Modification in damaged pelton runner of Kishanganga Power station – A case study

Kishanganga Power Station was commissioned in May 2018. Power House has three generating units having capacity of 110 MW operating at rated head of 646 m. Prime Mover is Vertically mounted Pelton turbine 21runner buckets. Rated speed of the turbine is 375 rpm and it is being operated by 5 nozzles.

Two incidents of dislodging of one no. runner bucket from the hub has happened in the same unit i.e unit-1 in the power station since commissioning. After the first incidence happened in Aug-2018, the unit was restored after installation of available spare runner. The second incident took place in Dec 2019. Due to non-availability of spare runner, Unit-1 was under break breakdown. In view of long lead time of supply of runner, inevitable circumstances of revenue loss due to non-operation of the unit and to minimize the continued non-availability of the Unit, alternatives to modify the damaged runner for its reuse were envisaged. Root cause of the bucket failure and metallurgical defects of the material is being investigated.

After going through the information available on the subject matter, two alternatives were feasible keeping in view their implementation in the shortest possible time, reliability and cost effectiveness.

The first one was to weld the dislodged bucket to runner. The second was to remove one or two buckets in a manner so that the runner should be dynamically balanced. In Pelton turbines, root area of the bucket is subjected to high concentration of stress due to the cantilever structure subjected to high bending stress. Position and the manner in which bucket was dislodged from the hub, ruled out any possibility of weld. Accordingly, the option of welding of bucket was not considered. Instead out of 21 buckets, two equidistant buckets were removed in addition to broken bucket. The cutting operation was carried out, and Unit was made operational at a reduced power output due to vibration constraints at high loads.

This paper describes the methodology and steps involved in the modification.