// Numbas version: exam_results_page_options {"name": "DC Machines - Practice", "metadata": {"description": "", "licence": "None specified"}, "duration": 0, "percentPass": "40", "showQuestionGroupNames": false, "showstudentname": false, "question_groups": [{"name": "Group", "pickingStrategy": "random-subset", "pickQuestions": 1, "questionNames": ["", "", "", ""], "questions": [{"name": "DC Series Generator", "extensions": [], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "contributors": [{"name": "Jane Courtney", "profile_url": "https://numbas.mathcentre.ac.uk/accounts/profile/2154/"}], "tags": [], "metadata": {"description": "", "licence": "None specified"}, "statement": "

In testing, a separately excited DC machine, operating at a speed of $\\var{Ntest}\\ rpm$, produces $\\var{Vtest}\\ V$ with an open circuit armature, when operated at a fixed field current of $\\var{IF}\\ A$.

\n

Its intrinsic resistances are:

\n

Field Resistance: $R_F = \\var{RF}\\ \\Omega $

\n

Armature Resistance: $R_A = \\var{RA}\\  \\Omega $ 

\n

The machine is then connected as a series generator to supply a load with a current of $\\var{IF}\\ A$ when running at a speed of $\\var{N}\\ rpm$ .

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What is the magnetism on the machine?

\n

$k_a \\phi = $ [[0]]

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What is the torque on the shaft?

\n

$T$ = [[0]] $ Nm $

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What is the output voltage to the load?

\n

$V_L$ = [[0]] $ V $

\n

What is the load resistance?

\n

$R_L$ = [[1]] $\\Omega$

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The following test data was measured for a separately excited DC machine operating at a speed of $\\var{Ntest}\\ rpm$ with an open circuit armature:

\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
\n

Field Current

\n

IF [A]

\n
\n

0

\n
\n

0.1

\n
\n

0.2

\n
\n

0.3

\n
\n

0.4

\n
\n

0.5

\n
\n

0.6

\n
\n

0.7

\n
\n

0.8

\n
\n

0.9

\n
\n

1.0

\n
\n

Armature Voltage

\n

VA [V]

\n
{VA[0]}{VA[1]}{VA[2]}{VA[3]}{VA[4]}{VA[5]}{VA[6]}{VA[7]}{VA[8]}{VA[9]}{VA[10]}
\n

\n

The intrinsic resistances are:

\n

Field Resistance: $R_F = \\var{RF}\\ \\Omega $

\n

Armature Resistance: $R_A = \\var{RA}\\  \\Omega $ 

\n

The machine is then connected as a shunt generator to supply $\\var{VL}\\ V$ to a $\\var{RL}\\ \\Omega$ load.

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What is the magnetism on the machine?

\n

$k_a \\phi = $ [[0]]

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How much current is it flowing in the armature conductors?

\n

$I_A$ = [[0]] $ A $

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At what speed is it running?

\n

N = [[0]] $ rpm $

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The following test data was measured for a separately excited DC machine operating at a speed of $\\var{Ntest}\\ rpm$ with an open circuit armature:

\n

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
\n

Field Current

\n

IF [A]

\n
\n

0

\n
\n

0.1

\n
\n

0.2

\n
\n

0.3

\n
\n

0.4

\n
\n

0.5

\n
\n

0.6

\n
\n

0.7

\n
\n

0.8

\n
\n

0.9

\n
\n

1.0

\n
\n

Armature Voltage

\n

VA [V]

\n
{VA[0]}{VA[1]}{VA[2]}{VA[3]}{VA[4]}{VA[5]}{VA[6]}{VA[7]}{VA[8]}{VA[9]}{VA[10]}
\n

\n

The intrinsic resistances are:

\n

Field Resistance: $R_F = \\var{RF}\\ \\Omega $

\n

Armature Resistance: $R_A = \\var{RA}\\  \\Omega $ 

\n

The machine is then connected as a shunt motor to a supply providing $\\var{VS}\\ V$. The motor is used to lift a weight which creates a torque of $\\var{T}\\ Nm$.

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What is the magnetism on the machine?

\n

$k_a \\phi = $ [[0]]

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How much current is it drawing from the supply?

\n

$I_S$ = [[0]] $ A $

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At what speed is it running?

\n

N = [[0]] $ rpm $

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In testing, a separately excited DC machine, operating at a speed of $\\var{Ntest}\\ rpm$, produces $\\var{Vtest}\\ V$ with an open circuit armature, when operated at a fixed field current of $\\var{IF}\\ A$.

\n

Its intrinsic resistances are:

\n

Field Resistance: $R_F = \\var{RF}\\ \\Omega $

\n

Armature Resistance: $R_A = \\var{RA}\\  \\Omega $ 

\n

The machine is then connected as a series motor to a supply providing $\\var{VS}\\ V$. It is found to draw the same current of $\\var{IF}\\ A$.

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What is the magnetism on the machine?

\n

$k_a \\phi = $ [[0]]

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What is the torque on the motor?

\n

$T$ = [[0]] $ Nm $

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At what speed is it running?

\n

N = [[0]] $ rpm $

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