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Low Voltage Regulation for the integration of power generation plants into the high-voltage-grid / Description

Grid code

The grid and the operating system rules of the transmission system operator, also called grid codes or transmission codes, are considered the mandatory requirements for generating plants on the high- and extra-high voltage grid. In Germany the regulation VDE-AR-N 4120 is used. When grid codes are applied, and they are applied globally, the system stability is at the forefront of the operating strategy for all grids.

VDE-AR-N 4120

The VDE-AR-N 4120 describes the technical conditions for the connection and operation of customer systems to the high-voltage grid (technical connection conditions). The application rules apply to the mains connection such as flicker, harmonics levels or reactive power behavior.

Specifically for generating plants there are rules which provide grid services. To fulfill these requirements the manufactures are allowed to use additional devices. This must be taken into account when the certificates of the power plant are prepared.


Essential requirements for voltage stability


Quasi-steady operation (47.5 Hz to 51.5 Hz)

Generating plants must not be separated from the grid when the voltage in the range of 96 kV to 123 kV. This corresponds to an extended voltage range from UN -13% to UN +12%. Stress gradients <5% UN / min are regarded as quasi-stationary.

In the case of a 10% voltage deviation, the generating unit must not disconnect from the grid, if the generating system was previously in a steady state.

Dynamic grid services

The dynamic grid services should prevent unwanted disconnections of generation power and thus a threat to grid stability.

A generating plant shall not disconnect from the mains at:

  • 1,30 UN for 100ms
  • 1,25 UN for 20s
  • 1,15 UN for 60s
  • 0,80 UN for 60s

Many components in the generation plant are not designed for long-term over-voltages.

 

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Low-voltage-regulation-system LVRSys™

The LVRSys™ mitigates overvoltages within 15-25ms and improves static voltage stability within the generating plant. The longitudinal regulator system helps to attain the requirements and hence obtain certificates according to VDE-AR-N 4120. The system can be used in 400 V as well as in 690 V grids. Because of the compact design, it can be easily integrated into customer-control cabinets.

The system can be understood as a backpack for distribution transformers. The control takes place directly at the transformer (controllable local distribution transformer). However, the control speed through the thyristor technology is significantly faster.

Advantages:
  • Integration into customer-specific control cabinets
  • Response time <25 ms
  • Grid voltage level 400 V & 690 V
  • Version as longitudinal controller without distribution transformer
  • Version as a controllable transformer with thyristor technology

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