Developing the holistic approach - from single element testing to system validation

Authors: T. Schossig and C. Pritchard, OMICRON electronics Gmbh, Austria

Elements become Systems

The first protection systems were built with single function primary devices (Figure 1). But the complexity of the panels very early on lead to electromechanical (EM) relays aggregating multiple elements (e.g. direction and impedance).
EM relays are still in operation and survived their successor electro-static relays (Figure 2). But in the early 1980's we finally saw a technological revolution – the microprocessor-based or digital relays, which still to this day are the de-facto standard when building or refurbishing a protection system. Digital relays brought the benefits of:

  • Reducing the complexity, size and cost of the protection panel by combining the functionality of many EM relays into one digital relay
  • No setting drift caused by mechanical components
  • Adding fault reporting
  • Possibility to add communication

Since the first digital relays many evolutionary steps followed, that are important when we want to shape the future of protection testing.

From multifunctional protection relays to multipurpose devices:   What used to be a protection relay with the single purpose of protecting the power system, nowadays must fulfill multiple purposes, for example be a:

  • Phasor measurement unit (PMU)
  • Meter
  • Power Quality device
  • Automation and control unit

IED + Communication = System: Out of all technological evolution, communication and the available data has the biggest impact on PAC systems today. There is almost no transmission line today, that is not protected either by a differential protection scheme or a permissive transfer tripping scheme or both. Distribution schemes use communication for isolation and restoration.  Inside substations, the effort of applying breaker failure, reverse blocking and fast bus transfer schemes is decreasing. With IEC 61850 communication, the engineer can simply decide if he wants to engineer such schemes, without the need for wiring changes. And with the first implementations of centralized protection and wide area protection systems, we get a glimpse of what is next.

History of control systems: Control was an important topic from the beginning. Figure 4 shows an example from the 1920s. The driving mechanism stored 100 operations. After that it was operated by hand back. This included a visual check.
Multifunctional digital relays come with hundreds of functions and include control.
With IEC 61850 and Sampled Values, often combined with none conventional measurement transformers IEDs (Intelligent Electronical Devices) and even digital centralized protection, automation and control became possible. As the  readers of this magazine are well aware of this.

Developments:  So, we have the development from classical control to complex control systems as it was with protection to combined PAC. Automation functions as busbar change, interlockings, visualization of topology, load control became reality.  When in the past line communication with 150 or 300 Baud was sufficient for control operation and transmission of sum alarms more bandwidth was required. Network technology entered the substation. When IEC 60870-5-104 was the first step describing the communication via Ethernet a new concept should be developed containing data modelling, description of services and flexibility.
Communication, especially with IEC 61850 became a part of the PAC system. Realtime communication with GOOSE opens a wide range of opportunities. Position indications can be exchanged via multicast, protection as automation information distributed fast within and even outside substations. Digital substation as covered in the last issues, pushed this development dramatically.
This has an impact on testing and testing technology.

Let?s start with organization in protection testing