Turbo Generators

Description

1. General

The two-pole generator uses direct hydrogen cooling for the rotor winding and indirect hydrogen cooling for the stator winding. The losses in the remaining generator components, such as iron losses, friction and windage losses and stray iosses, are also dissipated through hydrogen.

The generator frame is pressure-resistant and gastight and equipped with end shields at each end. The hydrogen coolers are arranged horizontally inside the stator frame.

The generator consists of the following components.

StatorStator frameStator coreStator windingHydrogen coolers

RotorRotor ShaftRotor WindingRotor retaining ringsField Connections

Bearings Shaft seals

The following additional auxiliaries are required for generator operation:

Oil System Gas System Excitation System

2. Cooling System

The heat losses arising in the generator interior are dissipated to the secondary coolant (raw water condensate. Etc) through hydrogen.

Direct cooling of the rotor essentially eliminates hot spots and differential temperatures between adjacent components, which could result in mechanical stresses. Particularly to the copper conductor, insulator and rotor body.

3. Hydrogen Cooling Circuit

The hydrogen is circulated in the generator interior in a closed circuit by two axial-flow fans arranged on the rotor shaft journals. Cold gas is drawn by the fans from the cooler compartments. The cooling gas flow a divided into three flow paths after each lan.

Flow path 1 is directed into the rotor end winding space and cools the rotor winding.

Part of the cooling gas flows past the individual coils for cooling the rotor end winding and then leaves the end winding space via bores in the rotor teeth at the end of the rotor body.

The other portion of the cooling gas flow is directed from the rotor end winding space into the slot-bottom ducts from where it is discharged into the air gap via a large number of radial ventilating slots in the coils and bores in the rotor wedges. Along these paths the heat of the rotor winding is directly transferred to the cooling gas/

Flow path 2 is directed over the stator end winding to the cold gas ducts and into the cold gas compartment in the stator frame space between the generator housing and the stator core. The gas then flows into the air gap through ventilating slots in the stator core where it absorbs the heat from the stator core and stator winding.

A small part of the cooling gas is supplied to the terminal bushings. The cold gas flows into each terminal bushing via the space between the insulator and the copper conductor. The gas flow is revered at the opposite end of the copper conductor and then returned to the hot gas compartment via the central bore.

Flow path 3 is directed into the air gap via the rotor retaining rings. The gas then flows past the clamping fingers and via ventilating slots in the stator core into the outer hot gas compartments in the stator frame for being returned to the coolers. This flow path mainly cools the rotor retaining rings. The ends of the rotor body and the end portions of the stator core.

All the flows mix in the air gap. The cooling gas then flows radially outward to the hot gas compartments through ventilating slots in the core. Thereby cooling further portions of the stator core and stator winding. The hot gas leaving the hot gas compartments is returned to the coolers for recooling and drawn again by the fans.

The hydrogen cooler is a shell and tube type heat exchanger which cools the hydrogen gas in the generator. The heat removed from the hydrogen is dissipated through the cooling water. The cooling water flows through the tubes. While the hydrogen is passed around the finned tubes.

The hydrogen cooler is subdivided into sections which are horizontally mounted in the stator frame.

At the turbine end, the water connections are brought out from the stator frame through gland-type seals allowing for free movement. At the exciter end, the cooler tubesheet is solidly bolted to the stator frame.

The cooler section are parallel-connected on their water sides. Shutoff values are installed in the lines upstream of the cooler sections.

All parallel-connected water paths must have equal flow resistances to ensure a uniform cooling water supply to the cooler sections and equal cold gas temperatures downstream of the individual sections. The required cooling water volume flow is adjusted by control values on the hot water side. Controlling the cooling water volume flow on the outlet side ensures an uninterrupted water flow through the cooler sections so that proper cooler performance will not be impaired.

To maintain the cold gas temperature at an approximately constant level under all operating conditions, a motor-operated control value is arranged in the common cooling water outlet line. This control value is activated by temperature transmitters located upstream and down stream of the cooler sections.

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Rotar shaft

The rotor shaft is a single forging manufactured from a vacuum casting .slots for insertion of the field finding are milled into the rotor body. the longitudinal bits are distributed over the circumference so that two lid peoples are obtained. the rotor poles are designed with ansverse slots to reduce twice system frequency rotor operations caused by deflections in the directions in the direction of the people and neutral axis.

To ensure that only high-quality forgings are used, strength tests, material analyses, and ultrasonic tests are performed during manufacture of the rotor.

After completion, the rotor is balanced in various planes different speeds and then subjected to an over speed for two minutes.

Rotor winding

The rotor winding consists of several coils which are inserted into the slots and series-connected such that two bil groups from one pole .each coil consists of several series-connected turns, each of which consists of two half turns which are connected by brazing in the end section.

The rotor winding consists of silver-bearing de-oxidized copper hollow conductors with two lateral cooling ducts.

L-shaped strips of laminated epoxy glass fiber fabric with nomex filler are used for slot insulation .the slot wedges are made of high-conductivity material and extend below the shrink

seat of the retaining ring is silver-plated to ensure a good electrical contact between the slot wedges and rotor retaining rings .this system has long proved to be a good damper winding.

Retaining rings

The centrifugal forces of the rotor end windings are contained by single-piece rotor retaining rings .the retaining rings are made of non-magnetic high-strength steel in order to reduce stray losses .each retaining rings with its shrink-fitted insert ring is shrunk onto the rotor body in an overhung position .the retaining ring is secured in the axial position by a snap ring .

Field connections

The field current is a supplied to the rotor winding through radial terminal bolts and two semicircular conductors located in the hollow bores of the exciter and rotor shafts .the field current leads are connected to the exciter and rotor shafts .the field current leads are connected to the exciter leads at the exciter coupling with multikontakt plug-in contacts which allow for unobstructed thermal expansion of the field current leads .

1 .Bearing oil system

All bearings are connected to the turbine tube oil supply .

2 .seal oil system

The shaft seals are supplied with seal oil from a separate circuit which consists of the following principal components ;

Seal oil tank

Main seal oil pumps

Stand by seal oil pump

Vacuum pump

Oil coolers

Seal oil filters

Pressure regulating value A1

Pressure regulating value A2

Pressure reducing regulators

Intermediate oil tank

A vacuum pump keeps the seal oil in the seal oil tank under vacuum and largely extracts the gas absorbed by the oil while passing through the hydrogen and air atmospheres .

The seal oil is drawn from the seal oil tank and delivered the shaft seals via a cooler and filter .

In the event of a failure of seal oil pump1 ,seal oil pump2 automatically takes over seal oil supply .

Upon failure of seal oil pump2 ,the stand by seal oil pump automatically started and takes over the oil supply to the shaft seals .

The seal oil pressure required at the shaft seal is controlled by pressure regulating value A1 according to the present value i.e. the required pressure difference between seal oil pressure and hydrogen pressure .in the event of a failure ,pressure regulating value A2 takes over this automatic control function .

Oil drained from the air side of the shaft seals is direct returned to the seal oil tank .if the oil level in the seal oil tank too low ,oil from the seal oil storage tank is automatically admitted . oil drained from the hydrogen side of the shaft seal is first discharged into the generator prechambers and the returned to the seal oil tank .the prechambers serve for initial defoaming of the oil .a level control value in the intermediate of tank keeps the oil level at a predetermined level ,thus preventius gas from entering the oil drain system .

Stator

1 .Stator frame

The stator frame is of gastight and pressure-resistant welded construction and accommodates the laminated core ,the winding and the coolers arranged horizontally in the senator housing .both the gas ducts and the welded circuit ribs provide for the rigidity of the stator frame .end hields containing the shaft seal and bearing components are bolted to the frame end walls .the flanged connections are sealed gastight by means of a viscous cement .

Feet are welded to the stator frame to bolt the stator to the machine sole plates .the stator is firmly connected to the foundation with anchor bolts through the machine sole plates .

2.the stator core is stacked from insulated electrical sheet-steel laminations with a low loss index and suspended directly in the stator frame from insolated dovetailed guide bars .axial compression of the stator core is obtained by clamping fingers ,pressure plates ,and non-magnetic through –type clamping bolts ,which are insulated from the core .the clamping fingers ensure a uniform clamping pressure ,especially with in the range of the teeth ,and provide for uniform ,intensive cooling of the stator core ends .