**HOPKINSON’S TEST**

**AIM:**

To conduct Hopkinson’s test on a pair of identical DC machines to pre-determine the efficiency of the machine as generator and as motor.

**APPARATUS REQUIRED:**

S.No. | Apparatus | Range | Type | Quantity |

1 | Ammeter | (0-1)A (0-20) A | MC MC | 1 2 |

2 | Voltmeter | (0-300) V (0-600)V | MC MC | 1 1 |

3 | Rheostats | 1250W, 0.8A | Wire Wound | 2 |

4 | Tachometer | (0-3000) rpm | Digital | 1 |

5 | Resistive Load | 5KW,230V | - | 1 |

6 | Connecting Wires | 2.5sq.mm. | Copper | Few |

**PRECATUIONS:**

1. The field rheostat of the motor should be in the minimum position at the time of starting and stopping the machine.

2. The field rheostat of the generator should be in the maximum position at the time of starting and stopping the machine.

3. SPST switch should be kept open at the time of starting and stopping the machine.

**PROCEDURE:**

1. Connections are made as per the circuit diagram.

2. After checking the minimum position of field rheostat of motor, maximum position of field rheostat of generator, opening of SPST switch, DPST switch is closed and starting resistance is gradually removed.

3. The motor is brought to its rated speed by adjusting the field rheostat of the motor.

4. The voltmeter V

_{1 }is made to read zero by adjusting field rheostat of generator and SPST switch is closed.5. By adjusting field rheostats of motor and generator, various Ammeter readings, voltmeter readings are noted.

6. The rheostats and SPST switch are brought to their original positions and DPST switch is opened

**.****TABULAR COLUMN:**

S.No. | SupplyVoltageV(Volts) | I_{1}(Amps) | I_{2}(Amps) | I_{3}(Amps) | I_{4}(Amps) | I_{1} + I_{2}(Amps) | MotorArmatureCu LossW (watts) | GeneratorArmatureCu LossW(watts) | TotalStraylossesW (watts) | StrayLossPer M/c w/2 (watts) |

| | | | | | | | | | |

**AS MOTOR:**

S.No. | V(Volts) | I_{1}(Amps) | I_{2}(Amps) | I_{3}(Amps) | Motor ArmatureCu LossW (Watts) | Field Loss(Watts) | stray losses/_{2}(Watts) | Total LossesW(Watts) | Output Power(Watts) | Input Power(Watts) | Efficiencyh% |

| | | | | | | | | | | |

**AS GENERATOR:**

S.No. | V(Volts) | I_{1}(Amps) | I_{2}(Amps) | Motor ArmatureCu LossW (Watts) | Field Loss(Watts) | Stray losses/2(Watts) | Total LossesW(Watts) | Output Power(Watts) | Input Power(Watts) | Efficiencyh% |

| | | | | | | | | | |

**PROCEDURE:**

1. Connections are made as per the circuit diagram.

2. Supply is given by closing the DPST switch.

3. Readings of Ammeter and Voltmeter are noted.

4. Armature resistance in Ohms is calculated as R

_{a}= (Vx1.5) /I**TABULAR COLUMN:**

S.No. | VoltageV (Volts) | CurrentI (Amps) | Armature ResistanceR_{a }(Ohms) |

| | | |

**FORMULAE:**

Input Power = VI

_{1 }wattsMotor armature cu loss = (I

_{1}+ I_{2})^{2}Ra wattsGenerator armature cu loss = I

_{2}^{2}Ra wattsTotal Stray losses W = V I

_{1 }- (I_{1}+I_{2})^{2 }Ra + I_{2}^{2 }Ra watts.Stray loss per machine = W/2 watts.

**AS MOTOR:**

Input Power = Armature input + Shunt field input

= (I

_{1}+ I_{2}) V + I_{3}V = (I_{1}+I_{2}+I_{3}) VTotal Losses = Armature Cu loss + Field loss + stray loss

= (I

_{1}+ I_{2})^{2}Ra + VI_{3 }+ W/2 watts Input power – Total Losses

Efficiency h% = ------------------------------------- x 100%

Input Power

**AS GENERATOR:**

Output Power = VI

_{2}wattsTotal Losses = Armature Cu loss+ Field Loss + Stray loss

= I

_{2}^{2 }Ra + VI_{4 }+ W/2 watts Output power

Efficiency h% = -------------------------------------- x 100%

Output Power+ Total Losses

**MODEL GRAPH:**

**RESULT:**

Thus Hopkinson’s test is conducted on a pair of identical DC machines the efficiency of the machine as generator and as motor are pre-determined

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