Case study of complementary simulations of technical regulations

In the previous blog post we analysed the simulation programs currently most commonly used to carry out the complementary simulations described in the Technical Supervision Standard (NTS). These simulations make it possible to certify the compliance of a generation plant with the technical requirements of the grid connection code in Spain.

In this post we analyse, by means of a case study, each of the complementary simulations that a generation plant must carry out to certify compliance with the grid code.

Description of the power plant under study

A 40 MW wind farm connected to the transmission grid at a voltage level of 220 kV has been chosen as the study plant. The Grid Connection Point (RCP) is shared with other installations, so the requirements will be assessed at the Central Busbars (CB), instead of at the RCP, according to the indications of the NTS for the case of shared installations.

Technical requirements applicable to the generating plant

The wind farm under study is a type D plant, according to the significance defined in the NTS, as it is connected at a voltage level (220 kV) higher than 110 kV. Consequently, all the technical requirements described in the NTS will apply to it, as it is the most demanding type of plant (with the exception of the exclusive requirements for synchronous generation). Among the different applicable requirements, compliance with the following can be certified by carrying out the complementary simulations described in the NTS.

• 5.1. Over-frequency limited power-frequency regulation mode (MRPFL-O)
• 5.2. Underfrequency limited power-frequency regulation mode (MRPFL-U)
• 5.3. Mode of power-frequency regulation (MRPF)
• 5.7. Reactive power capability
• 5.8. Reactive power control

For each of these five technical requirements, we analyse the complementary simulations below.

Over-frequency limited power-frequency regulation mode (MRPFL-O)

This simulation allows the dynamic response of the wind farm to significant increases in the grid frequency to be evaluated. To do this, a frequency sweep is carried out from 50 Hz to 51.4 Hz, as shown in the following figure, and it is checked that the power reductions of the wind farm and the stabilisation time comply with the ranges indicated in the standard.

Underfrequency limited power-frequency regulation mode (MRPFL-U)

This simulation makes it possible to evaluate the dynamic response of the wind farm to significant drops in the grid frequency. To do this, a frequency sweep is carried out from 50 Hz to 48.4 Hz, as shown in the following figure, and it is checked that the power increases of the wind farm and the stabilisation time comply with the ranges indicated in the standard.

For both MRPFL-O and MRPFL-U modes, the results of the simulations show that the power values required by the standard are reached, but in a slightly longer time than required. We would therefore recommend adjusting the necessary parameters of the plant controller to speed up the response of the power-frequency control module, subject to the approval of the controller manufacturer.

Mode of power-frequency regulation (MRPF)

This simulation makes it possible to evaluate the dynamic response of the wind farm to slight variations in the grid frequency. To do this, a frequency sweep is carried out between 49.7 Hz and 50.3 Hz and it is checked that the power variations of the wind farm and the stabilisation time comply with the ranges indicated in the standard.

The following figure shows the simulation results for the overfrequency case, which comply with the requirements of the standard, both in terms of power variation and stabilisation time.

Reactive power capability requirement

This static simulation makes it possible to evaluate the generation and reactive power absorption capacity of the wind farm both at its maximum power (Fig 4 left) and at power levels below the maximum (Fig 4 right).

In Fig 4 we can see the compliance with the requirement as the capacity curve of the wind farm (dashed line) is outside the curve required in the NTS. If you are interested in knowing more about this simulation you can read about it in a previous post on the Norvento blog.

Reactive power control requirement

The reactive power control simulations make it possible to evaluate the dynamic reactive power response of the wind farm to variations in the reactive power setpoint, the power factor setpoint or the wind farm input voltage. To do this, it is necessary to simulate the three reactive power control modes separately:

• Reactive power control mode
• Power factor control mode
• Voltage control mode

The following figure shows the results obtained in the simulation of the reactive power control mode, where it can be seen how the wind farm reaches the required reactive power setpoints in times lower than those required by the standard.

What documentation do I have to submit to certify compliance with the technical requirements?

In order to certify compliance with the technical requirements mentioned above, the reports of the complementary simulations, in addition to the certificates of the plant equipment, must be submitted to an authorised certifier. Once compliance with all applicable requirements has been verified, the authorised certifier will issue the final plant certificate, which certifies compliance with the grid codes.

Desde Norvento ayudamos a nuestros clientes a certificar el cumplimiento de los códigos de red, requisito indispensable para la entrada en operación comercial de una planta de generación.