# Iberdrola Hydroelectric Plant

A developed section of a representative Iberdrola underground hydroelectric plant on the Duero: reservoir, intake, penstock, Francis units, draft tube, tailrace and step\-up\.

By Alejandro Marco

Topic: Energy

[Open the interactive Jig](https://ask.jig.com/j/ASLlDQiLjceo)

## Guide

### 1. Aldeadávila\-type underground plant

Developed section of a representative Iberdrola conventional plant on the Duero, modelled on Aldeadávila I: arch\-gravity dam, bank intake, inclined penstocks, an underground hall of vertical Francis units, draft tubes and tailrace to the river\. Three of the six main units are drawn\. Drag the background to turn the section\.

Aldeadávila I \(1962–63\): 6 Francis units of 119–140 MW, net head about 140 m; complex total about 1,139–1,242 MW and 2,400 GWh/yr depending on source \(Wikipedia, Andritz, Iberdrola\)\.

### 2. Reservoir and arch\-gravity dam

The reservoir stores potential energy as head times volume\. The concrete arch\-gravity dam bows upstream and carries its load partly into the abutments, partly by weight\. The gated chutes on its downstream face are the flood spillway, not the generating path\.

Aldeadávila: 140 m high, 250 m crest; 114\.8 hm³ gross, 56\.6 hm³ live storage; spillway capacity 11,700 m³/s \(Wikipedia\)\.

### 3. Intake: trash rack and gate

Each bay draws water through a trash rack into a gated opening at the head of its penstock\. The wheel gate in the slot isolates the waterway for dewatering or emergency closure\. Close it and that unit loses its flow and coasts down\.

The gate and rack geometry are representative; Iberdrola does not publish the Aldeadávila intake drawings\.

### 4. Penstock

A pressurised steel conduit, ring\-stiffened and seated on concrete saddles, drops the water to the hall and converts elevation into pressure\. A spherical inlet valve at the foot isolates the spiral case\. The orange pulses trace the flow of each unit\.

Static pressure at the foot is ρgH ≈ 1000 × 9\.81 × 140 ≈ 1\.37 MPa \(calculated, net head\)\. For scale, La Muela II’s penstock is 840 m long and 5\.45 m in diameter\.

### 5. Spiral case and wicket gates

The front generator is lifted to expose the distributor\. The spiral case narrows around the stay ring to keep the inflow uniform, and sixteen wicket gates set the swirl and the discharge reaching the runner\. Opening them raises flow and power; on the grid the speed stays synchronous\.

The governor positions the wicket gates through servomotors and a regulating ring; flow rates are not published for Aldeadávila\.

### 6. Francis runner and generator

The runner turns hydraulic energy into torque on a single vertical shaft with the generator rotor; there is no gearbox\. Tap a generator to take that unit off line or return it to service\.

Aldeadávila: runner Ø 4\.1 m, 187\.5 rpm; 32\-pole generators, 13\.8 kV, 142\.5 MVA\. 187\.5 rpm × 32 / 120 = 50 Hz\. Rotation is slowed here for legibility \(Andritz; GE record\)\.

### 7. Draft tube and tailrace

Below the runner the draft tube expands and turns horizontal, recovering kinetic energy as pressure\. The culvert returns the water to the river at low velocity\. The water is not consumed\.

The runner sits below tailwater to suppress cavitation; draft tube dimensions are representative\.

### 8. Step\-up and grid

Generator output at 13\.8 kV runs by bus duct up to the step\-up transformer, which raises it to transmission voltage for the line\. Overall plant efficiency is about 90–95 %\.

Transformer rating and transmission voltage for Aldeadávila were not found in the sources consulted and are not stated\.

### 9. Pumped\-storage operation

Reversible units run the same machine backwards: off\-peak, the motor\-generator drives the pump\-turbine and lifts water to the upper reservoir; at peak the flow reverses and it generates\. Switch the mode to compare runner rotation and flow direction\.

Aldeadávila II \(1986\): 2 reversible Francis units of 210\.5 MW\. Cortes\-La Muela: 524 m head, 1,762 MW generating\. Pumped storage is a net consumer of energy \(round\-trip losses\)\.