Wednesday, 28 September 2016
09:00 - 10:30 Making T&D networks fit for wind integration
Integrating wind power into the electricity market  
          

Distributed generation can offer clear benefits but also challenges for existing distribution systems. Wind and photovoltaic power from rural areas cause voltage fluctuations and over-voltages after disturbances. High-voltage ride through (HVRT) testing procedures, pilot projects, guideline and code drafting all help to address the HVRT requirement for distributed generation. Using smart components such as line voltage regulators and smart transformers, which include power-electronics and reactive-power compensation, are among other ways to stabilise distribution-level voltage. Applying International Electrotechnical Commission (IEC) standards, ensuring cybersecurity and deploying real-time data exchange communication between wind farms and the distribution system operator (DSO) can easily control and facilitate the integration of more wind power into distribution networks.

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Learning objectives

• Include the HVRT requirements into the grid codes;
• Propose smart components with power-electronics to mitigate distribution-level voltage fluctuations and rises in rural areas, both by real experience and using simulations;
• Enhance data exchange between wind farms and DSOs by ongoing standardisation and deployment of modernised and cyber-secure communication.

 

This session will be chaired by:

Frank Cornelius ABB AG, Germany
Co-authors:
Frank Cornelius (1) ^F Jens Tepper (1) Joel A. (2)
(1) ABB AG, Brilon, Germany (2) ABB AG, Raleigh, United States

Line voltage regulators offer an innovative approach to increasing the capacity of distribution grids to accommodate wind power

Introduction

The increasing penetration of power generated from renewable resources, especially wind and photovoltaics, is changing the structure of distribution networks. Traditional centralized systems based around only a few large power producers are changing into systems containing many small producers, which directly feed into the local distribution grid. This can result in large voltage variations, an increased risk of the voltage exceeding the prescribed voltage range, and the need to limit or even interrupt the renewable generation. Conventional solutions involve costly network upgrades – but a line voltage regulator (LVR) can solve the problem quickly and economically by automatically adjusting the voltage, within a certain range, to a desired value.

Approach

This paper outlines the potential line voltage issues that can result from incorporating wind power into distribution grids, where in rural areas in particular the load can exceed the planned load power by a factor of 2 or 3, and even up to 10 in the most severe cases. It then explains the functionality of an LVR to address this issue in distribution grids and presents the technology behind the LVR. It concludes by presenting a detailed case study of an LVR installation in rural Germany.

Main body of abstract

In contrast to large centralized power plant, many renewable energy projects feed into the local distribution grid, either at low voltage (LV) or medium voltage (MV). However, traditional distribution grids are designed to cope with the existing and expected future power flow of their consumer loads, but were not designed for significant levels of infeed, which can sometimes be higher than the load power.

While a high load on a distribution grid causes a voltage drop along the line, especially in case of long radial lines the introduction of decentralized generation causes a voltage rise on the existing distribution network. This sounds like an ideal combination, but unfortunately the load and generation do not happen concurrently in time or location. For many utilities dealing with this voltage fluctuation has become a daily challenge, especially in rural areas where the planned load factor can quickly be exceeded by a factor of 2 to 3 and up to 10 in severe cases. The voltage rise can therefore be very significant, well in excess of European standards that require the voltage at a customer site to be maintained within plus or minus 10 percent. Therefore generators can be required to stop infeed and to disconnect.

There are various established solutions to this voltage rise problem, including grid reinforcement and the use of reactive power. An LVR provides an elegant solution by using booster/feeder technology in combination with mechanical switches to automatically adjust the power line voltage to match voltage requirements under all load and generation conditions. An LVR can be installed at any place in the LV or MV network and integrated within an overall distribution management system, making the grid “smarter” and preventing power disturbances, as well as avoiding the need for costly grid extension projects.

An excellent example of an LVR application is a 10 MVA MV installation in rural Germany and this is presented in detail in this paper including operational performance, measurement data and proof of the benefits delivered.


Conclusion

Voltage rises on distribution networks are an increasingly significant issue as more renewable energy resources are connected to the grid. LVR technology is demonstrated to offer an effective, economically reliable solution that avoids the need for major investment in grid reinforcement.


Learning objectives
This paper describes why voltage rise is becoming an issue for distribution grids and how it can be addressed by deploying LVRs and details the experience gained from an installation in rural Germany.