Applications of DC Generators

Different DC generators have different voltage-current characteristics. The applications of these DC generators depend on their field connection, voltage regulation and required control. Many examples below are established or historical uses; modern power electronics now perform several of the same functions.

Applications of Separately Excited DC Generators

These type of DC generators use an independent field supply. Unlike self-excited DC generators, their field current does not depend directly on terminal voltage. The added supply and control equipment increase complexity, but they also allow independent output adjustment.

1. Laboratories use separately excited machines when a controllable field is needed to measure generator characteristics across a range of voltage values.
2. A separately excited generator can supply the armature of a DC motors while its field controls output voltage. This principle was used in Ward Leonard motor-speed-control systems and remains useful for teaching machine control.

Applications of Shunt Wound DC Generators

Shunt generators have a moderately drooping terminal-voltage characteristic as load rises. A field regulator can adjust their no-load voltage, but their self-excitation makes voltage regulation less stiff than a separately excited source. These type of DC generators were used where a local DC supply needed reasonably steady voltage.

1. They historically supplied local DC lighting circuits.
2. With suitable voltage and current regulation, they can charge a battery. The charging system must control current and prevent overcharge.
3. DC shunt generators have served as exciters that supply field current to alternators.
4. They can provide a small local DC source, although a modern portable generator normally uses an alternator and electronic conversion rather than a shunt DC generator.

Applications of Series Wound DC Generators

Series wound generators use load current to supply the field winding. Terminal voltage therefore changes strongly with load. The falling part of the characteristic can approximate constant current over a limited range, but a series generator is not an ideal regulated current source.

1. Series generators were used in traction equipment to supply field excitation during regenerative braking. This function is different from circuit-breaker breaking current.
2. They were connected as feeder boosters to compensate for voltage drop in long DC distribution and railway circuits.
3. Series DC generators historically supplied constant-current series arc-lighting systems.

Applications of Compound Wound DC Generators

Compound wound DC generators combine shunt and series field windings. Cumulative compounding can offset armature resistance and armature reaction as load rises. The number of series-field turns and any field diverter determine whether the generator is under-compounded, flat-compounded or over-compounded.

1. Cumulative compound generators were used for DC lighting and power services that needed better load-voltage regulation than a shunt generator. Flat compounding holds the no-load and full-load voltages near one another, while over-compounding can offset feeder drop.
2. They supplied DC motors and other loads with changing current demand.
3. Flat- or over-compounded machines historically supplied local DC distribution in buildings and industrial sites.
4. Differential compound generators have a steeply drooping characteristic and were used for arc welding, where the source must limit current as the arc voltage changes. Modern welding sources normally use rectifiers or inverters.

Direct generation now accounts for a limited share of the applications of DC generators. Most utility Electric power is generated as AC, and rectifiers, converters and electronic controls produce regulated DC where required. Rotating DC generators remain relevant in legacy machines, laboratories and specialised excitation systems.