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A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A?
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A shunt machine connected to 250V mains has an armature resistance (in...
Problem Statement: A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A?
Solution:
Given:
- Shunt machine connected to 250V mains
- Armature resistance = 0.120
- Field circuit resistance = 1000
- Line current = 80A
Formula:
- Speed as a motor = (V-IaRa)/ϕ
- Speed as a generator = (V+IaRa)/ϕ
Where,
- V = Voltage
- Ia = Armature current
- Ra = Armature resistance
- ϕ = Flux
Calculation:
Speed as a motor:
- V = 250V
- Ia = 80A
- Ra = 0.120
- ϕ = V/(Ra+Rf)
Where,
- Rf = Field circuit resistance = 1000
ϕ = 0.249Wb
Speed as a motor = (250-80*0.120)/0.249 = 818.47 rpm
Speed as a generator:
- V = 250V
- Ia = -80A (Negative sign indicates that the current is flowing out of the machine)
- Ra = 0.120
- ϕ = V/(Ra+Rf)
Where,
- Rf = Field circuit resistance = 1000
ϕ = 0.249Wb
Speed as a generator = (250+(-80)*0.120)/0.249 = 1014.06 rpm
Ratio of speed as a generator to speed as a motor:
Ratio = Speed as a generator/Speed as a motor = 1014.06/818.47 = 1.239
Explanation:
- The given shunt machine is connected to 250V mains.
- The armature resistance of the machine is 0.120 and the field circuit resistance is 1000.
- The line current in each case is 80A.
- Using the formula for speed as a motor, the speed is calculated as 818.47 rpm.
- Using the formula for speed as a generator, the speed is calculated as 1014.06 rpm.
- The ratio of the speed as a generator to the speed as a motor is calculated as 1.239.
- This ratio indicates that the speed as a generator is higher than the speed as a motor by a factor of 1.239.
- This is because the machine is more efficient as a generator than as a motor due to the back EMF produced by the machine when it is acting as a generator.
Solution:
Given:
- Shunt machine connected to 250V mains
- Armature resistance = 0.120
- Field circuit resistance = 1000
- Line current = 80A
Formula:
- Speed as a motor = (V-IaRa)/ϕ
- Speed as a generator = (V+IaRa)/ϕ
Where,
- V = Voltage
- Ia = Armature current
- Ra = Armature resistance
- ϕ = Flux
Calculation:
Speed as a motor:
- V = 250V
- Ia = 80A
- Ra = 0.120
- ϕ = V/(Ra+Rf)
Where,
- Rf = Field circuit resistance = 1000
ϕ = 0.249Wb
Speed as a motor = (250-80*0.120)/0.249 = 818.47 rpm
Speed as a generator:
- V = 250V
- Ia = -80A (Negative sign indicates that the current is flowing out of the machine)
- Ra = 0.120
- ϕ = V/(Ra+Rf)
Where,
- Rf = Field circuit resistance = 1000
ϕ = 0.249Wb
Speed as a generator = (250+(-80)*0.120)/0.249 = 1014.06 rpm
Ratio of speed as a generator to speed as a motor:
Ratio = Speed as a generator/Speed as a motor = 1014.06/818.47 = 1.239
Explanation:
- The given shunt machine is connected to 250V mains.
- The armature resistance of the machine is 0.120 and the field circuit resistance is 1000.
- The line current in each case is 80A.
- Using the formula for speed as a motor, the speed is calculated as 818.47 rpm.
- Using the formula for speed as a generator, the speed is calculated as 1014.06 rpm.
- The ratio of the speed as a generator to the speed as a motor is calculated as 1.239.
- This ratio indicates that the speed as a generator is higher than the speed as a motor by a factor of 1.239.
- This is because the machine is more efficient as a generator than as a motor due to the back EMF produced by the machine when it is acting as a generator.
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A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A?
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A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A? for Electrical Engineering (EE) 2024 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A? covers all topics & solutions for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A?.
A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A? for Electrical Engineering (EE) 2024 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A? covers all topics & solutions for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for A shunt machine connected to 250V mains has an armature resistance (including brushes) of 0.120 and the resistance of the field circuit is 1000. Find the ratio of the speed as a generator to the speed as a motor. The line current in each case being 80A?.
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