Matching Characteristics of Electric Machine and Load The machine and the load are the two components of an electro-mechanical energy-conversion system, and the machine characteristics, generally, play a predominant part in the operating behaviour of the complete system. In choosing an electric motor its speed-torque characteristic is needed to be known to a fair degree […]

### ROTATING MACHINES

## Rating and Loss Dissipation Rating

Rating and Loss Dissipation Rating The rating of a synchronous generator is its operating voltage, frequency, speed and kVA/MVA output at a specified power factor*. In case of motors the output rating is given in kW (older practice was to specify the rated output in horse-power (1 hp = 746 W)). The dc machines are […]

## Rotating Machines Losses Classification

Rotating Machines Losses Classification: Rotating Machines Losses Classification – The Losses and Efficiency of a transformer have been studied in Sec. 3.6. As in the case of transformers, it is more accurate to determine the efficiency of a rotating machine by determination of its losses rather than by the direct load test in which the […]

## Magnetic Leakage in Rotating Machines

Magnetic Leakage in Rotating Machines: Magnetic Leakage in Rotating Machines – The leakage flux in rotating machines is that flux which links only the stator or only the rotor windings. Because of the presence of air-gap in the magnetic circuit of machines, the leakage in these is quite significant and cannot be neglected in analysis […]

## Induction Machine Principle

Induction Machine Principle: Induction Machine Principle has not been introduced so far. Consider a cylindrical rotor machine with both the stator and rotor wound for three phases and identical number of poles as shown in Fig. 5.40. Assume initially the rotor winding to be open-circuited and let the stator be connected to an infinite bus […]

## Synchronous Machine Torque Equation

Synchronous Machine Torque Equation: Figure 5.36 shows a Synchronous Machine Torque Equation with a round rotor. The rotor is initially stationary with fixed north-south poles created by dc excitation. Let the 3-phase winding of the stator be connected to a 3-phase supply of fixed voltage V (line) and fixed frequency f (this is known as […]

## Torque in Round Rotor Machine

Torque in Round Rotor Machine Torque in Round Rotor Machine – When the stator and rotor windings of a machine both carry currents, they produce their own magnetic fields along their respective axes which are sinusoidally distributed along the air-gap. Torque results from the tendency of these two fields to align themselves. The flux components […]

## Rotating Magnetic Field

Rotating Magnetic Field Rotating Magnetic Field – It was seen in Sec. 5.4 that the sinusoidal current in any phase of an ac winding produces a pulsating mmf wave in space whose amplitude varies sinusoidally with time. The expression for the fundamental component of this mmf is given in Eq.(5.36). The harmonics of the mmf […]

## Current sheet Concept

Current sheet Concept Current sheet Concept – It was seen above that a distributed winding gives rise to a stepped mmf wave having a strong fundamental component which will be considered in machine modelling while all the harmonic components will be neglected (justification for the same has been advanced). Now the kind of space distribution […]

## MMF of Distributed AC Windings

MMF of Distributed AC Windings MMF of Distributed AC Windings – It has been seen earlier that the armature of a practical machine has distributed winding wound for the same number of poles as the field winding. As the armature carries current, the resultant field of its current-carrying coils has the same number of poles […]

## DC Machine

DC Machine With reference to the single-coil elementary dc machine of Figs 5.13 and 5.14(a) which shows the B-wave of the machine relative to the elementary full-pitched coil, let Consider that the coil is lying in the interpolar region so that the full flux/pole (0) links it positively. Let it now move through one pole-pitch […]

## Two layer Winding

## Short Pitched Coils

Short Pitched Coils (Chorded) Short Pitched Coils – So far it was assumed that the stator coils are full-pitched (a span of iv rad elect). Coils may have a span of less than the full-pitch. This arrangement offers certain advantages. Consider that the coil-span is less than the full-pitch by an elect. angle Osp (short-pitching […]

## Harmonic Content in the Distributed Winding

Harmonic Content in the Distributed Winding The flux density wave of a synchronous machine is never exactly sine wave. Because of odd symmetry of poles (alternately north-south), the space harmonic content of the B-wave comprises odd harmonics only, which induce the corresponding harmonic emf s in the winding. Figure 5.19 shows the fundamental B-wave, and […]

## Distributed Winding

Distributed Winding Distributed Winding – It may be seen from Eq. (5.7) that the flux/pole is limited by the machine dimensions and the peak flux density which cannot exceed a specified value dictated by saturation characteristic of iron. Therefore, for inducing an emf of an appropriate value in a practical machine (it may be as […]

## Generated Voltage of ac Winding

Generated Voltage of ac Winding Generated Voltage of ac Winding – The B-wave of a synchronous machine (in general multi-polar) assumed sinusoidal is drawn in Fig. 5.15 and a single full-pitched coil (coil-side space separation r rad (180Â°) elect.) is shown in cross-sectional form. The B-wave moves towards left with a speed of co elect. […]

## DC Machine Diagram

DC Machine Diagram: Figure 5.13 shows a 2-pole elementary DC Machine Diagram with a single coil rotating armature. It may be seen that the field winding is stationary with salient poles whose pole-shoes occupy a major part of the pole-pitch. An alternating emf is induced in the coil due to rotation of the armature past […]