38H

THE COLLIERY GUARDIAN

August 23, 1918.

of the primary survey. It consists of adding such
information as has been gained in mining, and correct-
ing the geological boundaries where new excavations
have shown that they need it. Some of the six-inch
maps, however, were made upwards of 50 years ago,
and in such cases revision would entail a practically
complete resurvey.

Reference has been made to the fact that the staff
of the Geological Survey was understood by the Com-
missioners of 1905 to be inadequate to complete the
primary six-inch survey as quickly as was desirable,
and to undertake the revision that was required. For
several years past the operations of the staff have
been divided between areas in which extensions or new
coalfields may occur and other parts of the country
where this possibility does not exist. Attention has
been more immediately directed to the former, but
problems of scarcely less economic importance in con-
nection with the distribution of ores, minerals, sources
of water, &c., arise in the other parts of the country.
Whatever steps may be taken to expedite the six-inch
mapping of coalfields and their surroundings, those steps
should not be at the expense of the six-inch mapping
of the country as a whole, or of the investigation of
other economic and scientific applications of geology,
apart from the working of coal. It appears to be
necessary to increase the strength of the staff in order
to attain the desired object.

The inter-departmental correspondence which has
been laid before us shows that various estimates have
been made of the length of time required to complete
the primary six-inch survey of the coalfields of Great
Britain at the present rate of progress, and of the
reduction in the time if certain additions were made
to the staff. It appears unnecessary to enter into a
detailed discussion of the data on which such estimates
are founded, but steps should be taken in the near
future to secure: —

(1)	The completion of the primary six-inch survey

of all coalfields and of the areas into which
their concealed parts may extend, and the
revision of coalfields originally surveyed on
the six-inch scale but not revised during
the last 30 years, at as early a date as pos-
sible.

The decennial revision of the six-inch geo-
logical maps of all areas where coal mining
is in progress.

(2)	With regard to boreholes and sinkings, it is

the opinion of the Sub-Committee that it
should be made compulsory to give notice of
the making of any borehole, shaft, or other
sinking, which is expected to reach, or does
reach, a depth of 100 feet.

That free access to boreholes, shafts, or
other sinkings while in progress, and free
access to all cores and journals of boreholes,
should be permitted to the Geological Survey
at all times; and that records of the strata
passed through should be preserved by the
z Geological Survey.

That these records should be treated as
strictly confidential, if desired by the in-
terested parties, for a period not exceeding
10 years after their deposition.

(3)	That powers to put down boreholes should be

conferred upon some Department of the
State.

Without expressing any opinion upon the question
of a distinct Department of Mines and Minerals (which
does not come within the scope of the reference to
the Sub-Committee) the opinion is expressed that, if
any such Department were created, the question of the
relations of the Geological Survey and Museum to that
Department should be remitted to this Sub-Committee
for consideration.

The Report is signed by A. Strahan (Vice-Chair-
man), W. Forster Brown, J. Horne, John Kemp, Adam
Nimmo, R. A. S. Redmayne, Robt. Smillie, J. Allen
Howe (Secretary).

Note by Mr. J. Kemp.

. In order to give effect to some of the Sub-Commit-
tee’s recommendations, it will be necessary to confer
new-powers and duties upon the Geological Survey or
upon the Government Department to which it is
attached. It is therefore desirable to refer to the
statutory powers under which the Geological Survey
of Great Britain is carried on, especially as it has
been brought to the attention of the Sub-Committee
in the course of their inquiries that the law with regard
to this matter does not appear to be in a satisfactory
state at present.

The duty of carrying on the Geological Survey of
Great Britain was transferred from the Board of
Ordnance to the Commissioners of Woods, Forests,
Land Revenues, Works, and Buildings in 1845, and by
the Geological Survey Act of that year (8 & 9 Viet.,
c. 63), the power to enter upon private land, break up
the surface, and do such other things as are necessary
for the purpose of making a geological survey are con-
ferred upon surveyors and other persons appointed by
or acting under the orders of the First Commissioner
of Woods and Works.

In 1851 the Department of Woods, Forests, Land
Revenues, Works, and Buildings was divided into the
two departments of “ The Commissioners of Her
Majesty’s Woods, Forests, and Land Revenues” and
“ The Commissioners of Her Majesty’s Works and
Public Buildings” (14 & 15 Viet., c. 42), and by Sec-
tion 22 and the Schedule to the Act, all the duties and
powers under the Geological Survey Act, 1845, are
transferred to the First Commissioner of Works and
Public Buildings.

In 1853 the Geological Survey became part of the
Science and Art Department, which was formed under
the Board of Trade. By a Treasury Minute of 1853,
referring to a letter of the 16th of March of that year
from the Committee of the Privy Council for Trade,
the Lords of the Treasury concur in a proposal to unite
in one Department under the Board of Trade a number
of educational institutions, including the Museum of
Practical Geology and the Geological Survey, and they

state that they have given directions that the estimates
for all the institutions referred to shall be brought
together under the general head of “ Board of Trade
Department of Science and Art.” There is, however,
no statutory enactment transferring to the Board of
Trade the powers under the Geological Survey Act,
1845, which were vested in the First Commissioner of
Works and Public Buildings by the Act of 1851.

By an Order in Council of 1856 the Education
Department was founded, including (a) the Educa-
tional Establishment of the Privy Council Office, and
(b) the Department of Science and Art; and by section
2 of the Board of Education Act, 1899, it is enacted
that the Board of Education shall take the place of
the Education Department (including the Department
of Science and Art).

The powers of the Geological Survey Act, 1845,
appear still to belong to the First Commissioner of
Works, although they are constantly exercised by the
surveyors and ether persons employed in carrying on
the geological survey who are all officers of the Board
of Education.

(To be continued.)

THE POWER FACTOR.

[Specially Contributed.]

Three-phase currents have come to stay, so far as
mining work is concerned. The extreme simplicity of
the squirrel-cage induction motor, the entire absence
of a commutator in all forms of induction motors,
except a few very special designs, and the great con-
venience with which large amounts of power can be
transmitted over long distances, and their pressures
converted to any figure that may be desired at the
points of consumption, have given the three-phase
service an enormous pull over the continuous current
service, which was first used for lighting and power
in mines. Moreover, the use of three-phase currents
for the main power system does mot preclude the use
of continuous currents where these are necessary or
advisable, and it is also perfectly feasible to run any
continuous-current generators, that are already on the
ground, by three-phase motors, and so to continue the
use of the continuous-current plant, while economising
in the cost of generation and bringing the whole
system of transmission and distribution into one power
house.

But the development of the distribution of power
by three-phase currents has gradually revealed a source
of trouble, the cause of which may be summed up
in the necessity for the use of the power factor in
all calculations where alternating currents are em-
ployed. It will be remembered that the simple calcula-
tions for power that are employed with continuous
currents have to be modified, when alternating
currents are employed, by the addition, to one side
of the equation, of cosine </>, known as the power factor.
As the power’ factor is always less than unity, this
means that the actual power transmitted from a
generating station, or received by an electric motor,
is less than it would be, for the same pressure and
current, if continuous currents had been employed.
In a few cases, with alternating currents the power
factor is very near unity. With incandescent elec-
tric lamps, for instance, it may be as high as 0-95,
which practically makes no difference in the calcula-
tion. On the other hand, cases have been reported
of induction motors working with as low a power factor
as 0-5, while a very common figure for the whole
of the service at a colliery is 0’7. These figures mean
that a motor having a power factor of 0’5^ is only
able to deliver less than 50 per cent, of the apparent
power that the electric currents deliver to its coils;
and in the case of the complete system which has a
power factor of 0-7, the generating station is able to
deliver less than 70 per cent, of its apparent output.
With a generating station, for instance, designed to
furnish 1,000 kw. with unity power factor, something
less than 700 will be furnished at 0-7 power factor.
The reason for the output being less than 70 per
cent, is that, in addition to the actual lowering of
the output on account of the power factor, there is
a wattless current—also equal to 70 per cent, of the
output—that circulates through the coils of the arma-
tures of the generators, delivering additional heat to
them, and lessening the useful current that can be
allowed to be delivered by them. It will be remem-
bered that the output of any generator or any motor
is limited by the heat liberated by the current circu-
lating in their coils. If currents above a certain
strength are allowed to pass through the coils, there
is a danger that the heat liberated will damage the
insulation from the increased temperature, and from
the pressure that the expansion of the conductors
exposes it to.

How the Power Factor Arises.

The power factor may be of two kinds, due to a
lagging current or a leading current. With three-
phase currents, of course, there will be three lagging
(or three leading) currents. In colliery work a lead-
ing current is not often met with, but is a great boon
where it is; but in large distribution services, such
as they have in America, where very large areas are
covered, the leading current is very often an important
factor in the transmission. In California, for instance,
power is transmitted 154 miles from a large power
plant at Big Bend to Oakland, opposite San Fran-
cisco. The power is transmitted at a pressure of
100,000 volts, and provision is made for 10,000 kilo-volt-
amperes at Oakland. When the transmission lines
were connected to the busbars at Big Bend, before
connection had been made at Oakland, the circuits
being quite open at that end, a leading current of
48 amperes was found to be flowing into the trans-
mission line.

In colliery electrical installations it is the lagging
current and the lagging power factor that form the
trouble. As will be explained later, leading currents
are being artificially introduced into mining installa-
tions in order to neutralise the lagging current. A

leading current having a power factor of 0*7 would
bring the resultant power factor up to unity and
release the locked-up power in generators and motors
mentioned above. The leading current in the Big
Bend-Oakland transmission system must be a real boon
to the engineers who are working the electrical supply
from the sub-station at Oakland if they have many
induction motors in service.

The lagging current, the lagging of the current
behind the pressure which causes it, is due to electro-
magnetic induction between the wires on the
generators, motors, etc., in which the currents are
circulating, whilst the leading current, the current
being in front of the pressure that causes it, is due
to electro-static induction in the condensers, of which
the conductors carrying the transmission currents form
part. There is a lag and a lead with continuous
current, but they are of no consequence, because they
only slightly delay the starting up of the apparatus
that is using the current, the delay being so small
that very sensitive instruments would be required to
show its presence.

When an electric pressure is applied to the two ends
of a conductor, a current does not instantly circulate
through the conductor, even when it is a straight
overhead conductor, apart from every other. If suffi-
ciently sensitive apparatus is available, it can be shown
that a certain definite but very short time elapses
between the closing of the circuit, the application
of the pressure to the conductor, and the circulation
of the current through the whole length of the con-
ductor. It has, on the one hand, to create a magnetic
field round every portion of the conductor before it
can pass on, and also to charge every portion of the
electro-static condenser. When the circuit is opened,
the energy that was taken from the current to create
the magnetic field and to charge the condenser returns
to the conductor, circulates through it, and creates
a temporary pressure, leading to the sparking and
other troubles with which all are familiar when a
switch is opened or a cable is broken.

When the current circulates through a coil of wire,
as it does in the case pf the electro-magnets forming
the armature coils and the field magnet coils of
generators and motors, a new factor is introduced,
called self-induction. It will be remembered that when
two conductors are arranged side by side and parallel
with each other, if a current commences to circulate
in one direction through one of the wires, a current
in the opposite direction will immediately commence
in the other conductor. In a coil of wire, such as
that upon the armature of a generator, the adjacent
turns of wire act as independent conductors. In fig. 1,
calling the turns that are on the same side of the coil
1, 2, 3 and 4, when the current commences in 1, a
current will commence in the opposite direction, in 2,
also in 3 and in 4; but it must be remembered that
turn No. 2 forms part of the coil with turn No. 1,
and the reverse current in turn No. 2 will lessen the
strength of the current flowing in turn No. 1—that
is to say, in the whole of the coil. What happens
between turns 1 and 2 happens between all 'the turns.
As the .current commences to flow through any indi-
vidual turn, currents in the opposite directions com-
mence to flow in all the other turns near. The re-
sultant action is very complicated, as the reverse
currents also act inductively upon the conductors in
which the primary currents are circulated, tending to
increase them. In addition to the above, the lines
of magnetic force created by the current have an
important effect upon the inductive action between
the currents circulating in the coils. The same action
takes place between the different turns of the coils
when any change takes place in the strength or direc-
tion of the currents. Any increase in the strength of
the current in one turn of the coil causes a tendency
to a reverse current in all the other turns, whilst
any decrease causes a tendency for currents in the
other turns in the same direction as that in the
primary turn. Remembering that alternating currents
are continually changing in value and in direction,
it will easily be understood that those circulating in
each turn of the coil are constantly inducing currents
in the opposite direction in all the other turns, and
that the direction and number of the lines of magnetic
force in the magnetic circuit for which the coils are
furnishing current will also be constantly changing in
value and in direction. The net result is that the
passage of alternating currents through the coils is
delayed after the pressure giving rise to them is
applied to their terminals, and the delay is increased
by every additional turn in the coil and by every
change in the strength and direction of the current.
The self-induction of a coil with a large number of
turns is very much greater than that of one with a
smaller number, and it also varies directly with the
number of cycles, being greater with a service of 50
cycles than with one of 25, and greater with one of
100 than with one of 50. This is why the periodicity
of power services is being reduced. It is this self-
induction that causes the current to lag, and brings
the power factor into the power equation. Fig. 2
is an elementary diagram showing how the lag of the
current behind the pressure affects the power equa-
tion. The diagram is based on the usual convention,
by which the successive values of the pressure and
current in alternating current services are expressed
by the value of the sine of the angle swept out by
the radius of a circle, such as OA in the diagram, as
it revolves round the centre O. The sines of the
successive angles are obtained by dropping perpendicu-
lars from the ends of the radius, in whatever position
it may be at any instant, on the base line XOY. The
values are given in any table of sines. In the diagram
the radius is supposed to revolve from the position
OX to OA, then to OA1? then to OA2, and then to
OY. At OA and OA2, the radius makes angles of
45 degs. with both the base line and the perpendicular
OAX. The positions OX and OY represent the zero
values at the commencement and at the end of the first
half of the cycle; the position OAX represents the
crest value, the maximum value to which pressure or
current attain in the first half of the cycle. It will