II
RECORD
Four troubles were studied, occurring respectively on
September
18th, 1919,
3:47 P.M.
September 18th, 1919,
5:27 P.M.
October 22nd,
1919, 12:20 P.M.
May
19th,
1919,
7:25 A.M.
The generating system
is
divided
into
four
sections,
connected
in
tandem, with the A section of Fisk Street, and the Northwest Station as
the two ends of the chain, and with power limiting reactors stated to
be
1.75 ohms each, between Fisk A and Quarry
Street, and between
Quarry
Street and Fisk B, and
six
tie cables of negligible reactance
and about .3 ohms joint resistance between Fisk B and the Northwest
Station.
1.)
Sept. 18th, 19193:47 P. M.
a)
A short circuit close to the busbars of B section of Fisk Street
held on for several seconds, before
it was opened.
As there are no power limiting reactors between Fisk B and North-
west Station, and the six tie cables between these stations are of very
low resistance, the Northwest Station was just as seriously affected as
Fisk B, and indeed acted like a part of Fisk B.
b)
All the synchronous machines on Fisk Street B, and on North-
west Station dropped out, and many synchronous machines on Fisk A
and Quarry
Street:
44 synchronous machines on Fisk B and 18 on
Northwest are recorded as shut down.
Of 26 machines on Fisk A, 12
dropped
out and
14 stayed
in;
of 8 machines on Quarry
Street, 4
dropped out and 4 stayed in.
[[END_PDF_PAGE:16]]

[[PDF_PAGE:17]]
Report of Charles P. Steinmetz
11
c)
Due to the voltage dropping to zero under the short circuit, the
turbo-alternators in Fisk B and Northwest Station dropped out of syn-
chronism with each other, and out of synchronism with Quarry Street
and Fisk A; but Quarry Street and Fisk A remained
in synchronism
with each other.
d)
Due
to the load being taken
off by the dropping out of syn-
chronous machines, the turbo-alternators
in Fisk B and in the North-
west
Station
speeded up
until
the emergency
governors
tripped
the
steam valves.
The turbo-alternators were put back on the governors
immediately.
e)
The turbo-alternators
in Fisk B and
in Northwest Station did
not pull into step with each other, but remained out of synchronism;
the voltage
at the busbars of these two
stations remained
practically
zero, and an
excessive current fed
into
Fisk B from Quarry
Street,
heating the power limiting reactor B.
f )
After 7 minutes, the tie line between Fisk Street B and Quarry
Street, that
is, the power limiting reactor B, was opened, and Quarry
Street and Fisk A, came back to normal.
About the same time, the
30,000 KW machine in Northwest Station began to lose
its excitation,
and was disconnected.
g)
Fisk B and Northwest remained out of synchronism with each
other,
with
practically zero voltage
at the
busbars,
for
six minutes
longer.
Then the voltage suddenly came back, the alternators in Fisk
B pulling into synchronism with each other and with the one remaining
(20,000 KW) machine in Northwest.
Remarks :
a)
A short circuit at the busbars of a station
section, pulling the
voltage down to zero, necessarily must drop out
all the synchronous
machines on this section, unless the short circuit is opened so quickly,
that the synchronous machines during the period of zero voltage did
not yet drop behind by half a pole, but at the reappearance of voltage
are still in step.
With a dead short this would usually require opening
the short in a fraction of a second.
b)
The purpose
of
sectionalizing
the
system by power
limiting
reactors was to
limit trouble occurring on one station section
to
this
section, and keep
it from affecting the other sections.
The system of sectionalizing therefore has not worked satisfactorily
in this case, as all the synchronous machines in Northwest, and nearly
[[END_PDF_PAGE:17]]

[[PDF_PAGE:18]]
12
Report of Charles P. Steinmetz
half in Fisk A and Quarry Street have dropped out due to the trouble
in Fisk B.
There
is no power
limitation between
the Northwest
Station and
Fisk B, and any trouble on one of these two stations thus
affects the
other with practically the same severity. This is undesirable, as thereby
trouble on one of these stations affects too large a part of the entire
system.
It
is dangerous, as Fisk B and Northwest combined give too
large a power for safe handling under all emergencies.
Furthermore,
due
to
the
connection
between
these
stations
being
practically
all
resistance and no reactance, the synchronizing power between Fisk B
and Northwest must be small, and when synchronism is once lost under
short circuit, etc., trouble must be anticipated in these stations pulling
into synchronism with each other.
The interference between Fisk A, Quarry Street and Fisk B sections
which are connected with each other by power limiting reactors
re-
sults in serious trouble on one of these sections dropping out numerous
synchronous machines in the other
sections.
It may partly be direct
interference between
the
station
sections,
partly through
substations
fed simultaneously by several of these sections, and either requires fur-
ther investigation.
c)
If the busbar voltage of a station section drops to zero by short
circuit,
for
a
sufficiently
long time
to permit
the turbine
speeds
to
change
appreciably,
this
station
section
is
out
of synchronism with
the rest of the system, as at short circuit of zero voltage there is nothing
to hold
it in step.
As soon, however, as the short is removed, the volt-
age should come back and the station section drop into step again with
the rest of the system.
This did not occur, but station sections remained
out of step with each other at practically zero voltage for a considerable
time, about a quarter of an hour.
Apparently, the synchronizing power
between the station sections is lower than desirable, and the speed con-
trol of the
alternators not such
as to bring them promptly so
close
together in speed as to drop into
step.
d)
The tandem or chain connection of the stations has the disad-
vantage that
if an intermediary
station,
as Fisk B
or Quarry
Street,
even momentarily drops
out
of synchronism by
a
short
circuit,
the
system
is cut in two.
Ring connection
of the
station
sections would
have the advantage
that,
if one
station
section drops
out of step by
some
accident,
all the other
station
sections are
still
connected with
each other and thereby can remain in synchronism.
[[END_PDF_PAGE:18]]

[[PDF_PAGE:19]]
Report of Charles P. Steinmetz
13
2.)
Oct. 22nd, 191912:20 P. M.
The trouble was very similar to that on September 18th, 3:37 P. M.,
a short circuit close to the busbar of Fisk B, except that:
a)
The short circuit apparently opened very quickly.
b)
The
tie
lines were operated manually, separating Fisk B and
Northwest stations.
c)
Most of the synchronous machines on Fisk B and Northwest,
and a few on Fisk A and Quarry Street dropped out:
Of 52 synchron-
ous machines on Fisk B and Northwest, 46 are recorded
as dropped
out, six as remaining in synchronism; of 6 machines on Quarry Street,
2, and of 35 machines on Fisk A, 4 dropped out, the remaining stayed
in step.
d)
In Fisk Street B, and Northwest, the voltage dropped to prac-
tically zero, but came back at the opening of the tie line.
Remarks:
Apparently,
the
interference between
the
stations was
less
in
this
case, probably due to the short duration of the short circuit, and the
opening of the tie line B, so that only few synchronous machines
fell
out in the other sections, and some even stayed in step in the disturbed
section if the report is correct.
3.)
Sept. 18th, 19195:27 P. M.
a)
One hour forty minutes after the
first trouble, resulting from a
short near the busbars of Fisk
B, a short
circuit occurred near
the
busbar
of Fisk A, and held
for
several
seconds, while
the
tie
line
reactor B was
still open, that
is, Fisk B and Northwest cut
off from
Quarry Street and Fisk A.
b)
All synchronous machines on Fisk A dropped
out, and a few
on Quarry Street, Fisk B and Northwest; 39 synchronous machines on
Fisk A are recorded as having dropped out, 3 on Quarry Street, 5 on
Fisk B and 1 on Northwest.
Remarks:
a)
Some synchronous machines dropped out on Fisk B and North-
west, although
the
tie
line between
these
stations and
the
station
in
which the trouble occurred, was
open, showing
interference between
generating
stations
through
the
substations;
these
synchronous
ma-
chines were
in the same
stations with machines
fed from Fisk A or
Quarry Street.
[[END_PDF_PAGE:19]]

[[PDF_PAGE:20]]
14
Report of Charles P. Steinmetz
b)
The synchronous machines on Fisk B, Northwest and Quarry
Street, which dropped out, did so by overload.
This
is undesirable as
with numerous synchronous machines, fed from the troubled station A,
dropped out, those which receive power from the other stations should
hold on to carry the load.
4.)
May 19th, 1919
7:25 A. M.
a)
A generator in Fisk Street A burned out, short circuiting with
only the generator power limiting reactance, of about .4 ohms, between
the short and the busbars.
b)
The voltage dropped about 1,000 volts in
all four
station sec-
tions
a little more in Fisk A, where the trouble occurred, a little less
in Fisk B and Northwest, the stations most remote from the trouble.
c)
A violent fluctuation of voltage resulted in all four stations, with
an amplitude apparently of 1,000 to 2,000 volts, most severe in Fisk A,
where the trouble originated, of an irregular period of about 1 second
per beat.
d)
The tie line reactor B, got very hot.
e)
The drop
of voltage and the voltage
fluctuation
lasted
for 18
minutes, with only slight decrease.
Then they suddenly disappeared
and normal voltage returned.
f)
During the disturbance, the frequency of the system fluctuated
by about two cycles, that is 8%, and three machines in Fisk A
where
the trouble originated
tripped their excess speed governors and
cut
off steam.
g)
Some synchronous machines dropped out of step, but the exact
record
is no more available.
Remarks:
a)
The
fluctuation and drop
of voltage, extending over
all
four
stations, and
its long duration, probably were of similar nature and
cause
as the
loss
of voltage
in
the trouble on September
18th and
October 22nd.
b)
The most serious
question, which unfortunately cannot be
de-
cided with the present data,
is
:
whether this voltage drop and fluctua-
tion was an
actual
hunting
of
the
generating
stations
against
each
other, due to lack of synchronizing power, or whether
it was hunting
of the steam governors of the stations against each other, or whether
it was only apparent, and due to the reaction on the generators of the
substations when starting synchronous machines.
This should be fur-
ther investigated.
[[END_PDF_PAGE:20]]

[[PDF_PAGE:21]]
Report of Charles P. Steinmetz
15
c)
It appears to me certain that in this case the generating stations
have remained in synchronism with each other throughout the entire
18 minutes of disturbance.
If the station sections had dropped out of
synchronism with each other, materially greater voltage drops should
have occurred.
d)
The observed speed fluctuation, by 8%, then would mean that
the
entire system
simultaneously
speeded up and slowed down, but
not that material speed differences existed
at the same time between
different turbines.
During such periodic speed pulsations, temporarily
some machines may run
faster than
others, but
for such
short time
only, as not to slip out of synchronism.
As the observed speed fluctua-
tion is close to the range, for which the excess speed governors are set,
it may be expected that some machines may trip their emergency cut
off, and as the speed fluctuation may be expected to be greatest at the
source of disturbance, Fisk A, the tripping out may be expected first in
Fisk A, as was observed; 3 machines tripped out there.
e)
Suppose a large number of synchronous machines are tripped
out by a momentary short circuit, but the voltage immediately comes
back at the opening of the short, and a number of substations immedi-
ately proceed to start their synchronous machines from the alternating
side.
Even
with such
large
station
sections,
the
starting
of
several
large synchronous machines would temporarily pull down the voltage.
The voltage would rapidly recover by the speeding up of the synchron-
ous machines which had been
started.
This would cause some other
substations
to
start their synchronous machines and again pull down
the voltage, and so a series of successive voltage drops and recoveries
would result in irregular sequence, until the last synchronous machine
is started.
This would, in the voltage curve, give the appearance of a
hunting pulsation, such as shown by the records.
This theoretically
is
a possibility, but whether
it was the cause, cannot be decided from the
records.
Synchronoscopes between the station sections, however, would
indi-
cate that
it
is not
a
true
hunting, due
to
instability
of
the
station
sections, but a voltage fluctuation due to excessive fluctuating lagging
load, as given by the starting of synchronous machines.
f)
Sufficiently
sensitive synchronoscopes between
the
station
sec-
tions would
indicate whether the
station
sections
are
in phase with
each
other
or out of synchronism, whether they are hunting against
each
other, and whether and what phase displacement
exists between
the station sections.
[[END_PDF_PAGE:21]]

[[PDF_PAGE:22]]
16
Report of Charles P. Steinmetz
HI
OPERATION
Momentum of Alternators
The emergency steam cut offs of the turbo-alternators are stated to
he set for an excess speed of about 10%.
Considering the 12,000 KW units typical and of most interest, since
most of the units in Fisk Street where the trouble originated are of this
size.
An increase of speed of 10% with the steam valve open for full load,
would require 2 2/3 seconds.
With the steam valve opened for over-
load, by a momentary short circuit, the speeding up to the speed limit
would occur
still more rapidly.
The ordinary steam governor cannot
well be made to act quicker than this, in cutting steam off completely,
without danger of steam governor hunting interfering with the stability
of the system; furthermore, all the steam in turbine and the passages
beyond the valve would still accelerate
it.
Thus tripping of the excess
speed emergency steam cut
off may be expected whenever a serious
short circuit on a station section drops out all the synchronous machines
and thereby suddenly relieves the load.
Deceleration
tests were made by the operating engineers on
four
turbo-alternators, with excitation and without excitation, by allowing
the machines to speed up on the
throttle,
until the excess speed cut
off tripped, and then observing the rate of slowing down.
The observed excess speed above normal,
at which the emergency
cut off operated, varied from 6.7% to 12% with the different machines,
and varied by as much as 1.3%
in successive tests of the same ma-
chine.
With the steam valve wide open during acceleration, an appre-
ciably higher excess speed may be expected.
The rate of slowing down, after the steam is cut off, varied from 4%
to 13.4% per minute at no excitation and from 6.75%
to 20.4% per
minute with the field excited.
It follows herefrom:
suppose by a short circuit
lasting an appre-
ciable time, the load
is dropped, and the turbo-alternators speed up
and trip their emergency steam valves and then begin to slow down.
Then the individual turbo-alternators in the different station
sections,
and even
in the same station
section, may be expected
to
differ ma-
terially from each other in speed, probably as much as 5 to 10%.
With such great differences of speed, between the different machines,
diffiulties in synchronizing, that
is, in the machines pulling each other
into step, may be expected, especially between different station sections.
[[END_PDF_PAGE:22]]

[[PDF_PAGE:23]]
Report of Charles P. Steinmetz
17
SYNCHRONIZING
A
If two alternators, or groups of alternators, such as station sections,
are connected together in synchronism, that
is, at the same speed, but
out of phase with each other, they tend to pull each other into phase.
The machine which
is ahead
in phase, gives
off power and thereby
drops back, slows down, and the machine which
is behind in phase,
receives power and thereby runs ahead, speeds up, and as the
result,
when the two machines have come in phase with each other, the one
which was ahead,
is going slower, the one which was behind
is going
faster, and the former now drops behind, the latter runs ahead in phase,
and the phase difference between the machine
reverses, and the ma-
chines thus oscillate against each other, while the interchange current
between the machines fluctuates between a maximum value at maximum
phase difference, and zero or a minimum value when machines are in
phase.
If there were no damping effects, this
oscillation would con-
tinue with constant amplitude. Due to the damping effects exerted mainly
by the lag of the
field
flux behind the resultant field excitation
(the
armature
reaction
component
of
the
synchronous
impedance),
the
amplitude of the
oscillation steadily diminishes,
until the oscillation
disappears.
That
is, the interchange current between two alternators
which are in synchronism but out of phase, pulsates, with approximate-
ly constant frequency of the beat, but with an amplitude, which grad-
ually decreases to nothing.
If the EMFs of the two machines are equal, then
at the moment
when the two machines are in phase, there
is no resultant EMF, and
thus no current, and when the machines are out of phase, the resultant
EMF
is approximately in quadrature with the EMF of either machine.
If then
the
circuit between
the two
machines
should
contain
only
resistance but no reactance, the interchange current between the two
machines would be in phase with the resultant EMF, thus in quadrature
to the EMF of either machine, or a wattless current with regards to the
EMFs of the machines, that
is, there would be no power transfer be-
tween the machines, or no synchronizing power.
If, however,
in the
circuit between the two machines the resistance
is negligible compared
with the reactance, the interchange current lags
(approximately), 90
degrees behind the resultant EMF, thus is in phase with the EMF of the
one machine, in opposition with that of the other machine, thus
is an
energy current consuming power from the one and delivering power
to the other machine.
Thus only the reactive component of the inter-
change current between two alternators which are in synchronism but
[[END_PDF_PAGE:23]]

[[PDF_PAGE:24]]
18
Report of Charles P. Steinmetz
out of phase, transfers power between the alternators and is synchron-
izing current, while the energy component of the interchange current
does not contribute to bring the machines into phase.
If the EMFs of the two machines are unequal, then upon the power
transferring or synchronizing current due to the phase difference, super-
poses a reactive current which magnetizes the machine of lower voltage
and thereby raises its voltage, and demagnetizes the machine of higher
voltage and thereby lowers its voltage, but does not transfer power be-
tween the machines and does not appreciably change the phenomena
of power transfer by the synchronizing current, so that here and in the
following, where we
are mainly
interested
in
the magnitude
of the
effects, we may for simplicity assume equality of EMF of the machines.
B
If two alternators or groups of alternators such as station sections,
are connected together out of synchronism, that is while differing from
each other in frequency, they slowly slip past each other, and during
each cycle of slip, or beat, a periodic energy transfer takes place, while
the interchange current periodically rises and falls.
During one-quar-
ter the cycle of slip, or beat, the alternators are partly in phase with
each other, that
is, their EMFs are in the same direction.
The slower
machine then receives energy and accelerates, the faster machine gives
off energy and slows down and the two machines thus
are brought
nearer
to each other
in speed, pulled towards synchronism.
During
the next quarter cycle of speed, however, the alternators are partly in
opposition, that
is their EMFs are in opposite directions.
The faster
machine then receives energy and speeds up, the slower machine gives
off energy and slows down, and the two machines pull apart again, by
the
same
amount by which
they
pulled
together
in
the
preceding
quarter cycle of
slip.
Thus the machines can pull
into step only
if
the energy transferred during one-quarter cycle of slip
is
sufficient to
bring them
into
step,
that
is,
is
larger than the energy
required
to
speed the momentum of the slower machine up to synchronous speed
(or slow down the momentum of the faster machine to synchronism)
.
This gives the maximum value of slip from synchronism, at which the
machines will promptly pull into step, or the limits of synchronizing
power.
c
If, however, the two machines, or station
sections,
are out of syn-
chronism with each other by a greater speed difference than that from
which they can pull each other into step
in one-quarter cycle of slip,
[[END_PDF_PAGE:24]]

[[PDF_PAGE:25]]
Report of Charles P. Steinmetz
19
and
if the machine voltage were perfectly constant, then the machines
would never come into synchronism, but would continue
indefinitely
to slip past each other, coming nearer together during the one-quarter
cycle of slip where their voltages are in the same direction, and drifting
apart again by the same amount during the next quarter cycle of slip,
where their voltages are in opposition.
In reality, however, the EMF
of the machines
is not constant, but must vary periodically with the
frequency of the current fluctuations,
that
is, twice the frequency of
the
slip.
The current in the
circuit between the two alternators pul-
sates, between large values during the quarter cycle of slip, when the
EMFs
of the
alternators are
in opposition, and small values during
the next quarter cycle of slip, when the EMFs are in the same direction,
and with it varies the armature reaction.
The phase difference between
the
resultant
current, and
the EMF
of each
alternator
periodically
changes from
to 360 degrees, during each cycle of
slip.
With the
periodic
fluctuation of the current and
its phase angle, the armature
reaction of the machine fluctuates, and thereby
gives a periodic
fluc-
tuation of voltage.
As, however, the armature
reaction
requires an
appreciable time
to
develop,
the voltage
fluctuation
is not
in
phase
with the fluctuating current, but lags behind
it, by an angle depending
on the time required for the armature reaction to exert its magnetizing
effect.
The result thereof
is that the power interchange between the
two
alternators
is not
entirely
alternating with the frequency
of the
slip,
that
is,
alternately
accelerating
each machine and
then
again
slowing
it down by the same amount, but has a constant though small
component, which
is positive, that
is, accelerating
in the slower, and
negative, that
is
retarding,
in the
faster machine.
This represents
a
continuous
synchronizing power, which
steadily
pulls
the
machines
together in speed, until their speed difference has become small enough
to pull suddenly
into
step.
If thus two
alternators, or
station
sections, are out of synchronism
with each other by so great a frequency difference,
that they cannot
pull each
other
into
step
within
one-quarter
cycle of
slip, then
the
alternators
continue
slipping
past each
other,
with
large
fluctuating
currents
flowing between them.
These current
fluctuations
and
the
voltage fluctuations caused by them
do not decrease
(as
in hunting
or in other synchronous oscillations), but remain practically constant
in amplitude, but the fluctuations gradually become slower, that
is, the
frequency of beats decreases, while the machines pull nearer together
in frequency, that
is, their speed difference decreases, until the critical
speed difference
is reached, where the acceleration during one-quarter
[[END_PDF_PAGE:25]]

[[PDF_PAGE:26]]
20
Report of Charles P. Steinmetz
cycle of slip brings the machine up to
full synchronism.
Then sud-
denly the machines drop into step with each other, the excess current
vanishes and normal voltage comes back, after a short oscillation of
constant frequency of beats, but rapidly decreasing amplitude.
Apparently, this is what happened in the trouble on September 18th,
1919.
If two alternators or groups of alternators such as station sections,
are connected to each other through a reactance, and the driving power
of each group of alternators equals its load (plus losses), then no cur-
rent and no power flows over the dividing reactor, and both alternators
are in phase.
If now, with the same load, the driving power on one
alternator is increased, on the other decreased, or with the same driving
power, the load on the one
is increased, on the other decreased, but
the terminal voltage kept the same, then current and power flows over
the dividing reactor, resulting in a phase displacement between the two
alternators
(or
station
sections).
This phase displacement
increases
with the increase of power transfer.
This gives a case where current
and power is carried over a reactance from one circuit to another one,
without any voltage drop.
It
is
this, on which
the
use of
limiting
busbar reactors
is based.
The power transfer reaches a maximum at
90 degrees phase displacement;
this gives the limits of synchronizing
power, and any further increase of power transfer causes the two alter-
nators to drop out of synchronism with each other.
Too large reactance between the alternators reduces the synchroniz-
ing power by limiting the synchronizing current;
too small reactance
may again reduce the maximum synchronizing power by lowering the
EMF by the large voltage drop due to the large interchange currents.
With a capacity of about 60,000 KW per station section and machines
of the general
characteristics
of those involved (100%
synchronous
reactance, \2^/^% true reactance, in average) , maximum synchronizing
power would require a reactance between each station section and the
rest of the system of a
little
less than one ohm, so that the proposed
arrangement of ring connection of the stations through power limiting
reactors of 1.75 ohms should give about the maximum synchronizing
power.
Mathematical and numerical
data pertaining
to
the preceding
are
given in the Appendix.
[[END_PDF_PAGE:26]]

[[PDF_PAGE:27]]