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Oct. 29, 1946.
. .1.‘ H. MILLER
F'i_led March 13, 1942
Qmdrofare 3
Patented Oct. 29, 1946
John H. Miller, Short Hills, N. J., assignor to
Weston Electrical Instrument Corporation,
Newark, N. J., a corporation of New Jersey
Application March 13, 1942, Serial No. 434,577
5 Claims. (Cl. 175-183)
This invention relates to electrical testing ap
This electrodynamometer type of testing ap
paratus is open to several objections. Inasmuch
paratus for measuring the in-phase and quadra
ture components of a voltage'with relationship
as the ?eld coils of the electrodynamometer re
to a reference source, and more particularly to
quire a fairly large current, the condenser network
which is required to bring the magnetic ?ux into
an electrical instrument and circuit for testing
potential transformers.
The invention contemplates the provision of
an electrical indicating instrument, and a phase
discriminatory network and its associated ener
gizing and switch elements combined in a com
phase with the exciting voltage is unduly large.
The prior apparatus is therefore bulky, expensive
and not readily portable. Also the requirement of
two voltage sources displaced-by 90 or 120 degrees
10 restricts the use of the device to polyphase sys
pact, portable case. The apparatus will be par
ticularly described as a transformer tester, but
tems or, alternatively, requires the provision of
it will be understood that this description is not
An object of this invention is the provision of
such voltage sources in some other manner.
a compact portable apparatus for determining
intended as a limitation of the invention to any
particular use.
15 the in-phase and the quadrature components of
Potential transformers are employed to actu
a voltage source with respect to a reference
ate watt-hour meters which register the amount
of electrical energy consumed by individual
An object is the provision of a novel electrical
branches of a common supply line. Failures such
testing apparatus by which the voltage output
as are likely to develop in the transformer usu 20 of a transformer may be quickly and easily deter
ally result in a reduced voltage output, where
upon the watt-hour meter runs slow with a con
sequent loss in revenue to the public utility com
pany furnishing the power.
Present equipment available for checking po
mined in the field.
Another object of this invention is the provision of a compact, portable transformer tester
for determining the voltage output of a trans
. former without the need of a polyphase voltage
tential transformers is both elaborate and cum
bersome, and requires a certain degree of labora
test transformers are connected.
A further object is the provision of a trans
tory re?nement to obtain reliable data. One of
former tester comprising a direct current indi
the simpler forms of such equipment, known as
cating instrument, a phase .discriminatory net
a comparator voltmeter, comprises an electro~ 30 work, and associated circuit elements for obtain
dynamometer instrument having a separately ex
ing, by direct readings upon the closure of ener
cited ?eld coil. The movable coil is actuated by
gizing switches, two voltage values from which
the 'exactvoltage and phase displacement of the
the differential voltage existing between the sec
particular transformer may be determined.
ondaries of the transformer under test and a
A still further object is the provision of a trans
standard transformer of known characteristics - 1
former tester comprising a direct current indi
when the secondaries are connected in series op
position. The de?ection of the instrument point
cating instrument, a recti?er modulator bridge,
a source of exciting or switching voltage for the
er represents the magnitude of the differential
modulation bridge, circuit elements for obtain
voltage between the two transformer secondaries
or rather, that component of the differential volt 4.0 ing a quadrature voltage for exciting the bridge,
a source of voltage for checking the circuit con
age which is in phase with the magnetic flux
emanating from the ?eld coils of the instrument.
ditions by reference to the indication of the in
strument, and selective switching devices by
A similar reading is obtained under conditions
which a test transformer of unknown output
wherein the exciting voltage is dis-placed 90 or
voltage may safely be connected into the circuit
120 degrees from that to which the standard and
There is thus
obtained the magnitudes of ‘two voltage compo
_ _
These and other objects and advantages will
nents that are displaced in space, and these may
be added vectorially to obtain the actual value
be ‘apparent from the following description when
standard transformer to obtain exact data as to
purpose, to the appended claims.
taken withv the accompanying drawing. The
and phase position of the dilferential voltage. 50 drawing is intended for purposes of illustration,
This resultant voltage may then be added vec
and is not to be construed as de?ning the lim
torially to the known secondary voltage of the
its of the invention, reference being had, for this
the output voltage of the transformer under
f In the drawing, wherein like characters
55 identify like parts in the. several ?gures:
direct current measuring circuit from the alter!
Figure 1 is a complete circuit diagram of an
nating current input circuits may be effected by
comiecting the measuring circuit directly be
tween the electrical midpoint of the energizing
electrical testing apparatus embodying the in
Figures 2 to 4, inclusive, are simpli?ed, sche
matic diagrams illustrating the directions of the
currents in the various circuits under different
winding 2 and a tap on a resistor that replaces
the jumper l2, i. e. the electrical midpoint of
the serially connected secondaries of the power
Figure 5 is‘a vector diagram of the measured
Legends such as “300 volts” are placed adjacent
voltages indicated by the measuring instrument.
A testing apparatus made in accordance with . 10 the several pushbutton switches l5-—I8 to indi
cate the measuring range established by each
this invention may be housed in a small port
able casing and provides a quick .and accurate
A separate winding 28 on the energizing trans
means for checking potential transformers by a
former provides acheck potential for testing the
semi-skilled operator. The circuit comprises a
recti?er modulator bridge I consisting of .four 15 condition of the apparatus before a test is made.
A resistor 29 is connected between the winding
recti?er elements a-d arranged in the same
.28 and the front contact of the switch 23, and a
sense in a closed ring. The modulator bridge '
leadi? from the other side of the winding 28
is excited by the secondary winding 2 of a trans
to the bridge junction opposite that to which
former which is connected to an alternating cur
rent source S by any suitable leads. One side of 20 switch '23 is connected. This check circuit is
normally open at the switch 23, and a legend such
the secondary winding 2 is connected to one
as “Circuit check” is preferably placed on the
junction of the modulator bridge by the wire 3
panel adjacent the switch 23.
and the other end of the winding is connected
As indicated above, the secondary windings of
to theopposite bridge junction byIthe wired, the
normally closed side of the manually operable 25 the standard transformer 3! and of the trans
former 32 under test are connected across the
switch 5, and the ‘resistor 6. The other contact
terminals H, II’ and l3, l3’, respectively. The
of switch 5 is connected to the bridge junction
conditions; and
secondary windings must‘be in series opposition
through'the condensers 1, 8 in series, and the
for the test but, as will be explained later, no
common terminal of the condensers is connected
to the wire *3 and its associated ‘bridge junction 30 harm will result if the transformers are so con
nected to the apparatus terminals and to a cur
through theresistor 9. The depressing of switch
rent source $ that the voltage outputs of the
5 substitutes acapacitive reactance for the ohmic
secondary windings are in series additive rela
resistance “that is normally connected between
tion. For simplicity and clarity, separate alter
the secondary winding 2 and the modulator
bridge, thereby shifting the bridge exciting volt 35
nating current sources S are indicated as con
age by 90°. The serially connected condensers
nected to the energizing transformer and to
the standard and test transformers but it is to
‘I, 8 and the shunt resistor 9 result in a current
be understood that all current is drawn from the
flow to the bridge that is exactly in quadrature
same power distribution system.
with ‘the line voltage. The legend “Quadrature
Assuming that the circuits of the transform
test” preferably appears on the panel adjacent 40
ers 3| and 32 are properly connected with the
the pushbutton of the switch 5‘ to identify its
secondary voltages opposed to each other, no po
tential whatever exists across the terminals I I,
The "conjugate diagonal arm ‘of the modu
I3’ when the secondary voltages are equal. If
lator bridge I is to include the secondary wind
the test transformer 32 differs from the stand
ings of a “standard” transformer and of the
ard transformer 3!, a small voltage results across
transformer under test, and a resistance-switch
these terminals and is impressed across the mod
network for adjusting ‘the voltage measuring
ulator bridge I through vthe lead It! on one side
range of v‘the ‘indicating instrument. The ele—
ments of ‘this circuit ‘that are built into the
and through lead 24, the resistor-switch network,
portable testing apparatusjinclude the lead ill
and lead 14 on the other side. The magnitude.
and sense of this differential voltage are indi-
from ‘a bridge. junction to terminal i I of
the pair across which one transformer is to be
connected, a jumper l2 from the other terminal
ll’ of that pair of termina1 ‘[3 of the pair of
terminals l3, l3’ across which the other trans
former secondary is to be connected, and the
resistor-switch network. A lead I4 connects
terminal [3' to the ?xed contacts of normally
open pushbutton switches l5—l8 that have con
tact blades serially connected through voltage
multiplier resistors I9, 20 and 2|. The blade of
cated by the direct current measuring instrument
2'! on the voltage range scale that is determined
by the particular switch I5--l8 that is closed.
It will be apparent that the de?ection of the
direct current instrument 2‘! is a function of
the phase and magnitude of the alternating cur
rent components that are impressed across the
respective diagonals of the modulator bridge.
60 The mathematical analysis of this bridge net
work with three mutually isolated circuits across
the recti?er bridge is quite complex and it is not
switch 15 is also connected ‘through the “low
presented here as the general operation of the
range” resistor 22 to the back contact of a push
apparatus can be explained from the known char
button switch .23 having a blade connected ‘by
lead 24 to the ‘bridge junction point. Center 65 acteristics of the copper-oxide recti?ers a-d of
the bridge I.
tapped resistors 25, 25 are shunted across the
It is apparent that the current components
described conjugate bridge arms, and a multiple
entering the bridge I are of the same frequency
scale, direct current voltmeter 21 is connected
as all transformers are energized from the same
across the midtaps of the resistors 25, 2B. These
shunt, resistors facilitate the connection of the 70 source. Referring now to Figure 2, which is a
simpli?ed circuit diagram of the phase discrim
measuring circuit to those points of the modu
inatory network, the “+” and “—” signs ad
lator bridge network across which each alter
jacent the ends of the energizing transformer
nating current'input circuit establishes a direct
winding 2 and the terminals II, I3’ indicate the
current potential but not an alternatingv cur-_
rent potential. ‘This’ electrical isolation ‘of the 75 polarity of the potentials established at a given
instant. The heavy lines and arrows indicate
the path and direction of the current ?ow from
the winding 2, and this current will hereafter be
referred to as the “switching current.” The light
lines and arrows indicate the path and direc
tion of the current ?ow from the terminals ll,
l3", i. e. the current established by the differ
ential voltage existing between the secondary
Copper-oxide recti?ers are asymmetrical con
ductors and the resistance-current relationship
approaches the form of a quadratic curve. A
relatively small current ?ow in the normal or
forward direction causes a sharp decrease in the
recti?er resistance but further increase of the
current ?ow produces progressively smaller, in
cremental decreases in the resistance. It may be
said, therefore, that the recti?er is subject to cur
windings of the “standard” and "test” trans
formers 32, 3|; and this current will hereafter 10 rent saturation in that a further increase in the
be referred to as the “actuating current.” It is
current ?ow produces only a minor change in the
apparent that the two recti?er elements a, b, are
resistance. This characteristic is employed to
conductive at the indicated polarity of the switch
good advantage in the present circuit. By as~
ing current from winding 2, and that the low
signing a proper value to the resistor 6, Figure 1,
resistance conducting path for the ?ow of the 15 with respect to the potential of the winding 2, the
actuating current includes the element b. Some
magnitude of the switching current ?owing
part of the actuating current ?nds a return path
through the modulator bridge is kept somewhat
through the relatively high resistance recti?er
above the saturation point. This current re
arm 0, and another part ?ows through the lower
duces the resistance of the recti?er elements to
section of the resistor 26 but the major portion 20 substantially the lowest value. Hence, voltage
of the actuating current takes the path, as in
?uctuations of the alternating current source do
dicated by the arrows, through recti?er b, the
not introduce serious errors in the indications
lower half of resistor 25, instrument 21, the upper
of the instrument. Tests have demonstrated that
half of the resistor 26, and the lead 10 to the
varying the line voltage between 100-430 volts
terminal II.
25 produces less than 1% error in the instrument
The recti?er elements 0, d are conductive one
reading when the switching current input at this
half cycle later when the polarities of the switch
minimum source voltage produces saturation or
ing current and of the actuating current are
incipient saturation of the recti?er bridge. This
simultaneously reversed. This condition is shown
condition is satis?ed when the potential across
in Figure 3 and inspection of the circuit will show 30 the secondary winding 2 is about 100 volts or
that the current ?ow through the instrument 21
greater. Thus it is apparent that the circuit is
has not changed direction. Thus, a pulsating,
inherently stable and obviates the need for the
direct current ?ows through instrument 2'! so
adjustable resistors usually employed to compen
long as the polarities of the switching and actu
sate for line voltage ?uctuations. The apparatus
ating currents change simultaneously. Further, 35 does not require continuous supervision .to as
it is to be noted that the instrument circuit is
sure accurate data.
conjugate to the winding 2, hence, the alternat
A quick check for ascertaining the condition of
ing, switching current is excluded from the in
the apparatus prior to use is provided by' the
double throw switch 23. By depressing switch 23
The Figure 4. schematic circuit is similar to 4.0. the di?erential voltage across terminals ll, I3’ is
that of Figure 3 except that the polarity of the
removed and the check voltage of winding 28 is
actuating current has been reversed. Inspection
applied to the bridge. The value of this check
of the circuit will show that the current now
voltage and the resistor 29 are predetermined so
?ows in the reverse direction through the in
that when the switch 23 is depressed, the pointer
strument 21. Although the path of high con 45 de?ection of the instrument 2‘! will fall within
ductivity across the modulator bridge is the same
in Figures 3 and 4:, the reversed polarity of the
actuating current is immediately re?ected into
the instrument circuit.
Analysis of the measuring circuit discloses
that the direct current ?ow in the measuring cir
cuit of instrument 2'! would be proportional to
the products of the two alternating current com
ponents in the modulator bridge if the recti?er
elements operated on a pure square law.
ever, the recti?er characteristics are such that
the response approaches a linear relation and
the instrument deflection is, therefore, not strictly
a predetermined range that may be identi?ed by
a suitable reference arc marked upon the scale
plate of the instrument. The design is such that
the de?ection of the instrument pointer, when the
switch 23 is depressed, will fall within the refer
ence are as long as the switching potential of the
energizing winding 2 is above 100 volts. Under
such check condition, registration of the instru
ment pointer with the reference are informs the
operator that conditions are proper for proceed
ing with his tests. A pointer de?ection of re
duced amount indicates that the line potential
is too low.
proportional to the product but to some smaller
Transformer defects, which become ‘manifest
value. The exact magnitude of the instrument 60 by a reduction of voltage output, are usually due
de?ection or the relationship between the in
to a partial short circuiting of the winding. Con
strument and alternating current components is
sequently, such reduction in voltage output is
not particularly important as the essential re
also accompanied by a change in the voltage
quirement is that the instrument provides sub
phase displacement. Inasmuch as wattage is a
stantial de?ections to opposite sides of the center
function of both voltage magnitude and phase,
zero to indicate the phase relationship between
transformers used to actuate watt-hour meters
the two potentials impressed across the bridge.
must be tested for both conditions, and the Switch
Once the constants of the electrical network are
5 and associated elements provide means for
determined, the scale of instrument 2'! may be
measuring the in-phase and quadrature compo
calibrated directly in “volts” and suitable mark 70 nents of the di?erential voltage existing between '
ings, such as “in phase” and “out of phase,”
the “standard” and “test” transformers. The
may be placed on opposite sides of the center
apparatus is more simple, compact and easy to
zero position. Thus, the instrument will indie
use than the present devices and methodsfor
catei the exact magnitude and' the phase rela~
accomplishing the same purpose since the source.
tionship of the two bridge potentials. '
.75 of quadrature exciting voltage is an" inherent l. '
part of the apparatus, whereas present devices
require a polyphase. source of supply. Thus, the
presentapparatus may be employed to check such
transformers on location, and without the neces
sity of changing the primary connections of the
exciting transformer from one phase to another.
_ As' explained, vthe exciting voltage of the wind
ing 2 isinormally applied to the bridge I through
thenormallyclosecl contact of switch 5. How
upon the instrument 2? indicates that component
on of the actuating voltage which is in quadra
ture with the line voltage. The resultant ex rep
resents the true voltage differential between the
“standard” and. “test” transformers, and this
voltage may be added vectorially to the known
secondary voltage Es of the “standard” trans
former to obtainthe exact voltage Erjofv the “test”
transformer. ‘ It is apparent that the phase angle
ever, by: depressing the switch 5 so that it closes 10 error of the “test” transformer is represented; by
the angle ¢.
- ‘
the lower contact, the condenser ‘E is inserted into
Inasmuch as the ?nal voltage, obtained as de
the bridge circuit. 1 Under this condition, the
bridge current becomes displaced by approxi
scribed hereinabove, represents the differential
voltage between the standard and test transe
denser‘ 8. and. shunting resistor 9 supplement the 15 former, it becomes necessary to know the actual
voltage output of the test transformer during the
condenser ‘I so that the current which flows
test procedure.‘ For example, if at the'time of
through the modulator bridge is exactly in
making the tests, the'two transformers are actu
quadrature with the line voltage. The manner
ally delivering l00 volts and the differential volt
in which this quadrature current is utilized in the
mately 90 degrees. 'The' additional series con~
age is found to be 3 volts, the test transformer
use of the' apparatus will be more fully described
has a 3% error. On the otherhand, if the same
hereinbelow, in connection with the actual use
differential exists when the transformers are de
of the device to test a potential trans-former.
livering 130 volts, the error is only 2.3%. The
To better point out the features of the inven
actual voltage output of the test transformer may
tion and the manner of its use, the actual pro—
cedure for testing a 110 volt potential trans 25 be obtained by transferring the jumper I2 from
terminal H’ to terminal H and depressing the
former will now be given. The apparatus may be
150 volt switch 30.
enclosed in a small case provided with binding
Having now described my invention, various
posts corresponding to the terminals H, I I’, 13,
modi?cations and variations will be apparent to
E3’ and pushbuttons for operation of the vari
ous switches. The primary of the exciting trans 30 those skilled in the art. These modi?cations and
variations may be made without departing from
former is connected to the power line or alter
the spirit and scope of the invention as de?ned
nating current source S by means of appropriate
in the following claims.
leads or a plug-in cable connection. The “stand:
I claim:
ard” and “test” transformers are also connected
1. In a portable apparatus for measuring the
to the same supply line, in any suitable manner,
in-phase and quadrature voltage components of
and their secondaries are connected to the ter
a test source of alternating current with respect
minals H, H’, i3, l3’ of the testing apparatus,
to a reference voltage, a modulator bridge having
as shown. To check the circuit conditions, the
recti?er elements arranged in the same sense
operator depresses the circuit check switch‘ 23
in the respective side arms thereof, a transformer
and observes the indication of the instrument 2i’.
having a primary winding for connection to the
If the pointer of the instrument registers within
source of reference voltage and a secondary
the reference arc on the scale plate, he may
winding for developing a voltage sufficient to
proceed with his test; if not, he is at once aware
saturate the modulator bridge, an energizing cir
that‘ the line potential is too low. He next de
cuit connected across one set of opposed junc
presses the 300 volt switch it which applies the
tions of said bridge and comprising‘ said second
voltage existing across the terminals 5 I, it’ upon
ary winding in series with a phase-shifting net
the modulator bridge. The instrument 2? indi
worl<:,,said phase-shifting network including a
cates the magnitude of this voltage on the 300
resistive and a capacitive impedance with a
volt scale.v A reading of 220 volts indicates that
switch for completing said energizing circuit
the “test” and “standard” transformers are con
through the resistive or alternatively the capaci
nected'series aiding instead of series opposition,
tive impedance, an actuating circuit connected to
which condition may be corrected by reversing
the other set of opposed junctions of said bridge
the leads of either transformer. Proper connec
and including terminals for receiving connections
tion of these transformers results in a very small
deflection- of the instrument pointer on the 300 55 from the test source of alternating current, a cen
ter-tapped resistor connected across each set of
volt- range; whereupon " the operator depresses
opposed bridge junctions, and a direct current
the switches iii to l5 in sequence until he ob
measuring instrument connected ‘between the
tains a maximum on-scale de?ection. The actual
center taps of said resistors.
reading thus obtained represents that component
2. In a portable apparatus, the invention as
er. of the voltage differential between the “stand 60
recited in claim 1, in combination with an addi
ard” and “test” transformers which is either “in
tional winding on said transformer for develop
phase” or exactly 180 degrees “out of phase”
ing a checking voltage, and a, switch for opening
with the exciting potential and, in most cases, is
said actuating circuit and for connecting said
best obtainedv on- the 3‘ volt scale. However, it
occasionally happens that an entire sectionv of a 65 additional winding vacross said bridge in place 0
said actuating circuit;
transformer winding becomes short circuited, in
_ 3. In a portable apparatus, ‘the invention. as
which .case, the voltage output is considerably
recited in claim 1, wherein said terminals of the
less than normal-- and may‘ best be read on the
actuating circuit comprise, in series, two pairs
Assuming that the pointer of the instrument 70 of terminals across which the secondary wind
ings of a standard transformer and of ‘a test
de?ects to that side ‘of the center zero marked.
‘?n-phase?’ the voltage component may be rep+
- 4. Inv apparatus for.connected.
~ the
' ' "operatin
resentedbyei. on they vector‘diagram of Figure 5.
characteristics‘of .a test transformer, a modula
Next-stile quadrature testswitch- 5 and the 3 volt
switch 1 15 are. depressed simultaneously," where 75 tor bridge havmg-recti?er'elements. in the respect‘
30»volt range.
tive side arms thereof and all arranged in the
same sense, an actuating circuit connected across
one set of opposed junctions of said bridge and
including sets of terminals to which the second
' each set of opposed bridge junctions, and a, direct
current measuring instrument, and circuit ele
ments connecting said instrument between the
center taps of said resistors.
5. In apparatus for determining the operating
characteristics of a test transformer, the inven
tion as recited in claim 4, in combination with
an additional winding on said energizing trans
former for developing a checking voltage, and
ary windings of said test transformer and of a
standard transformer may be connected in series
opposition, an energizing circuit connected across
the other set of opposed junctions of said bridge
to establish a substantially saturating current
through said modulator bridge, said energizing 10 switch means for connecting said additional
circuit including the secondary winding of an
winding across said bridge in place of said actuat
energizing transformer and. means adjustable to
shift the phase of the voltage input to the bridge
by 90°, a center-tapped resistor connected across
ing circuit.
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