Grid And System Protection NA003-M64 from TELE Meets Belgian Standard C10-11

With more and more renewable energy feeders the grid is becoming more unstable and the standards for components are constantly changing. The new C10-11 standard of the energy supplier Belgium as well as the European standard EN50549 require zero voltage detection and activation of a narrower frequency window in the event of a fault. This is intended to detect faults and short circuits in the higher-level medium-voltage network so that the network can be stabilized in good time. In order for devices for safe network separation to be able to do this, they must be able to calculate the so-called zero voltage or zero sequence. The NA003-M64 from TELE Haase now has this function integrated and is thus fit for international use.

What exactly is this zero voltage?

In systems for generating renewable energy, such as photovoltaic or small wind turbines, 230 volts are usually applied to each phase in 3-phase networks and the phase angle of each phase is 120 degrees. In this ideal grid condition, the zero sequence is 0 volts. However, if a fault occurs, such as a short circuit in the higher-level supply network, one or more phase voltages and the associated phase angles change, resulting in a zero offset (= Zero Voltage or Zero Sequence).

The Belgian C10-11 as well as the European standard EN50549 require that the grid and system protection must disconnect the generation grid from the main grid if the Zero Voltage becomes greater than 20 percent of the nominal voltage.

Mathematics and programming as a challenge

The TELE developer team developed a completely new algorithm for this task, which calculates the Zero Sequence from the shift of the three measured phase voltages and the three phase angles. On the one hand, the challenge was the mathematical implementation of the trigonometric functions; on the other hand, the algorithm had to be designed in such a slim way that it could fit on the existing limited memory space of the controller in the NA003-M64.

Two software engineers and an integration tester designed the architecture of the new calculation method, converted it to C code, and integrated it into the NA003-M64’s existing software. The project took nine months and was completed internally. Afterward, the certification process with a German testing institute was started and successfully completed. TELE’s grid and system protection now provides a total of 46 parameter sets for thirteen different countries.

Advantages of the solution

By integrating the calculation of the Zero Voltage into the existing software of the TELE grid and system protection, it is possible to set at which shift in the 3-phase network a network disconnection between the power generator and the main network should occur. With a further (much lower) threshold value for the Zero Voltage, activation of a narrower frequency window 49.7Hz to 50.3Hz (normally 47.5Hz to 51.5Hz) can take place with an already very small shift in the 3-phase network. This means that the Zero Voltage also has an indirect influence on other measured variables, in this case, frequency detection.

Zero Voltage calculation is universally applicable

The calculation model developed in-house for zero voltage can be used universally. For example, the changeover to the new model is also being prepared for the development of the new TELE Performance Sensor eCap.