Gulf Wind wind farm | Case study

1

CASE STUDY

Reactive power compensation in the largest solar plant in Latin America: El Romero Solar - Chile

Objective:

Acciona has built in Chile the largest solar plant in Latin America, El Romero Solar, located in the Atacama Desert. It has a maximum power of 246.6 megawatts (MWp) -196 nominal MW, which makes it one of the ten largest solar facilities in the world and the largest in Latin America to date. In spite of the capacity of the inverters to generate and absorb reactive power, in order to comply with the “NTSyCS” (Security Technical and Quality of Service Standard) or Chilean Network code, it was necessary to install 27 MVAr capacitors which were supplied in 4 capacitor banks of 6.75 MVAr each.

Scope:

For this project, Arteche North America participated in the project providing the following services and equipment:

1) Power quality measurements. 2) Power Quality Studies (Power Flows and Harmonics) to validate the proposed solution by

Acciona. 3) The design, manufacture and supply of 4 capacitor banks in 33 kV of 6.75 MVAr each. 4) SAT tests and commissioning of the reactive compensation system.

Gulf Wind wind farm | Case study

2

CASE STUDY

Company description:

Acciona is a leading group in sustainable infrastructure solutions and renewable energy projects throughout the world.

Acciona in Chile has been present for more than 20 years and in the energy area has built the 45MW Punta Palmeras Wind Farm and the 246 MWp El Romero Solar Plant. It currently has in its portfolio approximately 1000 MW in renewable energy projects to develop in that country.

Customer Requirements:

The client requests the supply of 4 6.75 MVAr capacitor banks. However, this supply must be validated with an Energy Quality Study in order to verify that the Chilean network code (NTSyCS) is complied with through that reactive power.

At the same time, it must be ensured that these capacitor banks do not cause an increase in harmonic distortion or that resonances are generated in the system.

As part of the study, energy quality measurements were also requested both before and after the reactive compensation solution was installed.

All supplies (study and equipment) had to be delivered in 20 weeks.

Use of capacitor banks prepared for conversion to filter: To obtain the delivery time, the following scheme was used.

It started with the manufacture of capacitor banks, which would be prepared to be converted into harmonic filters of the LC or HP type. The study was started simultaneously, and began at the same time as the previous energy quality measurements were made. In this way, it was possible to work on the manufacture of the capacitors and the construction of the bank without having to wait to decide whether to install the harmonic filters or if it can operate only with capacitor banks.

When the study was completed, the capacitor banks already had a large percentage of progress.

With the result of the study, it was recommended that harmonics filters be installed to absorb the harmonics generated by the inverters, and avoid the possibility of resonance.

However, the customer preferred to continue with the installation of only the banks and to test on-site if they could be operated without the necessity of the reactors in series. The design of the banks allowed this flexibility.

Application and implementation: The total reactive power of 27MVAr is delivered in 4 steps equal to 6.75 MVAr, which are input depending on the plant´s generation level.

The design of the capacitor banks is metallic in structure and their installation was made in such a way as to leave enough space to be able to intercalate the reactor in series if necessary. It should be noted that the capacitors have been selected to withstand such modification.

Each capacitor bank has its special disconnector switch for capacitive loads with pre-insertion resistors to mitigate the inrush current of the banks connection, which would increase in the back to back operation.

El Romero Solar solar farm | Case study

3

CASE STUDY

The monitoring of capacitor banks is performed by the plant management; however, each capacitor bank has a control cabinet where the necessary safety interlocks are implemented at the same time as the SF6 gas level of the disconnector switches for capacitive loads.

BENEFITS:

The capacitor banks allow the solar plant to meet the reactive power requirements imposed by the network code, thus obtaining authorisation to connect to the interconnected system and in this way to be able to inject the active power produced.

At the same time, by providing the reactive energy at the point of connection, greater efficiency is

achieved since the network inside the park only carries active power, minimizing losses.

As for this project, the capacitor banks are equipped disconnector switches for capacitive load with pre-insertion resistors, an additional benefit is achieved, which consists in minimizing the current and voltage transients produced by the switching of capacitor banks. This allows the power electronics of the inverters not to be subjected to overvoltage, maximizing operational life and decreasing the probability of faults.

Compliance with seismic requests

Because Chile is a zone of strong earthquakes, electrical equipment must justify its resistance to the mechanical demands generated by them.

The design of the equipment was accompanied by a seismic memory and finite element simulation that support compliance with NCH 2369 of 2003 and TSG 1020.

El Romero Solar solar farm | Case study

4

CASE STUDY

Studies, measurements and simulations

Arteche developed the studies of power flows and harmonics analysis and with this to assesses that the proposed solution would not present problems during the operation of capacitor banks.

The study of power flows was developed in the PSS software to different generation scenarios, so that the solar plant can operate within the limits of power factor and voltage of the applicable network code. The simulations were complemented with measurements made in the elevator transformer and in the plant inverters themselves.

The study of resonance and harmonics analysis was developed with Palladin software, and with this study it was validated that the operation of the capacitor banks does not generate resonances in the wind farm and the network code is fulfilled.

SAT Tests

Arteche also carried out on-site tests of the equipment which, in addition to the functional tests, included tests of contact resistance, capacity verification, insulation, polarity, and transformation ratio. In addition to the above, the load of SF6 gas from the disconnector switches and verification of the correct assembly of the equipment was performed.

Event #1 at 13-12-2016 16:17:51,080

Pre-trigger

Event Details/Waveforms

16:17:51,11

13-12-2016

Tuesday

16:17:51,12 16:17:51,13 16:17:51,14 16:17:51,15

-500

-250

0

250

500

Volts

A-B V B-C V C-A V

Created with DranView 6.6.3

AV BV CV A-BV B-CV C-AV AI BI CI

RM S 243.02 241.41 240.29 419.29 416.52 419.44 889.23 895.31 898.44

FND N/A N/A N/A 418.63 415.92 418.90 885.49 890.70 894.77

DC -0.73 -0.73 1.42 -0.02 -2.16 2.14 12.50 13.19 -17.69

T HD 12.84 13.27 12.13 23.20 21.89 21.01 73.60 82.69 71.09

Waveform harmonics

THD

0

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1.k

1.05k

1.1k

1.15k

1.2k

1.25k Hz

0

5

10

15

20

Volts

A-B VHarm B-C VHarm C-A VHarm

Dran-View 6.6.03 HASP : 1795003985 (6AFD9651h)

El Romero Solar solar farm | Case study

5

CASE STUDY

About the reactive power compensation system.

Power switches for overcurrent and short circuit protection on each capacitor bank (by customer)

Capacitor banks in galvanized steel structure for outdoor service

Capacitors connected in double star

Disconnector switch with pre-insertion resistors for each bank.

Capacity of capacitors to reconfigure to harmonic filters if required.

Grounding blades for each bank.

Station class lightning rod?

Current transformer for protection of neutral imbalance.

Central control panel for signals and supervision of interlocks.

Grounding interlock with kirkkey system.