Generator Course

April 1, 2019 | Author: prasad5034 | Category: Electrical Engineering, Electromagnetism, Electricity, Electric Power, Electrical Components
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Short Description

Generator...

Description

Generator

Principles Generator Construction Excitation System Operational aspects Generator Protections

Alternator: An Alternator is an equipment which converts Mechanical Energy into Electrical Energy.

Sources of Mechanical Energy Steam

Turbines Gas Turbines Hydraulic Turbines Other sources

This

forms the basis for the conversion of Mechanical Energy into Electrical Energy.

This

can be presented in two forms which are applicable to the operation of Generators.

N

R Y B S

When a Rotating Magnetic Field cuts the conductors, Voltage is induced in them.



This is applicable to the main generator



S

+  _

 N

 N

S

When a Rotating conductor cuts the Magnetic Field , Voltage is induced in the conductor. This applicable to the Exciter.





 A

DC Voltage is applied to the Rotor and it becomes a Magnet

When

this magnet is rotated,it induces voltage in the stator windings

STATOR ROTOR EXCITER SLIP

RINGS BRUSHES BEARINGS COOLING SYSTEM

PROVIDED

FOR EXTERNAL EXCITATION

USED

FOR ROTOR EARTH FAULT PROTECTION

SLEEVE

THEY

NDE

BEARINGS ARE USED

ARE MADE OF WHITE METALS

SIDE BEARING IS INSULATED TO  AVOID SHAFT CURRENT CURRENT CIRCULATION

Stator

frame Stator core laminations Stator windings End shield Rotor poles Rotor coils

: Mild steel : Silicon steel : Copper strips : Aluminum alloy : Alloy steel : Silver alloyed copper

To

take away the heat dissipated in the stator and the rotor

Maximum

loading of the machine depends on the effectiveness of cooling system.

 AIR

COOLING

WATER

-

COOLING

HYDROGEN

COOLING

-

For low ratings

For medium ratings

For higher ratings

TO SUPPLY THE FIELD WINDING OF THE GENERATOR WITH DC CURRENT AND CONTROL IT  THIS KEEPS THE TERMINAL VOLTAGE CONSTANT  ENSURES PROPER REACTIVE POWER SHARING  IMPROVES STABILITY 

STATOR STATOR

+

ROTOR

DIODE

ROTOR

SHAFT ROTOR

-

RECTIFIER

ROTOR STATOR

STATOR Powering

11 KV PT

AVR

STATOR

ROTOR

STATOR

+ DIODE

STATOR ROTOR

MAGNET

ROTOR

MAGNET

SHAFT ROTOR

-

RECTIFIER

STATOR STATOR

STATOR Feed back

11 KV PT

AVR

POWERING

Aux. power

AC - DC

+

CONVERTER

-

TO EXCITER

FIRING PULSE GENERATOR

Aux. power

CONTROLLER

Reference

Feedback REFERENCE

FEEDBACK

PROCESSING

PROCESSING

There

are two identical AVRs present The AVR will not come into line unless the turbine reaches 85% of full speed One of the AVR will be on line and the other one will remain as standby. If the main AVR fails , then the stand by AVR will automatically come onto line  A manual excitation control provision

Parameters List:  Voltage Frequency  Active

power Reactive power Excitation voltage / current Power Factor

Frequency - Real power  f  NL FSR 3

FL

FSR 2 FSR 1

P

Voltage - Reactive Power: V

 NL FL

IF 3 IF 2 IF 1

Q

TURBINE REACHES FULL SPEED

CLOSE THE FIELD BREAKER

BUILD UP VOLTAGE TO 11KV

SYNCHRONISATION

INCREASE THE LOAD

ISLAND OPERATION

PARALLEL OPERATION

6 MW

GT-A

6 MW

LOADS

Real and Reactive power supplied will be the amount demanded by the Load.

GOVERNOR SET POINT DECIDES THE FREQUENCY FIELD CURRENT DECIDES THE TERMINAL VOLTAGE

More

load in shared condition.

Increase

Flexibility

in Reliability.

in Maintenance.

GT-A

GT-B

ARE THE FREQUENCIES SAME? ARE THE PHASE SEQUENCES SAME?

LOADS ARE THE VOLTAGES SAME?

3 7 MW

GT-A

4 MW

GT-B

LOAD HAS TO BE SHARED BETWEEN THEM

7 MW

LOAD LOAD DEMAND IS CONSTANT



GT-A

P

6 MW

3 MW

GT-B

1MW 4 MW

P



Load demand is constant



Increase in Governor set point of one Generator increases the system frequency and Real power on that Generator



Increase in Field current of one Generator increases the system voltage and Reactive power on that Generator

Voltage and Frequency are constant i.e not in our control f

V

P

Q

WHEN INCOMING FREQUENCY IS GREATER THAN GRID: APTRANSCO

P

PAPTRANSCO



GT-A

PGT

P

WHEN INCOMING FREQUENCY IS LESSER THAN GRID: APTRANSCO

P

PAPTRANSCO -PGT



GT-A

P GT-A ACTS AS LOAD

WHEN THE GOVERNOR SET POINT OF GT-A INCREASES:

APSEB

P

6 MW 4 MW 2 MW



GT-A

1 MW 3 MW 5 MW

P

 Voltage

and Frequency are fixed by GRID

Governor

set point decides the Real

Power Field

current decides the Reactive power

To

prevent the equipment from severe damages during fault conditions

To

continuously track the various parameters and isolate the equipment when they deviate from the set value

Over

current Protection Stator Earth Fault Protection Differential Protection Unbalance Protection Reverse power Protection Loss of Excitation Protection Over / Under Frequency Protection Over / Under voltage Protection

CTS

Winding

R

Winding

Y

Winding

B O/C OCCURS

I > 540 A or 1941 A NGR 

RELAY

Relay operates in ‘ t ‘ sec

It monitors the overloading pattern of the generator and trips incase of heavy loading It follows an Inverse curve and so it trips in less time for a higher current •

The set point initiates the relay typically at 540 A or 1941 A t

I

Winding

R

Winding

Y

Winding

B

I >15.2 A or 20 A

CT Relay operates

NGR 

The

star point of the Generator is earthed through a Resistor to limit Earth fault current

So

whenever an Earth fault occurs , the fault current flows through NGR

When

the neutral current exceeds the set value , the relay operates

CTS

RELAY

CTS Winding

R

Winding

Y

Winding

B

I > 105 A (OR) 350 A Relay operates

This

relay is to protect the stator winding phase wise This is the fastest relay available Under normal condition both the CT currents are same and the differential current is zero. But when there exists a fault in the stator winding both CT currents differ leading to a differential current When this differential current is more than set value the relay operates

Unbalance

condition arises when the three phase loads are not same

This

relay operates if the percentage of unbalance exceeds the set value

Typically

8%

To

avoid reverse flow of power i.e power into the generator In this state Generator will act as a motor If continues to operate , this will cause overheating of turbine Typically 3% ( 5% ) reverse flow

To

avoid running the machine without excitation It works on the principle, Impedance=V/I. The terminal voltage falls if a sudden heavy load demand or AVR failure occurs, this will cause the current to increase and the impedance falls. The relay is an Impedance relay and it operates when Impedance falls below



UNDER VOLTAGE

= 7.4 KV

; 7.5 KV 



OVER VOLTAGE ALARM = 12 KV



OVER VOLTAGE TRIP

= 12.5 KV , 12.5 KV



OVER FREQUENCY

= 51.5 Hz , 52 Hz



UNDER FREQUENCY

= 47 Hz

; 11.5 KV

, 47.5 Hz

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