Synchronous Machines and Electromagnetic Principles

The two methods are the Dark lamp method and the Bright lamp method.

A synchronous motor is defined as a synchronous machine that converts electric power into mechanical power.

A synchronous motor operates on the principle of magnetic locking, where the rotor is aligned with the rotating magnetic field of the stator.

<p>The rotating magnetic field is created when three-phase AC power is supplied to the stator windings.</p> Signup and view all the answers

<p>The rotor must maintain synchronization with the stator's rotating magnetic field.</p> Signup and view all the answers

<p>Faraday's first law states that an emf is induced in a conductor when it cuts across a magnetic field.</p> Signup and view all the answers

<p>The law of interaction is significant in motor action as it describes how a current-carrying conductor experiences force when placed in a magnetic field, leading to motion.</p> Signup and view all the answers

<p>Field windings produce the main magnetic field, while armature windings are where the main voltage is induced.</p> Signup and view all the answers

<p>When the circuit is closed, current flows through the armature conductors, producing a second magnetic field.</p> Signup and view all the answers

<p>In synchronous machines, the rotor contains the field windings, while the stator contains the armature windings.</p> Signup and view all the answers

<p>Torque is developed due to the interaction between the magnetic fields produced by the current-carrying conductor and the main magnetic field.</p> Signup and view all the answers

<p>Emf is induced in the armature conductors when they cut across the magnetic field created by the field windings.</p> Signup and view all the answers

<p>The power angle curve represents the relationship between the load angle and the power output of the synchronous machine.</p> Signup and view all the answers

<p>Concentric winding arranges coils into a concentric or spiral shape under each pole.</p> Signup and view all the answers

<p>In lap winding, coils overlap each other, while in wave winding, the coils are always forward connected.</p> Signup and view all the answers

<p>Pole pitch is the distance between the neutral axes of two adjacent poles, calculated as the number of slots per pole.</p> Signup and view all the answers

<p>Coil pitch or coil span is the distance between the two active sides of a coil.</p> Signup and view all the answers

<p>Slot pitch is the distance between the center points of two consecutive slots or teeth.</p> Signup and view all the answers

<p>Phase spread indicates the angle or space of the pole face over which coil sides of the same phase are distributed.</p> Signup and view all the answers

<p>The stator core provides a path for magnetic lines of force and accommodates the stator winding.</p> Signup and view all the answers

<p>Enamelled copper wires are used for their excellent conductivity and insulation properties.</p> Signup and view all the answers

<p>Retentivity is the property of magnetic material that contributes to hysteresis losses.</p> Signup and view all the answers

<p>Eddy current losses are primarily caused by induced emf in the magnetic material when the flux linking it changes.</p> Signup and view all the answers

<p>Hysteresis losses can be minimized by using silicon steel, which has a low hysteresis constant.</p> Signup and view all the answers

<p>Lamination reduces eddy current losses by limiting the thickness of the magnetic material, thereby decreasing the induced currents.</p> Signup and view all the answers

<p>Mechanical losses are caused by air friction and friction at bearings or brushes, and they can be reduced through proper lubrication.</p> Signup and view all the answers

<p>Stray losses are losses due to distortion of the magnetic field under load conditions and insulation losses.</p> Signup and view all the answers

<p>The efficiency of a synchronous generator represents the ratio of output power to input power.</p> Signup and view all the answers

<p>The hysteresis constant (Kh) signifies the energy loss per unit volume of magnetic material during one magnetic reversal.</p> Signup and view all the answers

<p>Robust construction leads to noiseless operation and reduces windage loss.</p> Signup and view all the answers

<p>Salient pole structures are larger in diameter and shorter in length, typically covering 2/3rd of the pole pitch with pole shoes.</p> Signup and view all the answers

<p>Nearly sinusoidal flux distribution results in a better electromotive force (emf) waveform.</p> Signup and view all the answers

<p>Synchronous reactance is the fictitious reactance representing the combined effects of leakage reactance and armature reaction reactance, denoted by Xs.</p> Signup and view all the answers

<p>Synchronous impedance is the vector sum of armature resistance and synchronous reactance, represented by Zs.</p> Signup and view all the answers

<p>The value of synchronous impedance can be determined using open circuit and short circuit tests.</p> Signup and view all the answers

<p>The SCR indicates the ratio of field current required to produce rated voltage on open-circuit to the current needed for rated current on short-circuit.</p> Signup and view all the answers

<p>The synchronous speed (Ns) is defined by the formula $f = \frac{PNs}{120}$, indicating a direct relationship between these variables.</p> Signup and view all the answers

<p>The interaction between the magnetic field of the rotor and the stator produces torque, leading to the rotor's rotation and performing mechanical work.</p> Signup and view all the answers

<p>The synchronous impedance (ZS) is defined as the sum of the effective armature resistance (Ra) and the synchronous reactance (XS), expressed as $Z_S = R_a + jX_S$.</p> Signup and view all the answers

<p>Back emf (Ef) reduces the current flowing through the motor's coils and acts against the applied voltage, thereby stabilizing the motor's operation.</p> Signup and view all the answers

<p>A synchronous motor is over-excited when the resultant armature voltage (Er) is greater than the terminal voltage (V), indicating that Ef exceeds V.</p> Signup and view all the answers

<p>KVL states that the sum of the voltages around a closed circuit must equal zero, leading to the equation $V = E_f + I_a Z_S$ for a synchronous motor.</p> Signup and view all the answers

<p>A synchronous motor is normally excited when the resultant armature voltage (Er) equals the terminal voltage (V), indicating balanced operation.</p> Signup and view all the answers

<p>Armature current (Ia) can be calculated using the formula $I_a = \frac{V - E_f}{Z_S}$, where $Z_S$ is the synchronous impedance.</p> Signup and view all the answers

<p>At unity power factor, the phasor diagram shows that the supply voltage (V) is the reference, indicating that voltage and current are in phase, resulting in maximum efficiency.</p> Signup and view all the answers