Electrical Machines

External Characteristics of Compound Generator: External Characteristics of Compound Generator – The causes of voltage drop in the terminal voltage from no-load to full-load in a shunt generator can be partially/fully/over-compensated by use of an aiding series field (cumulative compound), which can be connected in a long- or short-shunt (long-shunt shown in. Fig. 7.34). The […]

External Characteristics of DC Shunt Generator: The External Characteristics of DC Shunt Generator can be predetermined from a knowledge of the OCC and armature and field resistances (which can be determined by simple dc test), without actually performing the load test which in fact is not feasible for a large generator. Assume for the time

Characteristics of Separately Excited DC Generator: With the advent of silicon-controlled rectifiers, the importance of the dc machine as a generator has considerably reduced as SCRs can be employed to draw dc power from standard ac supply and convert it to dc; also the dc voltage can also be varied with ease. For the sake

Self Excited DC Generator: Rather than arranging a separate dc source for excitation purposes, practical generators are always excited from their own armature terminals, this method of excitation being known as Self Excitation. A Self Excited DC Generator with connection as shown in Fig. 7.24 is known as a shunt generator by virtue of the

Magnetization Characteristics of DC Generator: The emf and torque equations, and power balance has been considered so far. The consideration of the Magnetization Characteristics in this section will set the stage for determining the performance of dc machines. Figure 2.3 depicted the magnetization curve of ferromagnetic material (iron) which is the B-H relationship. In a

Methods of Excitation of DC Generator: The performance characteristics of a dc machine are greatly influenced by the way in which the field winding is excited with direct current. There are two Methods of Excitation of DC Generator. Shunt excitation: Here the field winding is provided with a large number of turns of thin wire

Commutation in DC Machine or Generator or Motor: One coil each under an adjoining pole-pair is connected between adjacent commutator segments in a lap-wound dc armature, while in a wave-wound armature the only difference is that P/2 coils under the influence of P/2 pole-pairs are connected between adjacent segments. Coil(s) current is constant and unidirectional

Compensating Winding in DC Machine: Compensating Winding in DC Machine – It was seen from earlier section, that armature reaction causes the flux density wave to be so badly distorted that when a coil is passing through the region of peak flux densities, the emf induced in it far exceeds the average coil voltage. If

Armature Reaction in DC Machine: When the armature of a dc machine carries current, the distributed armature winding produces its own mmf (distributed) known as armature reaction in DC Machine. The machine air-gap is now acted upon by the resultant mmf distribution caused by simultaneous action of the field ampere-turns (ATf) and armature ampere-turns (ATa).

Circuit Model of DC Machine: The parallel paths of DC machine armature are symmetrical and each has an induced emf Ea and a resistance Rp. The armature can be represented by the Circuit Model of DC Machine with voltage Ea and a series resistance as shown in Fig. 7.5. The armature resistance is quite small so