Ligne 220 KV - (La Rivière-Monistrol d'Allier)

## Présentation:

La ligne Monistrol-La Rivière est une ancienne liaison à très haute tension qui reliait Saint Étienne à l'usine hydro-éléctrique de Monistrol d'Allier.

Déposée entre 2016 et 2018, elle a été remplacée par une nouvelle ligne 225 KV à deux circuits qui suit globalement le même tracé.

Chargement de la 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class=\"mw-parser-output\"\u003E\u003Cp\u003EMonistrol d'Allier\n\u003C/p\u003E\u003C/div\u003E","title":"Monistrol d'Allier\n","link":"","lat":44.96835394928133,"lon":3.6451998163622346,"icon":""},{"text":"\u003Cdiv class=\"mw-parser-output\"\u003E\u003Cp\u003ELa Rivi\u00e8re\n\u003C/p\u003E\u003C/div\u003E","title":"La Rivi\u00e8re\n","link":"","lat":45.412570680800435,"lon":4.406292437286794,"icon":""}]}
## Historique:

### Origines de la ligne :

Afin d'exploiter la force hydraulique de l'Ance et de l'Allier, La Compagnie Électrique de la Loire et du Centre (CELC) fit construire une centrale à Monistrol en 1926, en même temps que la mise en eau du barrage de Pouzas. La CELC réalisa à cette occasion une première ligne Saint-Étienne-Monistrol par le biais de sa filiale de transport d'électricité; la STEC (Société de Transport d'Energie du Centre).

Dans les années 1930, le besoin croissant en énergie engendra la création de 2 nouveaux barrages en 1939 et 1941. Entre temps, le réseau autour de l'usine s'était développé avec une ligne 150 KV vers Bagnols-sur-Cèze et la Méditerranée mais surtout une liaison 220 KV Rueyres-Monistrol pour relier les aménagements hydro-électriques du Haut Allier à ceux de la Truyère. Par ailleurs, un second poste électrique vit le jour durant cette décennie de l'autre côté de l'Allier, à 150m du premier.

C'est dans ce contexte que la STEC réalisa cette ligne à très haute tension. L'objectif était de créer une puissante liaison de transport d'énergie reliant les usines hydrauliques du Massif central au bassin industriel Stéphanois et à la région Lyonnaise. Elle constituait de fait un maillon du "super réseau" national de l'époque; la première grande boucle d'interconnexion à 220 000 volts entre Paris, le Massif central et les Alpes. Sa mise en service entraîna par ailleurs une extension du poste électrique de Monistrol 1 (que l'on aperçoit à côté de l'usine sur l'image) et une réorganisation du réseau environnant : raccordement de la ligne Rueyres-Monistrol au poste 1 et création d'une courte ligne à 220 KV entre les postes 1 et 2 de Monistrol.

### Evolution au cours du XXème siècle:

Sous la gouvernance d'EDF, un poste de répartition 225 KV est mis en service en 1950 à Pratclaux en surplomb de la vallée sur la rive droite. La ligne est alors sectionnée en deux pour s'y raccorder; devenant ainsi les lignes 225 KV Pratclaux-La Rivière et Pratclaux-Monistrol.

En 1987: la ligne fait une entrée en coupure dans le nouveau poste de Trévas, créé pour accompagner le développement de l’Yssingelais. Enfin en 2001 : elle est raccordée en coupure au poste de Sanssac, mis en service pour renforcer l'alimentation du Puy en Velay.

## La ligne aujourd'hui:

Dans le cadre du projet "2 Loires", la ligne vieillissante fut déposée en plusieurs étapes entre 2015 et 2018. Elle est remplacée par une liaison aéro-souterraine à deux circuits. Ironie du sort, le seul pylône encore debout est celui situé au dessus de la centrale de Monistrol d'Allier, retranché de la ligne en 1950 et réutilisé pour la ligne 225 KV Pratclaux-Margeride.

## Description du tracé:

* La ligne partait de l'usine hydro-électrique de Monistrol d'Allier et montait brusquement au dessus de la vallée.
* Suivant continuellement la direction du nord-est, elle passait au dessus d'un lotissement à Saint Privat d'Allier.
* Elle franchissait la D906 1km au Nord de Bains, passait au sud de Sanssac l'Église puis passait au dessus de la N102 au Nord de Polignac.
* À 1 km au sud de Lavoûte sur Loire, elle franchissait les gorges de la Loire puis se dirigeait vers Saint Maurice de Lignon, passant sur les communes de Rosières et Beaux.
* À Saint Maurice, la ligne traversait la N88 puis enjambait le Lignon pour se diriger vers Saint Didier en-Velay.
* Elle passait au dessus de Saint Didier en Velay et Saint Just Malmont puis entrait dans la Loire.
* Elle franchissait plusieurs vallées au sud de Saint-Étienne et plongeait enfin vers le poste de La Rivière.

## Tronçon récupérés pour la création de nouvelles lignes:

1. Ligne 225 KV - (Pratclaux-La Rivière).
2. Ligne 225 KV - (Pratclaux-Monistrol).
3. Ligne 225 KV - (Pratclaux-Trevas).
4. Ligne 225 KV - (Pratclaux-Sanssac-l'Église).
5. Ligne 225 KV - (Sanssac-l'Église-Trevas).
6. Ligne 225 KV - (La Rivière-Trevas).
7. Ligne 225 KV (Pratclaux-Margeride).