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CROSS-REFERENCE TO RELATED APPLICATION
Certain inventions related to those disclosed in the present application
are disclosed and claimed in copending application Ser. No. 504,404 filed
concurrently by W. Gary and G. R. Taylor, and copending application Ser.
No. 405,198 filed Oct. 10, 1973 by Wardell Gary and Emroy W. Lange, all of
which are assigned to the same assignee as the present application.
BACKGROUND OF THE INVENTION
This invention relates generally to the electrical control systems for
controlling the action of a circuit breaker and it relates specifically to
modular control systems utilizing plug-in modules which are universally
adaptable for use over a wide range of current values.
In the past it has been known to provide circuit breaker control systems
utilizing a multitude or a number of current and voltage sensors to
control functions such as inverse time overload to thereby cause a circuit
breaker to trip. Sometimes a separate circuit breaker is provided for each
function to be controlled. Sometimes it is necessary to provide a
multitude of current sensors each adapted to sense different ranges of
currents or different values of currents or different rates of change of
currents or voltage to in turn supply that information to a logic device
which in turn can cause a certain circuit breaker to trip. Devices of this
kind are described in U.S. Pat. No. 3,713,005 entitled "Circuit Breaker
Including Improved Overcurrent Protective Device" issued on Jan. 23, 1973
to J. C. Engel and assigned to the same assignee as the assignee of the
present invention, and in technical bulletin 980 of June 1972 entitled
"Phase Failure Relays" by the Wilmar Electronics, Inc. of 2103 Border
Avenue, Torrance, California and in a technical bulletin 948-B1 of June
1971, entitled "Overload Relays" by the Furnas Electric Company of
Batavia, Illinois. It would be advantageous if a universal control system
for a circuit breaker could be found which is utilizable over a wide range
of circuit currents and voltage conditions and which is adaptable to
utilize plug-in logic modules to control or cause the circuit breaker to
trip in response to a variety of different kinds of circuit functions.
SUMMARY OF THE INVENTION
In accordance with the invention an electrical circuit protective device is
taught having a sensor means for sensing circuit current in an electrical
circuit and providing an output current related to the circuit current.
There is included a replaceable load resistor means connectable to the
last-mentioned output for converting the current into a voltage the value
of which is variable within a predetermined range regardless of the value
of the circuit current. There is also provided a replaceable module which
is connectable in parallel circuit relationship with the load resistor
means which is capable of initiating a circuit breaker trip function. The
module is operable over the predetermined range of voltage. There is also
provided a circuit breaker trip means which is connected to the circuit
module for opening the electrical circuit when the trip function occurs in
the module.
In another embodiment of the invention, more than one of the previously
described replaceable modules is provided in parallel circuit relationship
with the load resistor means and with each other. The previously described
modules may comprise an inverse time overload module, an instantaneous
overcurrent module, a phase failure module, an underload logic module, a
phase imbalance module, and in another embodiment of the invention a field
test panel or an overload condition indicator, the latter two modules not
having control over the circuit breaker but providing an indication of the
status of the electrical circuit to be controlled.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention reference may be had to the
preferred embodiment exemplary of the invention, shown in the accompanying
drawings in which:
FIG. 1 shows a universal plug-in type control system for a circuit breaker
for a three-phase electrical system;
FIG. 2 shows a system similar to that shown in FIG. 1 but for a one-phase
electrical system;
FIG. 3 shows a circuit block diagram of a portion of the system shown in
FIG. 1;
FIG. 4 shows a curve of the characteristic of a portion of the system shown
in FIG. 3; and
FIG. 5 shows a physical interconnecting plan for the apparatus shown in
FIGS. 1 and 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings and FIG. 1 in particular, a circuit
protective system 10 is shown. The circuit protective system 10 comprises
in this embodiment of the invention a three-phase line having leads,
conductors or lins L1, L2 and L3 which are connected on the right to a
three-phase load and which are connected on the left to a three-phase
source of electrical power. Intermediate to the load and the source of
electrical power is a current sensor 12 and a serially connected circuit
breaker or motor starter appartaus 45. In the embodiment of FIG. 1 a
single current IL is shown flowing in the line L1. It is to be understood
that other currents may and usually do flow in the other lines L2 and L3
and the other currents may be related to the current IL. The choice of
current IL is merely made for the purpose of simplicity of illustration.
There are two output terminals for the current sensor 12, which terminals
are designated 14 and 16. Shown connected to the terminals 14 and 16 is a
load resistor module 18. The load resistor module 18 comprises a resistive
element which is connectable across the terminals 14 and 16 to convert the
current IL into a utilizable voltage V which may be utilized by other
circuit protective means in the apparatus of FIG. 1. Connected in parallel
circuit relationship with the load resistor module 18 may be a long
acceleration module 20, an inverse time overload logic module 22, an
instantaneous overcurrent logic module 24, a phase failure logic module
26, an underload logic module 28, a phase imbalance logic module 30, a
field test panel 32, and a motor in reverse indicator 34 if the load to be
protected includes a motor. Numerous other combinations of logic modules
may be provided in the same parallel circuit relationship as shown with
respect to the elements 20 through 34 of FIG. 1. The remaining elements
would be connected to terminals 38 and 36 for example. It is to be
understood that any of the modules 20 through 34 may be removed or
replaced and other modules may be added provided the parallel circuit
relationship with the load resistor module 18 is maintained. Each of the
previously described modules 22 through 30 for example have an output
terminal which is connectable to a line 40 which in turn is connected to
an output switch 42 which in turn is connected to the previously described
circuit breaker means or circuit interrupter means 45. In the preferred
embodiment of the invention, the field test panel 32 and the motor in
reverse indicator panel 34 have no output to the line 40. In the preferred
embodiment of the invention the voltage V at the output terminals 14 and
16 is proportional to the current IL. If the expected raise of current IL
becomes significantly large a different load resistor may be disposed
across terminals 14 and 16 to make the voltage between the terminals 14
and 16 approximately the same even though the current IL is significantly
larger. The same would apply if the rated current range IL is
significantly lower. This means that the elements 20 through 34 need not
be changed as they are sensitive only to the voltage V. It also means that
the output switch 42 need not be changed. In a typical embodiment of the
invention the long acceleration module 20 will perform a function which
will be described hereinafter. The inverse time overload logic module 22
provides what is typically known as the I.sup.2 t = K function as is well
known in the art. The instantaneous overcurrent logic module 24 performs
the instantaneous tripping function that is well known in the art and
which is related to extremely high values of overload current or short
circuit current. The phase failure logic 26 provides an indication that
one of the phases or lines L1, L2 or L3 has failed and provides adequate
switching in accordance therewith. The underload logic module 28 provides
an indication that the load has dropped below what is considered to be a
safe predetermined value of current IL. The phase imbalance logic module
30 provides an indication and an automatic signal to the output switch 42
if the currents flowing in the lines L1, L2 and L3 become significantly
disproportionate to one another. The field test panel 32 provides an
output indication of current IL and other useful output functions. The
motor in reverse indicator 34 provides a function typified by its name,
namely an indication that motor which may be attached to the three-phase
load is in a reverse wired polarity.
Referring now to FIG. 2 there is another protective device 10' shown for
utilization where there is a single phase or DC load and source. In this
embodiment of the invention there is provided a single phase or DC line
L1' which provides power to a single phase or DC load on the right from a
single phase or DC source on the left. There is also provided a single
contact circuit breaker or motor starter apparatus 45' having a contact A
therein for interrupting the current IL'. The current sensing means 12'
may be the same as shown in FIG. 1. The load resistor module 18' is
different from the load resistor module 18 shown in FIG. 1 if the range of
current IL' is significantly different than the range of current IL shown
in FIG. 1. However, the long acceleration module 20, the inverse time
overload logic module 22, the instantaneous overcurrent logic module 24,
the underload logic module 28, the field test panel 32, and the motor in
reverse indicator 34 are or may be all the same as those corresponding
modules shown in FIG. 1. This demonstrates the versatile use of the
circuit protector apparatus. It will be noted that there is no phase
failure logic module or phase imbalance logic module in this embodiment of
the invention as those functions are typical of polyphase AC electrical
apparatus. It will be also noted that the outputs of the modules 22, 24,
and 28, for example, are connected to the line 40 which in turn is an
input to the output switch 42 which in turn controls the line 44 causing
the circuit breaker 45' to be actuated.
Referring now to FIG. 3, there is shown an embodiment of the invention for
use with a three-phase line having a three-phase supply and controlling a
motor M which is a three-phase load. In this embodiment of the invention
the electrical and electronic elements comprising the current sensor 12,
the load resistor module 18, the inverse time overload module 22, the
output switch 42, the long acceleration module 20 and the circuit breaker
45 are shown in schematic form. Also shown in block diagram form are the
previously described functional blocks 24, 26, 28, 30, 32 and 34 as well
as the interconnecting terminals 38 and 36, the line 40 and the output
line or lines 44. In this case, a current IL flowing in the line L1 is
sensed by a transformer T1 in the current sensor 12. The resistor R1 shown
in the module 18 comprises the load or motor current range determining
resistor previously described. It is across this resistor that the output
voltage V exists.
Resistors R9, R10 and capacitor C1 form the time delay network for the
overload trip switch comprising transistors Q3 and Q4. The timing
capacitor C1 is held at a discharged state until the motor is near an
overload condition by the full load sense switch comprising transistors Q1
and Q2. The trip signal from the transistors Q3 and Q4 is held by the
automatic reset delay network comprising elements C3, R13, and R16. The
overload relay 80 is equipped with manual reset, relay RA1. Relay RA1
operates and is held on to prevent the motor starter 45 from actuating.
The motor starter coil is controlled by the output series switch
comprising SCR Q7 and bridge B1. The output series switch SCR Q7 is
normally biased on by the reset control switch comprising transistors Q5
and Q6. When a trip signal appears, the reset control switch is turned off
for a fixed time period.
The DC voltage proportional to line current IL that appears across R1 will
be referred to in the following circuit description as the "input
voltage".
Resistors R3 and R5 form a voltage divider that presents a fraction of the
input voltage to base resistor R4 of transistor Q1. The input voltage
corresponding to full load current may be 10 volts in a preferred
embodiment of the invention. At input voltages below about 9.5 volts, the
voltage at the emitter of Q1 is at least 0.7 volts above the voltage at
the base thereof. Thus Q1 is biased on. The collector current of
transistor Q1 flows through resistor R6 and into the base of transistor
Q2. Transistor Q2 is therefore biased on, and time delay capacitor C1 is
held to about 0.8 volts above ground.
When the input voltage rises above approximately 9.5 volts, the voltage at
the emitter of transistor Q1 cannot rise above 7.7 volts because the Zener
diode D14 clamps at about 8.4 volts (at the current levels permitted by
series resistor R12). When the voltage at the junction of resistor R4,
resistors R3 and R5 is not sufficiently below this latter value to allow
Q1 to remain on and the collector current of Q1 ceases flowing through
base resistor R6 and into transistor Q2. Thus Q2 turns off, and timing
capacitor C1 begins to charge through resistors R9 and R10. Resistor R7
prevents undesired turn-on of Q2 due to high temperature reverse current
leakage through the collector-base thereof. Diode D7 prevents C1 from
being charged through resistors R12 and R8. Diode D8 prevents C1 from
being robbed of charging current by the otherwise relatively low impedance
path to ground of diode D7, resistor R8 and Zener diode D14.
When the full load sense switch Q1, Q2 turns off, the time delay capacitor
C1 begins to charge through resistors R9 and R10. The rate of charge
depends on the value of the input voltage: the greater the overload
current IL, the faster capacitor C1 will charge. Trip signal switch Q3 and
Q4 uses Zener diode D14 as a reference voltage device. As long as the
voltage at the emitter of Q3 is less than the base voltage thereof, Q3
remains off. Transistor Q4 is also off, and the trip signal (voltage
across R11) is zero. When the voltage at the emitter of Q3 (voltage across
C1) exceeds by 0.7 volts the voltage on the base of Q3, the Q3 begins to
turn on. Base-emitter current through Q4 begins to turn on Q4 and lower
the collector-to-emitter voltage of Q4. The reduced voltage at the
junction of the collector of Q4 and base of Q3 causes Q3 to turn on
harder, thus producing the snap-action switch-on of the transistor device
comprising transistors Q3 and Q4. The energy normally stored in capacitor
C2, which is charged through resistor R12 and diode D9, is dumped or flows
through Q4 by the sudden turn-on thereof. Most of the energy stored in C2
is dumped into two parallel paths: automatic reset delay capacitor C3, and
relay coil RA1. Resistor R11 is relatively high in impedance compared to
the other two parallel paths, but provides a path to ground for Q4 when Q4
is normally off. Diodes D10 and D11 isolate C3 and RA1 from each other.
When a trip signal charges reset delay capacitor C3, the reset control
switch Q5, Q6 is turned off, and remains off until C3 discharges through
reset delay resistors R13 and R16 to a value of about 2 volts or less. The
ouput series SCR, Q7, which is normally gated on is also turned off for
this time period.
Under normal conditions when 110 volts AC control voltage is applied to the
starter coil K, the series SCR Q7 is gated on every half cycle. The full
wave AC voltage (rectified by B1) appears across the anode to cathode of
SCR Q7. When the voltage at the anode of Q7 rises to 2 volts or more,
transistor Q5 turns on, provided the reset delay capacitor C3 is
discharged. The collector current of Q5 flows through the base-emitter of
Q6 and into the gate of SCR Q7. When SCR Q7 turns on, the anode-to-cathode
voltage of Q7 drops to about 1.5 volts, and most of the AC voltage appears
across the starter coil K.
When a trip signal has charged capacitor C3 to at least 3 volts or more,
then at the beginning of the next half cycle, the base-emitter junction of
transistor Q5 is reverse biased and Q5 does not turn on. Thus transistor
Q6 is turned off, and no gate current is supplied to SCR Q7. As the AC
voltage continues to rise, when the voltage at the emitter of Q5 reaches
about 21/2 to 3 volts, light-emitting diode or LED D13 and series diode
D12 conduct. This prevents the voltage at the emitter of Q5 from rising
further, and Q5 thus remains off. During the remaining portion of each
half cycle, the voltage across Q7 continues to rise and then fall. This
provides enough current through R19 and D13 to produce a visible
indication that the overload 80 has caused starter 45 to open or trip. If
the AC control voltage to the starter coil K is removed when the overload
relay 80 trips (as in the case when the starter 45 is operated by a
pushbutton and auxiliary contact on the starter, not shown), there will be
no available voltage to operate the light emitting diode D13. When the
start button is pushed, however, if the overload relay 80 is still in a
tripped condition the LED D13 will turn on and illuminate.
Resistor R15 limits the collector current of Q6 to a reasonably low value,
and resistor R14 prevents undesired turn-on of Q6 due to high temperature
reverse leakage current through the collector-base of Q6. Resistor R17
helps prevent undesired turn-on of SCR Q7 due to high temperature leakage
or transient noise. Resistor R18 and capacitor C4 provide a snubber
network to protect SCR Q7 against actuation thereof by excessive dv/dt.
If the circuit is equipped with a manual reset, then relay coil RA1 is
energized by the current through D12 and D13 and also by the trip signal
through D10. If the voltage to the starter coil K is applied through a
pushbutton and an auxiliary contact of the starter (not shown), the
voltage applied to the SCR Q7 could be removed too soon to energize the
coil RA1 in the event the auxiliary contact operates too quickly. This
condition would cause the reset circuit to operate in the automatic mode,
and the motor M could be restarted in a few minutes by pushing the start
button, not shown (without requiring operation of the reset button). For
this reason RA1 is energized by both the trip signal through D10 and the
current supplied through R19, D13 and D12.
When the relay coil RA1 is actuated, the contacts close and short the gate
of SCR Q7 to the cathode, turning Q7 off. If the reset delay capacitor C3
has discharged, the output series SCR Q7, will turn on again when voltage
is re-applied to the starter coil K. If the manual reset mechanism is
operated before the reset delay network has timed out, the relay RA1
contacts will open, but they will be reclosed by the coil of RA1 if the
start button (not shown) is pushed before the reset delay time had
elapsed. The manual reset mechanism (not shown) must then be operated
again before the start button can actuate the starter 45. If the manual
reset mechanism is operated before the reset delay has timed out, but the
start button is not pushed until after the reset delay time has elapsed,
then the starter 45 will operate. In any event, the starter 45 cannot be
energized until three conditions are met: the manual reset mechanism has
been operated at least once; the reset delay time has expired; and the
start button (not shown) is pushed or actuated.
It can be seen that the trip signal is provided by way of line 40 to the
output module 42 and then by way of lines 44 to the circuit breaker
apparatus 45 where the contacts A, B and C are opened under appropriate
conditions. It can be seen that any of the devices 20, 22, 24, 26, 28 and
30 can provide an output signal which can independently provide a signal
on line 40 to cause tripping.
Referring now to FIG. 4, a plot of percent motor full load current versus
trip time in seconds for the apparatus of FIG. 3 is shown. Under normal
conditions the trip time versus percent motor full load current follows
line 50. However, the utilization of a Zener diode 20 connected between
the terminals 14 and 16 allows for what is generally called a long
acceleration characteristic. This means that a motor or other device which
takes a long period of time to accelerate where overload current such as
IL may therefore exist for a long period of time will not necessarily
cause tripping of the circuit breaker apparatus 45. Other circuit breaker
apparatus not shown and interconnected to other portions of the lines L1,
L2 and L3 will provide protection for severe overload.
Depending upon the characteristics of the Zener diode 20, the time which is
allowed for the acceleration of the motor into a fairly high overload
condition may be varied. As an example, if a Zener diode 20 is chosen
which corresponds to line 52 of FIG. 4, a full 40 seconds of motor
acceleration in the overload range may be allowed without the tripping of
the circuit breaker 45. On the other hand if the Zener diode 20 is chosen
with the characteristic 54 shown in FIG. 4, then a limited acceleration
time of 20 seconds is allowed for the motor to reach speed before a
tripping operation will occur. Also as an example, if the Zener diode 20
is chosen with the characteristic 56 shown in FIG. 4, then only 15 seconds
for acceleration is allowed. The Zener diode 20 can be replaced in the
field according to the overload characteristics of the apparatus being
protected by the system 10" shown in FIG. 3.
Referring now to FIG. 5, the packaging concept utilizing the invention is
shown. In this case the three-phase lines L1, L2 and L3 are shown
connectable to a three-phase load on the right (not shown) and a
three-phase source on the left (not shown). A module 12-42 which comprises
the current sensors 12 and the output switch 42 is provided and
interconnected with the lines L1, L2 and L3. Terminals 40, 16 and 14 are
provided, the functions of which have been described previously with
respect to the other figures. A plug-in module such as 22 which
corresponds to the inverse time overload logic module shown in FIGS. 1, 2
and 3 is shown having plug-in pins interconnectable with the connectors
40, 16 and 14 of the module 12-42. A second plug-in module which may
comprise the instantaneous overcurrent logic module 24 is interconnectable
with other pins 40, 38 and 36 which may be on the back part of the
previously described module 42. As can be seen the plug-in modules 22 and
24 may be disconnected or interplaced with each other. The module 12-42
has a set of output terminals 44 which correspond to the line 44 shown in
FIGS. 1, 2 and 3. To this line may be connected a circuit breaker, not
shown, but which is generally designated as 45 or 45' in FIGS. 1, 2 and 3.
It is to be understood that with respect to the embodiments of this
invention that other modules than those shown in FIGS. 1, 2 and 3 may be
provided at terminals 38 and 36. It is also to be understood that this
circuit protective concept may be utilized with multiphase or direct
current protective apparatus. It is also to be understood that the motor M
shown in FIG. 3 is not limiting. It is also to be understood that the
curves 52, 54 and 56 shown in FIG. 4 are not limiting and that other
operating characteristics may be utilized depending upon the choice of the
Zener diode means 20.
The apparatus taught in this invention has many advantages. One advantage
lies in the fact that the apparatus may be utilized over a wide range of
operating characteristics which may include full rated currents which vary
significantly from apparatus to apparatus. Another advantage lies in the
fact that the apparatus may be changed in the field or reprogrammed in the
field by replacing the load resistor 18. Another advantage lies in the
fact that if any of the operating modules fail, that module may be
replaced without having to replace the entire system. Another advantage
lies in the fact that devices such as motors which may take long periods
of time to reach normal speed after start, may be utilized without causing
an unnecessary tripping of the circuit breaker or motor starter 45 or 45'
if the means 20 shown in FIGS. 1, 2 and 3 is utilized.
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