by Alex Apostolov, Editor-in-Chief
Busbar Protection in the 21st Century
Busbar protection is probably the most critical to the stability of the electric power system due to the impact of the fault and its clearing by tripping several transmission lines and transformers connected to it.
At the same time, depending on the operating principle and the design, it may face different challenges that impact its performance under various conditions, and result in undesired operation.
The changes in many industrial and other processes, and the understanding of the impact of prolonged voltage sags on computer equipment that may shut down these processes is forcing utilities to implement busbar protection not only at the transmission level, but also at the distribution level of the electric power system. While in the past centralized busbar differential protection has been the typical, and costly, solution, now with the development of advanced communications based technologies and especially with the global acceptance of IEC 61850, we have the opportunity to achieve fast clearing of busbar faults and reduce the impact of the different factors on the behavior of the busbar protection systems without increasing the cost of the substation protection system.
We have talked many times about the need to ask different questions as a first step in the process of finding a solution to a specific problem. In the case of busbar protection we can start with:
- What are the cases that require busbar protection?
- What are the principles for protecting busbars at the transmission and distribution levels of the electric power system?
- What is the technology available today to provide adequate busbar protection?
- What are the benefits of the new technology compared to the 20th century technology?
- How do we make sure not only that the new solutions work, but that they work better than the old ones?
These questions are some of the reasons to dedicate this issue of the magazine to busbar protection in an attempt to open a discussion about the advancements in busbar protection that have already been achieved in the first decade of the 21st century. The importance of this discussion is clear by the fact that both the IEEE Power Systems Relaying Committee and CIGRE Study Committee B5 have established working groups focused on busbar protection.
The cover story of this issue summarizes CIGRE SC B5 Working Group 16 report entitled “Modern Techniques for Protecting Busbars in HV Networks”. The impact of IEC 61850 on busbar protection is one of the main technological changes in this century that is mentioned in the report. That is why it is discussed from different points of view in several other articles, making it clear that with such approach we can improve the protection solution by using different operating principles, reducing the fault clearing time and the impact of current transformers' saturation, while improving the reliability, availability and dependability of the busbar protection scheme.
The use of high-speed directional detection methods in advanced transmission line protection relays or other multifunctional IEDs, combined with peer-to-peer GOOSE messages is a perfect example of how we can significantly improve a protection system based on interoperable devices from different manufacturers.
A similar result can be achieved at the distribution level through message exchange between feeder and transformer protection IEDs, that will dramatically reduce the busbar fault clearing time compared to the backup overcurrent protection based distribution busbar protection of the last century.
But again, to take advantage of everything that the new technology provides us, we need to answer all the questions above, and most importantly, not to be afraid to do something different that will help us achieve a better busbar protection solution.
“There is no meaning to a flower unless it blooms.”
Zen proverb
I am sure we can quote many similar stories that allow us to paraphrase "If it is not broken, don't fix it!" to "If it is not broken, don't test it!"
However, in both cases we can ask the question "How do we know that it is not broken?"
In the last century the technology that we used in substations for protection, measurements and control was Dumb Electromechanical Devices (DEDs). They have a tendency to change their performance over time, which required periodical testing in order to ensure that they will operate correctly when a short circuit fault or another abnormal condition occurs. It was due to their dumbness – they could not tell us when they did not feel well. Scheduled testing of protection, measuring and control devices requires the use of specialized testing equipment, skilled personnel, plenty of time and equipment outages. Last, but not least, there is a possibility for a human error, with all the consequences it can bring.
Now we are in the twenty first century, surrounded by zillions of Intelligent Electronic Devices (IEDs) – not only in our pockets, but also in the electrical substations. We read all the time about the Smart Grid, but still keep doing things "as we always did". With the intention to raise awareness, we decided to focus in this issue of the magazine on the issues of condition monitoring and protection.
The extraordinary changes in computer technology and communications have transformed the hardwired protection and control systems of the past into communications based intelligent distributed systems that continuously monitor all primary and secondary components of the electric power system and adapt their behavior to improve the efficiency of the system.
When we talk about monitoring, in this issue, we include articles about the:
- Monitoring of transmission lines, so more power can be transferred when necessary, as well as
- Monitoring a power system to prevent the spread of a wide area disturbance
Since the clearing of a short circuit fault or any other abnormal conditions is not the result of the operation of a single device, but of the complete fault clearing system, it is obvious that we need to monitor all its components in order to detect any potential problems that may result in a failure to operate when necessary, or undesired operation under acceptable system conditions.
The advanced multifunctional protection IEDs of today have many condition monitoring functions that can help us detect potential or existing problems in different components of the fault clearing system and thus minimize the need for scheduled testing to only the elements that cannot be monitored.
This relationship between multifunctional protection IEDs and condition monitoring represents a very good example of what can be achieved through:
- Interaction and
- Common understanding of the issues that our industry faces and make the electric power grid smarter in the most efficient way
By self-monitoring their surroundings and themselves, the advanced intelligent electronic devices installed in the substation achieve the awareness required to improve their performance in the ever-changing world around them.
The capabilities are there, we just need to improve our awareness of their existence and use them.
“The world is not a problem; the problem is your unawareness.”
Bhagwan Shree Rajneesh
(1931 – 1990)
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