Clyde Hydropower Station Adds Air Gap Monitoring to Its SETPOINT® System

The Clyde hydropower station in New Zealand has added air gap monitoring to its existing vibration monitoring installation, giving operators a clearer view of a developing stator-rotor clearance problem.

An Aging Fleet Under Watch

The SETPOINT® system was installed several years ago on Contact Energy hydropower stations on the Clutha River, among them the Clyde hydropower station, a plant with a capacity of 4 x 116MW. Since that installation, the stations have been successfully monitored for vibration, and the time between overhauls has been extended. That alone is a meaningful return on a condition monitoring investment: fewer planned teardowns, more run time between them.

But vibration data recently pointed to something vibration data alone could not fully explain.

Deformation Behind the Imbalance

The aging generator stator frames at the Clyde power station showed signs of deformation. That deformation caused stator-rotor eccentricity, which in turn produced electromagnetic imbalance. The vibration monitoring system detected the issue, but the operators needed more diagnostic resolution to understand what was actually happening in the stator-rotor gap.

This is a familiar pattern in aging rotating machines: the symptom shows up in vibration, yet the root cause lives in geometry that vibration sensors cannot directly measure.

A Phased Rollout of Gap Measurement

The decision was made to extend the monitoring system with air gap monitoring functionality, allowing operators to more closely monitor and analyze the variable stator-rotor clearance. Rather than retrofitting all four units at once, the air gap monitoring functionality was first installed on Unit 1. The intent was to gain experience with the new capability before rolling it out to the other units. A cautious, single-unit pilot before fleet-wide deployment is sound practice when modifying instrumentation on machines of this size.

A detailed account of the application was published in the September issue of the International Water Power and Construction magazine, by Will Rucker of Brüel & Kjaer Vibro.

M4S Take:: For shops and service providers working in rotating machinery repair, the Clyde case underlines two things. First, vibration monitoring bought Contact Energy real value by extending time between overhauls, but it could only flag the stator problem, not characterize it. Second, pairing vibration data with direct air gap measurement turned a detected anomaly into a diagnosable condition. When quoting monitoring or overhaul work on aging generators, expect customers to want both capabilities, and expect the air gap discussion to come up once the stator frames start showing their age.