TURBO GENERATOR

The Genera to r cons is ts o f the fo l low ing components :

STATORStator Frame,Stator Core,Stator Winding,Generator Coolers,Stator End Covers.

ROTORRotor shaft,Rotor winding,Rotor Retaining Ring,Field Connections.

TURBO GENERATOR :

High speed, synchronous generator is called Turbo Generator. This turbo

generator is run by prime mover which converts Mechanical Energy to Electrical

Energy. The energy conversion for all rotating machine are based on Faraday’s law

of Electromagnetic induction.

Faraday’s law:

It is stated that “Whenever there is a relative motion between any

conductor and magnetic field i.e. when a moving conductor cut the magnetic

field then E.M.F. induce in the conductor. This induces EMF cause current to

flow if the conductor circuit is close.

The turbo generators are used in thermal power plants, combined cycle

power plants, cogeneration plants and captive power plants in industries like

fertilizer, petrochemical refineries, steel plants etc. Mostly these generators are

driven by high-speed turbine using a speed reduction gearbox. Some low capacity,

low speed generators are even driven by diesel engines. The generators are

supplied along with auxiliaries like A V R, brush less exciter, control panels,

busducts, static excitation system etc., according to the requirements of the

customer.

Regardless of size, all electrical generators, whether dc or ac, depend upon

the principle of magnetic induction. An EMF is induced in a coil as a result of a

coil cutting through a magnetic field, or a magnetic field cutting through a coil. As

long as there is relative motion between a conductor and a magnetic field, a voltage

will be induced in the conductor. That part of a generator that produces the

magnetic field is called the field. That part in which the voltage is induced is called

the armature. For relative motion to take place between the conductor and the

magnetic field, all generators must have two mechanical parts —

Rotor

Stator

The Rotor is the part that Rotates; the Stator is the part that remains Stationary.

The rotating-field alternator has a stationary armature winding and a rotating-field

winding. The advantage of having a stationary armature winding is that the

generated voltage can be connected directly to the load.

NOTES ON GENERATOR

INTRODUCTION

Types of Generators

GENERATOR BEARINGS

The generator rotor is supported at two journal bearings. The bearings consist of

a bearing pedestal and bearing shell is split into two halves to facilitate assembly. The

bearing pedestals are iron castings and the bearing shells are steel castings. The

bearing pedestal is provided with a spherical seating surface and the bearing shell rests

in it with its outer spherical surface. The inner surface of bearing shell is provided with

spiral grooves and cast with Babbitt metal.

Bearing Oil Supply:

The oil required for bearing lubrication and cooling is obtained from the turbine oil

supply system and supplied to the lubricating groove in the bottom-bearing sleeve. The upper

bearing sleeve consists of a wide over flow groove through which oil is distributed over the shaft

journal and fed to the lubricating gap.

Bearing Temperatures:

The temperature of each bearing is monitored by one double-element RTD. The

RTD is screwed in position on side of the lower bearing sleeve from outside with the

detector extending to the Babbitt liner.

STATOR

INTRODUCTION: Stator frame is of welded construction, supports the core and the windings. It

consists of air duct pipes and radial ribs, which provide rigidity to the frame.

Footings are provided to support the stator on the skid. The stator frame should be rigid due to

the various forces and torques during operation. The welded stator frame consists of two end

plates, axial and radial ribs. The arrangement and dimensioning of the ribs are determined by the

cooling air passages, the required mechanical strength and stiffness. The end covers are

aluminium alloy castings. The stator frame is fixed to the skid with the help of hexagonal bolts.

The skid is interim fixed to the concrete foundation through foundation bolts.

Stator core:

The core packed into the stacking frame is pressed firmly together between the

end plates of the machine frame and fixed in this position by welding the axial ribs of the

core and the end plates of the frame. End fingers on the inside diameter of the end

plates transmit the pressure to the teeth of the core. The compressive force produced

prevents the laminations and teeth from vibrating. An eye is welded to each end plate

for attaching suitable lifting gear with adequate lifting capacity for transporting the

complete machine. All the forces that occur during normal operation or on short circuits

are transmitted from the stator yoke to the base frame via the seating plates and into

the foundation.

Location of Bars:

A semi-conducting wrapper of graphite paper in the slot protects the bar. The stator winding is

protected against the effects of current forces in the slot section. To ensure tight seating of the

bar at the slot bottom, a slot bottom-equalizing strip of press path is inserted. A top ripple spring

is arranged between two compression strips to exert a continuous pressure on the bars. The bars

are shaped so that, cone shaped end windings are obtained. In order to reduce the stray losses a

small cone taper of (13-20) is used. On the wide sides of the bars spacers of insulating material

are inserted at regular intervals.

Bearings :

The rotor runs in two floating type guide bearings, designed as pedestal bearings, with

forced oil or oil-ring lubrication. The driven end bearing is secured to the base frame

and insulated from the latter. As the connections are designed to prevent short-circuiting

of the insulation.

Enclosure :

The enclosure consists of the inner and outer components. The inner components

comprises of the winding covers, which form an angular enclosure of the overhang of

the stator winding and are also used as air ventilator rings.

The outer enclosure consists of top and bottom parts and is designed as required for

the particular degree of protection, as indicated in the dimension drawing or in

“Technical data”. The ventilating circuit is of the double - ended symmetrical

arrangement.

STATOR CORE:

Stator core is stacked from insulated electrical sheet laminations and suspended in the

stator frame from insulated dovetailed guide bars. Axial compression is obtained from

clamping fingers, clamping plates and non-magnetic clamping bolts which are insulated

from the core. In order to minimize the hysterics and eddy current losses of the rotating

magnetic flux which interacts with the core. The entire core is built up of laminations,

each layer of which is made from a number of individual segments. The segments are

punched from silicon steel. In the outer circumference the segments are stacked in

insulated trapezoidal guide bars, which hold them in position. The guide bar is not

insulated to provide for grounding the core. The laminations are hydraulically

compressed and heated during the stacking procedure. The complete stack is kept

under pressure and fixed in the frame by means of cell

STATOR

Stator frame is of welded construction, supports the core and the windings. It consists of

air duct pipes and radial ribs, which provide rigidity to the frame.

STATOR

Stator frame is of welded construction, supports the core and the windings .It consists of

air duct pipes and radial ribs, which provide rigidity to the frame. Footings are provided

to support the stator on the skid. The stator frame should be rigid due to the various

forces and torque’s during operation. The welded stator frame consists of two end

plates, axial and radial ribs. The arrangement and dimensioning of the ribs are

determined by the cooling air passages, the required mechanical strength and stiffness.

The end covers are aluminium alloy castings. The stator frame is fixed to the skid with

the help of hexagonal bolts. The skid is interim fixed to the concrete foundation through

foundation bolts.

Electrical Connection of Bars and Phase Connections:

Brazing makes Electrical Connection of Bars: Electrical connection between the

top and bottom bars, one top bar being brazed to associated bottom bar. The coil

connections are wrapped with tapes. The thickness of the wrapper depends on the

machine voltage. After taping, an insulating varnish is applied.

Phase Connectors: The phase connectors consist of flat copper sections, the cross-

section of which results in a low specific current loading. The connections to the stator

winding are of riveted and soldered type. The phase connectors are wrapped with resin-

rich mica tape, which contain synthetic resin having very good penetration properties.

The phase connections are then cured at a certain temperature, with the shrinking tapes

contracting so that a void free insulation is obtained.

Output Leads:

The beginning and ends of the three phase windings are solidly bolted to the

output leads with flexible. The output leads consist of flat copper sections with mica

insulation. To prevent eddy-current losses and inadmissible temperature rises; the

output leads are brought out through insulating plates.

ROTOR

Introduction:

ROTOR WINDING

Construction:

The field winding consists of several series connected coils inserted into the

longitudinal slots of the rotor body. The coils are wound so those two poles are

obtained. The solid conductors have a rectangular cross-section and are provided with

axial slots for radial discharge of the cooling gas. The individual conductors are bent to

obtain half turns. After insertion into the rotor slots, these turns are combined to form full

turns of series connected turns of one slot constituting one coil. The individual coils of

the rotor winding are electrically series connected so that one north and one south

magnetic pole are obtained.

Insulation:

The insulation between the individual turns is made of layers of glass fiber

laminate. The coils are insulated from the rotor body with L shaped strips of glass fiber

laminate with Nomex interlinear. The strips are provided with axial slot of the same

cross- section and spacing as used on the rotor windings.

Rotor Slot Wedges:

To protect the winding against the effects of the centrifugal force, the winding is

secured in the slots with wedges. The slot wedges are made from an alloy of high

strength and good electrical conductivity, and are also used as damper wedged bars.

The retaining rings act as short circuit rings to induced currents in the damper windings.

ROTOR SHAFT:

The rotor shaft is forged from a vacuum cast steel ingot. The high mechanical

stresses resulting from the centrifugal forces and short circuit torque’s call for high

quality heat-treated steel. The rotor consists of an electrically active portion and two

shaft ends. Approximately 60% of the rotor body circumference has longitudinal slots,

which hold the field winding. Slot pitch is selected so that 180 displace the two solid

poles. The rotor wedges act as damper winding within the range of the winding slots.

The rotor teeth at the ends are provided with axial and radial holes, enabling the cooling

gas to be discharged into the air gap after, intensive cooling of the end windings.

COOLING OF ROTOR WINDINGS:Each turn is subdivided into four parallel cooling zones. One

cooling zone includes the slot from the center to the end of the rotor body, while another covers half the end winding to the center of the rotor body. The cooling Air for the slot portion is a limited into the slot bottom ducts below the rotor winding. The hot gas at the end of the rotor body is then discharged into the air gap between the rotor body and stator core though radial openings in the conductors and in the rotor slot wages. The cooling air for the end winding is drawn from below the rotor-retaining ring. It rises radically along the individual coils and is then discharged into the air gap via axial and radial slots in the end portions of the rotor teeth.

Direct Cooling : Usually use in the rotor to eliminate hotspots and differential

temperatures between adjacent components, which would result in mechanical stress

particularly in the copper conductors.

Indirect Cooling: Used for stator windings.

AIR COOLING CIRCUIT:

Air is circulated using two axial flow fans arranged in the rotor shaft. The fans draw cold

air from the cooler unit, which is divided, into 3 flow paths.

1. It is directed into rotor end winding space. Part of it also flows over the individual

coils for cooling in the rotor end winding and then leaves the end windings via the

bores in the rotor teeth. Other part flows from the rotor end winding space into

slot bottom ducts. From this it will discharge into the air gap via radial ventilating

ducts.

2. Air is directed over stator end windings to the air ducts into the space between

the generator housing and the stator core. Then air flows into the ventilating slot

of the stator core, where it absorbs heat from the stator core and stator windings.

3. It is circulated into the air gap via the rotor-retaining ring. The air then mixes with

the hot air flowing via ventilating ducts in the stator core into the outer hot air

compartment in the stator frame for being returned to the cooler.

The three flow paths in the air gap and hot air is returned to the cooler via hot

air ducts for re-cooling and drawn again by the fans.

ROTOR WINDING

Construction:

The field winding consists of several series connected coils inserted into the

longitudinal slots of the rotor body. The coils are wound so those two poles are

obtained. The solid conductors have a rectangular cross-section and are provided with

axial slots for radial discharge of the cooling gas. The individual conductors are bent to

obtain half turns. After insertion into the rotor slots, these turns are combined to form full

turns of series connected turns of one slot constituting one coil. The individual coils of

the rotor winding are electrically series connected so that one north and one south

magnetic pole are obtained.

Insulation:

The insulation between the individual turns is made of layers of glass fiber

laminate. The coils are insulated from the rotor body with L shaped strips of glass fiber

laminate with Nomex interlinear. The strips are provided with axial slot of the same

cross- section and spacing as used on the rotor windings.

Rotor Slot Wedges:

To protect the winding against the effects of the centrifugal force, the winding is

secured in the slots with wedges. The slot wedges are made from an alloy of high

strength and good electrical conductivity, and are also used as damper wedged bars.

The retaining rings act as short circuit rings to induced currents in the damper windings.

ROTOR RETAINING RING:

The rotor retaining rings with stand the centrifugal forces due to the end windings one

end of each ring is shrunk on the rotor body, while the other end of the ring overhangs the end

windings without contact on the shaft. The shrunk on hub at the free end of the retaining ring

serves to reinforce the retaining ring and secures the end winding in the axial director at the same

time. The shrink seat of the retaining ring is silvered plated, ensuring a low contact resistance for

induced current. To reduce the stray losses and have high strength, the rings are made of non-

magnetic, cold worked materials.

FIELD CONNECTIONS:

The field connections provide the electrical connection between the rotor winding

and the exciter.

Terminal Lug:

Consists of a copper conductor of rectangular cross-section. One end of the

terminal lug is brazed to the rotor winding, while the other end is screwed to the radial

bolt.

Radial Bolt :

The field current lead located in the shaft bore is connected to the terminal lug

through a radial bolt. The radial bolt is made from steel and screwed into the field

current lead in the shaft bore.

ROTOR FAN:

The generator cooling air circulated by two axial flow fans located on the rotor shaft one

at either end. To augment the cooling of the rotor winding the pressure established by the fan

works in conjunction with the air expelled from the discharge ports along the rotor. The blades of

the fan have threaded roots for being screwed into the rotor shaft. The blades are forged from an

aluminum alloy. Threaded root fastening permits the

blade angle to be changed.