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The sequence of events is similar for manual or automatic synchronization. The generator is brought up to approximate synchronous speed by supplying more energy to its shaft - for example, opening the valves on a steam turbine, opening the gates on a hydraulic turbine, or increasing the fuel rack setting on a diesel engine.
When the motor is over excited, the back emf will be greater than the motor terminal voltage. This causes a demagnetizing effect due to armature reaction. [42] The V curve of a synchronous machine shows armature current as a function of field current. With increasing field current armature current at first decreases, then reaches a minimum ...
If the field current is increased beyond this point, the armature current becomes leading, power factor decreases, and grows again. [4] The data from the V curves can be used to set up the synchronous motor to correct the power factor of the overall system, as the power factor of the motor can be changed by simply adjusting the field current. [3]
Synchronous impedance curve (short-circuit characteristic curve), showing armature current as function of field current. The curve is obtained by rotating the generator at the rated RPM with the output terminals shorted and the output current going to 100% of the rated for the device (higher values are typically not tested to avoid overheating).
In a synchronous generator, [1] the short circuit ratio is the ratio of field current required to produce rated armature voltage at the open circuit to the field current required to produce the rated armature current at short circuit. [1] [2] This ratio can also be expressed as an inverse of the saturated [3] direct-axis synchronous reactance ...
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This change in power factor is larger than the change in with increase in load. The phase of armature current varies with field excitation. The current has larger values for lower and higher values of excitation. In between, the current has minimum value corresponding to a particular excitation (see graph on right).
Fleming's left-hand rule. Fleming's left-hand rule for electric motors is one of a pair of visual mnemonics, the other being Fleming's right-hand rule for generators. [1] [2] [3] They were originated by John Ambrose Fleming, in the late 19th century, as a simple way of working out the direction of motion in an electric motor, or the direction of electric current in an electric generator.