Selectivity is an often underestimated topic in electrical engineering. Yet, selectivity is of crucial importance for the functionality of electrical systems.
In this article, you will learn what selectivity is and why it is so important in electrical engineering.
If you are interested in electrical engineering, you should definitely know about selectivity! Because only with selective components can certain devices function properly. We explain everything you need to know about selectivity.
Table of Contents
What is selectivity?
Selectivity is an important principle in electrical engineering. It describes the ability of a switch to close only the desired circuit and leave all other circuits open. This prevents unwanted current flows that could lead to shutdowns.
Some electrical systems are very complex and have many different components. In these systems, it is essential that selectivity works properly. Otherwise, issues with the system can occur.
Why selectivity is so important
Selectivity is very important in electrical engineering because it prevents faults from spreading from one area of the electrical system to other areas. Selectivity ensures that only the intended components or areas of the system are affected rather than the entire system. This prevents system damage and enables faster troubleshooting.
Types of selectivity
Partial selectivity
Selectivity is an important principle in electrical engineering. There are various types of selectivity, with partial selectivity being one of the most common. Partial selectivity refers to the ability of a switch to conduct current only when it is in the correct position. This is important because it prevents current from flowing unintentionally, which could damage equipment or even cause a fire.
Full selectivity
Full selectivity means that a device or system is capable of distinguishing between different electrical currents and conducting only the current required for the respective function. This is particularly important in power grids, for example, where multiple different currents can be present simultaneously. Selectivity ensures that only the current intended for the specific application flows.
Categories of selectivity
Time-current selectivity
Time-current selectivity is an essential part of the selectivity hierarchy in electrical engineering. But what exactly is time-current selectivity?
Time-current selectivity describes the behavior of circuit breakers during faults in electrical systems. The selectivity of circuit breakers is a key criterion for the reliability of electrical installations. Time-current selectivity describes how quickly a circuit breaker reacts to a fault and interrupts the current flow. A circuit breaker with high time-current selectivity reacts to a fault more quickly and interrupts the current flow faster. This increases the reliability of the electrical system and minimizes potential sources of error.
Current selectivity
Current selectivity is the ability to generate or conduct specific types of current. Current selectivity is a core characteristic of electrical engineering and one of the main reasons why it is so useful.
Current selectivity enables us to develop and build various types of devices that function in different ways. For example, we can design a circuit that only allows certain frequencies of the electric current to pass through. This frequency selectivity can be used to develop devices that can process only specific types of signals.
Current selectivity is also useful for operating certain types of devices. For example, we can only run a computer with the correct type of current. If we were to try running it with a different type of current, it might not function properly.
Current selectivity is also important for safety. When using electrical devices, we want to ensure they are not operated with a type of current that could harm them. For example, we should not operate electrical devices in highly humid environments, as this increases the risk of electric shock.
Time selectivity
The time selectivity feature is an evolution of current selectivity. In addition to the tripping threshold, a tripping time is defined: a specific current value triggers protection after a predefined time delay. This setting strategy makes it possible to incrementally increase the current thresholds and tripping times the closer they are located to the power supply sources (setting level in direct correlation with the hierarchical level).
The time selectivity product is an effective means to prevent power outages. The delayed tripping thresholds ensure that the tolerances of both protective devices and the effective currents flowing through them are taken into account. The difference between the delays of the series-connected protective functions must account for the fault detection and release times of the load-side device and the response time of the supply-side device. As in the case of current selectivity, the setting values are established by comparing the time-current tripping curves of the protective devices.
Energy selectivity
Energy selectivity is the ability to use the right amount of energy at the right time. Energy selectivity coordination leverages the current-limiting properties of compact circuit breakers. By using current-limiting circuit breakers, we can ensure that the current is not overloaded and energy is thus used more efficiently.
Energy selectivity is an important yet dynamic phenomenon that depends heavily on the interaction between the two series-connected devices. Therefore, the end user cannot determine the energy selectivity values themselves. Manufacturers provide tables and programs to determine the limiting current selectivity values under short-circuit conditions for various combinations of circuit breakers. These values result from the theoretical integration of results from previously conducted tests.
Zone selectivity
The zone selectivity system is an advancement of time selectivity. Zone selectivity is implemented through communication between the current measurement devices, which immediately upon exceeding the threshold allows the correct identification of the faulty area and interrupts the power supply to that faulty area. This system is particularly useful for large industrial plants where a power outage can quickly become very costly.
Zone selectivity can be implemented in two ways:
The measuring devices send information about the exceeded threshold to a monitoring system, which determines which protective functions need to intervene; the monitoring system can also be directly connected to the protective functions so that they are activated automatically.
When current values exceed their setting, each protective device sends a blocking signal via a direct connection or a bus to the hierarchically higher protective device (on the supply side relative to the direction of power flow) and verifies before intervening that no similar blocking signal has been received from the load-side protective device. Thus, only the supply-side protection is triggered immediately.
With these 10 tips, selectivity in electrical engineering is a success
1. Identify the areas to be addressed
2. Rank the areas by importance
3. Look for potential improvements
4. Implement improvements
5. Review your results
6. Ensure all areas are covered
7. Create a backup plan in case things do not go as expected
8. Be cautious with new technologies
9. Keep an eye on costs
10. Work continuously on selectivity
Conclusion
Selectivity in electrical engineering is an essential feature for the quality of electrical installations. It helps prevent major outages. Therefore, we should definitely pay attention to selectivity when choosing our electrical systems. This is the only way to ensure that our systems always function reliably.
