|  Visit Old Website

Idamalayar Hydro Electric Project

Capacity : 2x37.5 MW

Idamalayar Hydro Electric Project is located at Idamalayar in Ernakulum District about 80 km from Kochi. Idamalayar river is a tributary of river Periyar and it originates from Anamala hills of western ghat. The Idamalayar reservoir is the second largest reservoir in Kerala – next only to Idukki Dam. For collection of water, a straight gravity dam is constructed at Ennakkal across Idamalayar river with a reservoir capacity of 1153.6 MCM at MWL. Energy equivalent is 270MU. Because of its reservoir capacity, Idamalayar generation is kept minimum during monsoon period. The main source of water inflow into dam is natural inflow in the catchment area (Idamalayar 380.79 m2 & Nirar 101m2) and the water available through the Vachumaram discharge from Poringal during monsoon.
            This project is a multi- purpose scheme. The commissioning of power project was in 1987. The erection of this project started on 2-01-1981 and the trial run was on 24-01-1987.The total number of turbines in the power plant is two and capacity per each turbine is 37.50 MW. The total installed capacity of power plant is 75 Megawatt. The type of Turbine used in the power house is Francis. The manufacturer of both Turbine and Generator of Power Plant is by M/s Bharat Heavy Electrical Limited, India. After power generation, tail race water from the power house is collected in the barrage at Bhoothathankettu, constructed across river Periyar.  
Salient Features:    
Location with District    :Idamalayar, Ernakulam District
Category     :    Hydro Power Project
Capacity     :    75MW
River     :    Idamalayar(tributary of river Periyar)
Dam     :    Idamalayar Reservoir
Annual Energy Potential    :    380MU
Reservoir :     
Catchment Area (101m²) Sq.K.M    :    Idamalayar 380.79 m2 & Nirar
Gross Storage at MWC    :    1153.00 Mm³
Gross Storage at FRL    :    1089.80 Mm³
Generation per MCM     :    0.25 MU
Design Head     :    108.576 Metre
Full Reservoir level (FRL)     :    169.00m
Min. Draw Down Level (MDDL)     :    115.00m
Discharge of water at rated head and output    :    40.1 M³/sec
Date of Commissioning:    
Unit – 1 (37.5 MW)    :    03.02.1987
Unit – 2 (37.5 MW)    :    28.02.1987
Date of Rennovation:    
Unit – 1     :    July 2011
Unit – 2     :    August 2012
1. Turbine    :    Francis (Vertical) Radial  axial flow type   reaction turbine
Make     :    BHEL  
Design Net Head    :    108.576 Mts.
Rated Out put     :    75 MW
Out put Max./Min.    :    37.5 MW/20 MW
Normal Speed     :    333.33 RPM
Runway Speed     :    620 RPM
Disc. Through Machine    :    40.1 M3/s
Maximum Head    :    126.75 Metre
Minimum Head    :    74.1 Metre
Rated Output    :    38600 kW
Rotation    :    Clockwise from top
Optimum Efficiency    :    92.70%
Diameter of Runner    :    2161 mm.
Height of guide vanes    :    588 mm.
No. of guide vanes    :    24 Nos.
Governor    :    Electro Hydraulic
2. Generator:    
Type     :    Synchronous Vertical Semi Umbrella
Make     :    BHEL
Rated Voltage    :    11 kV
Rated Out put     :    44117.7 kVA
Speed    :    333.33 RPM
Power Factor    :    0.85 lagging
Core Diamter    :    5400 mm
Core Length    :    980 mm
Frequency    :    50 cycles
No. of poles    :    18 Nos.
Direction of rotation    :    Clockwise from top
Type of Excitation    :    Static
Rated current of exciter    :850 Amps
Rated voltage of exciter    :206 V
3. Generator Transformers:    
Type     :    Single
Make     :    TELK
Rated Voltage     :    11/110 kV
Rated Out put     :    16 MVA
Type    :    Delta-Star
Type of cooling    :    Oil natural Air forced
Normal pressure of oil    :    0.35 kg/cm²
4. Power Evacuation    
a) 110 kV IMMA (Idamalayar-Malayattoor)    
b) 110 kV IMAP (Idamalayar-Ayyampuzha)    
 The power generated at Idamalayar power House is evacuated through two single circuit transmission line at 110 KV to Chalakkudy and Kalamassery substation named IMMA and IMAP feeders. These two 110kV feeders for power evacuation from the Power House, namely IMAP (Idamalayar-Ayyampuzha - Chalakudy) and IMMA (Idamalayar -  Malayattoor - Rayonpuram - Perumbavoor - Kalamassery). Split bus operation ensures unit-1 machine is feeding to IMMA feeder while unit-2 feeds IMAP feeder.110/11kV, 10MVA Power Transformer from 110kV Bus which feeds Chakkimedu, Dam/colony and power station feeders is situated adjacent to the existing 110kV yard.  The ongoing yard extension works are in final stage to improve the power evacuation capacity of Idamalayar HEP by strengthening the 110 kV network. The 110 kV feeder (upgraded) from Kothamangalam S/S to Bhoothathankettu HEP is to be extended to Idamalayar PH, with LILO arrangement at Bhoothathankettu. Moreover, one additional 110 kV feeder is also directly proposed from Kothamangalam s/s to Idamalayar HEP. These double circuit lines are proposed to be terminated at the old 66 kV yard area, for which the existing 66 kV feeder bay is to be upgraded to 110 kV standard. This work is in the final stage.

Annual Maintenance Schedule


Unit # 1

15.06.2023 to 19.07.2023

Annual maintenance and RLA study

RLA study 35 days

Unit # 2

01.11.2023 to 05.12.2023

Annual maintenance and RLA study

RLA study 35 days



Please rate us and give your valuable feedback if you are satisfied with this KSEBL website service.