Ground faults can cause unbalanced currents and need sensitive and directional protection to detect the fault location. Arc faults can cause fire hazards and need arc flash protection to reduce the arc energy.

2 Choose the relay technology

The second step is to choose the appropriate relay technology for your project, such as electromechanical, solid-state, or microprocessor-based relays. Each technology has its own advantages and disadvantages, depending on the application, complexity, and cost. For example, electromechanical relays are simple, robust, and inexpensive, but have limited functionality, accuracy, and speed. Solid-state relays are more reliable, flexible, and fast, but have higher power consumption, sensitivity to temperature, and maintenance requirements. Microprocessor-based relays are the most advanced, versatile, and intelligent, but have higher initial cost, software dependency, and cyber security risks.

3 Select the relay functions

The third step is to select the specific relay functions that match the fault types and the power system characteristics. Relay functions are codes that indicate the type and mode of protection that the relay provides, such as overcurrent, distance, differential, frequency, voltage, etc. For example, a 51 function means an overcurrent protection with a time delay, a 21 function means a distance protection that measures the impedance of the line, and a 87 function means a differential protection that compares the currents at both ends of the protected element. You can combine multiple relay functions to achieve comprehensive and reliable protection for your project.

4 Consider the relay settings

The fourth step is to consider the relay settings that determine the operating parameters and characteristics of the relay, such as the pickup value, the time characteristic, the reset value, etc. Relay settings are crucial for ensuring the sensitivity, selectivity, and stability of the protection system. You need to calculate and adjust the relay settings based on the power system data, such as the fault current levels, the impedance values, the coordination intervals, etc. You also need to test and verify the relay settings using simulation tools or field experiments.

5 Compare the relay options

The final step is to compare the different relay options that meet your project requirements, based on the criteria such as the cost, the performance, the availability, the compatibility, the support, etc. You can use a decision matrix or a scoring system to rank the relay options and select the best one for your project. You should also consider the feedback and recommendations from other energy engineers who have used the relay options in similar projects or applications.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?