Bieudron power station

Bieudron power station-The world's highest water head hydroelectric Plant

today, let me introduce the world's highest water head hydropower station to every one. it's name is "Bieudron power station".

The Bieudron Hydroelectric Power Station is a hydroelectric power plant located in the Swiss Alps in the Canton of Valais in Switzerland. The power plant is fed with water from the Grande Dixence Dam's reservoir, Lac des Dix and is part of the Cleuson-Dixence Complex. The 1269 MW power plant is operated by Grande Dixence SA.

The Bieudron power station alone holds three world records, for the height of its head (1883 m), the output of each Pelton turbine (3 x 423 MW) and the output per pole of the generators (35.7 MVA).

Bieudron hydropower station unit parameter
item	unit	value
Max. Water head	m	1883
Each capacity	MW	420
Water turbine type		Pelton
speed	r/min	428.6
Rated flow	m3/s	75
Turbine runner diameter	m	4.65
Turbine weight	t	120
nozzles exit flow velocity	km/h	690
generator rated capacity	MVA	465
Rated voltage	kV	21(±10%)
Rated frequency	Hz	50
Generator stator weight	t	281
Generator rotor weight	t	454
Installation capacity of power plant		3×420MW
total investment	billion dollar	0.8
《ABB Review》1994，No.10。

This facility houses three Pelton turbines, with each turbine rated at 423 MW (~567,000 HP); note that the turbine acceptance testing process reported a maximum turbine output power of 449 MW each (~602,000 HP) due to better than expected efficiency and ideal test conditions.[1]

At the rated power of 423 MW each turbine operates at a head of ~1869 meters (6130 feet) and a flow rate of 25 cubic meters per second, with an efficiency in excess of 92% (~92.37%). The turbine assembly is a five-jet configuration; the stream of each jet is 193 mm (7.6 inches) in diameter with an exit velocity of 192 meters/second (630 ft/s). The kinetic energy of each of the 5 streams (i.e. 1 from each jet) is approximately 92.16 MW (Q = 5 cubic meters per second, v = 192 m/s, H = 1869 m). The assembly rated pressure is 203.2 bars (2944 psi).

The combined flow rate for the three turbines is 75 cubic meters per second. The facility peak power production is ~1269 MW. The turbines and associated valves were designed and developed by VA Tech of Switzerland.

On December 12, 2000, at approximately 20:10, the Cleuson-Dixence penstock, feeding the Pelton turbines at Bieudron, ruptured at ~1234 meters AMSL (under more than 1000 meters of head). The failure appears to have been due to several factors including the poor strength of rock surrounding the penstock at the rupture location. The rupture was approximately 9 m long by 60 cm wide. The flow rate through the rupture was likely well in excess of 150 m3/s (5,300 cu ft/s). The ensuing rapid release of a very large quantity of high pressure water destroyed approximately 100 hectares (1 km²) of pastures, orchards, forest, as well as washing away several chalets and barns around Nendaz and Fey. Three people were killed.[2]

The Bieudron facility was inoperative after the accident; however, it became partially operational in December 2009, and fully operational in January 2010. Much investigation went into the accident resulting in the almost complete redesign of the penstock. Legal action is still in process and the root cause of the rupture is unknown.

However details regarding the redesign are available. The redesign calls for improvements in the pipe's lining as well as the addition of grouting around the penstock to reduce water flow between the penstock and the surrounding rock due to dynamic variation of the pipe diameter during operation (it expands due to water loading during operation then contracts when the load is removed, leaving a gap). The damaged section of the penstock was rerouted around the previous location to where new (undamaged) more stable rock is available. Construction on the redesigned penstock was completed in 2009. Redesign considerations include operational control of maximum agreed design limits under all conditions of assembly, design and service conditions (including water hammer pressure spikes).

https://en.wikipedia.org/wiki/Bieudron_Hydroelectric_Power_Station

Pelton turbine

Pelton Hydro Turbine  for high water head Project

The Pelton turbine is widely used in hydropower station with the heads from 80-1000m.
Pelton turbine is consisted of runner, turbine case, nozzles assembly, inlet pipe, deflector etc. The runner is assembled in the shaft of the generator, torque transmission by ping.
lt utilizes the dynamic power of high pressure water flow to rotate the runner and force the rotor work, The centre line of the jet is in the same plane as the runner while rotating.
Pelton turbine has the advantages of compact construction, stable running and easy operation. Normally, Small pelton turbine always arranged with horizontal shaft and one or two nozzles,   Medium size and larger Pelton turbines are most often arranged with vertical shaft, and equip four or six nozzles to obtain more power.

1. Runner

The runner is the principle part of the turbine. It has influence over the characteristic of the turbine. The runner consists of vanes, the hub and the outer ring of runner. The shape of vane is three dimension cambers. The outer ring applies to strengthen the runner and to reduce the loss of wind.

The runner disc and buckets are CNC machined from and integrally forged 13%Cr 4% Ni steel, the faces of buckets which are in contact with water must be CNC machined and ground to a smooth surface with a maximum surface roughness of 0.8 Microns. The buckets  must be controlled by a coordinate measuring machine via a certified measuring company and must be submitted for approval. The center line allowance between the buckets is 0.57mm

Additional tests for material must be completed according to specification for Inspection of steel castings for hydraulic machines CCH 70.3. A detailed chemical analysis, Ultrasonic tests UT70.3, magnetic particle tests MT 70.3, and dye penetrant tests PT70.3 must be performed via a certified company and results should be submitted for approval.

Runner must be statically balanced according to ISO 1940/1 class G6.3 and G2.5.

2. The case and the cover of the case

The case used is a fine gradewelding steel with a minimum yield strength of 550 Mpa (St52 or equivalent), it has enough intensity and is convenient for maintenance. There is trachea on the case, which should be connected to the ventilating pipes from the tailrace channel and shall not use air from the power house. it is for complementing the air the jet takes, avoid vacuum in the house, keep the circulation, and there is a gate in the unit for overhauling, between up cover and down seat there is o-washer for overhauling.

3. Jet deflectors

Deflectors be manufactured from a monolithic stainless steel. Deflectors be

designed to withstand maximum discharge from the nozzle without vibration. The deflectors

be controlled by a double acting servomotor located outside the turbine casing.

4. Nozzle

The nozzle is components of the distributor of the pelton turbine.The intake pipe conduits pressure water flow to the nozzle via the guide support which is used to support the needle stem to provide against a vortex. In practice the nozzle is just a needle valve; however the valve plays a role of shut off and of transform energy in impulse turbine. The pressure water flow enters the nozzle body. Then the velocity of water flow shall be increased rapidly at the nozzle tip and the water flow is formed a jet to inject to the vanes of runner.

 So pressure energy of the flow changes to velocity energy and the runner does a work. The opening of nozzle shall be adjusted by nozzle control mechanism which is consisted distributing valve, the servomotor of needle and by combination mechanism. The operation oil pressure is 6.3Mpa, it used internal control structure, the opening of the needle is 75%~85% on the full-load. The server-motor piston and the piston rod is made of 35 steel welding.

Allowance of the position of the jet center line and the rotor pitch circle is ±1.2mm. Allowance of the position of the jet center line and the pelton watershed edge is ±1.2mm as per the IEC standards.

5. Needle control mechanism

The needle control mechanism includes a jet deflector; the jet deflector is also called deviator. It is used to deflect the jet on a sudden load rejection in order to avoid run away of the unit and pressure over rise for excessive water hammer in the penstock.