USEFUL INSTRUMENTATION AND MONITORING FOR THE STATOR COOLING WATER SYSTEM

Both high- and low oxygen water chemistry regimes with different pH ranges can be found in the industry. This means that instrumentation depends on the configuration and chemistry regime the system is run at. However, some general rules apply for all systems:

Conductivity:
This most important chemical parameter serves both as a protection for the generator against leak currents and boiling cooling water, and as an indicator for general water purity and pH. As this is such an important parameter, it is recommended to have redundant measurements in place. Preferably, the probe should be installed in a side stream of the main stator cooling water flow.
Conductivity at the demineralizer outlet is an important indicator for resin exhaustion and worth monitoring continuously.
In alkaline systems, system conductivity is used to indirectly monitor the pH.

Dissolved oxygen (dO):
This is an essential parameter that directly relates to the copper-water chemistry. It should be monitored continuously, as an inadequate oxygen concentration increases the likelihood of stator hollow conductor plugging.

pH:
pH measurement in high purity water is prone to errors and often misleading, thus should only be done indirectly via conductivity (combined with Na+ concentration for alkalized units). As long as the conductivity is <0.1 µS/cm, the pH is between 6.8 and 7.4, which is sufficient for safe operation.

Electrochemical corrosion potential (ECP):
The ECP gives valuable information for all chemistry regimes. It often provides an early warning that cooling water chemistry is trending away from equilibrium long before the consequences are visible. Especially in low-oxygen systems it gives a more complete picture than oxygen monitoring alone.

Water flow and pressure:
Flow should be measured both in the system (ideally separately for the stator) and the demineralizer bypass loop. Pressure needs to be monitored on various locations. Stator inlet and outlet pressure are important parameters for all systems. Filter and strainer pressure drop is an indicator for filter/strainer plugging, and an indicator for adverse conditions. Other potentially useful measurement points depend on cooling water system design. Such locations include pump suction and discharge sides, and expansion tank gas pressure. Generally, and especially for monitoring stator plugging, pressure values must be put in relation to the corresponding flow.

Temperatures:
Important primary temperature monitoring locations are generator inlet and individual Teflon outlet hoses, as well as slot temperatures (RTDs). To monitor for plugging, temperatures must be normalized to a standard load and inlet temperature.

DATA ANALYSIS AND TRENDING

One of our key competences is to analyze data from the stator cooling water system and provide independent expert supervision. Feel free to directly contact us.

SUMMARY

Proper instrumentation can help you identify problems before it is too late. Consequences of improper monitoring can range from forced outages to irreversible damage to the generator. In other words, keep your monitoring and instrumentation up-to-date.

Tom will travel around the globe...

…and present "Reduced cooling in water cooled generators due to plugging of hollow conductors: chemical cleaning and OPEX" at the EPRI 2018 Generation Australian Workshop and User Group Meeting in Brisbane (16th-18th October).

He will stay down under and later present “Plugging Of Stator Cooling Water System: Root-Cause Analysis And Chemical Cleaning” at the Austorque Machines 2018 in Sydney, Australia (29th-31st October).

NEXT NEWSLETTER TOPIC

The next newsletter will cover OPEX on plugging filters, strainers and stators in the stator cooling water system.