DC Machines: Types, Characteristics, and Applications, Slides of Electrical Engineering

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Electrical Machines

DC Machines-

Generators

Nuha Nadhiroh

• Equivalent Circuit
• Magnetization Curve
• Speed Control
• Excercises

Overview

Voltage Regulation of Generator

All generators are driven by a source of mechanical power, which is usually called the prime

mover of the generator. A prime mover for a dc generator maybe a steam turbine, a diesel

engine, or even an electric motor. Since the speed of the prime mover affects the output voltage

of a generator, and since prime movers can vary widely in their speed characteristics, it is

customary to compare the voltage regulation and output characteristics of different generators,

assuming constant speed prime movers

× 𝟏𝟏𝟏𝟏𝟏𝟏𝟏

Equivalent Circuit of DC Generator

Exercise

A separately excited dc generator is rated at 172 kW, 430 V, 400 A, and 1800 r/min. This machine

has the following characteristics:

RA= 0.05 Ohm; RF = 20 Ohm; Radj= 0-300 Ohm; VF = 430 V; NF = 1000 Turns/pole

(a) If the variable resistor Radj in this generator's field circuit is adjusted to 63 Ohm and the

generator 's prime mover is driving it at 1600 r/min, what is this generator ‘s no-load tenninal

voltage?

(b) What would its voltage be if a 360-A load were connected to its terminals? Assume that the

generator has compensating windings.

(c) What would its voltage be if a 360-A load were connected to its terminals but the generator

does not have compensating windings? Assume that its armature reaction (iN) at this load is 450

A · turns.

As with de motors, it is customary to define an equivalent field current that would produce the same output voltage as the combination of all the MMF in the machine. The resulting voltage E (^) A can then be determined by locating that equivalent field current on the magnetization curve. The equivalent field current of a separately excited de generator is given by

Terminal Characteristic of

Shunt DC Generator

The terminal characteristic of a shunt dc generator differs from that of a separately excited dc generator, because the amount of field current in the machine depends on

its terminal voltage. Notice that the voltage drop-off is steeper than just the l (^) ARA drop in a separately excited generator. In other words, the voltage regulation of this generator is worse than the voltage

regulation of the same piece of equipment connected separately excited

Series DC Generator

A series dc generator is a

generator whose fi eld is connected in series with its armature. Since the armature has a much higher current than a shunt field, the series field in a generator of this

sort will have only a very few turns of wire, and the wire used will be much thicker than the wire in a shunt field.

Cumulatively Compounded

DC Generator

Differentially Compounded

DC Generator

Any Question