In
Turbine Supervisory Instrumentation (TSI), case expansion is an important
measurement. Case expansion (or shell expansion) is the growth of the
machine case with increase of temperature during machine startup and on-line
operations. The LVDT is mounted to the foundation at the opposite end from
where the turbine casing is attached. The LVDT provides information on the
change of position of the point measured relative to the foundation.
Case expansion should be measured by a pair of LVDTs. This provides
information on the position of both of the sliding feet on the machine case.
This allows for a comparison of readings preventing damage should one foot
become obstructed or jammed.
Case expansion measurements also allow determination of whether expected
thermal growth differentials are being exceeded on the machine. This is
primarily a startup parameter allowing the machine casing and rotor growth
to increase at a similar rate. Thermal growth at different rates can cause
internal rubbing between rotating and stationary parts of the machine.
How a case expansion transducer works:
The spring loaded rod in the LVDT presses against the machine, and as the
machine case grows the rod moves inside the LVDT. The change of position of
the rod causes a change in the output signal of the LVDT. The signal is
conditioned electronically and is output to a monitor for display and
alarms.
CMCP's Linear Variable Differential Transformers have a range of 0-2 inches.
The output is 0-5 VDC or 2.5 mV/mil. CMCP-LVDT-AC is our High
Temperature model which will withstand temperatures up to 300°F or 150°C. |
