National Electric Light Association. Convention.

Convention, Volume 42, Part 5 online

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storage of hot water in the heaters and in auxiliary tanks to
assist in maintaining maximum evaporation during the first few
minutes of active turbine operation.

It appears that the operation of steam turbines at no load
in parallel with hydro-electric systems is tending to become less
frequent, not only on account of the necessity for rigid econ-
omy, but because hydro-electric plants and transmission lines are
becoming more and more reliable. It is in general only for
the most important load and with inferior hydro-electric system
operation that this standby operation is advisable. When the
floating service becomes necessary, great care and skill should be
exercised in keeping steam plant costs at a minimum; this is
especially necessary with steam plants not specially designed for
economy during standby operation, but even in stations planned
specifically for such service a considerable saving can usually
be made by careful study of operating methods.

MANUFACTURERS' STATEMENTS

Your Committee is in receipt of statements from the fol-
lowing manufacturers covering developments during the past
year:

AlliS'Chalmers Manufacturing Company

Since the last meeting of the National Electric Light Association,
manufacturers have had little opportunity for special development work
on steam turbines. The requirements of the Government for equipment
for use in connection with the prosecution of the war, on account of the
urgency of this demand, of necessity restricted the choice of the appara-
tus to the standard lines of equipment, and development work has had
to be postponed until the return of normal times.



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The most prominent and significant feature in the course of steam
turbine progress during the last twelve months is the return to favor
of the medium size unit of approximately 10,000 to 12,000 kw. capacity,
from which it would appear that operating engineers are beginning to
realize the disadvantage of installing units of unduly large capacity,
preferring rather to install medium size units with slightly less thermal
efficiency but with greater reliability, and the fact that the shutting down
of any one piece of apparatus on account of trouble or for periodic in-
spection and overhauling causes much less interruption in the service,
is no doubt a reason for the popularity of this size of unit.

During the last year we placed in operation a number of units of ap-
proximately the sizes given above, and in each case the machines were
started up without a hitch and have maintained an enviable operating
record to date. Six machines have been placed in service and seven
others are nearing completion.

In all cases the generators were manufactured in pur own shops, and
in four of the installations already in operation we also manufactured
the condensers and condenser auxiliaries, which in these cases places the
responsibility for the complete generating equipment up to one manu-
facturer, an undoubted advantage from the purchaser's point of view.

On account of their excellent operating record, a brief description
of these machines may be of interest to the members of the Association.
To obtain maximum economy the turbines are of the single flow
reaction type, embodying all the improvements gained by our engineers
in fifteen years' experience in the manufacture of steam turbines. The
blading is of our well-known substantial construction, mounted in an
exceptionally rugged spindle, and the special care taken during all proc-
esses of manufacture to insure an accurate balance, not only of the
spindle and spindle rings but also of the segments of blading, without
doubt contributes very largely to the smooth operation of the completed
rotor.

The turbine spindle and generator rotor are each carried in their
own bearings, suitably connected through a flexible coupling efficiently
lubricated by a patented method of lubrication. The four bearing method
of support permits the ready inspection of either turbine or generator
without disturbing the other element.

The turbine cylinder is split along the horizontal joint, thereby per-
mitting ready access to the interior of the machine for periodic inspec-
tion, and the ends of the cylinder where the spindle passes through are
effectively sealed against any inleakage of air by means of our well-
known water sealed glands. These glands, not being subject to wear
except to that occasioned by the churning action of the water, insure
effective sealing after long continuous operation, and contribute to the
maintenance of the best possible vacuum obtainable by the condensing
equipment

The bearings of both generator and turbine are of the ball and



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socket type lined with babbitt, and are lubricated by means of forced
Ittbrication. Above each bearing a visibile leak-off is provided, which
enables the operator to observe at all times that oil under pressure is
maintained at each bearing, and also permits any air which might accu-
mulate at the bearing to escape without endangering operation. This par-
ticular feature is patented and is the exclusive right of our company.

The turbine and generator are mounted on a continuous bedplate of
very rugged construction, and the throttle valve and steam chest, includ-
ing the steam strainer and inlet valve with its oil relay mechanism, are
bolted rigidly to this bed plate, a flexible steel connection being provided
between the steam chest and the cylinder. This construction prevents
the possibility of any strains being imposed upon the turbine cylinder,
due to steam piping, etc., and permits the free expansion of the turbine
C)'linder under variations in steam temperature.

In addition to the usual pedestal supports at each end of the cylinder,
a substantial foot is provided around the exhaust nozzle which is sup-
ported on the bed plate. With this added stiffness in construction the
expansion joint usually provided in the exhaust pipe can be eliminated,
if the condenser is suitably supported on springs to carry the weight of
this part of the equipment.

As is customary, a by-pass valve is provided directly operated by
the governor to admit steam to a lower stage of the turbine in the event
of an exceptionally high load, or to maintain operatioh in case of an
extreme drop in the steam pressure.

A self-contained forced lubricating system, including a suitable oil
cooler, is provided for bearing and governor lubrication, and for the
purpose of supplying oil for the relay system for operating the valves.
In addition an oil filter of large capacity is furnished to withdraw con-
tinuously a portion of the oil for the purpose of removing water and
other impurities, automatically returning the cleansed oil to the system.
For use when starting up and stopping, and also in case of emer-
gency, a steam turbine driven submerged centrifugal oil pump is pro-
vided and a suitable pressure regulator is installed to start up this
auxiliary oil pump automatically in case of an undue drop in pressure
in the system from any cause whatever.

In general, the turbine is of rugged construction, built for continuous
service and is of pleasing appearance, and, judging from the reports
furnished by customers who are operating these units, they have given
unqualified satisfaction.
• A cross section of our standard machine is shown in Fig. 1.

General Electric Company

Since our last statement two years ago in reference to turbines, war
conditions, have, of course, made the undertaking of new commercial
development on a large scale very difficult. It was necessary, never-
theless, to carry through the new designs which we had already started



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and to do a great deal of development work to meet the requirements
of the Navy and Emergency Fleet Corporation.

At a time when we were hard pressed for skilled labor of all kinds,
it was extremely difficult to give the time and attention necessary to the
development of new designs. The engineering and manufacturing or-
ganizations could not be expanded quickly enough, by the addition of
thoroughly trained men, to meet fully the enormous demand which sud-
denly came upon us. We, like all other manufacturers, suffered severely on
account of the loss of skilled men who went in the service, over 8000
employees leaving us on this account. These men had to be replaced by
less skilled men and in addition a greatly increased force recruited
from all sources.

We also experienced great difficulty in securing the quantity and
quality of materials required for the manufacture of turbines. The
producers of all lines of materials and accessories were surfeited with
business, were required to carry on production under the same disad-
vantages that we suffered from, and in endeavoring to meet the demands
for maximum production undoubtedly encountered most serious obstacles
in the way of maintaining quality equivalent to pre-war standards.

The severe handicaps under which we were working were neces-
sarily reflected to some extent in the turbines manufactured during this
period of stress, and a number of machines have been subject to trouble
of one kind or another. Cases of trouble have not, by any means, been
confined to turbines of new types but have occurred in recently built
turbines of the older types.

Actual experience was required to show that our inspection system,
which had previously proved to be amply protective, was not under the
new conditions sufficiently thorough or comprehensive, and it has been
necessary to elaborate it. This has been done, and with the return to
more nearly normal conditions the severe handicaps under which we
have been working during the last two years are being removed. We
feel greatly encouraged by the results already attained and have the
utmost confidence that from this time on the production and operation
of Curtis steam turbines will be on the same satisfactory basis that
existed in former times. No radical changes in existing designs of tur-
bines are contemplated. The general features of design of a 7500 kw.
and a 45,000 kw. machine are shown in Fig. 2 and Fig. 3.

A very large number of turbines and gears have been furnished to
the Emergency Fleet Corporation for propelling cargo boats and to the
U. S. Navy for destroyers. In addition, turbo-generators have been sup*
plied and are on order for the electric propulsion of large warships for
the Navy. For the latter purpose turbo-generators of individual capacity
up to 35,000 kw. are on order.

The Company has built and will continue to build direct current
turbo-generators, also turbo-generators for special application, indud-
' ing steam extraction, low and mixed pressure units, and turbines for
mechanical drive.



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Fig. 2— General Electric 7,500 Kw. Unit



Fig. 3 — General Electric 45,000 Kw. Unit



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Kerr Turbine Company

Kerr turbines are of two principal types— the older or multi-pressure
impulse type, and the newer or velocity stage turbine. They are built
for high pressure, condensing, noncondensing low or mixed pressure ser-
vice. A large number of turbines for marine propulsion and many of
the extraction or bleeder type have also been built.

Recent developments on our turbines consist chiefly of thi perfecting
of mechanical details on the multi-pressure stage machine, and complete
design of the velocity stage machine for small horse powers.

Our turbines are designed primarily to be absolutely reliable, safe
and satisfactory in operation, as this, in the opinion of engineers, con-
stitutes the main requisites of a piece of machinery. All rotating parts
are designed to give the maximum strength, and are carefully machined,
ground and balanced. Clearances between rotating and stationary parts,
are large. Bearing temperatures are kept low.

Even though steam economy is considered of secondary importance,
particularly for small machines, our turbines embody certain features
of design, as. will be outlined later, which permit them to show a per-
formance for the majority of conditions unexcelled by any other turbine
builder.

The casings in both of the above-described types of turbines are
made up of steam and exhaust ends which are provided with supports
for bolting to bed plate and between which are the circular steel or iron
diaphragms containing the nozzles for the pressure stage turbine, and
intermediate holders with reversing chambers for the velocity stage type.
The diaphragm castings are arched at the center and are centered with
each other and with the two end castings by turned and bored tong^ue-
and-grroove joints packed with fibrous packing laid in graphite and oil.
The sections are boUed together by continuous stay bolts passing through
drilled holes in the flange of one end of the casting and tapped into the
flange of the other. The diaphragms are split and when bolted together
with exhaust and steam ends, the upper halves form a cover which may
be lifted, exposing the entire rotor for inspection or repairs. For smaller
size turbines the end castings are each bored to receive the main bearing
cases. A section through one of the smaller types of turbines, as shown
in Fig. 4, brings out the general features of design.

It is generally known and appreciated that the fact that diaphragms
can be added or removed from certain frames of turbines without any
change other than lengthening or shortening the turbine shaft, is of the
greatest advantage from the thermodynamic standpoint. The thermody-
namic efficiency of a turbine of any type, excluding windage friction, is
a function of the ratio between blade and steam velocities. By adding
stages for exceptional conditions, such as low rotating speeds, high
steam pressures and good vacuum, and removing stages for conditions
in the opposite extreme, namely high rotating speeds, low steam pressures
and high exhaust pressures, it is possible to adjust the number of stages



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so as to get the best possible efficiency for each condition. The sectional
construction lends itself extremely well to complex conditions of opera-
tion. So, for instance, condensing turbines are built to develop full load;
non-condensing and bleeder turbines can be made to bleed the total



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amount of steam at bleeder pressure; in other words, operating non-
condensing, etc.

On rotors of the larger size machines the bucket wheels arc forged
integral with a central hub and forced by hydraulic pressure onto a
tapered steel shaft. In the smaller units each bucket wheel is bolted onto
a three-piece split hub, fitted to the shaft and kept from lengthwise or
rotating movement by pin keys. A split mitred key is forced by a lock-
nut into the bore of the disk and against a turned taper on the hub. The
wheels are machined from sheet steel or steel forgings, depending upon
their size, and are drilled and slotted to receive the shanks of the buckets.
The buckets are made of a nickel steel particularly well adapted to with-
stand erosion. Buckets undergo a heat-treatment to get the maximum
strength and are restruck by a special method to get the best possible
finish, which will decrease the steam friction and increase the efficiency.
Buckets are provided with a shank and bulb at the inner end and are
inserted sideways into the rim of the wheel and securely rivetted into
place. This type of blading is undoubtedly the safest of any used in
modem steam turbine practice.

Steam is admitted through a double beat balance valve, the stem of
which is connected on the smaller turbines through one single lever to
the governor. On larger machines instead of the direct acting governor,
a so-called oil relay governor controls the movement of the valve through
a small oil pilot which operates the piston of the main steam valve.
Turbines are provided with an overspeed governor on the main shaft
as an additional precaution in case, through some accident, the main
governor should fail to ftinction.

Leakage of steam along the shaft at the steam and exhaust ends
and between stages is prevented by floating carbon packing rings, held
in place by spiral springs and stops. The packing at the steam end
consists of a number of these rings with two leakage connections taken
from selected points between them and piped to the low pressure stages.
On condensing turbines one of these leakage pipes is connected to the
exhaust end packing so as to form a steam seal and prevent air from
being drawn through this packing to the condenser.

The main bearings arc of the self-aligning split, babbitt lined type,
and on the larger size arc provided with oil under a pressure of about
six pounds, the oil being supplied by a reservoir in the bed plate and
the required pressure being obtained from a gear pump attached to the
lower end of the governor spindle. Before being used the oil is forced
through a nest of water-cooled brass tubes located in the bedplate, and
after having passed through the bearings is returned to the reservoir.
On the large units a small auxiliary turbine-driven centrifugal oil pump,
bolted to the reservoir and with impeller submerged in the oil, automati-
csijly serves the bearings with oil while the turbine is being started or
stoppe4. On smaller size turbines ring oil lubrication is employed.

The genera! design of Kerr turbines in both large and small sizes
is illustrated in Figs. 5 and 6.



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Westinghouse Electric and Manufacturing Company

The accompanying figures give information regarding our tandem
and cross compound turbines:



Type


Weight


Length Width


Height


Rating


Tandem


1,200,000


72' 9" 20' r


20' 9W


35,300 kv-a.


Cross Compd.,


. 1,360,000


47' 8" 42' 2"


18' 9"


47,200 kv-a.



The above data cover the tandem machine we built for the Com-
monwealth Edison Company and the cross compound we built for the
Duquesne Light Company and the Narragansett Electric Lighting Com-
pany. In both cases they are 60 cycle units, the Commonwealth running
at 1200 RPM, while the cross compound runs at 1800 RPM for the high
pressure and 1200 RPM for the low pressure. You will see that the
weight per kilowatt for the tandem is somewhat greater than the cross
compound. However, this weight per kilowatt would be very close for
both cases if we could compare exact sizes.

The cost per kilowatt of the two sizes may be assumed to be practi-
cally identical. The steam end of the tandem machine is somewhat more
expensive, while the two generators on the cross compound will exceed
the cost of the single generator about enough to equalize. The difference
in efficiency between the two types is within 2 per cent.

As to a general comparison of the two types from a manufacturing
standpoint, we can build either type quite comfortably, although it is per-
haps a little easier to turn out the cross compound machine. It is more
of a job to assemble the tandem machine complete on the testing founda-



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tion than it is to test the high and low pressure elements of the cross
compound separately. The stresses in both types are quite low, the
materials employed are of ordinary, readily obtained quality, and the
testing and inspection is all of a character well within the usual stand-
ards of good shop practice.

Whatever there is to be said about the two types bears more par-
ticularly upon the operation side, and on this question opinions will dif-
fer. There are some engineers who seem to prefer the single shaft unit,
as they feel that the single generator best fits the operating conditions.
The tandem machine has the merit of dividing the cylinder structure
into two parts, which removes the problem of design that comes with an
excessively large single cylinder structure with its possibilities of in-
stability. It also confines the high temperatures to a small steel cylinder,
a point of particular importance as we approach the question of higher
temperatures of steam. It is true that a mishap in either cylinder would
be likely to disable the whole machine.

Our own view has rather favored the use of two separate elements
in^ these larger sizes, and, as you know, we have gone to three elements
in the 60,000 kw. size. We think that the cross compound offers the
maximum assurance of operating reliability. We do not see anything
in the operation of a 40,000 kw. cross compound that presents any new
problems over operating two 20,000 kw. single units. The three 30,000
kw. machines at the 74th Street Interborough plant in New York have
had a four years' operating record, so there has been a good deal of
actual experience with them. If actual operation means anything, they
have proved out. From a design standpoint nothing could be much
simpler. The cross compound machine should perhaps be looked
upon from an operating viewpoint as one unit, but there is the point
that if anything happehs to the high pressure side, the low pressure can
be operated at about half the unit capacity, and so your eggs are not
quite all in one basket. The operating record of the tandem machines
at Chicago has been so good, however, that they have certainly justified
the type, but it still remains true that a mishap could put the entire tandem
unit out of service, which with the cross compound machine still enables
you to use half of its capacity.

Summing up a comparison of the two types, the choice between
them seems to be more a matter of taste or opinion than one of defined
judgment. The record of large turbines up to date has proved one thing,
that the single cylinder design has found its limit of reliability and
efficiency at 25,000 to 30,000 kw. ; that above 30,000 kw. we must go to
the multi-cylinder type in order to have the mechanical design sufficiently
reliable to justify these larger sizes. And it seems also true that we
must go to these larger sizes for our bigger stations in order to get
the operating cost where it belongs. If it be said that equally high
efficiency could be secured in smaller machines, such as 20,000 kw., the
answer is that the cost per kilowatt to achieve that result would be pro-
hibitive.



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In addition to the record of progress on large machines,
your Committee has received the following statements from
manufacturers regarding small turbines for driving auxiliar]^
equipment :

General Electric Company

About three years ago we developed a line of turbines particularly
for mechanical drive applications and known as the type "L." Since that
time, we have sold over 90,000 horse power for this class of service
alone, the number of machines being between 800 and 900, and the operat-
ing record of the machines has been exceptionally good.

The line of turbines includes machines from 10 to 500 horse power
at speeds up to 3600 rev. per min. Any steam pressure and superheat
may be used up to the highest in commercial use in large stations.

These turbines meet two conditions: First, that individual machines
are designed to suit each customer's particular operating conditions;
and second, that the foregoing can be accomplished with a machine made
up from parts manufactured on a quantity basis.

Both of the above ideas are carried out, and the type "L" machine
combines a machine designed to meet any given set of conditions, and,
at the same time, one which is built oh a quantity production basis.

Each machine is made up of standard parts, which are, in the main,
as follows: Nozzle plates, shaft and wheels, high pressure head, wheel
casings, exhaust head, operating governor, governor valve, emergency
valve.

Nozzle plates are made up in quantity, but the nozzles are not
drilled until an order is received. The shop is equipped with engineer-
ing data to make nozzles suitable for use with wheels having buckets
of different heights, and for each height there are reamers available
giving nine expansion ratios. A machine, for example, can be equipped
with from one to fifty small nozzles or from one to twenty-eight large
nozzles, and each one of these nozzles may be furnished with any one
of nine expansion ratios. The ratio of areas possible between one small
nozzle and the maximum number of large nozzles is 1 to 90, and, as may
be figured from the above data, the progress from the smallest to the



Online LibraryNational Electric Light Association. ConventionConvention, Volume 42, Part 5 → online text (page 5 of 41)