Overview

In Turbine Supervisory Instrumentation (TSI), case expansion (also called shell expansion) is a critical position measurement. It monitors the thermal growth of the turbine casing during startup and online operation. By comparing casing movement relative to the foundation, operators can assess mechanical integrity and thermal growth behavior.

Measurement Principle

• Case Expansion Transducer Assembly:

  • Based on a Linear Variable Differential Transformer (LVDT) housed in a weatherproof enclosure.

  • A connecting rod links the LVDT to the turbine case.

  • As the casing expands, rod movement alters the LVDT output, which is conditioned and sent to the monitoring system for display and alarming.

• Dual Transducer Arrangement:

  • Recommended for measuring sliding foot positions on the machine case.

  • Detects obstructions or jamming of a sliding foot, preventing case distortion and potential machine damage.

  • When paired with 3300 or 3500 series monitors, alarms can be generated to alert operators of abnormal conditions.

Applications

• Startup Monitoring:

  • Ensures that casing and rotor grow thermally at similar rates.

  • Detects excessive differential thermal growth, which can cause rubbing between rotating and stationary components.

• Condition Monitoring:

  • Provides long-term information on machine thermal growth trends.

  • Helps verify expected temperature expansion characteristics.

Compatibility

• Standard Case Expansion Transducer: Compatible with 3300 and 3500 monitors.

• High-Temperature Dual Case Expansion Transducer:

  • Compatible only with the 3500/45 Position Monitor.

  • Designed to meet TYPE 4 environmental requirements.