Generating Equipments

Part 1

By: Maria Romina P. AngustiaBSEE-5B

General Classification

DIRECT CURRENT (DC) GENERATOR ALTERNATING CURRENT (AC) GENERAT

OR

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DIRECT CURRENT GENERATOR(DC) GENERATOR

DIRECT CURRENT MACHINES

TWO-WIRE GENERATOR- have only two line terminals, one known as the positive terminal and the other as the negative terminal.

THREE-WIRE GENERATOR- a direct-current generator with both slip rings and a commutator used for supplying current to a direct-current three-wire system whose neutral wire is connected to the center point of a high-reactance winding connected across the slip rings and whose two main conductors are connected to the commutator brushes

Three-Wire DC Generator

MOTOR-GENERATOR SET-A motor generator set is a device used for the conversion of electrical energy, typically in the form of frequency or voltage, into another form of energy.

A motor-generator (an M-G set or a dynamotor for dynamo-motor) is a device for converting electrical power to another form. Motor-generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line.

In the context of electric power generation and large fixed electrical power systems, a motor-generator consists of an electric motor mechanically coupled to an electric generator (or alternator). 

Motor-Generator Set

ROTARY CONVERTER-A rotary converter is a type of electrical machine which acts as a mechanical rectifier or inverter. It was used to convert AC to DC or DC to AC power before the advent of chemical or solid state power rectification. They were commonly used to provide DC power for commercial, industrial and railway electrification from an AC power source.

Rotary Converter

MERCURY-ARC RECTIFIER- A mercury-arc valve or mercury-vapor rectifier or (UK) mercury-arc rectifier is a type of electrical rectifier used for converting high-voltage or high-current alternating current(AC) into direct current (DC). It is a type of hot cathode gas discharge tube but is unusual in that the cathode, instead of being solid, is made from liquid mercury and is therefore self-restoring. As a result, mercury-arc valves were much more rugged, long-lasting and capable of carrying much higher currents than most other types of gas discharge tube.

Mercury-arc rectifiers were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for radio transmitters and for high-voltage direct current power transmission. They were the primary method of rectification before the advent of semiconductor rectifiers such as diodes, thyristors and gate turn-off thyristors(GTOs).

Mercury-Arc Rectifier

DC Generator Classifications

Method of Excitation:› Self-excited

SERIESSHUNTCOMPOUND

1. SHORT SHUNT AND LONG SHUNT2. FLAT COMPOUNDED, OVERCOMPOUNDED AND DIFFERENTIALLY COMPOUNDED

Series Generator, Shunt Generator and Compound Generator

Types of Compound Generator

Long shunt - the series field coils are connected in series with the armature coils while the shunt field coils are connected across the series combination.

Short Shunt - the series field coils are connected in series with the load while the shunt field coils are connected across armature coils

Flat-compound – if the series field amp-turns are such as to produce the same voltage at rated load as at no-load.

Over-compound – if the series field amp-turns are such that the rated-load voltage is greater than the no load voltage.

Differentially compound-has an external characteristic similar to that of a shunt generator but with large demagnetization armature reaction. Hence, it is widely used in arc welding where larger voltage drop is desirable with increase in current.

•Separately-excited Generator

Number of Poles› Bipolar- two poles, one north and one

south› Multipolar- must always be equal to a

multiple of two because it was found necessary to use more than 2 poles; hence, today all DC generators have at least 4 poles.

› Homopolar- designed w/ the armature conductors revolving in a unidirectional field, thusthe emfs generated in them do not alternate during the revolution of the armature;hence, no commutator is needed.

Types of Armature Winding› Multiple or Lap

- contains as many parallel paths as the generator has many poles. -requires as many brush studs as the

generator has many poles. › Series, two circuit or wave

- contains only two parallel paths irrespective of the number of main poles.- requires only two brush studs irrespective of the number of main poles.

Combination of Multiple and Series- also known as “frog-leg winding”-consists essentially of a standard multiple winding and a standard series winding placed together in the same armature slots and connected to the same commutator.

Method of Prime-Mover Drive› Engine Type- has its armature mounted

on a continuation of the engine crankshaft.

› Direct connected to steam turbine- often used as spare exciters in steam power plants.

› Geared to steam turbines› Water Turbines- found in hydraulic

power plants where spare exciter units are direct- connected to water wheels.

Type of Service› General Power and Lighting- are generally

wound for 125 and 250 volts. The voltage regulation should not be more than 2%.

› Railway-have compound-wound fields and are designed for 550 or 600 volts for city railway service, 1200 volts for interurban service, and 3000 volts for trunk-line electrification.

› Electrolytic Works- usually low-voltage machines of large current capacity. Often separately excited from a source higher voltage.

Railway Generator

Electrolytic Generator

› Electric Furnace Work- shunt or differentially compound excitation is desirable, since such generators will not maintain large current on short circuit.

› Boosters- are DC generators connected in series with the line to raise or lower the voltage. They are generally low voltage machines of large current capacity and are usually driven at constant speed by shunt motors. They may be shunt, series, or compound-wound.

Furnace Generator

› Exciters- generally designed for 125 to 250 volts normal. They may be either shunt or compound-wound.

› Balancer- consists of two similar DC machines directly coupled to each other and connected in series across the outer conductors of a 3-wire system of distribution. Can be either shunt or compound wound.

Balancer Set

Special Feature of Construction› Noncommutating-pole Machines› Commutating-pole Machines› Compensating Wound Machines-

are essential on rolling-mill motors and generators subjected to sudden changes of load, as, for example, in railway service.

› Diverter-pole Machines

Commutating Pole

Diverter Pole Generators

Compound wound direct-current generator with the series winding of the diverter pole opposing the flux generated by the shunt wound main pole; provides a close voltage regulation.

Amplidyne Generator Similar to the conventional DC Generator.

Voltage Regulation and LossesBy voltage regulation of a generator is meant the change in its terminal voltage with the change in

load current when it is running at a constant speed. If the change in voltage between no-load and full load is small, then the generator is said

to have good regulation but if the change in voltage is large, then it has poor regulation.

The voltage regulation of a d.c. generator is the change in voltage when the load is

reduced from rated value to zero, expressed as percentage of the rated load

voltage.

Stray Losses› Mechanical

Windage Bearing Friction Brush Friction Hysteresis Loss Eddy- current Loss

Iron

Copper Losses› Shunt-Field Copper Loss› Series-Field Copper Loss› Armature Copper Loss› Commutating-Field Copper Loss Load Losses

Alternating Current (AC) Generator- A machine that converts mechanical power into alternating-current electric power.

Types of AC Generator Synchronous AC Generator-used

because they offer precise control of voltage, frequency, VARs and WATTs. This control is achieved through the use of voltageregulators and governors. A synchronous machine consists of a stationary armature winding (stator) with many wires connected in series or parallel to obtain the desired terminal voltage.

INDUCTION GENERATOR-The induction generator is nothing more than an induction motor driven above its synchronous speed by an amount not exceeding the full load slip the unit would have as a motor. 

PHASE CONVERTER-A phase converter is a device that produces three-phase electrical power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service.

FREQUENCY-CHANGER SET--A frequency changer or frequency converter is an electronic device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose.

Classifications of an Synchronous AC Generator

Frequency› 60 cycles per second› 25 cycles per second-railway service.

Number of Phases Single phase Two Phase Three Phase

Wye connected Delta connected

Reasons why all generators are three phase

More capacity can be obtained out of a given armature than when wound single or two phase.

It is more economical to transmit power over a 3-wire 3-phase circuit than over a 4-wire 2-phase circuit.

Relative Motion› Revolving Armature Type› Revolving Field Type

Type of Prime Mover› Engine-Type Alternators› Steam Turbine Type› Water-wheel Type Alternators

› Vertical› Horizontal

Main reasons why revolving field has entirely superseded the revolving armature of construction in the case of alternators

The armature end windings can be more satisfactorily braced in the case of a stationary armature.

With the terminal voltages obtained from present-day alternators, it is entirely out of the question to use rubbing contacts to collect the current from the armature.

Cheaper construction

Engine-Type Alternators Designed for

operation w/ reciprocating steam engines and internal combustion engines, which may be either gas or oil engines.

Water-wheel Type Alternator Units are

driven by water turbines, which may be of the impulse, reaction, or propeller type.

Steam-Turbine Type Alternator

Such generators are designed for operation with steam turbines.

In the early development of such units vertical mounting was considered feasible, but it was soon realized that the horizontal method of mounting was superior in many details.

Important Features of Turboalternators

Armature Yoke Armature Core-forms the part of the magnetic

circuit in the stator. Armature-Coil Supports-use to withstand the

large stresses produced under load, short-circuit conditions.

Rotor Field Windings- generally composed of strap

copper laid flatwise in the rotor slots. This bring pressure to centrifugal force on the flat side of the copper; hence there is no possibility of the insulation between turns becoming chafed or cut.

Turboalternator