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liiinois lestitute 

of Technology 


AT 120 

Morey, C. R. |[ 

Lighting arresters and ^r 

schemes foor testing fv;~ 

For Us3 In L::>r2ry Only 






O. R. M(^RP:Y and T. C. OEHNE, Jr. 








' ' ~^ 35WEST33ROSTRgF- 

■''-'""AGO i( f^nsip 

JFNB, 1908 


PART I. Page 1 


PART II. Page 8 

Description of Types of Lightning Arresters. 

PART III. Page 25 

Description of Tests Proposed and Used. 

PART rv. Page 36 

Performance of Proposed Tests, 

PART V. , Page J. 


PART VI. Page 






During thunder-storms slectrlc wires 
iDScoine charged from the atmosphere with an 
slectric potential, different from that of the 
earth; there is then a tendency to establish 
an equilibrium, --that is, for a discharge to 
or from the earth as the case may be. The ten- 
dency for a discharge to take place is not al- 
ways due to lightning but is often due to ef- 
fects similar to those caused by lightning a- 
rising from entirely different sources, as 
sv;itching, etc. If the discharge be left to 
choose its own path it will select one or more 
of the weaker points, usually the most vital 
part of the system, and thus rupture the in- 
sulation. It therefore "becoraes necessary to 
rid the line of this charge in some suitable 

manner, and without allowing it to damage any- 
port ion of the system. 

The most difficult charge to take 
care of is the direct stroke, A direct stroke 
frequently splinters poles, so violent is the 
discharge to earth. The commoner charge met 
with is one induced from a charged cloud, and 
when the cloud discharges to earth, a free 
charge exists on the line, which immediately 
begins to travel in "both directions v.-ith a ve- 
locity almost equal to that of light. Either 
of these forms of charges may expend their pow- 
er in traveling if they run a sufficient dis- 
tance "before encountering an obstruction. 
There may be a slow accumula,tion of charge due 
to rain, snow, or fog drifting across the line 
which will show itself as a series of small im- 
pulses. Charges may be accumulated from slip- 

ping "belts, etc. A surge may be started by a 
sudden change of load or connecting or discon- 
necting apparatus from ths line. 

When a wave of high potential travels 
to a generator, motor, transformer, or any 
piece of apparatus having a coil, a choking 
effect is experienced by the wave. It seem- 
ingly meets something having inertia, and as 
it rebounds and packs up the potential rises 
suddenly, and frequently a discharge results 
rupturing the insulation. This choking ef- 
fect is in all probability due to the highly 
oscillatory character of the surge. It is due 
to this fact that when a discharge seeks a path 
to earth through the coils of a dynamo, motor, 
or other apparatus, it punctures the insulation 
of the same, and takes the path to earth of 
least impedance, which is generally through 

the ?;ir-ding of an anuaturft to the core. 

In order to remove this rise of po- 
tential from the apparatus, a choke coil con- 
sisting of a few turns of wire is placed "be- 
tween the line and the apparatus to 'oe protect- 
ed. Now tha arrester is placed where the elec- 
tromotive force is apt to raise the highest, -- 
that is, on the line side of the choke coil. 

The statement has "been made and seems 
to have been "borne out in practice, that dis- 
ruptive dischargee form nodes. Therefore a 
lightning arrester cannot be said to protect 
any given distance as it may be at an anode 
and the discharge pass it completely. The 
choke coil tends to form a node, but at times 
it has been found advisable to use a number of 
coils and lightning arresters on the same line 
in a station. 


In 1844, v!h.en Morse established his 
first telegraph line, some means had to he de- 
vised to take care of the charge en the line. 
This v/as accomplished hy means of a lightning 
arrester. A lightning arrester pure and sim- 
ple is nothing more than a convenient part or 
outlet from the charged "body to a point of low- 
er or no potential. The arrester used hy iaorse 
which in its fundamental principle has been 
used ever since, v^as a spari gap through the 
air. When electric lighting was introduced 
the problem of protection became more compli- 
cated, due to the dynaiao short-circuit that 
invariably follows the discharge. Devices to 
interrupt the short-circuit and restore the ar- 
rester to normal condition had to be used. An 
ideal arrester for all purposes v/ould be one 
having a simple discharge gap of such a char- 

acter as not to penuit a short-circuit, or, 
"better yet, metallic ccrinections to ground 
without lesJcage. 

The reason for using an air gap in 
preference to that of substituting some form 
of resistance, is that it is of variable re- 
sistance, depending upon the conditions. 
Ordinarily it is a good insulator, but to a 
discharge it offers far less impedance than an 
artificial resistance of much less resistance. 
The second reason is that it can instantly be 
restored to normal. It absolutely prohibits 
the flow of the normal current unless it is 
broken down, under which conditions its re- 
sistance reduces to a minimum. 

The improvements in lightning ar- 
resters in the last fevi' years has been in the 
way of circuit-interrupting or arc-prohibiting 

features whicli have 118001116 necessary on account 
of the different currents employed. The suc- 
cess or failure of an arrester can be attribut- 
ed mainly to its successful performance of the 
duties devolving upon these additional features, 




The first lightning arrester devel- 
opment was along the line of telegraph protec- 
tion. These arresters, due to the lov/ line 
voltage, were extremely simple, consisting in 
general of simply an air gap hetwesn one line 
and the ground. A very sijiall air gap hetween 
copper or "brass electrodes sufficed to prevent 
the low voltage line current from following 
the discharge. Various tjrpes of relays were 
used for grounding the circuit automatically, 
which required resetting after the disturbance 
had passed. 

In power circuits the proposition 
was very different. The line voltage was suf- 
ficiently great to hreak across a simple air 
gap after it had passed a spark. Many devices 
were designed to overcome this difficulty. One 
of the most noteworthy types of early lightning 

arresters for power lines is one designed by 
Professor Thompson and described in the Elec- 
trical World for 1886. This consists primari- 
ly of a gap "between horn shaped electrodes. 
The air breaks down across the narrowest or 
lowest part of the horns and, due to the heat- 
ed air rising, there is a tendency for the arc 
to he carried upvra.rd to the v/ide portion of 
the gap. This much of the device had been used 
previously in Europe. To this, however, Pro- 
fessor Thompson added the magnetic field. He 
so placed a solenoid that its field enveloped 
the gap. The reaction between the air and the 
field also tends to raise the arc to the wider 
portion of the gap. This arrester is clearly 
ahovm in Pig. 1. When applied to direct cur- 
rent series arc lighting systems the gap was 
placed between the line and the ground, v^hile 

the solenoid was placed directly in series 
with the line. The connections are clearly 
shown in the figure. "li" is the machine ter- 
minal, "L" connection to the line, and "E" 
connection to the earth. For series arc 
lighting systems the arrangement was found 
quite satisfactory, the current remaining con- 
stant at ahout six or seven amperes and fur- 
nishing a constant fVjcK in the gap. For in- 
candescent lighting, however, the current 
varies greatly and could not always oe depend- 
ed upon for hlov/ing the arc. This necessitat- 
ed the solenoid oeing in the ground circuit, 
that is, in series with the gap. In this 
latter case it is evident hoth resistance and 
inductance have been introduced into the ground 
circuit, which is very undesirable. The re- 
quirements demanded by direct current series 

arc lighting systems not oeing particularly 
rigid, this lightning arrester has answered 
fairly well and it is in many of these instal- 
lations today. 

The "Central" lightning arrester, 
which came out a short time after the Thompson, 
represents another class in which the air gap 
is increased by a mechanism electrically con- 
trolled. This arrester is illustrated in Tig, 
2. The discharge passes through the solenoid, 
across the gap "C" , along the arm "D" , when it 
crosses to the revolving arm and thence to 
ground, A dynamic current which holds across 
the gap "C" energizes the solenoid and moves 
the armature. This motion increases the gap 
at "C" and loosens the revolving arm, and an 
arc is drawn out across the gap produced hy 
the motion of the revolving arm. The gap at 

"D" is of such size as to prevent the arc be- 
ing maintained. The rotation of the arm is 
accomplished "by winding a string, suspending 
a weight, upon a drui'i attached to the arm . 
In this arrester the circuit to ground contains 
a coil. This is a had feature, arcing is quite 
apt to occur across this coil. Another ohjec- 
tion to this arrester is the fact that it does 
not furnish a continuous path to earth hut one 
which may he hroken for much of the time. 

The Fulmen lightning arrester repre- 
sents one of the more successful designs of the 
fuse type arrester. This arrester came out 
about 1892. A fuse was placed in the circuit 
from the line to the ground. In order to keep 
the arrester in service after one fuse had 
blown it was necessary to automatically cut in 
another. Ten fuses were arranged in parallel 

with each end projecting into a channel. A 
carbon block in each channel made contact with 
the end of one fuse and the ground or live 
wire. As the first fuse "blew the blocks slipped 
in the channel due to gravity until caught by 
the projecting ends of the next fuse. As each 
fuse blows its endsare fused and the blocks 
slide down to the next. It is quite evident 
that this arrester was serviceable for only a 
limited nujuber of discharges. 

An interesting type of lightning ar- 
rester which came out about 1890 was known as 
the "Razzle -Dazzle." A metallic ball was sus- 
pended above a grounded plate. A discharge 
jumped the gap but the ball, being free to 
swing, was set in motion by a dynamic arc. 
Any motion of the ball increased the gap thus 
drawing out the arc. From such information as 

is availalole it is not believed that this ar- 
rester was ever very popular, 

Alexander J. ¥urts has had a great 
deal to do with the development of the light- 
ning arrester. One of his early types \ms the 
¥insor-¥urts lightning arrester. In this ar- 
rester the path to ground was first across a 
gap bridged by a carbon ball, then across a 
gap between carbon electrodes to ground. The 
second gap is contained in a chamber. In the 
neck which rises above this chamber is the 
first gap. A dynamic arc has an explosive ef- 
fect and the air raises the ball, thus placing 
another gap in circuit. If the arc should 
make across this gap also, the draft of air is 
calculated to blow it out. This arrester 
v/orked quite Satisfactorily on 1000 volts di- 
rect current but was not a success on 500 volts. 

A 500 volt arrester was larought out on the mar- 
ket composed of two chambers. The gap was be- 
tween carbon electrodes, one of which entered 
through the top. A dynamic arc blows this 
electrode out of the chainber and it revolves 
through 180 degress and drops into a similar 
chamber and is ready for another discharge. 
This arrester vas designed for 500 volt street 
rail7/ay service and was manufactured by the 
¥estinghouse Company. In his experiments Wurts 
discovered that when brass electrodes were 
used on alternating current some compositions 
of brass acted differently from others. Upon 
investigation he found that brass containing 
much zinc was the best. He explained it in 
this manner: Zinc and antimony supply the arc 
stream with oxide of metal, which chokes the 
arc with vapors of high resistance. Other 

metals, such as copper, aluminum, Toronze, etc., 
furnish the arc stream with pure vapors of the 
metal itself, r.hich offer comparatively no re- 
sistance to the passage of a current. Cadus- 
ium, hismuth, magnesium, and mercury were found 
to have this non-arcing property. The vapors 
of these metals are also unidirectional, — that 
is, they have a tendency to prevent a reverse 
of current. The non-arcing property is also 
very largely due to this. The arrester con- 
structed of non-arcing metal "best suited the 
alternating current and the gaps must be small-- 
1/32 or 1/64 of an inch, in order to hold the 
vapor hetv/een electrodes. In the type of ar- 
rester v.hich involves this principle the gap 
is made between metal cylinders which have 
knurled surfaces. In a 1000 volt arrester 
seven cylinders are used, numbers one and 

seven are connected to tlie lines and the piid- 
dle cylinder is connected to the ground, inaJc- 
ing three gaps from line to ground and six gaps 
hetween lines. Another arrester hrought out 
by ¥urts for street railway service was inade 
hy inclosing two copper electrodes between 
lignum vitae blocks. A number of paths burned 
into the blocks served to conduct the spark be- 
tween electrodes. Due to lack of oxygen vapors 
of the electrodes are not apt to form. 

The Garton-.Daniels lightning arrester 
is very widely used on both alternating current 
and direct current circuits. The path to earth 
is across a number of gaps, through a carbon 
rod of low resistance. Through a flexible con- 
nection it passes to a plunger in a solenoid 
and across a gap to ground. The solenoid is 
shunted across one or more gaps and the resist- 

ance bar. A static discharge avoids the solen- 
oid due to its inductance, Tout the dynamic cur- 
rent follows the path of least ohtnic resistance 
which is through the turns of the solenoid. 
The solenoid "being thus energized raises the 
plunger, introducing another gap in series with 
"both the static and the dynamic path. The arc 
across this gap is made in a cylinder which 
prevents violent burning due to a lack of oxy- 
gen. This arrester is largely used on the feed- 
ers of electric railways. 

The Wirt non-arcing lightning arrest- 
er described in the Electrical World in 1897 
has been used quite extensively. This arrester 
in the path, to ground has a resistance and an 
air gap between large metal cylinders. The 
grounded cylinder is the center one and serves 
for both sides of the line. The non-arcing 

property is due to the cooling effect of the 
metal cylinders. In order that the arc shall 
not hecome too hot a carton resistance is 
placed in the circuit to limit the flow of 
current. This arrester will break an arc on 
2400 volts alternating current "but v.'ill "burn 
up on 500 Tolts direct current. A reversal 
of the current is necessary. 

The Universal Non-Arcing lightning 
Arrester, also ]cno?m as the Shaw Lightning 
Arrester, is made up of a series of discs of 
non-arcing composition separated from each 
other by sheets of mica. A static discharge 
passes through the thin sheets of mica in very 
minute sparks which do not have sufficient body 
to pull an arc. The combined resistance of 
these mica sheets is much less than that of a 
simple aggregate thickness. For a time this 

arrester was ver^- popular. Its chief objec- 
tion is Its large depreciation. 

One of the most recent and extensive- 
ly used lightning arresters is the multi-gap 
arrester. It consists of a number of series 
gaps betv/een cylinders of non-arcing metal. 
Some of these gaps are shunted with a non-in- 
ductive resistance. The most recent designs 
have a number of resistance rods, each of which 
shunts a different niimber of series gaps. These 
resistances must be of different values, the 
greater resistance shunting the most gaps. The 
path which is chosen by the discharge depends 
upon the frequency. The ¥estinghouse Company 
also advocates the use of a series resistance 
which is placed between the series gaps and 
the ground. The function of the series and 
shunt resistances is described by Percy H, Thomas. 

The series gaps ars set so that they do not 
"break dov/n under line potential. An electro- 
motive force which will treak across the ser- 
ies gaps will also treak through the shunt re- 
sistance. As the alDnonnal electro-motive force 
is reduced the shunt resistance takes so much 
current that the arc goes out over the shunted 
gaps but holds over a few gaps and through two 
resistances, series and shunt. These resist- 
ances are of such a value that the current is 
too limited to hold over the gaps in series 
and thus the arc is extinguished. The lighter 
discharges are taken care of by the resistances. 
A discharge path containing considerable re- 
sistance can be set to discbarge v;ith a very 
slight rise in voltage. These arresters are 
made in panels for high voltage station work. 
The most promising type of lightning 

arrester is the Electrolytic Arrester. HWien 
aluminum is placed in certain electrolytes 
and a current passes it has the property of 
coating itself with a non-conducting film. 
This film forms for the impressed voltage "but 
will "break down in myriads of tiny punctures 
if the voltage is raised; that is, it has 
nearly infinite resistance for the impressed 
voltage and zero resistance for any voltage 
ahove . A sufficient number of these cells 
combined will act admirably as a lightning 
arrester. The cell has a slight leakage cur- 
rent and will take a charging current with an 
alternating electro-motive force. To prevent 
the cell from taking current continuously a 
gap is put in series. The film, however, de- 
teriorates hence making it necessary to con- 
nect the cell in circuit at intervals of tv/o 

or three days. Although this s-rrester has "been 
on the market only a very short time, it seems 
to have given general satisfaction. 

A lightning arrester used to a large 
extent in Europe and one which has given very 
good satisfaction is that known as the Perman- 
ent-Leak Lightning Arrester. The make up of 
this arrester is shown in Pig. 3. It consists 
of two horizontal water pipes, flow and return 
efficiently connected with the neutral of the 
generator and the station earth plate. These 
are vertical pipes of glass connected to the 
flow and return pipes. These vertical tubes 
are joined at the top hy pieces of glass tuh- 
ing in the form of an inverted "V" having a 
glass "bulb in the center, into which the point 
of the line wire dips, being made water-tight 
by a plug of India-rubber. The maximura resist- 

ance for one line through the pipes is about 
700,000 ohms making the laakage very sifjall. 

Other protective devices are used, 
such as grounded wires suspended near the line 
wires and lightning rods on the poles. In gen- 
eral it may he said that lightning arresters 
have protected apparatus and lines from serious 
damage due to disturhances of the most frequent 




It is very difficult to judge of the 
success of a lightning arrester due to the many 
conditions upon which the successful operation 
depends. One of the most important conditions 
is a straight connection to the line and ground, 
and a good ground. Up to the present time the 
only satisfactory method of determining the 
value of an arrester is service. Laboratory 
tests at hest only offer a means of comparison. 
In the laboratory it is impossible to reproduce 
conditions met with in practice. It is not ex- 
pected that an arrester will be of service in 
a direct stroke. In such cases a discharge 
usually occurs before any obstruction is met 
with and the arrester at best can only ward off 
a dangerous uss at some distant point. 

There have been a number of tests 
devised for obtaining some idea as to how a 

liglitning arrester vroutld operate ?;hen actually 
installed on a line. These tests have more or 
less come down to be comparatiTe tests. One 
of the earliest comparative tests that met with 
any success vvas that devised hy Er. Tagarde in 
1857. A diagram of his test is sho^A-n in ?ig. 4. 
He obtained his electricity from a 0,03 micro- 
farad Leyden jar charged by a ¥imshurst static 
machine. The Wimshurst machdne used was oper- 
ated at 1200 revolutions per minute, at v;hich 
speed it gave a spark from 0.15 to 0,20 meters 
in length. The spark on discharge through the 
apparatus was from 5 to 6 centimeters long. 
In setting pp his apparatus he avoided crossing 
any of his wires. The v/ires were placed at 
least 50 centimeters apart on account of the 
great difference in potential. He deemed this 
large distance necessary inasmuch as during 

his first test rrdth ths wires only 10 centi- 
meters apart a crackling of discharge passing 
through the pores of the insulation v/as ob- 
tained. All the wires used were insulated ■by- 
three layers of gutta-percha. 

In Pig. 4 the terminals of the 
charged Leyden jar are connected to points 1 
and 2. These tv^fo points are insulated from 
each other, as shoiNTi, by means of a plate of 
gutta-percha, C and C* are fuses put in to 
protect the apparatus. D and D' are 500 ohm 
hells. The circuits A B C D K and A B» C D' K 
are identical. E and E' are "indicators" con- 
sisting of a plate towards which a platinised 
screvr can be brought up. The test is conducted 
in the following manner: The charge divides, a 
part passing through the lightning arresters B 
and B' and the rest through the bells D and K', 

and the "indicators" E and E» . E and E» are 
cali"brated by means of a battery. The pitch 
of the screvr "being knovm. The number of turns 
of the screw being counted, thus giving the 
amount of charge over D and D' in comparison 
?;ith that over B and B'. In making use of 
this test M. Lagarde put a lightning arrester 
at B whose performance had been studied v/hile 
actually installed on a line, and at B' he 
placed the arrester which he wished to study. 
This is one of the most successful tests for 
the comparison of tv/o arresters and the results 
obtained by M. Lagarde were iDOst satisfactory--. 
In 1890 Alexander J. Wurts performed 
a large number of experiments on lightning ar- 
resters. In his first experiment he placed a 
saw tooth carbon arrester across the line of a 
1000 volt alternator. He used about 150 yards 

of line wire. In the circuit he placed a 
switch by means of which he cut the arrester 
in and out of the Just in frort of 
the alternator, across the line, he placed a 
short circuiting device 7/hich vi/as set to oper- 
ate at large currents, thus protecting the al- 
ternator. He bridged the air gap of the arrest- 
er with tin foil so as to start an arc. The 
first trial was very satisfactory, but after 
that the carbons of the arrester were heated 
to a white heat and the generator pressure re- 
established an arc across the hot air gap. The 
carbon did not conduct the heat away fast e- 
nough. In his second attempt he substituted 
solid round brass rods in place of the carbon 
saw tooth arrester. He kept the short circuit- 
ing device in circuit and the results were very 
good. In his third trial he omitted the short 

circuiting device and used a 3C00 light alter- 
nator. He o^btained a small arc and in all oth- 
er respects the test we.s very good. 

Twice the protection afforded in any 
case is directly proportional to the difference 
in resistance to static discharges offered hy 
the lightning arrester from that offered by the 
apparatus it is intended to shield; preference 
should be given to devices that have the lov.'est 
equivalent spark gap, which should always he 
considerably lower than that of the apparatus 
to be protected. By equivalent spark gap is 
meant that definite form of gap which, when 
placed in jnultiple v;ith the arrester, just 
fails to take the discharge. The length of 
this gap is the measure of the freedom of dis- 
charge of an arrester. 

Fig, 5 indicates a suitable method 

of measuring this equivalent spark gap given 
"by Ikr. R. P, Jackson. He makes uss of a high 
tension transfonner in series v/ith the second- 
ary of vvhich is placed a sv/ing switch, a series 
gap, and the lightning arrester virhose equiva- 
lent spark gap we wish to ootain. In multiple 
with the arrester is placed the measuring gap. 
Across the line is connected a condenser. The 
object of the condenser is to give volume to 
the spark. The little gap in series with the 
swing switch "breaks down when the switch is 
closed and adds to the suddenness of the v/ave 
striking the arrester. 

In 1907, ir. Percy H. Thomas devised 
some tests for lightning arresters to he sub- 
mitted to the Standardization Committee of the 
American Institute of Electrical Engineers for 
adoption in the standarization rules. He con- 

sidered that the purpose of the standardization 
rules should he to give such directions and in- 
formation for the comparison and test of light- 
ning arresters as may be likely to he of gener- 
al pratical use, and v/hich are of such a char- 
acter as to he generally agreed to and accepted 
hy engineers having experience with the use or 
design of lightning arresters. T7ith this in 
view Mr. Thomas proposed the following tests: 

The first test is the actual measure- 
ment of the hreak-down voltage of an arrester. 
This is best done at normal frequency. The 
needle point spark gap is employed in this test. 
The spark gap is placed in multiple with the 
arrester and the gap opened until it just neg- 
lects to take the spark. The distance betv;een 
the needle points is measured and the break- 
down voltage obtained from the calibration curve 

of the spark gap. 

The second test proposed is the de- 
termination of the protective power of the ar- 
rester which depends upon the maximum impedance 
offered to the discliarge. This can he nothing 
more than a coinparative tast due to the influ- 
ence which the characteristics of t'-^e circuit 
and apparatus to "be protected has upon this 
quantity. It is measured by subjecting the 
arrester to a high-frequency discharge frcan a 
condenser, and obtaining its static equivalent 
by the equivalent needle-gap method. Either 
of the circuits shovm in Figs. 6 or 7 may be 
used for this test, depending upon the apparat- 
us at hand. 

The next test proposed is the deter- 
mination of the power to suppress the generat- 
or arc. The test is made by reproducing oper- 

ating conditions; that is, connecting an ar- 
rester across a powerful supply circuit and 
passing a static discharge across the whole or 
part of the arrester to initiate the generator 
arc. The circuit for this test is shovm in 
Pig. 8. Any arrester, to he of commercial use, 
should he aole to suppress the generator arc. 

The capacity for frequent discharges 
is determined by the same method as the last 
test. The kind of arrester used has a great 
deal to do v/ith this property. High-voltage 
arresters v;ill presumably discharge much less 
frequently than will low-voltage arresters, as 
in the former minor disturbances will not be 
able to pass to the ground. Furthermore, on 
alternating-current circuits at least, dis- 
charges occurring at one part of a cycle are 
more severe than discharges occurring at anoth- 

er, which tends to relieve the arrester. 
In making this test a nviaber of discharges 
should he produced in succession at inter- 
vals of some seconds, the exact number of 
repetitions and the intervals being deter- 
mined according to the circumstances of the 

There have been a number of other 
tests proposed by different men well up on 
the subject of lightning arresters, but those 
already mentioned cover fairly v;ell the points 
to be considered by a person in purchasing 
lightning arresters. 


PART rv 





As previously stated, too much must 
not te expected of a lalDoratory test. Many 
schemes for testing laaTS been proposed from 
time to time--3ome employ a static machine, 
while others use a high potential transforra- 
er. An author, in writing of his methods 
for testing, is apt to over-estimate their 
importance. Since most of the literature 
on lightning arrester testing is "by some one 
advocating a particular test, the engineer 
who has had no experience in this work receives 
the impression that the results ootained are 
final and of primary importance. 

All the tests tried were with the 
use of a high potential transformer. Many 

proposed schemss were tried and the results 
obtained from some will be given. The method 
of measuring the voltage at which a spark oc- 
cuf"red gave some difficulty. Electrostatic 
voltmeters were tried, but, due to the ranges 
of the instruments available, they were not 
satisfactory. A spark gap between needle 
points is the standard method for measuring 
high voltages. In this case the gap is in 
parallel with the arrester, and set so that 
it divides the discharge or just fails to take 
the discharge. Whan the arrester discharge for 
minimum voltage is measured in this v/ay, the 
distance between the needle points of the spark 
gap is called the equivalent spark gap and is 
a measure of the arrester's impedance. Care 
must be taken that the readings are taken with 
sharp needles. The points frequently burn and 

a preliminary setting should "be made v;ith nee- 
dles which have "been slightly turned. The 
final setting and distance measured is that te- 
tv/een new points. In all tests nujnber 1 and 2 
sewing machine needles were used. The stand- 
ard calibration for a needle gap as given hy 
the standardization rules of the American In- 
stitute of Electrical Engineers is for mean 
effective pressures assvucing a sine wave. It 
is, however, the maximum voltage which hreaks 
down the gap and the wave form Lvust therefore 
he investigated. 

Another method used v;as to step down 
the voltage with a transformer whose ratio of 
transformation is absolutely known. Thus a 
reading could he obtained on a low potential 
voltmeter. For a potential transformer a Lakon 
and a General Electric transformer were checked 

and found to be very accurate within the lim- 
its for which they v;ere to "be used. The volt- 
meter method was the one which seemed to give 
the most consistent results. Some of the mod- 
ified forms of spark gaps, such as a gap "be- 
tween spheres or needles provided with shields, 
might he advisal'le, but were not tried. 

Among the first schemes tried v/ere 
those proposed by Mr. Percy H. Thonias and pre- 
sented before the American Institute of Elec- 
trical Engineers at 'JTiagara Palls ir June 1907. 
The scheme shown ir; Pig. 6, which was also pro- 
posed by Ivir. Creighton some time previous, was 
tried, using instead of the static machine a 
high potential transformer. A sv:itch vra,s put 
on the low tension side of the transformer. 
The voltage could not be satisfactorily meas- 
ured with a needle gap. The needle points were 

fused at almost every discliarge. In series 
with the gap a high ohjnic resistance Vv-as placed 
to limit the current. This was only partially 
successful. Tha quality of the discharge was 
much poorer. Aftar the employment of a swing 
switch and more capacity in the condensers than 
were in the condensers of the Leyden jar tuoe, 
this medthod was abandoned without having ob- 
tained any satisfactory data. In an effort 
to open the circuit more rapidly after obtain- 
ing a discharge, a very delicately adjusted 
relay was placed in the primary circu't. which 
in turn operated a circuit "breaker, thus open- 
ing the circuit. The device as a protection 
to the apparatus v/as quite a success as far as 
the opening of the circuit was concerned. It 
failed, however, to operate until after the 
needle points had "been fused. In the tests 

su-Dsequeritly tried tliis device was introduced 
as an emergency protection, inasmuch as it 
could "be used vdtliout interfering in any way 
with the operation of the test. 

The next test tried was that shown 
in rig. 7. The discharge gap ?7as made he- 
tween spheres of ahout one-half inch in diam- 
eter. Condensers of various capacities were 
also tried. Leyden jars proved the most suc- 
cessful. A plate condenser in v/hich the di- 
electric was oiled linen and paraffine paper 
gave considerable trouhle and was finally dis- 
carded. \"hen placed in circuit on three or 
four thousand volts the temperature of the con- 
denser rose until a "break dov/n occurred. 

The location of the swing switch was 
changed after considerahle experimenting, and 
was finally placed on the high tension side. 

It v/a6 njade in the form of a pendulimi, about 
tv/o and one-half feet long, provided with a 
sliding weight to change the period. Contact 
was made with the light flexible piece of brass 
for a very short length of time. It was found 
advisable to place the condensers between the 
swing switch and the transfonnerr, as the charg- 
ing current does not then pass through the 
switch. The objection to passing the charging 
current through the switch is that the switch 
draws out a considerable arc and the suddenness 
of the discharge was spoiled. With this ar- 
rangement a constant voltage was maintained on 
the secondary side and a step down transformer 
and low potential voltmeter was used to measure 
the voltage. TTith the scheme as described 
above, a supply spark was obtained over both 
the arrester and the needle gap. The data 

cttained with the spark gap could not te re- 
produced. J"ust to what this was due* could not 
be determir-ed. The setting of the series dis- 
cliarge gap prohably has some influence. The Yolt- 
meter readings, however, were reproduced quite 
satisfactorily in most cases. This led to the 
adoption of the voltmeter as the standard, and 
frequent attempts were made to check with the 
spark gap. "While data ?ra,s obtained with this 
scheme, it was not considered satisfactory and 
other schemes were tried. 

The scheme of Ivjr. R. P. Jackson, in 
the Electric Club Journal of ]«arch 1908, is 
quite similar to the one just described. The 
scheme of Jackson is shown in Jig. 5. The 
saDie swing switch, series discharge gap and 
condensers were used as in the previous schemes. 
The condenser was made up of twelve Leyden jars, 

quart size, plaxed in parallel. As an experi- 
ment, the condenser was placad in parallel with 
the arrester and needle or measuring gap. The 
series or discharge gap is now hetv/een the con- 
denser and the swing switch. This increases 
the arc at the switch, "but placing the series 
gap "betv/een the condenser and the switch gives 
this arc more the form of a hee-vy static dis- 
charge. A snappy spark was produced at the 
arrester. Very little difficulty was experi- 
enced v;ith the needle points. It was clearly 
demonstrated that the series gap effects the 
discharge. For this reason the setting of 
this gap was changed frequently to olitain the 
hest position. Using the arrangement shovm in 
Tig. 5, except for the change in location of 
the condenser as described, the following re- 
sults were obtained: The first arrester tested 

for equivalent spark gap ta^s a V'urts non-arc- 
ing lightning arrester. The lowest voltage at 
which a spark jumped the series of gaps from 
line terminal to line terminal was 3250 volts 
mean effective, or a maximum of ahout 5500, 
The arrester is designed for a line voltage 
of 1000 volts. This necessary rise is rather 
high. The condition of the insulation of the 
apparatus to he potential miust "be very good 
indeed to benefit much from the presence of 
the greater. It should he stated here that 
the arrester has never heen in service hut is 
far from new and not of recent design. This 
hreak down voltage vms measured hy the volt- 
meter method. The results obtained with the 
use of the needle gap will be taken up later. 
The voltage at which the condensers are charged 
and that impressed upon the arrester depends 

upon the points of the wave at whicS? the swing 
switch niakes contact. The switch may make con- 
tact on any point of the wave. Therefore, in 
order to ohtain the conditions looked for, name- 
ly, contact at maximum voltage, the switch is 
kept in motion and considera'ole time allowed, 
to make sure that contact must have heen made 
on the peak of the wave at least cnce. Tor 
this reason there is an argUinent in favor of 
the synchronous switch which shall always make 
contact on the peak of the wave. A device of 
this kind in the form of the contact -maker 
should not he difficult to construct and its 
use is advised. It is quite evident that if 
the swing switch did not make on the peak of 
the electro-motive force wave, the reading 
octained hy the voltmeter is not correct. 
There is then this chance for error in the 

matliod esiployed. Tlis form factor for the 
electro-motive force wave of the alternator 
used is 1.74, being a very peaked wave, With 
but very little load on the secondary side, 
this form factor will hold quite well for the 
Tftuve form on the secondarj'- side. Thus it vra-s 
assumed that the v/ave form remain practically 
unchanged. An oscillograph should be used to 
determine this definitely. 

In testing the art breaicing power 
of the arrester an effective pressure of 1000 
volts was impressed across the line terminals. 
An arc must be started by a discharge. It is 
evident that if a discharge is to pass clear 
across the series of gaps the terminals of the 
discharge circuit cannot also tap onto the line 
terminals, as the discharge v/ill pass back 
through the line and transformer or alternator 

supplying it. This was found to Tdb true in 
spit 8 of the inductance in this circuit. In 
this particular arrester ths scheme can "b.e 
satisfactorily employed hy placing the dis- 
charge terminals so that there are as rnany 
gaps or nearly as many in the circuit back 
through the transformer as across the remain- 
ing space between the discharge terminals. 
In this case they were made equal and the dis- 
charge voltage raised until the sparlc passed 
both v;ays , completely bridging all gaps between 
line terminals. The arc was satisfactorily 
bloTATi for all voltages tried wliich were as high 
as 1300 volts. This test cannot be relied upon 
as final as the alternator used to supply the 
imaginary line was of limited capacity and it 
is believed that the generator capacity must 
be considered. As regards frequency, 60 cycles 

were used for Tooth alternators. The discharge 
frequency, however, "being that from a condens- 
er, can only he estimated. 

After comparing data taken at vari- 
ous frequencies, it is helieved that frequen- 
cies "between 25 and 100 cycles have practically 
the saane effect. The slight variation which 
was shown in the data did not seem to hear any 
definite relation to frequency and so must have 
heen due to other causes. 

In the tests of the Wirt arrester, 
the lowest "break down voltage was 2950 volts. 
These tests were made at 60 cycles and the 
voltage was measured "by the voltmeter measure. 
This arrester was designed for a 2000 volt 
line and is one which has seen con3idera"ble 
service, and "before making the tests it was 
not thoroughly cleaned, only loose dirt "being 

removed. This arrester, therefore, represents 
more nearly the conditions apt to loe met with 
in service. Por the test to determine the ar- 
rester's ahility to hreak the arc, the same 
method as used on the ^'urts' arrester was em- 
ployed. There being five cylinders in series 
between the lines, tvro gaps could he put be- 
tween the discharge terminals, leaving two in 
the circuit through the line and transf or;uer. 
As in the case previously described, the spark 
was forced to divide, thus bridging all the 
gaps betv/een the lines. A line potentie.1 of 
2500 volts failed to produce an arc following 
a discharge, so the limiting device, while not 
considered perfect, compared favorably with 
other arresters tested. 

The next type tested was a Gifford 
3000 volt arrester. The gaps here are in 

parallel and adjustable. "tTo change whatever 
was made in the setting of the gaps, they hav- 
ing been set by the manufad:iirer. The break 
down voltage at 60 cycles was 2500 volts mean 
effective, or a maximum of approximately 3900 
volts. "Sow for a sine wave the mean effective 
pressure corresponding to this maximum falls 
below 3000 volts, the line voltage for which 
this arrester is intended. Seemingly this in- 
dicates that the arrester would be apt to dis- 
charge on line voltage. A 3000 volt line, 
however, was placed across it without a dis- 
charge. The data being for an impulse, it 
appears that in practice the arrester would be 
apt to discharge very frequently, not neces- 
sarily due to any use in potential but simply 
the normal electro-motive force suddenly ap- 
plied. To test the arc-disrupting ability of 

this arrester, the methods previously described 
did not apply, so it oecame necessary to oridge 
the gap with tin foil, thus producing an arc. 
The method in this instance was very unsatis- 
factory, due to the limited current that could 
he obtained at this voltage. Again this 
demonstrated the limitations of laboratory 
tests which are usually met with. This arrest- 
er is set very low, and unless it has unusual 
capacity is apt to injury from heavy currents 
and frequent discharges. There is danger in 
trying to male? an arrester too sensitive. As 
previously mentioned, the gaps are adjustable 
and this low break dovm voltage may be varied 
by slightly increasing the gap. In an arrest- 
er of this type it is impossible to uiake the 
paths of equal impedance and so some break dovm 
long before others. From watching operations 

of this arrester, it must "oe said that the 
quantity conducted to earth across each gap 
is small. The spark is very fine and noseless. 
A paper placed in the gap shows a clean small 
hole without any burning. An important test 
of an arrester of this kind and the V7irt type 
is one, of the carrying capacity of the carbon 
rods and their consistency as regards resist- 
ance. This test was not made but is advised. 

With this incomplete set of data the 
engiaeer has a key to the characteristics of 
the various types tested and a certain amount 
of comparison is possible, "NTow to take up the 
measurements of these voltages with a needle 
gap. As an example, the Wurts non-arcing ar- 
rester discharged at 3250 volts mean effective 
according to the voltmeter method of determina- 
tion, while with the spark gap the mean effect- 

ive was aloout 10,000 volti^ TDased on a. sine wave. 
The v/ave of the alternator used varied decided- 
ly from a sine v/ave . Therefore in this case 
the calibration in mean effective pressures, as 
given in the standardization rules of the Amer- 
ican Institute of Electrical Engineers, will 
not hold. However, hy using the form factor of 
a sine ?;ave these mean effective values may he 
replaced hy maximijim values and the actual mean 
effective for the Vz-ave used deducted from these. 
Employing this method, however, accounts for 

only a small part of the discrepancy. Some of 
the error it is safe to assvime is due to the 

contact not having "been made at the maximum 

point of the v/ave . This explains why the spark 

gap was not depended upon as a measuring device. 

While the actual data recorded is not 

of any particular importance, the testing of 


numerous proposed schemes gave considera-ble in- 
forme^tion. Many tests which have "been proposed 
are not practical, and even in the "best there 
are f lav.-s . Originally it was intended that af- 
ter finding a suitable scheme for testing, com- 
mercial tests v;ould be made on a nuinber of ar- 
resters. That these tests could not be made 
was due to lack of time. In connection with 
each scheme tried, considerable experimenting 
was required to determine if it could be laade 

practicable. The time and work put in in this 
way does not show in the report, as no numerical 

data was obtained on those that failed. Con- 
denser and transf or.ner troubles in the form of 
burn-outs consumed considerable time. The tests 
given were obtained with the scheme last developed 
It is believed that this is a practical scheme 
and can be used to advantage for a comparison of 
arrester characteristics. 




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