seal Oil presentation

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GEK 107237Revised July 200

GE Energy

Shaft Sealing System

Hydrogen-Cooled Unpackaged Generator

These instructions do not purport to cover all details or variations in equipment nor to provide for every possible

contingency to be met in connection with installation, operation or maintenance. Should further information be

desired or should particular problems arise which are not covered sufficiently for the purchaser's purposes the

matter should be referred to the GE Company.

General Electric Company, 2009. GE Proprietary Information. All Rights Reserved.


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GEK 107237b Shaft Sealing System

The below will be found throughout this publication. It is important that the significance of each is thoroughly

understood by those using this document. The definitions are as follows:

NOTE

Highlights an essential element of a procedure to assure correctness.

CAUTION

Indicates a potentially hazardous situation, which, if not avoided, could result in

minor or moderate injury or equipment damage.

WARNING

INDICATES A POTENTIALLY HAZARDOUS SITUATION,WHICH, IF NOT AVOIDED, COULD RESULT IN DEATH ORSERIOUS INJURY

***DANGER***

INDICATES AN IMMINENTLY HAZARDOUS SITUA-TION, WHICH, IF NOT AVOIDED WILL RESULT INDEATH OR SERIOUS INJURY.

2 General Electric Company, 2009. GE Proprietary Information. All Rights Reserved.


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Shaft Sealing System GEK 107237

TABLE OF CONTENTS

I. PURPOSE .......................................................................................................................................

II. DESIGN FEATURES ....................................................................................................................

A. Shaft Seal .................................................................................................................................

B. Seal Oil Control Unit ............................................................................................................... C. Differential Pressure Regulator...............................................................................................

D. Flowmeter ................................................................................................................................

E. Instrumentation ........................................................................................................................

F. Seal Drain Enlargements and Float Trap .................................................................................

G. Bearing Drain Enlargement......................................................................................................

III. OPERATION..................................................................................................................................

A. General .....................................................................................................................................

B. Checking the High Oil Level Alarm (Refer to P&ID Generator Systems)..............................

C. Putting the Shaft Seals in Operation (Refer to P&ID Generator Systems)..............................

D. Charging the Casing with Air (Refer to P&ID Generator Systems) ........................................

E. Adjustment of No. 1 Pressure Regulator (Refer to P&ID Generator Systems).......................

F. Adjustment of Seal-Oil Unit Pressure Switches (Refer to P&ID Generator Systems)............

G. Normal Flow through Float Trap (Refer to P&ID Generator Systems)...................................

H. Operation at Reduced Gas Pressures (Refer to P&ID Generator Systems) .............................

I. Shaft Seal-Oil Flow Check (Refer to P&ID Generator Systems) ............................................

J. Float Trap Vent Line (Refer to P&ID Generator Systems)......................................................

LIST OF TABLES

Table 1. Valve Position...........................................................................................................................

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I. PURPOSE

In order to safely and effectively employ hydrogen for generator cooling, it is necessary to contain the gas

in the generator casing. Therefore, shaft seals are required at each end of the generator where the rotor

extends through the casing. A radial oil film type seal is used for this purpose.

II. DESIGN FEATURES

A. Shaft Seal

The shaft seal at each end of the generator consists of a seal housing containing a pair of bronze or

steel rings. The segments are positioned against the side walls of the housing and are held concentric

with the shaft by a garter spring. The rings which have a bore diameter of only a few mils greater than

the shaft journal are free to float radially but are prevented from rotating with the shaft by a stop in the

upper half of the housing. This housing is bolted to the end shield. Oil from the seal-oil control unit at

a pressure of about 4.5 psi (0.316 kg/cm2) above the hydrogen pressure in the generator is supplied to

the seal housing. The oil then passes radially through the space between the rings and axially along the

shaft in both directions. It is this thin film of oil between the shaft surface and the rings that actually

seals the hydrogen within the casing.

The total oil flow to the inner or hydrogen side rings of the two shaft seals is approximately two gal-

lons (7.57 liters) per minute, while the flow from the outer or air side rings may be several times that

amount. A large air-side flow is needed to cool the rings while a low hydrogen-side flow is essential

for satisfactory operation of the continuous scavenging system.

B. Seal Oil Control Unit

Pressure oil for the seals is supplied from the main lubrication system to the seal oil control unit where

it is regulated to maintain the 5.5 psi (0.387 kg/cm2) differential. The quantity of the total seal flow

can be read directly in the flowmeter.

C. Differential Pressure Regulator

A differential pressure regulator is provided for controlling the seal-oil pressure at the shaft seal. The

valve in the pressure regulator is directly controlled by the oil pressure by means of a spring and a

diaphragm. The regulator is designed to maintain a constant differential pressure across its valve body.

The differential pressure setting is determined by the spring compression.

The upper connection to the diaphragm is piped to the seal drain enlargement and senses the gas pres-

sure in the generator casing. The lower connection of the diaphragm is piped to the seal-oil supply

line and senses oil pressure being supplied to the shaft seals. When the pressure differential is across

the valve body, an increase in downstream pressure tends to close the valve. This restricts flow into

the valve body so the downstream pressure is reduced. As the downstream pressure drops, upstream

pressure acts on the diaphragm to open the valve and maintain the pressure setting differential. Once

adjusted, the regulator will maintain a nearly constant 5.5 psi (0.387 kg/cm2) pressure differential be-

tween the seal oil and the generator hydrogen through the complete range of hydrogen pressures.



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D. Flowmeter

The flowmeter, with an optional transmitter, is provided for obtaining an instantaneous reading of th

total seal-oil flow. It may be read locally (with a flowmeter gauge) or in the control room (when

transmitter is selected).

E. Instrumentation

An instrument panel contains two pressure gauges, one differential pressure gauge, two differenti

pressure switches, a differential pressure transmitter and a pressure switch. These instruments sen

seal oil skid inlet pressure, seal oil pressure at the seals with respect to gas pressure, and seal oil supp

pressure. One differential pressure switch activates an alarm on low seal oil differential pressure an

the other starts the DC emergency seal oil pump located on the lube oil tank when a low/low se

oil differential pressure is reached. The DC emergency seal oil pump will also be engaged upon th

activation of the pressure switch when a low-pressure condition is experienced at the seal oil contr

unit inlet. The differential pressure transmitter indicates pressure to the control system for monitorin

Valving is provided for adjusting, testing and draining all instruments.

The seal oil pressure switches are adjusted to send alarm signals to the control system when seal odifferential pressure is low, or when filter differential pressure is high. The transmitters indicate tot

seal oil flow and seal oil differential pressure to the control system.

Differential pressure instruments, measuring gas pressure versus seal oil pressure, must be recalibrate

in the field due to the static oil head in gas pressure sensing lines from seal oil enlargement to ski

Instruments should read seal oil differential pressure as would be read at the generator seals.

F. Seal Drain Enlargements and Float Trap

Two small detraining chambers, known as seal drain enlargements, are provided for removing entrain

hydrogen gas from the oil which drains from the hydrogen side seal rings. One of these enlargemen

is mounted on each end shield and the two are drained through a common line to a float trap. Theflotrap, which is required to prevent the loss of hydrogen with the drain oil when operating at elevate

hydrogen pressures, drains to the bearing drain enlargement where further detraining takes place befo

the oil returns to the main oil tank. Thefloat trap assembly is separate from the seal oil control un

and is mounted in close proximity to the generator.

A vertical pipe open at the top terminates in the upper part of the turbine end of the seal drain enlarg

ment. Another vertical open pipe is also installed in one of the seal drain enlargements to collect th

oil which results from an abnormal oil level in the enlargement. This overflow is piped to a high lev

alarm switch. Since the two enlargements are connected by a common drain line, a high level in eithe

would normally result in the operation of the alarm. Abnormal oil level is usually caused by incorre

operation of the drain valves.

G. Bearing Drain Enlargement

The air side seal-oil and the generator bearing oil drains to a detraining chamber mounted under th

generator casing. This detraining chamber, which has been designated as the bearing drain enlarg

ment, provides a large surface area for detraining the oil before it is returned through the loop trap

the main oil tank. The bearing drain enlargement is vented to the roof. In the event of failure of th

shaft seal oil supply, hydrogen will pass from the generator into the bearing drain enlargement and b



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vented to the roof. The liquid loop seal provides a barrier to prevent the hydrogen from entering the

main lubrication oil tank.

III. OPERATION

A. General

Whether the generator is running, in air or hydrogen, it is necessary at all times to have the shaft seals

in operation.

When running in air, shaft sealing is necessary in order to supply oil to the seal rings to prevent their

heating up and seizing the shaft because of the small diametral clearances.

When running hydrogen, shaft sealing is necessary in order to confine the hydrogen in the casing.

B. Checking the High Oil Level Alarm (Refer to P&ID Generator Systems)

The high oil level alarm switch (LSH-3401) actuates an alarm when there is an abnormal rise in the oil

level in the seal drain enlargement.

To test the operation of this switch, first close valve (HV-3441), then remove pipe cap at switch housing

and pour in water. This should cause the float in the switch to rise and close the alarm contacts. After

testing, drain the water by removing pipe cap below sight glass. Replace both pipe caps and open valve

(HV-3441).

C. Putting the Shaft Seals in Operation (Refer to P&ID Generator Systems)

The shaft seals may be put into operation and adjustments made to the seal-oil control unit any time

after the lubrication system has been completely flushed and is ready for operation.

The adjustments of the seal-oil system must be made by supplying seal-oil through operation of eitherthe emergency pump in the main tank or from the AC bearing and seal-oil pumps.

Oil from the intermediate pressure header passes through the seal-oil pressure regulator, flowmeter,

thence to the shaft seals. Valves (HV3435 and HV3407) in the sensing lines to the pressure regulator

should be open approximately three-quarters of a turn. Restricting the opening of these valves will

sufficiently throttle the sensing line pressures so that sudden pressure changes will not damage the

diaphragm of the pressure regulator. This diaphragm is designed for a maximum differential pressure

of 125 psi (8.788 kg/cm2), and care should be taken never to exceed this value. Valve (HV3407) is in

the gas pressure sensing line, while valve (HV3435) is in the seal-oil pressure sensing line. All other

valves on the seal-oil control unit should be open or closed as shown on the diagram.

Check to make sure that seal-oil is flowing to the seals. This will be indicated by the flowmeter.

D. Charging the Casing with Air (Refer to P&ID Generator Systems)

Adjustment of the seal-oil control unit components should be made with air pressure in the generator

casing.

Start the AC bearing and seal-oil motor pump. Remove pipe plug at connection leg in the gas control

valve assembly, and admit dry air to the casing through this connection. Adjust the valves in accordance



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with the illustration and charge the casing with 15 psi (1.055 kg/cm2) of air as read on the casin

pressure gauge on the hydrogen manifold.

E. Adjustment of No. 1 Pressure Regulator (Refer to P&ID Generator Systems)

Adjust the pressure regulator valve to hold the shaft seal-oil pressure as read on differential pressur

gauge PDI-3402 at 4.5 psi (0.316 kg/cm2

) above the machine gas pressure.

It should be noted that this pressure regulator will then hold 5.5 psi (0.387 kg/cm 2) differential over th

entire range of casing gas pressures.

F. Adjustment of Seal-Oil Unit Pressure Switches (Refer to P&ID Generator Systems)

The emergency seal oil pump pressure switches (PS-3404, PDSL-3406) bring the DC motor drive

pump into operation when the switch contacts are closed. For steam turbine applications, an emergenc

pump running pressure switch (PS-268, or as specified by the lube oil P&ID-VD01), which is locate

on the lube oil tank, actuates an alarm in the control system upon the DC motor pump starting.

To adjust pressure switch PDSL-3402, close valve HV-3401 and crack open valve HV-3413 until gaugPDI-3402 reads 3.5 psi above the machine gas pressure. Make any internal adjustments necessary

switch PDSL-3402 to actuate contacts when this differential pressure is reached. Further reduce th

seal oil pressure at PDI-3402 to 2.5 psi (0.176 kg/sq cm) above machine gas pressure. Adjust switc

PDSL-3406 internally to actuate the contacts at this pressure. Adjust switch in accordance with switc

bulletin.

Adjust pressure switch PS-3404 by cracking open valve HV-3426 until pressure on gauge PI-3404

80 psig (30 psi and 45 psi generators). Make any internal adjustments, per switch bulletin, to actua

switch contacts at this pressure.

G. Normal Flow through Float Trap (Refer to P&ID Generator Systems)

In normal operation with gas pressure above 5 psi (0.352 kg/cm2), valves shall be in the position ind

cated in Mode 1,Table 1.

H. Operation at Reduced Gas Pressures (Refer to P&ID Generator Systems)

On some machines it will be necessary to operate with the float trap bypass open when operating

lower generator casing gas pressures in order to avoid flooding the seal drain enlargements. Valv

shall be in the position indicated in Mode 2, Table 1. When the generator casing gas pressure is lo

(approximately 5 psi [0.352 kg/cm2] or less) the gas pressure in the seal drain enlargement is not alway

sufficient to overcome the friction in the piping between the seal drain enlargement and bearing drai

enlargement, and flooding of the seal drain enlargements will occur. As casing gas pressure builds u

to approximately 5 psi (0.352 kg/cm2), the bypass valve must be closed so that gas will not be blow

into the bearing drain enlargement.

I. Shaft Seal-Oil Flow Check (Refer to P&ID Generator Systems)

The total quantity of oil passing through the shaft seals may be determined by reading the flowmete

The flow values should be equal to or less than those given on the Hydrogen Design Data sheet.

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The emergency pump mounted on the main oil tank or the AC bearing and seal-oil pumps should be

in operation supplying oil to the seals during the check of seal flows.

The hydrogen side seal flow is determined by draining from valve (HV-3406) into a measuring con-

tainer for a fixed period of time.

CAUTION

Seal oil might contain entrained hydrogen which in contact with any ignition points

could lead to a fire/explosion.

The most effective method of measuring hydrogen side seal oil flow, and the least likely to result in

oil ingress into the generator or hydrogen escape through the float trap and out the BDE vent, is the

method described in as Mode 3. Valves shall be in the positions as indicated inTable 1. Measuring

flow with Mode 3 does not involve any manipulation of the float trap bypass valve.

Hydrogen side seal oil flow can also be measured using Mode 2 in Table 1. In this method, all the hy-

drogen side seal oil flow is controlled by manual manipulation of the float trap bypass valve HV-3405.

HV-3405 is difficult to accurately control. Therefore this method often leads to oil flow fluctuations,which in turn may cause oil ingress and/or hydrogen escape as described above. To measure hydro-

gen side seal oil flow using Mode 2, throttle valve (HV-3405) to hold the level of the sight indicator

between valves (HV-3466, HV-3465) at approximately 1/2 full during the measuring period.

The total flow minus the hydrogen side flow equals the air side flow.

J. Float Trap Vent Line (Refer to P&ID Generator Systems)

Valves HV-3462 and HV-3438 are normally left open and are only closed when it is necessary to isolate

the float traps for servicing or when measuring gas side seal ring flow (close HV-3438 only).

Table 1. Valve Position

Valve

Mode 1

Normal Flow

through Float Trap

Mode 2

Float Trap

Bypass

Mode 3

Measure Gas

Side Sealing Flow

HV-3406, HV-3436 Closed Closed HV-3406 Open, HV-3436 Closed

HV-3466 Closed Open Closed

HV-3403, HV-3437 Open Closed HV-3437 Closed, HV-3403 Open

HV-3465 Closed Open Closed

HV-3404, HV-3444 Open Closed Closed

HV-3405 Closed Throttle Closed

HV-3462, HV-3438 Open Closed HV-3438 Closed, HV-3462 Open

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