2nd Class Power Engineering 2B2 Practice Exam

2ND CLASS POWER

ENGINEERING 2B2

PRACTICE EXAM

Question 1: In a single element feedwater control system, the variable used for

control is:

Choices:

1) Steam �ow 2) Feedwater �ow 3) Steam pressure 4) Drum level

Correct Answer: Drum level

Explanation: Single element uses only drum level.

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Question 2: Self operated single element feedwater systems such as

thermohydraulic systems typically:

Choices:

1) compensate for shrink and swell 2) maintain a reasonably narrow proportional band 3) close the feedwater valve on an initial increase in steaming rate 4) require an external source of power Correct Answer: close the feedwater valve on an initial increase in steaming rate Explanation: They react to the initial shrink/swell which can be opposite to required �ow.Question 3: Hydrostatic head is:

Choices:

1) dependent upon the volume of liquid 2) independent of the shape of the vessel 3) based on the expansion of liquids 4) only expressed in terms of pressure

Correct Answer: independent of the shape of the vessel

Explanation: Hydrostatic head depends only on height and density, not vessel shape.Page 2

Question 4: A feedforward control strategy where a ratio between two process

variables is desired to be maintained at a speci�c set point is referred to as:

Choices:

1) Cascade control 2) Derivative control 3) Integral control 4) Ratio control

Correct Answer: Ratio control

Explanation: Ratio control maintains a set ratio between two variables.

Question 5: A proportional controller is implemented to eliminate the _______ of an on/o� controller.

Choices:

1) derivative gain 2) reset time 3) cycling 4) o�set

Correct Answer: cycling

Explanation: Proportional control smooths out the constant cycling of on/o� control.Page 3