Speed Control of Dc Shunt Machine
EXPERIMENT NO-3 4 Aim of the Experiment: Speed control of DC Shunt Motor by Armature Voltage & flux control method - Speed Control of Dc Shunt Machine introduction. Apparatus Required: |Sl.
No |Name of the Equipment |Type |Range/Capacity |Quantity | |1 |Voltmeter |MC |0-300V |2 Nos | |2 |Ammeter |MC |0-2A |1 No | |3 |Ammeter |MC |0-10A |1 No | |4 |Rheostat |Wire wound |200? ,2A |1 No | |5 |Rheostat |Wire wound |200?
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,2A |1 NO | |6 |Tachometer |Digital | |1 No | |7 |Connecting leads |Multi-stand PVC copper |1. 5mm2 |As per required | | | |wire | | | Machine Specifications Type-DC Shunt, Rating-0. 5HP RPM-1400(No Load) Circuit diagram: Theory: To study the speed control of a DC shunt Motor by two methods a. Armature voltage control method: – Variation of speed with armature voltage at the field current remains constant (below the rated speed). b.
Field excitation method: – Variation of speed with field current at the armature voltage remains constant (above the rated speed). The speed of a DC shunt motor is given by the relation [pic] Where Va=Applied voltage in volts. Ia= Armature current in Amperes. Ra=Armature resistance in ohms. Ф=Field flux in Webers per poles. K=constant for a given motor is given by [pic] Where Z=Number of armature conductor. P=Number of poles of the motor. A=Number of parallel paths in armature circuit. From the relation of speed as above, the speed of DC shunt motor can be varied by varying 1. The voltage Va applied to the armature 2. Armature circuit resistance Ra and 3. The flux ф.
The speed is nearly proportional to armature voltage if armature drop is small while iy is inversely proportional to field flux ф. Procedure: Field Control Method (Flux Control Method) 1. Connect the circuit as per the given circuit diagram. 2. Using the 3-point starter the motor is started to run. 3. The armature rheostat is adjusted to run the motor at rated speed by means of applying the rated voltages. 4. The field rheostat is varied gradually and the corresponding field current and speed are noted up to 120% of the rated speed by keeping the armature voltage as constant. Armature Control Method (Voltage Control Method) 1. Connect the circuit as per the given circuit diagram. 2. Using the 3-point starter the motor is started to run. 3.
The armature rheostat is adjusted to run the motor at rated speed by means of applying the rated voltages. 4. The armature rheostat is varied gradually and the corresponding armature voltage and speed are noted keeping the Field current as constant. Tabulation:- |Sl. NO |Armature Voltage Control method |Field excitation control method | | |Field current (If) =…………………….. |Armarture voltage (Va) =…………….. | | |Armature voltage(Va) |Speed(N) in |Field current(If) |Speed(N) in | | |in volts |R. P. M |in Amps |R. P. M.
| |1 | | | | | |2 | | | | | |3 | | | | | |4 | | | | | |5 | | | | | Precautions:
1. Check that the earthing is properly connected to the machine. 2. Check the insulation resistance of the machine by using Megar. 3. The meters which is connected with the machine trainer kit, the pointers should be in their zero positions. 4. Make sure that Knob of the Dimmer stat is that zero position. 5. Make sure that the patch cords are connected according to the connection diagram. Graph: The graph are drawn as 1. Field current and Speed 2. Armature voltage and Speed Conclusion: From above observation I conclude that the speed of the DC shunts motor increases with increase in armature voltage & decreases with increase in field current.