The system described provides protection for phase sensitive loads from being or remaining connected to ac power lines whenever a phase reversal occurs. It comprises a solid state phase detection circuit, a dc power relay circuit, an ac-to-dc converter for energizing the relay circuit, and a bistable four terminal transducer coupled between the phase detection circuit and the power relay circuit, for controlling both circuits

Wong, W. J.

English

NASA Technical Reports Server

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REPLY TO
ATTN OF:
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.C. 20546
.JAN 21 1974
TOx KSI/Scientific & Technical Information Division
Attention! Miss Winnie M. Morgan \
FROM: GP/Office of Assistant General Counsel for
Patent Matters
SUBJECT} Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI; the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
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Yes /y / No / /
Pursuant to Section 305 (a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words "... with respect to
an invention of ... H
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https://ntrs.nasa.gov/search.jsp?R=19740006843 2020-03-17T14:36:05+00:00Z
United States Patent
Fletcher et al.
[ i n - 3,783,354
[45] Jan. 1, 1974
[54] PHASE PROTECTION SYSTEM FOR AC
POWER LINES
[76] Inventors: James C. Fletcher, Administrator of
the National Aeronautic and Space
Administration with respect to an
invention by; Wing J. Wong, 4054
Pelita Ave., Apt. 2, Los Angeles,
Calif.
[22] Filed: Sept. 29, 1972
[ 2 1 ] Appl. No.: 293,727
[52] U.S. Cl 317/33 SC, 317/43, 317/46,
317/47, 317/48, 307/127
[51] Int. Cl H02h 3/26
[58] Field of Search 317/43,47,48, 33 SC,
317/46; 307/127
[56] References Cited
UNITED STATES PATENTS
3,428,865 2/1969 Opad 317/48
3,213,321
3,495,130
10/1965
2/1970
Dalziel 317/33 SC
Bruner 3 I 7/48
Primary Examiner—J. D. Miller
Assistant Examiner—Harvey Fendelman
Attorney—Marvin J. Marnock et al.
[57] ABSTRACT
A phase protection system is provided for protecting
phase sensitive loads from being or remaining con-
nected to AC power lines whenever a phase reversal
occurs. It comprises a solid state phase detection cir-
cuit, a DC power relay circuit, an AC-to-DC converter
for energizing the relay circuit, and a bi-stable 4-
terrninal transducer coupled between the phase detec-
tion circuit and the power relay circuit, for controlling
both circuits.
5 Claims, 2 Drawing Figures
PATENTED JAN 11974 3,783,354
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3,783,354
1 2
PHASE PROTECTION SYSTEM FOR AC POWER Load L is protected by a phase protection system,
LINES generally designated as 10. System 10 prevents power
.._ . _ ', ,„„ _._ from being applied to load L when one of the phases isORIGIN OF THE INVENTION
 reversed * r ^  Qne of the |jnes A-C js QpPened Qr
The invention described herein was made in the per- 5 shorted (i.e., when a phase is lost). System 10 operates
formance of work under a NASA contract and is sub- independently of and does not require an external
ject to the provisions of Section 305 of the National power source. Throughout the description, the expres-
Aeronautics and Space Act of 1958, Public Law sion "phase reversal" or its equivalent will also include
85-568 (72 Slat. 435; 45 U.S.C. 2457). the case of an open or shorted line (loss of phase).
10 System 10 includes an AC-to-DC converter 12 pref-
BACKGROUND OF THE INVENTION
 erably having three input terminals ,4, 16, ,8> con.
Phase protection circuits for AC power lines are well nected to lines A, B, C, respectively. Converter 12 pro-
known. Such systems are described, for example, in vides a DC voltage to its output terminal 20. Terminals
U.S. Pat. Nos. 3,611,050, 3,536,957, 2,975,334, 14,18,16 are also connected to the input terminals 22,
3,202,877, 3,302,063 and 3,188,522. In the known 15 24, 26, respectively, of a phase detection circuit, gener-
prior art systems, as best exemplified by U.S. Pat. No. a"y designated as 28, having a pair of output terminals
3,611,050, a voltage sensitive relay is first used as the 29 and 30-
phase detection device to then activate a power relay. A DC power relay circuit, generally designated as 32,
The switching by the power relay will prevent AC is provided with a pair of input terminals 34, 36, and a
power from being applied to phase sensitive loads when 20 Pair of outPut terminals 37, 38. Across output termi-
the phase is reversed or when one of the power lines is nals 37' 38 is connected the coil 40 of relay R for con-
opened or shorted. Such known circuits in addition to trollin8 the opening of the relay's terminals ra-re.
being expensive to manufacture also lack in reliability A "-terminal bi-stable transducer, generally desig-
because, among other things, they require two relays. „ nated "* 42'is connected between terminals 29, 30 and25
' terminals 34,36, as shown. Transducer 42 is, therefore,
SUMMARY OF THE INVENTION common to both the phase detection circuit 28 and the
An inexpensive 4-terminal solid state transducer, power relay circuit 32.
such as a vqltage-to-light-to-impedance transducer is GENERAL MODE OF OPERATION OF THE
used to detect the phase reversal as well as to activate
 3Q SYSTEM
the power relay. The transducer is relatively inexpen- „ , , , . , ,.
. . • .. , . . . j .
 u When a phase reversal occurs in the power linessive and is very reliable, at least as compared to a volt- „ _ , .v . . • • - , „ • , , .
. . . , , , . . . . A-C, the phase detection circuit 28 will cause a change
age-sensitive relay. For as long as power exists on at . ' ,K , . . . , *
. . .. . _, . X^~ .in the voltage and phase across its output terminals 29,least one power line, an AC-to-DC converter energizes -„ . _ , • _ , - • _ , , _ -M
., , .
 0/-.r> • • • i_ i_ I 30' A corresponding, drastic, impedance change willthe power relay and an SCR in series with the relay. -is . , , r. . ". . ,,.,.., ~, . .
, r i i_ j- i_u . •" take place between terminals 34, 36. The impedanceIn a preferred embodiment, the phase protection sys- i. • r i • • . i u .
-
 K
. . , , , . change is from nearly an open circuit to nearly a short
tern for detecting a phase loss or reversal comprises a ^^
 A& a resu,t DC current can nQw flov/th h
phase-detection circuit including a light emitting de- ^
 re, ,g coj, 4Q Activation of re, R wi],
vice wh,ch becomes actuated upon the occurrence of
 a,, three fe| terminals and hence
a phase reversal. A power relay, in series with current 40 jjnes ^ g Q
flow control means, responds to the emitted light for
 The AC'.to;DC converter 12 supplies the DC power
opening a normally closed pa.r of relay contacts ,n each
 ri.quired for the operation of power rel R As previ.
power line, thereby protecting a phase sensitive load
 ous,y mentioned, converter 12 has an input adapted for
connected thereto. connection to at least one of lines A-C, but preferably
BRIEF DESCRIPTION OF THE DRAWINGS "*5 to a" three lines
FIG. 1 shows a preferred embodiment of the inven- DETAILED DESCRIPTION OF THE SYSTEM
tion, and Various circuit arrangements can be provided for
FIG. 2 is a table with typical operating values in the
 caiTying out the functions prescribed for the blocks
embodiment shown in FIG. 1. 50
 wjthin system 10.
GENERAL DESCRIPTION OF THE PROTECTION In a Preferred embodiment, the AC-to-DC converter
SYSTEM *^ includes three half-wave rectifiers 50 connected to
terminals 14, 16, 18, respectively, and to a common
FIG. 1 represents a phase-protected, polyphase net- junction 51. Between terminal 51 and the neutral line
work. For simplicity, it is shown to include three power 5S N is connected a relatively large capacitor 52.
lines A, B, C, and a neutral line N. The lines are ener- The phase detector circuit 28 includes resistors 60,
gized by a polyphase, AC source (not shown) operating 61, and a capacitor 62 connected to terminals 26, 24,
at a particular voltage and frequency, say 208 volts, 60 22, respectively. Resistor 60 and capacitor 62 have a
Hz or 400 Hz. Thus, lines A, B, C are generally pow- common junction Y which is connected directly to out-
ered for a particular frequency by voltages A </>„, B <f>b put terminal 30. Between a junction X and output ter-
and C <t>c respectively, where A, B, C are in volts, and minal 29 are connected, in series, a variable resistor 63
0 is the phase angle in degrees. In lines A, B, C, are in- and a resistor 64. The junction X is connected to input
serted, in series, normally closed, relay terminals ra, rb, 22 through a resistor 67. The potential difference be-
rc, respectively. The terminals are controlled by a ^ tween junctions X and Y is EXB.
power relay R. Each of lines A, B, C has a circuit The power relay circuit 32 includes a resistor 70 and
breaker CB. The lines are connected to a phase sensi- a silicon-controlled rectifier (SCR) 71 connected in se-
tive load L. ' ries with and on either side of coil 40. The SCR's anode
3,783,354
is connected to output terminal 38, its cathode is con-
nected to line N, and its gate is connected to terminal
36. Connected in parallel between terminal 36 and line
N is a resistor 72 and a capacitor 73. Between terminals
20 and 34 is connected a resistor 74. 5
The transducer 42 is a voltage-to-light-to-impedance
transducer and includes a photo-conductor 80 and a
"lamp" 81. The transducer is bi-stable with the lamp 81
either ON or OFF. Thus, resistors 72, 74, and photo-
conductor 80 constitute a voltage-divider network. 10
Depending upon the values of the components in the
various circuits, the protection system 10 can be used
on any three-phase source and at any frequency. Sys-
tem 10 can easily be modified, if desired, for a poly-
phase system with more than three phases. 15
DETAILED DESCRIPTION OF OPERATION
A. In the normal or in-phase operation the phase of
line A is the base reference, and the phases of lines B
• & C follow in sequence. 20
By way of example only, for 208 volts AC, 60-Hz
operation, the following component values provide
proper operational results:
Rectifier 50
Res
Res
Res
Res
Res
Res stor 70
Res
stor 60
stor 61
stor 67
stor 64
stor 74
Res stor 63
Capacitor 62
Capacitor 73
Capacitor 52
Capacitor 73
Relay R
SCR
Transducer 42
CB
Load L
1N5061GE
lOOKohms
lOOKohms
lOOKohms
200Kohms
SOOohms
I.SKohms, 5 watts
47.3Kohms, I watt
1 megohm
0.047microfarads
O.I microfarads
0.5 microfarads
0.1 microfarads
P&B PMI7DY 25 amps
2N1598 Motorola
CKI124 Raytheon
25 amps
25 amps
25
30
35
With the above component values and for the voltage
and phase values on lines A-C as indicated in FIG. 2, ._
the "normal" or in-phase potential difference En
between junction X and Y will be 104 volts, with the
phase of the voltage at junction X lagging the voltage
at junction Y by 60°, or EIB= 104 60° VAC.
With Ezy= 104 volts, lamp 81 will be OFF. Conse- 45
quently, the impedance between terminals 34 and 36
will be on the order of 10 megohms, and the SCR will
not "fire." The firing of the SCR is primarily deter-
mined by the proper selection of the values for resistor
60 and capacitor 62.
B. In the out-of-phase operation, the phases.of lines
B & C are reversed. The result is that the potential dif-
ference between X and Y will now be EIU= 275 161°
VAC. Resistor 63 was adjusted so that lamp 81 turns
ON, the resistance of the photoconductor 80 de-
creases, the potential at terminal 36 increases, and the
SCR 71 fires, whereupon heavy current flows through
the relay's coil 40 thereby causing its terminals r0, /•„,
rc to open. In this manner, load L will be protected
from a phase reversal or from an open or short-
circuited power line.
SUMMARY AND ADVANTAGES
It will be appreciated that the common, four-
terminal, transducer 42 'is an inexpensive, solid state
device which is used both for phase detection and for
power relay actuation. Transducer 42 is inherently
more reliable than a voltage-sensitive relay commonly
50
55
60
used as the phase detection element for actuating a
power relay which serves as the switching device.
In other words, in the present invention the SCR-
relay circuit accomplishes the switching function rather
than the phase-detection function. When one of the
power lines A-C is lost or reversed, the phase detection
circuit 28 will cause lamp 81 to light and relay R to di-
rectly open the power lines A-C without the interven-
tion of an auxiliary relay circuit.
Also, the activation of the power relay R is indepen-
dent of an outside power source and the relay circuit
32 will remain energized as long as at least one phase
or power line is "hot."
Although the invention has been described in great
detail and with reference to three-phase operation and
to particular components and values, it will be appreci-
ated that more than three phases can be employed and
other components and values may be used without de-
parting from the scope of the invention, as defined by
the claims appended hereto.
What is claimed is:
1. A phase protection system for detecting a phase
reversal in a polyphase AC power line network includ-
ing:
a phase detection circuit having at least three input
terminals and a pair of output terminals, each input
terminal being adapted for connection to one of
the power lines;
a realy circuit having a pair of input terminals and
comprising: a current control device, a power relay
having relay contacts and a coil connected in series
with said current control device, said coil control-
ling the switching of said contacts which are
adapted for connection to the power lines;
an AC-to-DC converter whose input is adapted for
connection to at least one of said power lines to
provide to its output a DC potential for energizing
said relay circuit;
a four-terminal bi-stable voltage-to-light-to-
impedance transducer, coupled between the out-
put terminals of said detection circuit and the input
terminals to said relay circuit, said transducer
being normally OFF, and
said transducer turning ON upon the detection of
said phase reversal by said phase detection circuit
to thereby energize said coil which activates said
contacts to open said lines, comprising
a first resistor connected to the first of the phase de-
tection circuit's input terminals,
a second resistor connected to the second of its input
terminals,
a first capacitor connected to the third of its input
terminals,
said first resistor and said first capacitor having a
junction Y,
a third resistor connected to the third terminal,
said second resistor and said third resistor having a
junction X,
' a fourth resistor connected between junction X and
a first terminal of said transducer, and
said junction Y being connected to a second terminal
of said transducer.
2. The system of claim 1 wherein said current control
device is a silicon controlled rectifier (SCR).
3. The system of claim 2 wherein said relay circuit
comprises:
a voltage divider circuit connected in series with the
3,783,354
third and fourth terminals of said transducer; and
an RC-network connected between the gate of said
SCR and one of the terminals of said'transducer,
whereby the voltage across said RC network is low
when said power lines are in phase, and said volt- 5
age is increased to a level sufficient to fire the SCR
when the power lines are out of phase.
4. The system of claim 3 wherein,
said AC-to-DC converter includes at least three recti-
fiers, each rectifier being connected between the 10
output of the converter and a power line.
5. A phase protection system for detecting a phase
reversal in a polyphase AC power line network includ-
ing:
a phase detection circuit having at least three input 15
terminals and a pair of output terminals, each input
terminal being adapted for connection to one of
the power lines;
a relay circuit having a pair of input terminals and
comprising: a current control device, a power relay 20
having relay contacts and a coil connected in series
with said current control device, said coil control-
ling the switching of said contacts which are
adapted for connection to the power lines;
an AC-to-DC converter whose input is adapted for 25
connection to at least one of said power lines to
provide to its output a DC potential for energizing
said relay circuit;
a four-terminal bi-stable transducer, coupled be-
tween the output terminals of said detection circuit
and the input terminals to said relay circuit, said
transducer being normally OFF, and
said transducer turning ON upon the detection of
said phase reversal by said phase detection circuit
to thereby energize said coil which activates said
contacts to open said lines,
said phase detection circuit comprising a
first resistor connected to the first of the phase detec-
tion circuit's input terminals,
a second resitor connected to the second of its input
terminals,
a first capacitor connected to the third of its input
terminals,
said first resistor and said first capacitor having a
junction V,
a third resistor connected to the third terminal,
said second resistor and said third resistor having a
junction X,
a fourth resistor connected between junction X and
a first terminal of said transducer, and
said junction Y being connected to a second terminal
of said transducer.
30
35
40
45
50
55
60
65


Phase protection system for ac power lines

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