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Mechanical Preliminary Test
1.
If ambient pressure decreases:
A.
GT useful power decreases and GT HR increases
B.
GT useful power decreases and GT HR remains approximately constant
C.
Both GT useful power and GT HR remain approximately constant
2.
When a mechanical system is in "resonance"?
A.
When system vibration amplitude become minimum
B.
When system vibration amplitude become maximum
C.
When the frequency of a periodic force applied to the system is the same of its natural frequency
3.
What can be the cause of decrease of the wheel chamber pressure?
A.
Fouling on high pressure buckets.
B.
High vibrations.
C.
Increase of the labyrinth seals clearance.
4.
The shrouds are items used for?
A.
Bearings' oil sealing purpose
B.
Compressed air sealing purpose
C.
Hot gas path sealing purpose
5.
Select the TRUE statement about the thrust bearing shims:
A.
the active side shim sets the axial position of the rotor
B.
the active side shim sets the thrust bearing clearance
C.
the non-active side shim sets the axial position of the rotor
6.
Select the TRUE statement about steam turbine impulse stage:
A.
An impulse stage is usually more efficient than a reaction stage
B.
An impulse stage needs higher peripheral speed than a reaction stage
C.
The optimum value of ψ for an impulse stage is around 2.3
7.
What is the possible cause of flow decrease in tandem dry gas seals system's primary vent?
A.
the gap between the two secondary seal rings increased
B.
the gap between the two secondary seal rings decreased
C.
the gap between the two primary seal rings increased
8.
Regarding the fuel gas system, which of the following sentences is TRUE?
A.
The SRV valve is used to cut the fuel gas supply out while the GCV controls the mass flow rate of the gas fuel to feed the GT.
B.
SRV and GCV are used together to control the fuel gas mass flow rate
C.
The SRV is used to cut the fuel gas out in case of trip and to keep the inter-valve pressure constant during the operation of the GT, to ensure an easier control of the fuel mass flow rate through the GCV.
9.
What is the pressure of the sealing steam?
A.
1.1 ÷ 1.3 bara.
B.
Atmospheric pressure.
C.
Condensing pressure.
10.
Which is the criterion used to define the maintenance intervals?
A.
Number of running hours
B.
Number of equivalent running hours and equivalent number of starts-stop sequences
C.
Number of equivalent running hours
11.
In case journal bearing's clearance is out of tolerance, what is the correct action to be taken?
A.
insert shims under the lower pads to lift up the rotor in the centered position
B.
replace the lower pads to restore the design clearance
C.
replace all pads
12.
"SALE" and "SALA" are controlled using:
A.
Dial gauge.
B.
Feeler gauge.
C.
Lead wire.