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Steam Turbine

Operation

Expansions

Fault Tracing

Fault

Other symptoms Cause Remedy

Alarm or display:

Differential expansion high

Positive (+) differential expansion Rotor longer than casing Check the annunciation to if posi-

or tive (+) or negative I-I expansion is

Negative (-) differential expansion Rotor shorter than casing high;

determine transient of expansion;

start measures to stop further

differential expansion;

shut down turbine generator unit if

permissible differential expansion is

reached and wait for expansion torecede;

Differential expansion of HP turbine

at front end high

Positive (+) differential expansion During non-steady-state operation, Wait for temperature equalisation

rotor heats up sooner than casing between rotor and casing or for differ-

ential expansion to recede before

performing speed or load changes;

Main steam temperature too Reduce main steam temperature;

high

Poor sliding of HP turbine during Improve sliding of HP casing during

warm-up of turbine casing next inspection;

NegativeH differential expansion During non-steady state operation, Wait for temperature equalisation bet

rotor cools down sooner than casing ween rotor and cBsing or for differen-

tial expansion to recede before

performing load changes;

Main steam temperature Raise main steam temperature;

during start-up too low.

Poor sliding of HP turbine casing improve sliding of HP casing during

during cool-down. next inspection

Differential Expansion of IP turbIne,

at rear end hIgh

Positive (+) differential expansion During non steady state operation, In many cases, better steam flow

rotor heats up sooner than casing through the IP turbine casing will brin

a reduction in differential expansion;

increase speed and load within

permissib.le limits and notice effects;

if this does not causes the differentia

expansion to recede. wait for temper-

ature equalisatiorl before performing

further speed or load changes;

Rehea temperature too high Reduce reheat temperature.

Poor sliding of IP turbine casing Improve sliding of IP casing during

next inspection

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Fault

Other symptoms Cause Remedy

Negative(-) differential expansion Negative differential expansion atthis measuring occurs only

under extremely un favourable op-

erating conditions, as positive (+)

different!al expansion is to be

expected due to the mean temperatures

of rotor and casing during operation

Pronounced drop in reheat stop reheat temperature drop

temperature immediately;

Severe restriction in expansion of Irnprove sliding of turbine casing.

turbine casing during cool-down.

High rate of expansion change Reduce air or steam flow;

due to forced cool- down of IP

turbine by means of air or steamDifferential expansion of LP turbine

at rear end high

Positive (+) differential expansion The maximum differential expansion Check differential expansion at rear

usually depends on the mean rotor end of IP turbine and start proper

temperature and the differential measures to reduce differentialexpansion of the IP turbine expansion;

Increase in mean LP turbine rotor Load the set and normalize rotor

temperature as a result of prolonged temperature;

no -load operation Note:When shutting down the turbine

due to impermissible expanslon, it must

be remembered that the LP tlKbine rotor

becomes shorter during rated speed

operation as a result of transverse

contraction;

So an increase in differential

expansion is to be expected during

shut-down;

Negative (-) differential expansion Negative differential expansion

occurs only if the differential

expansion at the rear end of the

IP turbine becomes negative.

This effect is to be expectedonly if expansion of IP turbine

is severely restricted

Reading of shaft position in thrust

bearing differs from previous readings

under otherwise identical conditions Check positive Qhanges in Higher residual thrust on thrust Check stage pressures;

positive( +) direction (thrust bearing;

towards the rear) or negative wear in thrust bearing Check bearing metal tempel ature at

(-) direction (thrust towards the thrust bearingthe front.