TESTS OF MINES AND APPARATUS.
After the mines have been planted the following tests are made daily,
or more frequently if need be, the results being recorded carefully on
the form given at the end of the chapter. (Note: This applies also to
such test mines as may be kept planted for purposes of observation and
instruction.)
=Caution.=—If A. C. power be supplied from the casemate motor-generator,
there is no possibility of accidental firing of mines if the
motor-generator is not running; and when it is running the chance
is remote, since it would require the committing of three blunders.
However, the following precautions must be enforced rigidly:
(_a_) _Never start the motor-generator during the planting of mines nor
when any friendly vessels are in the neighborhood of the mine field._
(_b_) _Before starting the motor-generator for testing it, see that
all automatic switches are up, all firing switches open, and the A. C.
operating switch (No. 8 of the power panel) open._
1. =Test of the D. C. voltage.=—Plug in at the proper receptacle and
read the voltmeter.
2. =Test of the A. C. voltage.=—_Caution._—_First see that all
automatic switches are up, that the firing switches are open, and that
the A. C. operating switch No. 8 is open._
Close switch No. 4 up; close starting switch of motor-generator, and
when the latter has attained its full speed close switch No. 9 up; plug
in at the proper receptacle, and read the voltmeter. When the source of
power is the storage battery, the battery rheostat should be adjusted
until the A. C. voltage is 500 or above; when the casemate generator is
used, its field rheostat should be adjusted for the same purpose.
3. =Test of the mines.=—Leakage in mine circuits will be indicated
automatically by an increased brightness of the green lamp on the
signal block; an excessive leakage in any mine circuit may cause the
automatic switch to trip.
However, each mine should be tested separately, as follows:
With the D. C. on the D. C. busses of the power panel, close switch
7 up, open the power switch on the mine block of the mine circuit to
be tested, and put the M-AM “plug” on the upper point of the power
switch. If the automatic switch falls, adjust the solenoid or hold the
switch up while testing the circuit, otherwise the reading obtained
will be that of the red lamp and bell circuit. These operations put the
mil-ammeter and its protective lamp in series with the mine circuit.
The circuit is as follows: From the negative D. C. bus on the power
panel, to switch 7 closed up, through the mil-ammeter and its
protective lamp, to the terminal bar, to the M-AM lead, to the plug,
to the upper point of the power switch P, through the solenoid, to the
middle of the testing switch T, to the upper point of same, to the
upper point of the automatic switch, to the middle of same, to the mine
switch, through same, to the terminal bar, through the 19-conductor and
the single-conductor cables, to the mine transformer primary, to the
mine case, to ground, to the D. C. “earth” terminal on the power panel,
to switch 7, and to the positive D. C. bus on the power panel.
With from 80 to 110 volts these readings should normally be between 30
and 40 mil-amperes. A mine may be fired if the reading with 80 volts is
between 14 and 120 mil-amperes. These limits increase with the testing
voltage. If the mine tests within the firing limits, the solenoid
should be adjusted if the current is above its normal setting (0.075
amperes). If the test indicates that the mine can not be fired, the
mine switch should be opened.
4. =Test of the automatic switch, red lamp, and bell.=—Throw the D. C.
power on the busses of the operating board by closing switch 3 up. Open
the bell switch. Next close the testing switch down on the mine block
under test. The red lamp should glow and the corresponding automatic
switch trip. (For circuit see fig. 18.) Now close the bell switch,
throwing the bell in parallel with the red lamp; the bell should ring.
Next open the bell switch and repeat the test for each mine block in
turn.
5. =Test of the alternating circuit.=—This circuit is tested with D.
C., as follows: Connect the A. C. and D. C. jaws on the master block
with a jumper, open the power switches, close switches 3, 8, and 9 up
on the power panel. The green and white lamps of the operating board
under test should glow. A break or an excessive resistance in the
casemate grounds, or elsewhere in the circuit, will be indicated by the
lamps not glowing, or glowing dimly.
The circuit is as follows: From the negative D. C. bus on the power
panel, to switch 3, to the “operating board” terminal, to the D. C.
lead, to the D. C. post on the signal block, through the green lamp, to
the D. C. jaw on the master block, through the jumper, to the A. C. jaw
on the master block, through the white lamp and resistance in parallel,
to the A. C. post on the signal block, to the A. C. lead, to the A. C.
“operating board” terminal, to switch 8, to the A. C. bus, to switch
9, to the casemate transformer secondary, back to switch 9, to the
other A. C. bus, back to switch 8, to the A. C. earth, through ground,
to the D. C. earth, to switch 3, and to the positive D. C. bus on the
power panel. With this circuit on, remove the 90-ohm resistance in
parallel with the white lamp; the white lamp should glow more brightly,
indicating continuity of circuit through the resistance as well as the
white lamp.
It will be observed that the above test is for only a part of the A.
C. circuit. To test the firing switch and the lower contact of the
automatic switch, open switches 3, 8, and 9, close 7 up, remove the
jumper, put the M-AM “plug” on the A. C. jaw on the master block, close
the firing switch, and trip in turn each automatic switch by raising
the corresponding knob on the solenoid and observe the reading of the
mil-ammeter. Close each automatic switch up before tripping the next
one.
The mil-ammeter reading should be from 30 to 40 mil-amperes, indicating
a circuit through the firing switch and the automatic switch. The
circuit is as follows: From the negative D. C. bus on the power panel,
to switch 7 closed up, through the mil-ammeter and its protective lamp,
to the operating board terminal, to the M-AM lead, to the “plug,” to
the A. C. jaw on the master block, through the firing switch F. S.,
to the A. C. bus on the operating board, to the lower point of the
automatic switch which was tripped, to the middle of same, to the mine
switch, through the same, to the terminal bar, through the 19-conductor
and the single-conductor cables, to the mine transformer primary, to
the mine case, to ground, to the D. C. “earth” post on the power panel,
to switch 7, to the positive D. C. bus on the power panel.
6. =Test of the delivery of the A. C. power to the operating
board.=—_See that all the automatic switches of the operating boards
are up and all the firing switches of the master blocks open._ Close
switches 4 and 9 up (or down) and 8 down; close the testing switch
T. S. on the master block. The white lamp should glow and the A. C.
bus-bar voltage should drop appreciably.
The circuit is as follows: From the A. C. bus on the power panel,
to the lower right terminal of switch 8, to the “operating board”
terminal, to the A. C. lead, to the A. C. post on the signal block, to
the white lamp and the resistance in parallel, to the A. C. jaw on the
master block, to the testing switch T. S., to the “earth” post on the
signal block, to the earth lead, to the D. C. earth, through earth, to
the A. C. earth terminal on the power panel, through the choke coil, to
switch 8, to the other A. C. bus on the power panel.
In this test it is imperative to see that all the automatic switches
are _up_ and all the firing switches are _open_.
7. =Test of the power.=—Insert two fuses in multiple across the fuse
leads from the power panel. Put the fuses in a place prepared for the
purpose outside of the casemate, so that there will be no danger from
flying fragments. With all the switches on the power panel open, all
the automatic switches up, and the firing switches on the master blocks
open, energize the D. C. busses of the power panel, close switch No.
4 up (or down), and close the starting switch; close switch No. 9 up
(or down); close switch No. 12 up (which connects the mine transformer
secondary to the fuses); and, finally, close switch No. 11 up (which
throws the A. C. power on the mine transformer primary). The fuses
should explode.
If fuses are not available for this test, a low-voltage lamp or a short
piece of fine wire may be heated to incandescence.
8. =Test of grounds.=—(_a_) “Separate” grounds shall be made for the A.
C. power and the D. C. power on the power panel. The word “separate” as
here used means actual connection to earth without metallic contact of
the earth leads. A convenient method of making a ground is to connect
to the armor of a cable running to salt water, a bond being made in
case the armor of the cable in the casemate does not reach water before
a joint is made. If a cable armor is used for one ground, the other
ground lead must go to earth without contact with that armor. This may
be accomplished by using the conductors of a cable, the ends of which
are grounded to an earth plate in salt water.
(_b_) Neither of the grounds made should have more than 10 ohms
resistance. To verify this, tests should be made as follows:
Close the double circuit breaker; close switch 7 up and plug the
extension cord of the mil-ammeter lead of the power panel on the upper
left-hand terminal of switch 8, the mil-ammeter extension cords for the
operating boards being disconnected.
Ascertain the voltage across the mil-ammeter and lamp, and across the
bus bars. Read the mil-ammeter.
From these readings the combined resistance of the grounds can be
determined.
A table or chart may be prepared giving the resistances for various
testing voltages and mil-ammeter readings.
[Illustration: _Form for record of tests, Group No._]