# Evaluation of the Operating Efficiency of a Hybrid Wind–Hydro Powerplant

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## Abstract

**:**

## 1. Introduction

## 2. Power System Description

## 3. Operating efficiency and operational strategies

#### 3.1. Operating Efficiency

_{Wind Produced}) and the maximum possible energy that can be generated in particular wind conditions (E

_{Wind∞}). The maximum possible energy corresponds to the operation of the windmills at maximum power mode; so, the pitch should be regulated to get the maximum energy at any wind speed condition and connected to an infinite power grid.

_{Wind Produced}) should be the maximum possible energy (E

_{Wind∞}). This is only possible to reach in a large power system, where the power system is able to absorb all the produced energy. In the case of a hybrid wind–hydro power plant installed in a small power system, depending on consumers demand and wind speed, the hydro power plant should store in some periods and generate in others. Therefore, the maximum possible energy cannot always be put on line. Both process, energy storage (pumping mode) and the posterior hydraulic energy generation (turbine mode), have losses. The operating efficiency is defined as the direct wind energy (E

_{Wind Grid}) put on line plus the hydro energy divided by the maximum energy that the windfarm would have produced in a large power system at maximum power mode (E

_{Wind∞}).

#### 3.2. Isolated Wind

#### 3.3. Restricted Wind Power

#### 3.4. Restricted Wind Penetration

#### 3.5. Non-Restricted Wind

## 4. Simulation Model

#### 4.1. General Power System Model

#### Power Assigning Rules

- 1)
- First, curtailments to wind power are checked and, if active, only the allowed power is considered.
- 2)
- Then, wind penetration limit is checked (percentage of system demand covered by the wind farm). According to this limit, wind power sent directly to the grid is established.
- 3)
- After these checks, if there is a surplus of wind power, pumping conditions will be evaluated and in case of missing power, turbine conditions will be evaluated.
- 3a)
- If wind power is larger than load demand, pumping conditions are evaluated:
- Is there enough water in the lower reservoir?
- Is the surplus of wind power lower than the maximum power of the installed pumps?

If there is not enough water in the lower reservoir, pumping will not be carried out and the power supplied by the wind farm will be limited. On the other hand, if the wind farm power surplus is higher than maximum power of the pumps, wind power will be limited to the sum of consumer demand plus the maximum power of the pumps. - 3b)
- If the wind power sent to the grid is not enough to cover consumers demand turbine conditions are evaluated. When the water level of the upper reservoir is not high enough, the turbines will not be activated. So, the diesel power plant will be activated to cover the demand. Additionally, if the wind power plus the turbines power were not enough to cover consumers demand, the diesel plant would also be activated to completely cover the demand.

#### 4.2. Wind Farm Model

#### 4.3. Hydropower Plant Model

#### 4.3.1. Pelton Turbines Model

#### 4.3.2. Electric Generators Model

P_{Out} | Output power. |

P_{In} | Input power. |

P_{Fix} | Synchronous machine fix losses. |

P_{Var} | Synchronous machine variable losses. |

P_{Cu1} | Stator windings losses. |

P_{Cu2} | Rotor windings losses. |

P_{Fe} | Iron core losses. |

P_{Add} | Additional losses. |

P_{fw} | Friction and windage losses. |

FdP | Power factor. |

S_{N} | Rated power. |

#### 4.3.3. Main Transformers Model

P_{Out} | Output power. |

P_{In} | Input power. |

P_{0} | No-load losses. |

P_{Sc} | Load losses. |

FdP | Power factor |

S_{N} | Rated power |

#### 4.3.4. Power Plant Model

#### 4.4. Pumping Station

#### 4.4.1. Pumps Model

#### 4.4.2. Electric Motors Model

#### 4.4.3. Main Transformer Model

#### 4.4.4. Pumping Station Model

#### 4.5. Diesel Power Plant Model

## 5. Results and Discussion

## 6. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## Appendix A

Pelton Turbines | 4 | |
---|---|---|

Rated Power | 2854 | kW |

Rated Flow | 0.5 | m^{3}/s |

Gross Head | 658 | m |

Net Head | 651 | m |

Rated speed | 1000 | rpm |

Number of jets per runner | 1 | |

Type | Horizontal | |

Efficiency | Figure 6 |

Hydro Synchronous Generators | 4 | |
---|---|---|

Rated apparent power | 3300 | kVA |

Rated Power Factor | 0.8 | |

Rated voltage (±5.0%) | 6 | kV |

Frequency | 50 | Hz |

Rated speed | 1000 | rpm |

Stator windings losses. P_{Cu1} | 23.31 | kW |

Rotor windings losses. P_{Cu2} | 10.88 | kW |

Additional losses. P_{Add} | 2.78 | kW |

Friction and windage losses. P_{fw} | 18.85 | kW |

Iron core losses. P_{Fe} | 27.35 | kW |

Hydro Generators Transformers | 4 | |
---|---|---|

Rated apparent power | 3300 | kVA |

Secondary rated voltage | 20 | kV |

Primary rated voltage | 6 | kV |

Frequency | 50 | Hz |

No-load losses | 3.5 | kW |

Load losses | 28 | kW |

Induction Motor | 2 | |
---|---|---|

Rated power | 1600 | kW |

Rated Voltage | 690 | kV |

Speed range | 0–2979 | rpm |

Frequency | 50 | Hz |

Efficiency | 96.3 | % |

Power factor | 0.88 |

Frequency Converters | 2 | |
---|---|---|

Rated power | 1750 | kW |

Rated voltage | 690 | V |

Losses at 1500 kW | <2 | % |

Losses at 500 kW | <2 | % |

Input transformer efficiency | >99 | % |

Global efficiency | ≥97 | % |

Variable Speed Pumps | 2 | |
---|---|---|

Head | 690 | m |

Rated flow | 690 | m^{3}/h |

Minimum flow | 221 | m^{3}/h |

Rated speed | 2830 | rpm |

Efficiency | Figure 8b |

Induction Motor | 6 | |
---|---|---|

Rated power | 600 | kW |

Rated Voltage | 6 | kV |

Rated speed | 2981 | rpm |

Frequency | 50 | Hz |

Efficiency at | ||

100% | 96.6 | % |

75% | 96.5 | % |

50% | 95.8 | % |

Power factor at | ||

100% | 0.92 | |

75% | 0.92 | |

50% | 0.89 |

Pumping Station Transformer | 1 | |
---|---|---|

Rated apparent power | 7200 | kVA |

Primary rated voltage | 20 | kV |

Secondary rated voltage | 6.1 | kV |

Frequency | 50 | Hz |

No-load losses | 4.6 | kW |

Load losses | 38 | kW |

Variable Speed Pumps | 2 | |
---|---|---|

Head | 690 | m |

Rated flow | 210 | m^{3}/h |

Rated speed | 2965 | rpm |

Efficiency | Figure 8a |

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**MDPI and ACS Style**

Briongos, F.; Platero, C.A.; Sánchez-Fernández, J.A.; Nicolet, C.
Evaluation of the Operating Efficiency of a Hybrid Wind–Hydro Powerplant. *Sustainability* **2020**, *12*, 668.
https://doi.org/10.3390/su12020668

**AMA Style**

Briongos F, Platero CA, Sánchez-Fernández JA, Nicolet C.
Evaluation of the Operating Efficiency of a Hybrid Wind–Hydro Powerplant. *Sustainability*. 2020; 12(2):668.
https://doi.org/10.3390/su12020668

**Chicago/Turabian Style**

Briongos, Francisco, Carlos A. Platero, José A. Sánchez-Fernández, and Christophe Nicolet.
2020. "Evaluation of the Operating Efficiency of a Hybrid Wind–Hydro Powerplant" *Sustainability* 12, no. 2: 668.
https://doi.org/10.3390/su12020668