3B2 POWER ENGINEER EXAM COMPLETE QUESTIONS WITH
100% CORRECT ANSWERS AND DETAILED EXPLANATIONS
QUESTION 1
What are the disadvantages of a gas turbine?
A) High cost of manufacture only
B) High levels of noise pollution only
C) Low thermal efficiency only
D) High cost of manufacture, high noise levels, low thermal efficiency, and
requires many auxiliaries to be efficient
Correct Answer: D
Explanation: Gas turbines have multiple disadvantages: high manufacturing cost
(precision components, exotic materials), high noise pollution (jet engine-like
noise requires sound attenuation), low thermal efficiency (simple cycle efficiency
25-35% compared to steam turbines 35-45%), and they require many auxiliary
systems (fuel treatment, lubrication, starting system, air filtration, etc.).
QUESTION 2
The most common process method of refrigeration is:
A) Absorption refrigeration
B) Lithium bromide refrigeration
C) Water vapor refrigeration
D) Vapor compression or mechanical refrigeration
Correct Answer: D
Explanation: Vapor compression refrigeration (mechanical refrigeration) is the
most common method used in residential, commercial, and industrial
applications. It uses a compressor to circulate refrigerant through the cycle
,(compression, condensation, expansion, evaporation). Absorption refrigeration
(lithium bromide or ammonia-water) is less common, typically used where waste
heat is available or electricity is expensive.
QUESTION 3
To facilitate the removal of moisture and oil from the compressed air, a/an
________ is installed.
A) Intercooler
B) Oil separator
C) Unloader
D) Expansion tank
E) Aftercooler
Correct Answer: E
Explanation: An aftercooler is installed downstream of the compressor to cool the
compressed air, condensing moisture and oil vapor that can then be removed by a
moisture separator. Intercoolers cool air between stages. Oil separators remove oil
but work best when the oil is condensed (cooled), which is the aftercooler's
function.
QUESTION 4
In a two-stage refrigeration system, the 1st stage compressor is also known as a
________ compressor.
A) Booster
B) Standby
C) Low volume
D) Extraction
E) Refrigerant
Correct Answer: A
Explanation: In a two-stage refrigeration system (for very low temperatures below
-40°C to -80°C), the first stage compressor is called the booster or low-stage
compressor. It compresses refrigerant from evaporator pressure to an
intermediate pressure. The second stage (high-stage) compressor compresses
from intermediate pressure to condenser pressure.
,QUESTION 5
In a rotary vane compressor:
A) Vanes are kept close to the central hub by centrifugal force
B) There is a rotor in the exact center of the casing
C) Refrigerant is trapped between the roller and the decreasing volume of the
eccentric casing
D) The rotor oscillates
E) The vanes move in and out of the rotor slots
Correct Answer: E
Explanation: In a rotary vane compressor, the rotor is eccentrically positioned in
the cylinder. Vanes slide in and out of rotor slots due to centrifugal force (and
sometimes spring pressure). As the rotor turns, the vanes maintain contact with
the cylinder wall, creating chambers that decrease in volume, compressing the
refrigerant. The vanes move in and out of the rotor slots.
QUESTION 6
In a gas turbine, there are fewer turbine stages than compressor stages because:
A) Energy can be extracted more efficiently in the turbine
B) Turbine blades are bigger so require fewer
C) Higher exhaust temperatures can be tolerated
D) The hot gases occupy more volume
E) Hot exhaust gases are required for the HRSG's
Correct Answer: A
Explanation: Energy can be extracted more efficiently in the turbine (expansion)
than added in the compressor (compression). Each turbine stage can extract more
energy than each compressor stage adds. Therefore, fewer turbine stages are
needed to drive the compressor and produce useful output power.
QUESTION 7
Pressure limiting devices of refrigeration systems shall be connected:
A) Between the compressor and the stop valve on the suction side
B) To a blowdown tank
C) Between the inlet of the condenser and the outlet of the receiver
, D) Between the compressor and the stop valve on the discharge side
E) To the receiver outlet
Correct Answer: D
Explanation: Pressure limiting devices (high pressure cut-outs or pressure relief
valves) must be connected between the compressor discharge and the stop valve
on the discharge side to protect the compressor and system from overpressure.
They should be installed as close to the compressor as practical.
QUESTION 8
The warm-up time required for a turbine is dependent on:
A) How quickly the turbine is required
B) The manufacturer's instructions
C) The size of the turbine
D) The type of turbine
E) Whether the steam is dry or wet
Correct Answer: C
Explanation: Larger turbines have more thermal mass (more metal) and take
longer to warm up evenly to prevent thermal stress, differential expansion, and
rotor "hogging" (bending). Warm-up time is primarily determined by turbine size
(rotor diameter, casing thickness). Manufacturer's instructions provide specific
ramp rates, but size is the fundamental factor.
QUESTION 9
________ compressors require intake and discharge valves.
A) Rotary
B) Centrifugal
C) Sliding vane
D) Rotary lobe
E) Reciprocating
Correct Answer: E
Explanation: Reciprocating compressors use automatic spring-loaded or pressure-
actuated intake and discharge valves that open and close based on pressure
100% CORRECT ANSWERS AND DETAILED EXPLANATIONS
QUESTION 1
What are the disadvantages of a gas turbine?
A) High cost of manufacture only
B) High levels of noise pollution only
C) Low thermal efficiency only
D) High cost of manufacture, high noise levels, low thermal efficiency, and
requires many auxiliaries to be efficient
Correct Answer: D
Explanation: Gas turbines have multiple disadvantages: high manufacturing cost
(precision components, exotic materials), high noise pollution (jet engine-like
noise requires sound attenuation), low thermal efficiency (simple cycle efficiency
25-35% compared to steam turbines 35-45%), and they require many auxiliary
systems (fuel treatment, lubrication, starting system, air filtration, etc.).
QUESTION 2
The most common process method of refrigeration is:
A) Absorption refrigeration
B) Lithium bromide refrigeration
C) Water vapor refrigeration
D) Vapor compression or mechanical refrigeration
Correct Answer: D
Explanation: Vapor compression refrigeration (mechanical refrigeration) is the
most common method used in residential, commercial, and industrial
applications. It uses a compressor to circulate refrigerant through the cycle
,(compression, condensation, expansion, evaporation). Absorption refrigeration
(lithium bromide or ammonia-water) is less common, typically used where waste
heat is available or electricity is expensive.
QUESTION 3
To facilitate the removal of moisture and oil from the compressed air, a/an
________ is installed.
A) Intercooler
B) Oil separator
C) Unloader
D) Expansion tank
E) Aftercooler
Correct Answer: E
Explanation: An aftercooler is installed downstream of the compressor to cool the
compressed air, condensing moisture and oil vapor that can then be removed by a
moisture separator. Intercoolers cool air between stages. Oil separators remove oil
but work best when the oil is condensed (cooled), which is the aftercooler's
function.
QUESTION 4
In a two-stage refrigeration system, the 1st stage compressor is also known as a
________ compressor.
A) Booster
B) Standby
C) Low volume
D) Extraction
E) Refrigerant
Correct Answer: A
Explanation: In a two-stage refrigeration system (for very low temperatures below
-40°C to -80°C), the first stage compressor is called the booster or low-stage
compressor. It compresses refrigerant from evaporator pressure to an
intermediate pressure. The second stage (high-stage) compressor compresses
from intermediate pressure to condenser pressure.
,QUESTION 5
In a rotary vane compressor:
A) Vanes are kept close to the central hub by centrifugal force
B) There is a rotor in the exact center of the casing
C) Refrigerant is trapped between the roller and the decreasing volume of the
eccentric casing
D) The rotor oscillates
E) The vanes move in and out of the rotor slots
Correct Answer: E
Explanation: In a rotary vane compressor, the rotor is eccentrically positioned in
the cylinder. Vanes slide in and out of rotor slots due to centrifugal force (and
sometimes spring pressure). As the rotor turns, the vanes maintain contact with
the cylinder wall, creating chambers that decrease in volume, compressing the
refrigerant. The vanes move in and out of the rotor slots.
QUESTION 6
In a gas turbine, there are fewer turbine stages than compressor stages because:
A) Energy can be extracted more efficiently in the turbine
B) Turbine blades are bigger so require fewer
C) Higher exhaust temperatures can be tolerated
D) The hot gases occupy more volume
E) Hot exhaust gases are required for the HRSG's
Correct Answer: A
Explanation: Energy can be extracted more efficiently in the turbine (expansion)
than added in the compressor (compression). Each turbine stage can extract more
energy than each compressor stage adds. Therefore, fewer turbine stages are
needed to drive the compressor and produce useful output power.
QUESTION 7
Pressure limiting devices of refrigeration systems shall be connected:
A) Between the compressor and the stop valve on the suction side
B) To a blowdown tank
C) Between the inlet of the condenser and the outlet of the receiver
, D) Between the compressor and the stop valve on the discharge side
E) To the receiver outlet
Correct Answer: D
Explanation: Pressure limiting devices (high pressure cut-outs or pressure relief
valves) must be connected between the compressor discharge and the stop valve
on the discharge side to protect the compressor and system from overpressure.
They should be installed as close to the compressor as practical.
QUESTION 8
The warm-up time required for a turbine is dependent on:
A) How quickly the turbine is required
B) The manufacturer's instructions
C) The size of the turbine
D) The type of turbine
E) Whether the steam is dry or wet
Correct Answer: C
Explanation: Larger turbines have more thermal mass (more metal) and take
longer to warm up evenly to prevent thermal stress, differential expansion, and
rotor "hogging" (bending). Warm-up time is primarily determined by turbine size
(rotor diameter, casing thickness). Manufacturer's instructions provide specific
ramp rates, but size is the fundamental factor.
QUESTION 9
________ compressors require intake and discharge valves.
A) Rotary
B) Centrifugal
C) Sliding vane
D) Rotary lobe
E) Reciprocating
Correct Answer: E
Explanation: Reciprocating compressors use automatic spring-loaded or pressure-
actuated intake and discharge valves that open and close based on pressure
