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**D.C. Generators and Motors
**

**Electrical Engineering
(ELE-232)**

**Problem
**

• A shunt generator supplies a 20 kW load at 200 V through cables of resistance, R = 100 mili-ohm. If the field winding resistance, Rf =50 ohm and the armature resistance, Ra = 40 mili-ohm, determine (a) the terminal voltage, and

(b) the e.m.f. generated in the armature.

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**Solution
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**Solution
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**Solution
**

MZS FKEE, UMP

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**Problem
**

• A d.c. shunt-wound generator running at constant speed generates a voltage of 150 V at a certain value of field current. Determine the change in the generated voltage when the field current is reduced by 20%, assuming the flux is proportional to the field current.

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**Solution
**

MZS FKEE, UMP

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**Solution
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MZS FKEE, UMP

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**Problem
**

• A d.c. generator running at 30 rev/s generates an e.m.f. of 200 V. Determine the percentage increase in the flux per pole required to generate 250 V at 20 rev/s.

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**Solution
**

MZS FKEE, UMP

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**Problem
**

• Determine the terminal voltage of a generator which develops an e.m.f. of 200 V and has an armature current of 30 A on load. Assume the armature resistance is 0.30

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**Solution
**

• With reference to Figure, terminal voltage,

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**Problem
**

• A generator is connected to a 60 load and a current of 8 A flows. If the armature resistance is 1 ohm determine

• (a) the terminal voltage, and • (b) the generated e.m.f.

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**Solution
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**Problem
**

• A separately-excited generator develops a no-load e.m.f. of 150 V at an armature speed of 20 rev/s and a flux per pole of 0.10 Wb. Determine the generated e.m.f. when (a) the speed increases to 25 rev/s and the pole flux remains unchanged, (b) the speed remains at 20 rev/s and the pole flux is decreased to 0.08 Wb, and (c) the speed increases to 24 rev/s and the pole flux is decreased to 0.07 Wb.

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**Solution
**

MZS FKEE, UMP

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**Problem
**

• A short-shunt compound generator supplies 80 A at 200 V. If the field resistance, Rf = 40 ohm, the series resistance, Rse = 0.02 ohm and the armature resistance, Ra = 0.04 ohm , determine the e.m.f. generated.

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MZS FKEE, UMP

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**Problem
**

• A 10 kW shunt generator having an armature circuit resistance of 0.75 ohm and a field resistance of 125 ohm, generates a terminal voltage of 250 V at full load. Determine the efficiency of the generator at full load, assuming the iron, friction and windage losses amount to 600 W.

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**Solution
**

MZS FKEE, UMP

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**Problem
**

• A shunt generator supplies a 20 kW load at 200 V through cables of resistance, R = 100 mili-ohm. If the field winding resistance, Rf = 50 ohm and the armature resistance, Ra = 40 mili-ohm determine (a) the terminal voltage, and (b) the e.m.f. generated in the armature.

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MZS FKEE, UMP

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**Armature Reaction
**

• In a d.c. generator: • The purpose of field winding is to produce

magnetic field (called main flux). • And the purpose of armature winding is to carry

armature current.

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**Armature Reaction
**

• Although the armature winding is not provided for
the purpose of producing a magnetic field, but the
current in the armature winding will also produce
magnetic flux **(called armature flux).
**

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