course 0212 7fa generator (7fh2) - tectrapro.com...3. seal oil system to ensure that the hydrogen...

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Course 0212

7FA Generator (7FH2)

Course GEN01A_0212_B5-7FA Generator



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7FA Generator Course

1. Generator Overview

The 7FA gas turbine generator, actual model 7FH2, is a hydrogen-cooled, 175MW machine. It

serves a dual-purpose as the starting motor via the use of the solid state LCI device.

2. Hydrogen System

The generator utilizes hydrogen gas for heat removal. The hydrogen gas system monitors

purity, maintains pressure, and provides protective actions.

3. Seal Oil System

To ensure that the hydrogen gas does not escape the generator frame, a seal oil system is

used. The seal oil system uses the turbine’s main lube oil system to maintain an oil seal around

the shaft areas that penetrate the frame.

4. Stator Design

This chapter shows the design of the interior of the generator. It explains how it is built and how

internal components are assembled.

5. Rotor Design

The rotor itself is a unique assembly of electrical components. This chapter will review the

construction and operation of the field.

6. Power Generation

This chapter discusses how the generator produces megawatts.

7. Reactive Power

This chapter covers the creation of reactive load and how it is adjusted for grid health.

8. Fault Protection

The generator utilizes devices to detect voltage and currents to provide protection. This course

covers the most common faults.

9. LCI Overview

The load commutated inverter is used to start the gas turbine using the generator as a motor.

The load commutated inverter is a solid state device and is equipped with a high-purity water

cooling system.

10. LCI Operation

This chapter reviews the operation of the LCI when utilizing the generator to start the gas

turbine.



212_B5_Ch1 – Overview

1. Generator

a. The turbine generator converts the mechanical energy provided by the combustion

turbine into electrical energy. This mechanical energy is in the form of rotation and

torque.

Classroom Discussion Point:

1. The 7FA gas turbine is typically paired with the “7FH2” generator and its various

configurations. To prevent confusion, we have referred to it as simply the 7FA

gas turbine generator.

2. Generators are the most efficient piece of equipment in any power block at

around 97% efficiency.

3. Although these machines are hydrogen-cooled, they are fully capable of

operating with air at a limited output.

4. See Reference 11 for the 7FH2 generator.



2. Bearings

a. The generator's two elliptical journal bearings, 3 and 4, reduce friction and allow for

stable high speed operation.

b. They share the combustion turbine lubrication and lift oil systems.



3. Hydrogen

a. To increase the efficiency and reduce the size of the generator, hydrogen is used as its

cooling medium. Due to its small molecular weight, hydrogen has excellent thermal

conductivity.

b. Along with excellent thermal conductivity, hydrogen has a wide explosive range. Due to

this danger, the generator has a seal oil system designed to prevent its leakage and

maintain its purity high.



4. Seals

a. At each end of the generator inside of the bearings, are the generator hydrogen seals.

Sealing is accomplished by the use of regulated seal oil which is supplied by the

turbine’s lube oil system.

5. Seal Oil



a. The seal oil supply to the seals is regulated by the seal oil regulator. The regulator

receives oil from the lube oil header and maintains a specific differential pressure

between the hydrogen gas pressure and the seal oil.

6. Seal Oil Drain

a. To further prevent hydrogen hazards, the generator is equipped with a vented bearing

drain enlargement tank and a loop seal on the drain pipe. This is where seal oil drains to.

b. Seal oil drains are sampled for hydrogen purity by the Hydrogen Sampling Panel.



7. Heat Exchangers

a. Heat created in the generator and absorbed by the hydrogen is removed via the unit’s 5

water cooled heat exchangers. Cooling water for the water coolers is provided by the

plant’s cooling water system.

b. Fans built at each end of the rotor create the differential pressure necessary to circulate

the hydrogen through the coolers and into all sections of the stator and rotor.



8. Collector

a. On the non-drive end of the generator is the collector and turning gear assembly. The

collector contains the brush rigging and a cooling fan attached to the rotor.

9. Turning Gear

a. Attached to the rotor is the turning gear assembly. The turning gear assembly contains

the motor, reduction gears, and synchro-self-shifting clutch.



Test

1) Overview

Mechanical energy converted by the generator is provided in which of the following two

forms?

A. Rotation and excitation

B. Hydrogen pressure

C. Rotation and torque

D. Cooling water flow and hydrogen pressure

2) Hydrogen Gas

Hydrogen’s excellent thermal conductivity is a result of __________.

A. Its small molecular weight

B. Pressurized environment

C. Wide explosive range

D. Low operating temperature



3) Conductivity Maintenance

What is hydrogen’s excellent thermal conductivity maintained by?

A. Keeping the generator cool

B. Keeping the generator pressurized

C. Monitoring of its purity

D. Using air to maintain pressure

4) Seal Oil

The main purpose of the seal oil system is to __________.

A. Minimize lube oil usage in the generator

B. Provide cooling for the hydrogen

C. Reduce the friction of generator bearings

D. Provide an oil seal to keep hydrogen in the generator



5) Generator Cooling

Cooling medium for use in the heat exchanger is provided from ________.

A. Fans at each of the rotor ends

B. Seal oil flow through the seals

C. Plant’s closed cooling water system

D. Differential pressure regulated by the seal oil regulator

6) Collector End

The generator brush rigging is located on the generator’s turbine end.

A. True

B. False



7) Components

The turning gear assembly contains which three main components?

A. Fans, rotor, and gear assembly

B. Clutch, brush rigging, and collector rings

C. Heat exchanger, reduction gears, and brush rigging

D. Motor, reduction gears, and clutch



Test Answers

1) C

2) A

3) C

4) D

5) C

6) B

7) D

course 0212 7fa generator (7fh2) - tectrapro.com...3. seal oil system to ensure that the hydrogen...

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