Found 1006 Articles for Electronics & Electrical

Following are the assumptions being made in the synchronous impedance method for finding the voltage regulation of the alternator or synchronous generator −The synchronous impedance is constant. For the synchronous generator, the synchronous impedance is determined from the open-circuit characteristics (O.C.C.) and short-circuit characteristics (S.C.C.). The synchronous impedance is the ratio of open-circuit voltage to short-circuit current i.e.$$\mathrm{Synchronous\:impedance, \:𝑍_{𝑠}=\frac{open\: circuit\:voltage\:per\:phase}{short\:circuit \:armature\:current}}$$When the O.C.C. and S.C.C. are linear, then the synchronous impedance is constant. Above the knee point of the O.C.C. when the saturation starts, the synchronous impedance decreases because in this condition, the O.C.C. and S.C.C. approach each other.Therefore, the synchronous ... Read More

In this article, we will take a look at some of the basic terms used in Electrical Machines and their definition.Field WindingThe winding of the electrical machine through which a current is passed to produce the main flux is known as field winding.Armature WindingThe winding of the electrical machine in which voltage is induced by the action of electromagnetic induction is known as armature winding.Some of the basic terms associated with the armature winding are as follows −Turn – When two conductors are connected to one end by an end connector, it is known as a turn.Coil – When several ... Read More

Consider the direction of rotation of the rotor is clockwise. The direction of the generated voltage in various conductors can be determined by applying the right-hand rule keeping in view that the direction of rotation of the conductors with respect to the rotor poles is anticlockwise.Consider the alternator is supplying current at unity power factor. The phase currents 𝐼𝑅 , 𝐼𝑌 and 𝐼𝐵 will be in phase with their respective generated voltage 𝐸𝑅 , 𝐸𝑌 and 𝐸𝐵 as shown in Figure-1. The positive direction of fluxes φ𝑅, φ𝑌 and φB are shown in Figure-2. The projection of a phasor on ... Read More

Armature Leakage ReactanceIn an AC electrical machine, the magnetic flux set up by the load current which does not contribute to the useful magnetic flux of the machine is known as leakage flux. This leakage flux sets up a self-induced EMF in the armature winding of the machine. The leakage flux may be classified into three categories as follows −Slot leakageTooth head leakageOverhang or coil end leakageThe leakage fluxes in the electrical machines induce EMFs in the armature windings. These leakage EMFs are taken into account by introduction of leakage reactance drops and lead the current producing them by 90°.Armature ... Read More

Consider a 2-pole alternator as shown in Figure-1. Suppose that the alternator is loaded with an inductive load of zero power factor leading.. Thus, the phase currents 𝐼𝑅 , 𝐼𝑌 and 𝐼𝐵 will be leading their respective phase voltages 𝐸𝑅 , 𝐸𝑌 and 𝐸𝐵 by 90°. Figure-2 shows the phase diagram of the alternator.Now, at time t = 0, the instantaneous values of currents and fluxes are given by, $$\mathrm{𝑖_{𝑅} = 0;\:\:φ_{𝑅} = 0}$$$$\mathrm{𝑖_{𝑌} = 𝐼_{𝑚}\:cos 30° = \frac{\sqrt{3}}{2}𝐼_{𝑚};\:\:\:φ_{𝑌} = \frac{\sqrt{3}}{2}φ_{𝑚}}$$$$\mathrm{𝑖_{𝐵} = −𝐼_{𝑚}\:cos 30° = −\frac{\sqrt{3}}{2}𝐼_{𝑚};\:\:\:φ_{B} = −\frac{\sqrt{3}}{2}φ_{𝑚}}$$The space diagram of the magnetic fluxes is shown in Figure-3. By the ... Read More

Consider a 2-pole alternator as shown in Figure-1. Suppose that the alternator is loaded with an inductive load of zero power factor lagging. In this case, the phase current 𝐼𝑅 , 𝐼𝑌 and 𝐼𝐵 will be lagging with their respective phase voltages 𝐸𝑅 , 𝐸𝑌 and 𝐸𝐵 by 90°. The phasor diagram of the alternator is shown in Figure2.Now, at time t = 0, the instantaneous values of currents and fluxes are given by, $$\mathrm{𝑖_{𝑅} = 0;\:\:φ_{𝑅} = 0}$$$$\mathrm{𝑖_{𝑌} = 𝐼_{𝑚}\:sin(−120°) = −\frac{\sqrt{3}}{2}𝐼_{𝑚};\:\:\:φ_{𝑌} = −\frac{\sqrt{3}}{2}φ_{𝑚}}$$$$\mathrm{𝑖_{𝐵} = 𝐼_{𝑚}\:sin(120°) = \frac{\sqrt{3}}{2}𝐼_{𝑚};\:\:\:φ_{𝐵} = \frac{\sqrt{3}}{2}φ_{𝑚}}$$The space diagram of the magnetic fluxes is shown in ... Read More

Practically, most of the synchronous generators or alternators have stationary armature and rotating field.A stationary armature-rotating field alternator has several advantages over a rotating armature type alternator, as given below −When a stationary armature is used in the alternator, the output current can be taken directly from the fixed terminals on the stationary armature without using slip rings, brushes, etc.The armature windings of the rotating field alternator, being stationary, are not subjected to vibration and centrifugal forces.A stationary armature can be easily insulated for the high voltage for which the alternator is designed. This generated voltage may be as high ... Read More

The synchronous impedance method or EMF method is used to determine the voltage regulation of the larger alternators. The synchronous impedance method is based on the concept of replacing the effect of armature reaction by an imaginary reactance.For an alternator, $$\mathrm{𝑽 = 𝑬_{𝒂} − 𝑰_{𝒂}𝒁_{𝒔} = 𝑬_{𝒂} − 𝑰_{𝒂}(𝑅_{𝒂} + 𝑗𝑋_{𝑠}) … (𝟏)}$$At first, the synchronous impedance (𝑍𝑠) is measured and then, the value of actual generated EMF (𝐸a) is calculated. Thus, from the values of (𝐸a) and V, the voltage regulation of the alternator can be calculated.Measurement of Synchronous ImpedanceIn order to determine the value of synchronous impedance, following ... Read More

The voltage regulation of an alternator or synchronous generator is defined as the rise in the terminal voltage when the load is decreased from full-load rated value to zero. The speed and field current of the alternator remain constant.In other words, the voltage regulation of the alternator can be defined as the change in terminal voltage from no-load to full load rated value divided by the full-load rated voltage, i.e., $$\mathrm{Per\:unit\:voltage\:regulation =\frac{|𝐸_{𝑎}| − |𝑉|}{|𝑉|}}$$Also, the percentage voltage regulation of the alternator is given by, $$\mathrm{Percentage\:voltage\:regulation =\frac{|𝐸_{𝑎}| − |𝑉|}{|𝑉|}× 100\%}$$Where, |𝐸𝑎| is the magnitude of generated voltage (or no-load voltage) perphase|𝑉| ... Read More

Unsaturated Synchronous ReactanceAt low excitations, the open-circuit characteristic (OCC) of an alternator coincides with the air-gap line, thus, the synchronous impedance of the alternator is constant and this value of the synchronous impedance is known as linear or unsaturated synchronous impedance.The unsaturated synchronous reactance (denoted by Xsu) can be obtained from the air-gap line voltage and the short-circuit current of the alternator for a particular value of the field current.Note – SCC is the short-circuit characteristic.From the characteristics, the unsaturated synchronous impedance is given by, $$\mathrm{𝑍_{𝑠𝑢} =\frac{𝐸_{𝑎𝑑}}{𝐼_{𝑎𝑏}}= 𝑅_{𝑎} + 𝑗𝑋_{𝑠𝑢}}$$If the armature resistance of the alternator is neglected, then the ... Read More