af consult

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1. Study of the existing problems and proposed remedial: A. To complete the study, we will need the details of the problems being faced by the project engineers. This should include the following: Chuzachen power Intakes Rangpo and Rongli are located on left and right banks of rivers Rangpo and Rongli respectively. There is a provision of Silt Barrier gate at the up-stream of trash rack. Silt barrier gates are lowered during monsoon allowing water enter at higher elevation. This provision has allowed less silt entry into the tunnel and has successfully served the purpose till data. However, following corresponding problems are observed: - Lowered Silt barrier gate creates a vertical flow column in front of Transh rack/Intake. This 11.0 column of water from top of silt barrier gate ( EL. 898.0 m) to Invert level of Intake ( EL.887.0 m) becomes a collection chamber for tree logs , debris and other foreign material. Since there is no TRCM , there is no way to remove these foreign material during plant operation and this lead to choking of trash racks. Depending on the volume foreign material , Trash racks opening gets choked during plant operation (Extent of choking is gauged by observing water level difference upstream and downstream of trash racks) requiring stopping plant and manually cleaning choked trash rack. It has been observed that when water level difference reaches around 3.0 meter , 50 % of trash rack opening gets choked. During pre-monsoon period (May) , flash floods are observed in River. Flash flood carry along with it huge amount of tree logs and foreign material in short span of time. During the last week of May , plant is generally running at full capacity and immediate choking of trash racks due to flash flood leave no time to stop plant / lower intake gate , leading to almost 100% choking of trash rack under plant running condition. This situation lead to catastrophe , breaking of trash rack panels and entry of foreign material inside tunnel. a) Flow passing through the inlet Refer : 1) AF Consult Report : Hydraulic Simulation Of Interconnected Reservoirs No. R 71.3726.05.110 July 2009 2) Actual plant operation and reservoir operation Flow passing through inlets Rangpo and Rogli sums up to design discharge of Chuzachen power plant. Maximum capacity of Plant to be considered for design shall be considered as 110 MW plus 10% continuous overloading.

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Trash Rack Design

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Page 1: Af Consult

1. Study of the existing problems and proposed remedial:

A. To complete the study, we will need the details of the problems being faced by the project engineers. This should include the following:

Chuzachen power Intakes Rangpo and Rongli are located on left and right banks of rivers Rangpo and Rongli respectively. There is a provision of Silt Barrier gate at the up-stream of trash rack. Silt barrier gates are lowered during monsoon allowing water enter at higher elevation. This provision has allowed less silt entry into the tunnel and has successfully served the purpose till data. However, following corresponding problems are observed:

- Lowered Silt barrier gate creates a vertical flow column in front of Transh rack/Intake. This 11.0 column of water from top of silt barrier gate ( EL. 898.0 m) to Invert level of Intake ( EL.887.0 m) becomes a collection chamber for tree logs , debris and other foreign material. Since there is no TRCM , there is no way to remove these foreign material during plant operation and this lead to choking of trash racks. Depending on the volume foreign material , Trash racks opening gets choked during plant operation (Extent of choking is gauged by observing water level difference upstream and downstream of trash racks) requiring stopping plant and manually cleaning choked trash rack. It has been observed that when water level difference reaches around 3.0 meter , 50 % of trash rack opening gets choked.

During pre-monsoon period (May) , flash floods are observed in River. Flash flood carry along with it huge amount of tree logs and foreign material in short span of time. During the last week of May , plant is generally running at full capacity and immediate choking of trash racks due to flash flood leave no time to stop plant / lower intake gate , leading to almost 100% choking of trash rack under plant running condition. This situation lead to catastrophe , breaking of trash rack panels and entry of foreign material inside tunnel.

a) Flow passing through the inlet

Refer : 1) AF Consult Report : Hydraulic Simulation Of Interconnected Reservoirs No. R 71.3726.05.110 July 2009

2) Actual plant operation and reservoir operation

Flow passing through inlets Rangpo and Rogli sums up to design discharge of Chuzachen power plant. Maximum capacity of Plant to be considered for design shall be considered as 110 MW plus 10% continuous overloading. Generation discharge for Plant is 42.65 cumces + 10% overloading = 47cumecs.

Under Normal condition (110 MW)Rangpo + Rongli = 31.05 + 11.60 = 42.65 cumecs

Under Overloading Condition ( 110 MW + 10% continuous overload)Rangpo + Rongli = 34.20 + 12.80 = 47.00 cumecs

Project monsoon is observed in the month of June, July, August & September ( 4 months). Pre monsoon ( April, May) and post monsoon ( October, November) are transition periods. During transition period , water availability in rivers fluctuates and generally Rongli river contribution goes down, resulting in relatively more drawl of water from Rangpo intake. During this period there could be a situation where plant is running at 121 MW capacity and maximum drawl is from Rango Intake.

Page 2: Af Consult

Rangpo + Rongli = 40.00 + 07.00 = 47.00 cumecs ( Refer attached discharge sheet , May end data )

Distribution of total discharge shall be considered as per design.

b) Observations of any problems

Chuzachen power Intakes Rangpo and Rongli are located on left and right banks of rivers Rangpo and Rongli respectively. There is a provision of Silt Barrier gate at the up-stream of trash rack. Silt barrier gates are lowered during monsoon allowing water enter at higher elevation. This provision has allowed less silt entry into the tunnel and has successfully served the purpose till data. However, following corresponding problems are observed:

- Lowered Silt barrier gate creates a vertical flow column in front of Transh rack/Intake. This 11.0 column of water from top of silt barrier gate ( EL. 898.0 m) to Invert level of Intake ( EL.887.0 m) becomes a collection chamber for tree logs , debris and other foreign material. Since there is no TRCM , there is no way to remove these foreign material during plant operation and this lead to choking of trash racks. Depending on the volume foreign material , Trash racks opening gets choked during plant operation (Extent of choking is gauged by observing water level difference upstream and downstream of trash racks) requiring stopping plant and manually cleaning choked trash rack. It has been observed that when water level difference reaches around 3.0 meter , 50 % of trash rack opening gets choked.

( Please see Photo set 1)

During pre-monsoon period (May) , flash floods are observed in River. Flash flood carry along with it huge amount of tree logs and foreign material in short span of time. During the last week of May , plant is generally running at full capacity and immediate choking of trash racks due to flash flood leave no time to stop plant / lower intake gate , leading to almost 100% choking of trash rack under plant running condition. This situation lead to catastrophe , breaking of trash rack panels and entry of foreign material inside tunnel.

Please see Report 1 - Flash Flood

c) Details (as much as can be provided) of silt/debris deposit between the silt barrier gate and existing trash rack location.

Please see photographs attached.

d) Details of vortex formation (extent, location and at what discharge), if any

PHOTO SET 1

Photographs of Trash Rack Cleaning on 6th September. Rangpo Trash Rack

Page 3: Af Consult
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