Found 1006 Articles for Electronics & Electrical

A synchronous machine under steady running conditions has a driving torque at every instant balancing its retarding torque. The retarding torque is developed by phase displacement ($\delta$) between the axis of the stator and rotor poles. A mechanical rotary system possesses inertia and restoring torque that tends to restore its position when displaced, thus the system has a natural frequency of oscillations.A synchronous machine operating in parallel with other machines or infinite busbars forms such an oscillatory system. Here, the restoring torque is due to the synchronizing torque that depends upon the phase displacement and opposes the displacement. The inertia ... Read More

In the ampere-turn method (which is also known as the MMF method), the effect of armature leakage reactance is replaced by an equivalent additional armature reaction MMF so that this MMF can be combined with the armature reaction MMF.In order to predict the voltage regulation of the alternator by the MMF method, the following information is required −Resistance of the armature (or stator) winding per phase.Open-circuit characteristic of the alternator.Short-circuit characteristic of the alternator.The MMF method uses the phasor diagram of the alternator for determining the voltage regulation. In order to draw the phasor diagram at lagging power factor, the ... Read More

Metadyne is a cross-field machine. The cross-field machines are special DC machines having an additional set of brushes on the direct-axis or d-axis. This arrangement of brushes enables the use of armature MMF to provide most of the excitation and achieve high power gains.Construction and Working of MetadyneAn ordinary DC generator can be converted into a metadyne by providing an additional pair of brushes on the direct-axis or d-axis (see the figure). The brushes lie on the quadrature axis or q-axis are short-circuited and the output of the machine is obtained from the d-axis brushes. The stator consists of a ... Read More

The synchronising torque coefficient is defined as the torque at which the synchronous speed gives the synchronising power. If represents the synchronising torque coefficient, then$$\mathrm{𝜏_{𝑠𝑦𝑛} =\frac{1}{𝜔_{𝑠}}𝑚\frac{𝑑𝑃}{𝑑𝛿}\:Nm/electrical\:radian …(1)}$$Also, $$\mathrm{𝜏_{𝑠𝑦𝑛} =\left (\frac{1}{𝜔_{𝑠}}𝑚\frac{𝑑𝑃}{𝑑𝛿} \right)\cdot \frac{𝜋𝑝}{180°}\:Nm/mechanical \:degree …(2)}$$Where, m is the number of phase of the machine, 𝜔𝑠 = 2𝜋𝑛𝑠 is the angular synchronous speed, 𝑛𝑠 is the synchronous speed in r.p.s.𝑝 is the total number of pair of poles of the machine.The synchronising torque coefficient may also be given by, $$\mathrm{𝜏_{𝑠𝑦𝑛} =\frac{𝑑𝜏}{𝑑𝛿}=\frac{1}{2𝜋𝑛_{𝑠}}\frac{𝑑𝑃}{𝑑𝛿}… (3)}$$$$\mathrm{∵\:\frac{𝑑𝑃}{𝑑𝛿}=𝑃_{𝑠𝑦𝑛} =\frac{𝑉𝐸_{𝑓}}{𝑍_{𝑠}}sin(𝜃_{𝑧} − 𝛿)}$$$$\mathrm{∴\:𝜏_{𝑠𝑦𝑛} =\frac{𝑉𝐸_{𝑓}}{2𝜋𝑛_{𝑠 }\cdot 𝑍_{𝑠}}sin(𝜃_{𝑧} − 𝛿) … (4)}$$In many synchronous machines, Xs >>R. Therefore, for a cylindrical rotor ... Read More

What is an Infinite Bus?Normally, in a power system, more than one synchronous generators or alternators operate in parallel. The alternators may be located at different places.A group of alternators located at a single place may be treated as a single large alternator.Also, the alternators connected to the same busbar but separated by transmission lines of low reactance may be considered as a single large machine.The capacity of this power system is so large that its terminal voltage and frequency may be taken constant. The connection or disconnection of a single alternator or a single small load would not affect ... Read More

The zero power factor characteristics (ZPFC) is the graph plotted between the armature terminal voltage per phase and the field current, when the machine being operating with constant rated armature current at synchronous speed and zero lagging power factor. The ZPFC is also known as Potier Characteristics after its originator.In order to maintain the power factor very low, the alternator is loaded by means of reactors or by an under-excited synchronous motor. The shape of the ZPFC is very much like that of the open-circuit characteristic (O.C.C.) displaced downwards and to the right.Phasor DiagramFigure-1 shows the phasor diagram of the ... Read More

When the flux density distribution in the alternator is non-sinusoidal, the induced voltage in the winding will also be non-sinusoidal. Thus, the pitch factor or coil span factor, distribution factor and winding factor will be different for each harmonic voltage.Pitch Factor for nth HarmonicAs the electrical angle is directly proportional to the number of poles and the angle between the adjacent slots, i.e., $$\mathrm{𝜃_{𝑒} =\frac{𝑃}{2}𝜃_{𝑚} … (1)}$$The chording angle increases with an increase in the order of the harmonics (n). In a short pitch coil, the chording angle is α° (electrical) for the fundamental flux wave. For the nth harmonic, ... Read More

When a synchronous machine is synchronised to infinite busbars, it has an inherent tendency to remain in synchronism.Rotor is accelerated – Consider an alternator delivering a steady power P at a steady load angle δ. Suppose, due to some transient disturbance, the rotor is accelerated so that the load angle increases by an angle $dδ$. The operating point of the machine shifts to a new constant power line and the load on the machine increases to (𝑃 + 𝑑𝑃)). As the power input to the machine remains unchanged, this additional load decreases the speed of the machine and brings it ... Read More

A synchronous generator is a synchronous machine which converts mechanical power into AC electric power through the process of electromagnetic induction.Synchronous generators are also referred to as alternators or AC generators. The term "alternator" is used since it produces AC power. It is called synchronous generator because it must be driven at synchronous speed to produce AC power of the desired frequency.A synchronous generator can be either single-phase or poly-phase (generally 3phase).Construction of Synchronous Generator or AlternatorAs alternator consists of two main parts viz.Stator – The stator is the stationary part of the alternator. It carries the armature winding in ... Read More

Short Circuit RatioThe ratio of the field current required to generate rated voltage on open-circuit to the field current required to circulate rated armature current on short circuit is called as the short-circuit ratio (SCR) of a synchronous machine.Calculation of SCRThe short circuit ratio of a synchronous machine can be calculated from the open-circuit characteristic (O.C.C.) and the short-circuit characteristic (S.C.C.) of the synchronous machine, which are shown in the figure.From the figure, the SCR is given by, $$\mathrm{SCR =\frac{𝐼_{𝑓}\:for\:rated\:open \:circuit\:voltage}{𝐼_{𝑓}\:for\:rated\:short\:circuit\: current}=\frac{𝑂𝑎}{𝑂𝑑}… (1)}$$Since the triangles "Oab" and "Ode" are similar triangles, $$\mathrm{SCR =\frac{𝑂𝑎}{𝑂𝑑}=\frac{𝑎𝑏}{𝑑𝑒}… (2)}$$Also, from the figure, for a field ... Read More