Brushless DC Motors: The term brushless dc motors is applied to many configurations of ac synchronous motors in which semiconductor control is used to control stator currents such that maximum torque is obtained at a given speed. In a conventional motor the mechanical contactor, the commutator, maintains 90° elect degrees space displacement between the rotor […]

### SYNCHRONOUS MACHINE

## Single Phase Synchronous Generators

Single Phase Synchronous Generators Single Phase Synchronous Generators – Certain applications, usually restricted to less than 10 kVA are better served by a single-phase synchronous generator. Examples are emergency, domestic/office supply, portable power for construction tools etc. Because of simplicity of distribution wiring, these loads are better served by a single-phase arrangement. Single-phase generator stator […]

## Short Circuit Transient in Synchronous Machine

Short Circuit Transient in Synchronous Machine: The Short Circuit Transient in Synchronous Machine being electrical in nature is much faster than the electromechanical dynamics discussed in Sec. 8.13. It will, therefore, be assumed that by the time the major features of the short-circuit phenomenon are over, the rotor speed remains constant at the synchronous value. […]

## Hunting in Synchronous Machines

Hunting in Synchronous Machines So far the operation of the synchronous machine under steady-state conditions at constant (synchronous) speed has been considered. Under these conditions where Pe= electrical power output of the machine Pm= mechanical power input to the machine the machine losses having been assumed negligible. […]

## Parallel Operation of Synchronous Generators

Parallel Operation of Synchronous Generators: Parallel Operation of Synchronous Generators – The operation considered in Sec. 8.8 is that of a synchronous machine connected to infinite bus-bars. Here the parallel operation of two finite size synchronous generators will be considered, which is the way large practical size generators are used. In a power system the […]

## Slip Test

Slip Test – Determination of Xd and Xq: Direct and quadrature axis reactances of a salient-pole synchronous machine can be estimated by means of a test known as the slip test. The machine armature is connected to a 3-phase supply whose voltage is much less than the rated voltage of the machine, while the rotor is […]

## Salient Pole Synchronous Machine Two Reaction Model

Salient Pole Synchronous Machine Two Reaction Model: In a Salient Pole Synchronous Machine Two Reaction Model the flux established by a mmf wave is independent of the spatial position of the wave axis with respect to the field pole axis. On the other hand, in a salient-pole machine as shown in the cross-sectional view of […]

## Capability Curve of Synchronous Generator

Capability Curve of Synchronous Generator: Capability Curve of Synchronous Generator defines the bounds within which it can operate safely. Various bounds imposed on the machine are: MVA-loading cannot exceed the generator rating. This limit is imposed by the stator heating. MW-loading cannot exceed the turbine rating which is given by MVA (rating) x pf (rating). […]

## Power Flow Transfer Equations

Power Flow Transfer Equations: Power Flow Transfer Equations – The flow of active and reactive power in a synchronous link will now be studied. The approach will be analytical and armature resistance will be considered for generality of results. Figure 8.42 shows the schematic diagram of a synchronous generator wherein E̅f leads V̅t by angle δ. The synchronous […]

## Operating Characteristics of Synchronous Machine

Operating Characteristics of Synchronous Machine: The Operating Characteristics of Synchronous Machine are examined here under conditions of variable load and variable excitation. One of these quantities will be assumed to be held constant at a time while the other will be allowed to vary over a wide range. Further, here too the armature resistance will […]

## Synchronous Machine on Infinite Bus Bars

Synchronous Machine on Infinite Bus Bars: Synchronizing to Infinite Bus Bars – A definite procedure has to be followed in connecting a synchronous machine to bus-bars which for the present purpose will be assumed to be infinite. Infinite bus-bars means a 3-phase supply of constant voltage and frequency independent of the load exchanged (fed into the […]

## Nature of Armature Reaction

Nature of Armature Reaction The nature of the armature reaction is dependent on the power factor at which the machine is operating and upon the operating mode-generating/motoring. For simplicity of explanation, it will be assumed here that the armature resistance and leakage reactance are negligible so that Figure 8.26 shows the phasor diagrams, with component […]

## Determination of Armature Reaction

Determination of Armature Reaction The simple circuit model of the synchronous machine was obtained in Sec. 8.3 by making the assumption that the magnetic circuit of the machine is linear. However, it is known that, under normal operating conditions, the machine operates in a somewhat saturated region. In order to take account of magnetic saturation […]

## Determination of the Synchronous Reactance

Determination of the Synchronous Reactance With the assumption of a linear magnetic circuit, the circuit model (per phase) of a synchronous machine is as given in Fig. 8.10c. If Ra is neglected, it then follows that It is immediately seen from Eq. (8.22) that for a given field current under short-circuit condition (/,„ = /so […]

## Circuit Model of Synchronous Machine

Circuit Model of Synchronous Machine Circuit Model of Synchronous Machine – By assuming linearity of the magnetic circuit, it is possible to obtain simple circuit model of the synchronous machine. The validity of this assumption stems from the fact that air-gap is the predominant component of the magnetic circuit of the machine. Approximate nonlinear analysis is […]

## Voltage Regulation

Voltage Regulation: The voltage regulation of a synchronous generator is defined on lines similar to that of a transformer. Consider the generator supplying full-load current at a specified power factor and rated terminal voltage, V, (rated). As the load is thrown off keeping the field current constant, the terminal voltage rises to The percentage […]

## Realistic Machine

Realistic Machine: Realistic Machine – A realistic synchronous machine will have resistance ra and leakage reactance x1 per armature phase which can be assumed to be lumped in series between the terminal voltage V, and the air-gap emf Er for each machine phase. The circuit diagram of the machine on a per phase basis is […]