I B6117

I B6117
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Superseding LB. 6117
Westinghouse Steam Turbines-I. B. 6117 (Rev. 1)
OVERSPEED TRIP MECHANISM
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Figure 1 shows the overs peed trip which automatically closes the
throttle valve, thereby shutting down the turbine, if the speed increases to
approximately 11 per cent above normal.
Oil is used as the operating medium.
art
M
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The trip body
(which is integral with the governing impeller)
is
threaded on the end of the turbine shaft
with a
thread
opposite
to
the
direction of rotation and is locked in place by a
set screw.
The
trip
weight "16" (shown in Section C-C) is carried in a
transverse
hole in
the
body, with its center of gravity offset from the
axis of rotation so
that
centrifugal force tends to move it outward
this
at all times.
Normally,
weight is held in its inner position by the compression spring "1411 and the
!
retaining nut 1 151!.
If the speed of the turbine increases to the point
for
which the mechanism is set to operate (approximately 11 per cent
above
nor­
mal), the weight (16), due to the
increased
centrifugal
force,
overcomes
the compression of the spring "14" and moves outward.
In this outer
posi­
tion the weight strikes the trigger 1111"
and rotates it so as to
disengage
7 ,
" 11
the latch between the lower end of the trigger and the sleeve
Disen­
H
gagement of this latch releases the load imposed by spring !l5 on the valve
/ 12/ 1, and therefore, releases the oil
pressure
below the
valve,
which
in
turn, releases the oil pressure below the throttle valve
operating
piston.
The throttle valve, therefore, closes,
thereby,
shutting
down
the
unit.
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After this mechanism has tripped, it must be reset by hand.
This
is done, by pulling upward on the resetting lever "24", which, by suitable
linkage, depresses the oil valve until the latch between
the
trigger "1111
ff711
is again engaged.
The valve ll2!! is then held
firmly
on
and the sleeve
its seat by the compression spring ll5!!,
This,. of course
cannot be
done
l
t16"
until the turbine speed has decreased sufficiently to allow the weight
to return to its normal position, which should occur at
approximately 2 per
cent above normal speed.
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The mechanism can be tripped
by hand
by
pushing
downward
or
ll
As shown in Fig. 1, this lever
is
ful­
striking the hand trip lever
3 9",
the
crumed so that it, in turn, strlkes the trigger ffll n, thus disengaging
latch and allowing the oil valve l!2" to open in the same manner as described
above.
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When desired, an electrical solenoid can be provided to
trip
the
mechanism,
In such cases, the solenoid (not shown in the illustration)
is
located on the end cover so that when energized, its plunger strikes the end
of the trip lever ll39" and thus disengages the trigger latch.
The following adjustments should be maintained in order
proper functioning of the trip mechanism.
With the mechanism latched in its normal position,
there should be 1/16-inch clearance between the
trigger "II" and the body.
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1.
to insure
2.
With the mechanism in its tripped position, there
should be at least 3/8-inch clearance between the
trigger I!llll and the body.
3.
With the trigger cam adjusted as above, there should
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be 1/16 -inch lap of the latch between the trigger f ll
11711,
a nd the sleeve
1
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om
Overspeed
Mechanism
A turbine should be overspeeded occasionally to check
the speed
at which the weight 1f161f flies out and actuates the tripping mechanism . It
is not sufficient to disengage the trigger latch by hand because this tests
only the automatic throttle valve.
als
In order to check the overs peed of the turbine properly, the gov­
erning valves should be blocked open.
The throttle valve should
then
be
opened very slowly, due attention being given
to the tachometer,
and
the
it
is
speed slowly increased to the tripping pOint.
During
this
test,
advisable to have an operator stand by the overspeed trip, ready to trip it
by hand instantly if it does not trip automatically at the 11 per cent over­
speed .
the instructions given in
governor .
the instruction
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u
If the governor on the turbine is equipped
with
an
overspeed
testing device, the· unit should be tested for overspeed in accordance
with
book supplement
covering
the
art
M
In case the weight 1t16tf fails to fly out at the correct speed the
unit should be shut down and the mechanism checked.
Make sure
that
the
The overspeed
test
should
a¥t ain
be
weight is not sticking in its body .
is
run and if the same trouble results, it is evident that the spring 114"
compressed too much thus preventing the weight 1f16" from flying out
at the
correct speed.
should
In order to correct the adjustment, the lock spring
tf19"
The retaining nut "15t! should then
be removed and the lock "17" pulled out.
be backed out part of a turn to decrease the compression of the spring "14".
The lock "17" should be reassembled so that it fits into one of the notches
the
in the retaining nut and is secured by the lock spring "1911.
Turning
nut one notch will chan e the turbine s eed a
on an 1 00 rpm.machine and 50 rpm. on a 3 00 rpm. machine.
roximatel
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retalnin
Should the unit trip out at less than 11 per cent overspeed, the
of
a turn
and
again
spring retaining nut "15" should be screwed in part
locked in place.
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"14"
a
final
After making a change on the compression spring
is again put in
overs peed test should always be made
before the turbine
service .
An arrangement is
provided by means of which the trip mechanism
can be tested without actually overspeeding the turbine, and, if
the re­
setting lever "24" is held to prevent opening of the oil valve "2", it can
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be tested without taking the turbine off the line or
removing
the
load.
This is accomplished by admitting oil, under pressure, to
the
bottom
of
the trip weight t!
" and noting the oil
pressure
required
to move
the
weight outward.
As shown in section A-A-A-A, the test plunger "30"
which
passages
is located at the center of the end cover 1133", contains
connect with a high pressure oil supply and direct this
oil
into
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responding passage in the end of the rotating overspeed trip body .
which
a cor­
This
plunger is normally held away from the end of the body by t he compression
spring "29".
When it is held inward against the rotating body and the oil
test valve 1f31t! is opened, oil pressure is established at
the
bottom of
1
the weight "1611.
"
1 and a
This pressure is regulated by the hand valve
pressure gauge is provided by means of
which
the
pressure
required
to
w
operate the weight at norm&l speed can be ascertained.
The readings obtained in this manner are,
tive and must be compared with previous readings.
of course,
only
rela­
With the spring adjust­
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ment made correctly by actually overspeeding the turbine, t he speed chang­
er should be adjusted to maintain exactly normal full speed and
the
over-
2
Mechanism
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om
Overspeed
als
speed
operated by oil pressure as described above.
The pressure at
Then at
which the trip operates should be recorded for future reference.
any future time, the mechanism can be tested by means of oil pressure alone.
If the oil pressure required to operate the trip is the same as that
originally recorded, it can be assumed that the mechanism is functioning
properly.
It is important to have the turbine operating at exactly normal
otherwise the
full speed whenever the trip is operated by oil pressure,
readings will not be of any value.
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In order that the �xial location of the
rotor in the cylinder
may be checked at any time, provision is made for using a depth micrometer
against the end of the overspeed trip body.
The micrometer pin should be
(shown in
inserted in the hole drilled near the center of the end cover
the end view) and adjusted until the pin just touches the rotating body.
In order to insert the micrometer pin, the cover plate "41" should be ro
tated to clea� the hole.
to facilitate ordering spare
The following list has been c
or renewal
number
by item number and name, together with the serial
of the turbine.
Item No.
.E
art
M
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20
21
22
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,. ..
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29
30
"
33
34
"
39
40
41
Overspeed Trip Valve Seat
Overspeed Trip Valve
Overspeed Trip Valve Stem
Overspeed Trip Valve Spring
Overspeed Trip Valve Stem Spring
Overspeed Trip Valve Stem Spring Seat
Overspeed Trip Valve Stem Sleeve
Overspeed Trip Valve Body Cover Bushing
Overspeed Trip llalve Body
Overspeed Trip Valve Body COlTer
Overspeed Trip Trigger Spring
Overspeed Trip Trigger
Overspeed Trip Trigger Fulcrum Pin
Overspeed Trip Body Balancing Block
Overspeed Trip Weight Spring
Overspeed Trip Weight Spring Retainer
Overspeed Trip Weight
Overspeed Trip Weight Spring Re.tainer Lock
Overspeed Trip Weight Wearing Ring
Overspeed Trip Weight Spring Retainer Lock Spring
Overspeed Trip Re-settlng Cam Stop Pin
Overspeed Trip Re-setting Cam Shaft
Overspeed Trip Re-setting Cam
Overspeed Trip Re-setting Lever Stop Stud
Overspeed Trip Re-setting Lever Spring
Overspeed Trip Re-s
Lever
Overspeed Trip Re-setting Lever Nut
Overspeed Trip Re-sett
Lever Indicator
Overspeed Trip Test Plunger
Overspeed Trip Test Plunger Packing Retainer Ring
Overspeed Trip Test
Packing
Overspeed Trip Test Plunger Spring
Overspeed Trip Test Plunger Head
Overspeed Trip 'I'est Valve
Overspeed Trip Test Gauge
Overspeed Trip End Cover
Gasket
Overspeed �rip Hand
Lever Cam Stop
Overspeed Trip Hand Trip
Cam
Overs peed Trip Hand
Shaft
Overspeed Trip Hand
Spring
Overspeed Trip Hand
Overspeed Trip Hand
Nut
Micrometer Hole Cover
tric
1
2
3
4
5
6
7
7 -A
8
9
10
11
12
13
14
15
16
17
18
Name
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om
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als
/31/
SECTION CC
NORMAL
TRIP
TESTr,AUGE
"r,
HAND
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·5
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5"
RE-SETTING
'L EVER
OILOi/TLET
-4
3
. .-2
TRANSV[RSE
THRU
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MECIj,
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5"
SECT
OVD?- SPEED TRIP
LEVER
&8-&8
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"
SEC TlON
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art
TRIPPED POSmON,
89
Ma
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IS
Figure 1
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