Auxiliary Equipment of Generator 1

8/8/2019 Auxiliary Equipment of Generator 1

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Auxiliary equipment of generator

1. Stator air coolers: (water cooling) for cooling of stator, located on the

periphery of stator.

2. Oil coolers for thrust, lower and upper bea

2. Oil coolers for thrust, lower and

upper bearings: Bearing

submerged in oil for reduction of

friction, oil sucked the heat

produced by bearings and then oil

cooled by the water cooling system.

Whole weight of rotating part rest

upon the thrust bearing.

Guide bearing: Guide bearing is

used to hold the shaft in place and

guide it properly during rotation. It

also prevents the vertical &

horizontal movement of shaft during

rotation. Distance b/w the shaft &

bearing is in microns.

Bearing of any kind helps in rotation or movement. Stationary parts dont

require any kind of bearing as they are stationary with no rotation associate with

them.

Each of the thrust bearing and guide bearing (upper & lower) shall be equipped

with:

1. Oil level indicator with high & low alarm indicator.

2. Two dial type thermometers to indicate the temperature of the bearing

pads & one for that of the oil.

3. Resistance temperature detector (RTD) located in all balance pads & in

the oil reservoir.

4. Oil water contamination detector.

5. Water flow meters of electro-magnetic induction type shall be provided at

**Resistance temperature detector (RTD): (RTDs) are temperature sensors that exploit thepredictable change in electrical resistance of some materials with changing temperature. As theyare almost invariably made of platinum, they are often called platinum resistance thermometers(PRTs). They are slowly replacing the use of thermocouples in many industrial applications below600 C, due to higher accuracy and repeatability.

Auxiliary equipment of

generator


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3. Anti condensation heaters: (Thermostats: - Determine the temperature of

a system) In order to avoid water condensation during long non-operative

period of machine, heating elements are installed inside the generator

housing. These elements are rated for three phase 415 V AC, 50 Hz. Duringthe stoppage or non-operative period of machine, temperature starts

decreasing gradually as a result, formation of moisture takes place because of

presence of air cooling system which directly affects the insulation of

machine. At this instant we used anti condensation heater to stop the

formation of moisture due to water cooling ducts around the periphery of

machine. Anti condensation heater will be remain on till the machine attains

90 % rated speed after that machine temperature would be sufficient to

ensure the absence of moisture, therefore heater will be get switched off.

4. Brake/jet system: This system is used for braking, this system used brake

liner located below the rotor, and Brake system is equipped with LP air

compressor pressure system (Pneumatic system). Each generator is equipped

with pneumatically operated asbestos-free brakes of sufficient capacity to

bring the rotating parts of generator and turbine to stop from 20% rated

speed in normal condition. Under emergency condition it shall be possible to

apply the brakes at 50% of rated speed without any damage to brakes and

break ring. Brakes can be operated from unit control board and brake control

panel.

5. High pressure hydrostatic lubrication: This lubrication required at thestarting & stoppage of machine, shaft of the machine is surrounded by a disk

of metal that hold the shaft on thrust bearing. When shaft starts rotating in

certain direction, the surface of metal grate with the surface of thrust bearing.

This will reduce the life of the metal disk as well destroy the thrust bearing. In

order to prevent the metal disk as well as thrust bearing, Metal disk provided

with some holes through which oil can be injected to lubricate its surface,

there by facilitating the movement of metal disk as well as shaft without any

disturbance.

For startup-shut down, a high pressure lubrication system shall be

provided for thrust bearing.

6. Sole plates, Foundation bolts, Sleeves, Anchor plates: These parts are

used to fix the stationary parts of the system.


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7. Fire protection system: Fire extinguishing device or system. Fire fighting

system is just outside the generator barrel. The thermostatic temperature &

smoke detectors are located at the strategic points inside the generator

housing. Upon sensing smoke, system will generate audible alarm and signal

for related action through protection system and plant SCADA system.

8. Carbon dust collection system: The purpose of brushes is to ensure

electrical connections b/w the rotating commutator & stationary external load

circuit. The brushes are made of carbon and rest on the commutator. Brush

pressure is adjusted by means of adjustable springs. If the brush pressure is

very large, the friction produces heating of the commutator and the brushes.

On the other hand if it is too weak, the imperfect contact with the commutator

may produce sparking & impaired by wear. So, carbon dust collection system

suck carbon dust generated from carbon brushes.

9. Brake dust collection system: Each generator is equipped with pneumatically

operated asbestos-free brakes of sufficient capacity to bring the rotating parts of

generator and turbine to stop from 20% rated speed in normal condition. Brake

residues must be efficiently sucked by brake dust collector. Dust collection system is

used to suck brake dust generated during braking action. It is the same as that of

carbon dust collection system.

10.Oil, air & water pipes ,fittings, valves ,pressure gauges and flow relay

11.Piping, tubing & valves: All the internal piping and valves for the following shall be

included in the scope of the generator manufacturer:

a. Cooling water inlet, outlet and drain for generator air and oil coolers.

b. High pressure lubrication oil supply to thrust bearing meant for lubrication during

start up & shut down of the unit.

c. Oil fills and drains connections at the bearings.

Advantages of

carbon brushes

1. They lubricate &

polish the commuator.

2. If sparking occurs,

they damage the

commuator less than

with the copper

brushes.

3. They provide good

commuataion.

Disadvantages of carbon

brushes

1. The contact resistance is high

& causes a loss of about 2V.Hence

they are unsuited for low voltage

machines in which this forms a

larger percentage loss.

2. Due to high voltage drop, the

commutator must be made larger

than for copper brushes.

3. Their low current density

necessitates large brush holders.


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d. Piping for brakes and jacks (mechanical device used to lift the heavy load).

e. Tubing for connections b/w temperature sensing elements (vapor bulbs) to dial

type thermometers, pressure gauge tubing.

12.Creep detector with alarm & tripping control

13.Metering instruments/devices/ports for SCADA

14.Couplers for measuring partial discharge: Partial discharge means remnant of air

bubbles & vacuum in an insulation which left there as a manufacture defect, which

has to be remove from the point of view of good insulation otherwise it will break

down the insulation of the system.

15.Moisture detector system for upper & lower bearing oil: It is a solid state type

instrument based on resistance principle.

16.Special lifting and turning devices along with hardware

17.Electrical brazing/Soldering equipment/devices

18. Ventilation & cooling system

Flywheel effect: Flywheel means stored energy. Suppose we suddenly stop the flowing

of water from head race level or we suddenly close the main inlet valve. As a result the

whole coupled system (turbine+Generator) speed decreasing gradually but doesnt stop

suddenly due to inertia or because of stored energy; it is the energy system gains while

running.

As the load varies time to time, the speed of the turbine has to be varied in order to meet

the load requirement. Therefore, during varying period of load, coupled system or

machine may experience jerk of large extent. In order to avoid the occurrence of jerk,

flow of water to the turbine has to be varied in such a way that machine doesnt

experience any kind of vibration or jerk.


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For example, if the machine is running at full load, suddenly the load requirement gets

reduced to 50% of full load, during this switch over, machine experience huge jerk .By

varying the flow of water to turbine from full load to 50% load ,we can reduce the jerk

within the tolerable range.

Run-away speed: Run-away is the max. Speed governor being disengaged, at which a

turbine would run when there is no external load but operated under full level head

discharge. The generator shall be designed and constructed in such a way that it will be

capable of withstanding maximum run away speed as defined by the turbine

manufacturer, for a period of 30 minutes without incurring damage from stresses under

such condition. (Runaway speed is 50% of rated speed of turbine in teesta project Rated

speed-166.67 rpm, max.run away-166.67+83.34(50% of rated speed)=250 rpm)

**Crawling due to the torque contribution of 7th harmonics mainly (for induction machines)

**Hunting is the oscillation of rotor about its final equilibrium position due to high speed

because of weakening of field.

**Creeping:

DESIGN CLACULATION

1. Electrical calculation & characteristics including magnetic circuit

2. Structural analysis of different generator parts

3. Foundation loads

4. Runaway speed

5. Critical speeds

6. Strength of all rotating parts to withstand run away speed and vibration.

7. Number of coolers for stator and all bearings, the normal working pressure

and pressure drop through the coolers.

8. GD2 calculations.


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9. Coupling bolts size

10.Stress calculation on shaft and rotor

11.Size of thrust bearing, effective surface area /specific load on thrust

bearing with respect to total load (static/dynamic) etc. under worst

conditions/runaway condition.

12.Max. Stresses / loads during normal operation, run away speed conditions,

two phases and three phases short-circuit conditions or single phase earth

fault at max. Output for which generator are capable of 180 degree and 120

degree out-of-phase synchronization, magnetic unbalance at rated speed

with 50% of the poles short-circuited and brake application.

13.Guide bearing coolers, stator air coolers ,temperature rise calculations

14.Ventilation of generator.

15.Size and no. of brake /jack assemblies.

Classification generator on the basis of bearing location

1. Umbrella type: Lower bracket-Guide bearing, thrust bearing

Lower bracket-NO bearing

2. Semi-umbrella Type: Lower bracket-Thrust bearing ,guide bearing

Upper bracket- guide bearing

3. Suspended type: upper bearing-Thrust bearing, lower bracket-guide bearing.

4. Short coupled: Upper bearing-Thrust & guide bearing, lower bracket-no bearing

Used for high speed, most

common, mostly used in hi

areas

Rarely

used

For small

project

For medium

project

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Auxiliary Equipment of Generator 1