Power controller enclosure

A power controller (10) for supplying power to a power distribution network (N) in which power from a polyphase source (G) is routed to using equipment (E) connected to the network through the power controller. A plurality of solid-state power devices (82) switch each separate phase of the polyphase power to the equipment. A firing circuit (14) controls gating of the switches to route the power. Fuses (F) are connected between the switches and the using equipment to interrupt power flow to the equipment if excessive current begins to be drawn. A con, roller (20) controls a shutdown sequence employed by the controller to eliminate current spiking at shutdown. The various components are housed in an enclosure (22) which includes a mounting structure (56) for mounting the aforesaid components. A cooling system (26) employs a fan (88) for directing air flow through the mounting structure to cool the components. The circuit breaker and fuse mounting configurations are such as to allow the enclosure to be more compact than previous, similar enclosures so to provide a smaller, cheaper, more versatile power controller installation.

BACKGROUND OF THE INVENTION 
This invention relates to control units for industrial power applications 
in which high voltage, high amperage single or three-phase power is 
supplied to a using system and, more particularly, to an enclosure for the 
power controller and a method of controlling the application of power by 
the enclosure. 
Power controllers are used in industrial applications for example, to 
supply power to machinery, manufacturing equipment, support systems such 
as heating and air conditioning, etc. For a particular installation, the 
controller may handle three-phase voltages of between 208Vac to 600Vac, 
with currents ranging from 50 A to 2500 A. The power controller provides 
the interface between the power supplied by an electrical utility, user 
owned power generating facility, or other supplier, and the electrical 
distribution network being served. The controller functions to supply 
power to using equipment under normal operating conditions, as well as 
interrupt supply of power in the event of overloads or other extraordinary 
circumstances, to prevent damage to the network and the equipment 
connected to it. 
Power controllers typically require large, expensive installations which 
involve numerous switches, sensors, and indicators by which power is 
automatically distributed through the network. The controller, for 
example, includes a silicon controlled rectifier (SCR) type of power 
controller, as is well-known in the art. The controller is preceded by 
either a circuit breaker or an automatic disconnect switch. Also, the 
controller is wired to the circuit breaker or disconnect switch with this 
connection usually requiring between two feet and five feet (0.61 m-1.27 
m) of cabling. There is not a straight run between the circuit breaker or 
switch and the power controller. Rather, to preserve space, the cables are 
bent or folded. However, because of the size and length of the cables, 
even this type of installation takes up considerable space. And, the cost 
of the controller includes the cost required to install the cabling in 
place. 
Most large electrical resistance heaters utilize a three-phase circuit with 
each circuit being individually fused. The SCR type power controller then 
regulates the amount of electricity supplied to the heater. SCR's, as is 
well-known in the art, are gated on to allow current flow in a particular 
direction. Once gated into conduction, the SCR continues conducting until 
current flow in the desired direction stops. In alternating current power 
distribution networks, each SCR must be gated into conduction for each 
half-cycle of the AC input wave form during which current flows to a 
particular phase. The output of the power controller is first connected to 
a power distribution unit, and then to a number of three-phase fuse 
blocks. For example, the output may be wired to six or eight of such 
blocks. Installation of the distribution unit and fuse blocks consumes 
between eight and fifteen square feet (2.9 m.sup.2 -5.5 m.sup.2) of 
enclosure space. This constitutes a substantial volume. In addition to the 
power distribution unit and fuse blocks, the controller also includes a 
firing unit or firing package. This firing package has outputs connected 
to the respective gate input of each SCR. Control or gate inputs for the 
SCR's are supplied as inputs to the circuitry within the firing package. 
The firing package, in turn, produces gating signals supplied to the SCR's 
to gate them into conduction at the proper times. If an overtemperature 
condition occurs, it is desirable to shut down the controller in a 
controlled manner to prevent damage to the using equipment. Also, 
conventional controller designs make it difficult to replace a SCR. 
An additional concern with respect to the supply of power to using 
equipment is the generation of DC components within the system. DC 
current, for example, can damage not only transformers upstream from the 
controller, but also downstream inductive loads. Because of the amount of 
heat generated within an enclosure, the SCR power controllers are either 
air cooled or water cooled. The SCR's are the primary heat generators 
within the enclosure. If air cooled, a fan is mounted on the enclosure to 
blow air over heat sinks on which the SCR's are mounted to remove the heat 
generated by their operation. In standard enclosure designs, the fan is 
installed to one side of the enclosure so it will either pull air into, or 
push air through, the enclosure. For this purpose, a side or back panel of 
the enclosure is formed with a series of louvers to allow appropriate air 
flow. However, this type of cooling arrangement is inefficient. Usually, 
unless additional fans are used to aid air circulation through the 
enclosure, temperature increases of 25.degree. F.-35.degree. F. 
(13.degree. C.-19.degree. C.) within the enclosure may routinely occur. 
Each of the foregoing indicate problems with controller designs which 
either add to the overall cost of the enclosure, render the controller 
unable to perform as efficiently as possible in supplying power to the 
network and equipment connected to it, or both. An improved design of the 
power controller and its installation enclosure would provide for a lower 
cost, more versatile installation assembly. 
SUMMARY OF THE INVENTION 
Among the several objects of the present invention may be noted the 
provision of a controller for use in a power distribution network for 
supplying single-phase, or three-phase power, as appropriate, to using 
equipment connected to the network; the provision of such a controller 
having a compact design so to be less costly to manufacture and assemble, 
and to require less space when installed at a using site; the provision of 
such a controller employing bus bars rather than cabling for connecting 
between a power controller installed in the enclosure and a circuit 
breaker or control switch which controls power flow to the controller; the 
provision of such a controller further to incorporate fuse bars in the 
output of the controller rather than fuse blocks; the provision of such a 
controller in which use of fuse bars requires substantially less space 
(approximately only 10%-15% as much space) within the enclosure as 
conventional fuse blocks; the provision of such an enclosure in which 
components installed therewithin are easily and readily cooled; the 
provision of such an enclosure in which a fan for moving air through the 
enclosure is so situated that the last components over which air is drawn 
prior to being exhausted from the enclosure are those components which 
generate the most heat; the provision of such an controller employing a 
pair of firing packages for controlling power to using equipment; the 
provision of such an enclosure in which one firing package employs a 
reference waveform to ascertain the ratio of power for the time when power 
is supplied to the equipment and the time when it is not supplied during a 
given interval, and the other firing package uses the inverse of the 
waveform for the same purpose whereby power supply to the equipment occurs 
fully throughout the interval but with each firing package supplying power 
for a different portion of the interval; the provision of such a 
controller having a unique shutdown sequence for powering down the 
controller; the provision of such a controller in which the sequence first 
enables the power controller to be rendered inactive prior to opening any 
circuit breakers so the circuit breakers are opened under no load 
conditions thereby eliminating electrical arcing; the provision of such a 
sequence to prolong the useful life of the circuit breakers; the provision 
of such a controller to sense the heat sink temperature of the heat sinks 
on which SCR's of the power controller are mounted, and to initiate the 
unique shutdown sequence if the sensed heat sink temperature exceeds a 
predetermined value; the provision of such a controller further to 
initiate a shutdown sequence if control signals supplied to a firing 
package which gates the SCR's into conduction are found to be out of 
tolerance; the provision of a simplified mount for holding the SCR's in 
place and for facilitating their replacement; the provision of such a 
controller to provide an audible alarm in the event of a shutdown, the 
provision of such a controller to incorporate two separate power 
distribution network controls; and, the provision of such a controller to 
provide both a master and a slave firing package. 
In accordance with the invention, generally stated, a power controller 
supplies power to a power distribution network in which power from a 
polyphase source is routed to using equipment connected to the network 
through the power controller. A plurality of solid-state power devices 
switch each separate phase of the polyphase power to the equipment. A 
firing circuit controls gating of the switches to route the power. Fuses 
are connected between the switches and the using equipment to interrupt 
power flow to the equipment if excessive current begins to be drawn. 
Circuit breakers are connected between the power source and the switch 
means to interrupting flow of current to a piece of using equipment if the 
piece begins drawing excessive current. A controller controls a shutdown 
sequence employed by the controller to eliminate current spiking at 
shutdown. The various components are housed in an enclosure which includes 
a mounting structure for commonly mounting the aforesaid components. A 
cooling system is provided for directing air through the mounting 
structure to cool the components. Other objects and features will be in 
part apparent and in part pointed out hereinafter.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to the drawings, a power distribution network N including a power 
controller 10 of the present invention is shown in FIG. 20. Power 
controller 10 provides the interface between the power supplied by an 
electrical utility G, user owned power generating facility, or other 
source of supply, and electrical equipment E being connected to the 
network. For example, the power controller may be used to supply power to 
one or more industrial heaters. Although only one representational piece 
of equipment E is shown in FIG. 20, it will be understood that more than 
one piece of equipment may be connected to the network. Although described 
in more detail hereinafter, power controller 10 includes a switch means 12 
for muting each separate phase of the polyphase power from source G to the 
using equipment E. A firing means 14 operates to gate the switch means 
into conduction to route the power to the equipment. Fuse means 16 are 
connected between the switch means and the using equipment to interrupt 
power flow to the equipment if the equipment begins drawing excessive 
current. A circuit breaker means 18 is connected between the power source 
and the switch means and interrupts flow of current to the switch means if 
excessive current is drawn by the using equipment. A control means 20 
controls a unique shutdown sequence, as described hereinafter, when a 
shutdown occurs. An enclosure 22 is provided for the various means. The 
enclosure includes a mounting means 24 for mounting commonly the switch 
means, firing means, fuse means, circuit breaker means, and control means. 
Finally, a cooling means 26 is provided for directing air flow through the 
mounting means to cool the aforesaid components. 
Referring to FIGS. 1-3, a first embodiment of enclosure 22 is indicated 
generally 22A. The enclosure includes a rear panel 28, opposed side panels 
30, 32, top and bottom panels 34, 36, and a hinged front panel 38 which 
forms a door for accessing the enclosure. Door 38 attaches to side panel 
30 by a hinge 40 which extends the vertical length of the door. The 
respective panels are of a sheet metal or a suitable plastic material. 
Spaced locking members 42 are attached to the opposite side of the door 
for locking the door in place and preventing inadvertent contact with the 
power controller components. In FIG. 3, three such locking members are 
shown, one at the upper and lower ends of the front panel, and one in the 
middle. A handle 44 attaches to this side of the door for a person to 
swing the door open or shut after it is unlocked. It is a feature of the 
invention that enclosure 22A be substantially smaller than prior 
enclosures. This makes the enclosure more compact to facilitate its 
installation in more locations than was previously possible. Enclosure 22A 
is, for example, 30" (76.2 cm) wide, 60" (152.4 cm) high, and 12" (30.5 
cm) deep. Further, the enclosure is a lighter weight enclosure than 
previous models and cheaper to manufacture. Because of its compact size 
and light weight, enclosure 22A can be wall mounted. For this purpose, 
mounting plates 46 attach at the upper end of the rear panel, and mounting 
plates 48 at the lower end thereof. The plates 46 have screw holes or bolt 
holes 50 for mounting the enclosure; while, the plates 48 have slots 52 
for the same purpose. 
Referring to FIG. 2, a power controller assembly is indicated generally 54. 
The assembly is shown in more detail in FIGS. 9A-12 and comprises mounting 
means for mounting switch means 12, firing means 14, fuse means 16, 
circuit breaker 18, and control means 20. In FIG. 10, the mounting means 
is shown to comprise a generally U-shaped frame 56 having opposed legs 
58a, 58b, and a base or top 60. A circuit board 62 is mounted on the 
outside of plate 60. This circuit board includes a master firing package 
64 (see FIG. 7) and other control electronics. A cover plate 66 is 
installed over the circuit board. L-shaped flanges 68 attach to legs 58a, 
58b of the flange for mounting the frame to rear panel 28 of the 
enclosure. When installed in the enclosure, as shown in FIG. 2, the power 
controller assembly is oriented such that the circuit means extends from 
the top of the assembly, and the fuse means from the bottom thereof. For 
safety of personnel gaining access to the inside of the enclosure, a 
plexiglass or similar type of clear shield or cover H is installed over 
the outer face of the power controller assembly, fuse means, and circuit 
breaker means. 
Power lines L1-L3 for three-phase power supplied by source G are routed 
into enclosure 22A through an opening 70 in the top of the enclosure. The 
power lines are terminated at one side of a circuit breaker 72a (see FIG. 
2) or 72b (see FIGS. 9A and 10). These circuit breakers are, for example, 
1200 A circuit breakers and comprise part of circuit breaker means 18. 
Either circuit breaker incorporates an ON/OFF or power disconnect switch 
74 which is operable by control means 20 to open the circuit breakers as 
described hereinafter. Once power to the using equipment has been 
disconnected, switch 74 is manually reset to reconnect the power. Means 18 
further includes electrical connectors 76a-76c for connecting each phase 
of the three-phase power input through the circuit breaker to power 
controller assembly 54. Each connector comprises a flat plate type 
electrical connector. In FIG. 2, the power lines L1-L3 on the output side 
of the circuit breaker are respectively terminated to one of the 
connectors 76a-76c. In FIGS. 9A and 10, each power output line from the 
circuit breaker comprises a bus bar 78. A middle bus bar 78b comprises a 
flat bus bar which electrically connects with connector 76b. The 
respective end bus bars 78a, 78c each include a first L-shaped flat bus 
bar section 80a, an intermediate flat plate section 80b, and a second 
L-shaped bus bar section 80c which electrically connects with the 
respective connectors 76a, 76c. The use of the three segment bus bar 
construction for two of the three phases allows circuit breaker 72b to 
abut against the rear enclosure panel 28 when power controller assembly 
54, to which the circuit breaker is both mechanically and electrically 
attached, is installed in the enclosure. 
Switch means 12 includes a plurality of solid state power devices which, 
when gated into conduction, allow current flow to the using equipment. In 
FIGS. 7, 10, and 20, these solid state devices are shown to be silicon 
controlled rectifiers (SCR's) 82a-82d. Two SCR's 82a, 82b are connected in 
inverse parallel for one phase line; and the other two SCR's 82c, 82d are 
connected in inverse parallel for a second phase line. There are no SCR's 
or other solid state power control devices associated with the third phase 
line. The SCR's are used because they can be cycled faster than other 
types of switches. A contactor type switch can be cycled, for example, at 
a rate of three times per minute. SCR's 82a-8d can be cycled once per 
second or faster. By using SCR's instead of mechanical switches such as 
contactors, power controller 10 can modulate small amounts of power to a 
load. In doing so, it allows closer temperature control than is available 
with these other types of switches. Gating of the SCR's is via the 
circuitry incorporated in the master firing package 64 of firing means 14. 
In conventional power controllers, the circuit breakers are wired to the 
solid state switches. The circuit breaker are supplied with connectors for 
this power wiring. In large power prior art controllers, several square 
feet of enclosure space is required for bending this wiring so proper 
electrical connections can be made. With enclosure 22 of the present 
invention, and the power controller assembly and circuit breaker means, as 
described, this wiring, and the space required to accommodate it are 
eliminated altogether, or substantially reduced. This enables the 
enclosure to be substantially smaller than conventional enclosures. 
Each of the SCR's 82 is separately mounted on a heat sink 84 one of which 
is shown in FIG. 10. Each heat sink is sized so it can be installed 
between the legs 58a, 58b of frame 56. Further, each heat sink has four 
sections 86, one of which is formed along each side of the heat sink for 
distributing the heat generated by operation of the SCR. An open space is 
formed between the various sections 86 of the heat sink. A fan 88 of 
cooling means 26 is installed at one end of the power controller assembly. 
The fan draws air through a channel formed by the sides of frame 56. Since 
the SCR's are mounted on their heat sinks in this channel, the circulating 
air in the enclosure is drawn directly through the channel immediately 
before being exhausted from the enclosure. The resultant cooling provided 
by fan 88 allows the SCR's to operate at higher currents than otherwise 
would be possible. 
Next, fuse means 16 includes a plurality of fuse bars 90a-90c through which 
power is distributed to individual heaters or other pieces of using 
equipment. Most large electric resistance heaters, or similar equipment, 
consist of several three-phase circuits. These circuits typically are 
individually fused. When a power controller 10 is used to regulate power 
to this equipment, the controller output is provided to a power 
distribution unit including the fuse bars. A fuse bar 90a is connected to 
the SCR circuit comprising SCR's 82a, 82b. Similarly, a fuse bar 90c is 
connected to the SCR circuit comprising SCR's 82c, 82d. A fuse bar 90b is 
directly connected to circuit breaker bus bar 76b. Each fuse bar has an 
associated fuse mounting assembly 92 for installing individual fuses F for 
a particular heater or other piece of equipment. Each assembly 92 includes 
a pair of spaced posts 92a, 92b. The posts are separated from each other 
by a spacer 94. Each fuse F is mounted on an assembly 92 between 
respective posts 92a, 92b. The input line to the equipment then has an 
in-line fuse. Each assembly 92 can accommodate up to ten fuses F. If 
enclosure 22 is made deeper than 12" (30.5 cm), the posts can be longer 
and more fuses can be accommodated. 
The provision of fuse means 16 as described herein above greatly reduces 
the amount of enclosure space required to properly fuse the equipment 
supplied power through controller 10. Use of the fuse bar construction 
saves up to 85%-90% of the space previously required for fusing, 
substantially reducing both enclosure size and cost. 
Cooling means 26, as noted, includes a fan 88. The fan is enclosed in a 
shroud or housing 96 located at one end of power controller assembly 54. 
Respective side panels 30, 32 of the enclosure each have openings 98 
formed toward their upper ends, each opening being covered by a grating 
100 attached to the respective side panel. A circular opening 102 is 
additionally formed in side panel 30 adjacent the location of fan 88 when 
the power control assembly is mounted in enclosure 22A. The outer end of 
housing 96 has a circumferentially extending mounting flange 104 which has 
spaced openings for attaching the housing to panel 30 using screws 106. 
Flange 104 abuts against the inside wall of side panel 30. The location of 
fan 88 allows circulating air drawn into the enclosure through openings 98 
to be drawn over the heat sinks 84 on which the SCR's are mounted. The fan 
provides a forced air flow through the channel portion of frame 56 to 
ensure heat is extracted from the heat sinks and a lower operating 
temperature for the SCR's is provided. In conventional air cooled power 
controllers, the fan is mounted such that air is forced over, rather-than 
drawn over, the heat sinks. Cooling means 26 is a more efficient cooling 
means than those previously used. 
Referring again to FIG. 10, the power controller further includes a holding 
means 110 for holding the bolts of SCR clamps in place so they cannot 
rotate and drop out when the top of the clamps and the top of a heat sink 
are removed to replace an SCR. This makes replacement of a failed or 
faulty unit much simpler than would otherwise be possible. 
Referring to FIGS. 4-6, a second embodiment 22B of the enclosure of the 
present invention is shown. This enclosure includes a rear panel 128, 
opposed side panels, 130, 132, top and bottom panels 134, 136, and a pair 
of hinged front panels 138a, 138b forming access doors for the enclosure. 
Door 138a is attached to side panel 130 by a hinge 140a, and door 138b to 
side panel 132 by a hinge 140b. Door 138b has a handle 142 for opening the 
door. Handle 142 has a lock for preventing unauthorized access to the 
power controllers housed in the enclosure. Because of its weight, 
enclosure 22B is designed to rest on a floor rather than being wall 
mounted. For this purpose, the enclosure has legs 44 on each side to 
support it. Eyebolts 146 are fitted into top panel 134, on opposites of 
the enclosure, to facilitate lifting and moving of the enclosure. And, a 
plate 148 attached to the upper end of side panel 132 has a grounding 
connection 150 for grounding the enclosure. Enclosure 22B is designed to 
house two power controller assemblies 54 and its dimensions are 
accordingly, for example, 60" (152.4 cm) wide, 60" (152.4 cm) high, and 
12" (30.5 cm) deep. Thus, although enclosure 22B is larger than enclosure 
22A, the enclosure is still a more compact unit than comparable previous 
units. As such, it is also a lighter weight and cheaper to manufacture 
enclosure. 
Referring to FIG. 5, enclosure 22B is provided with two power control 
assemblies 154a, 154b installed in a side-by-side configuration within the 
enclosure. Each assembly is similar to the assembly 54 as shown in FIGS. 
9A-12 and described herein above. Accordingly, these power controller 
assemblies are not described in detail. Again, each assembly includes a 
frame 56 for mounting the SCR's 82 and their associated heat sinks 84, a 
circuit board 62 including a master firing package 64, circuit breaker 
means 18, and fuse means 16. Each unit 154 shown in FIG. 5 has its cover 
plate 66 installed. Also, a shield H', which is a clear plexiglass shield, 
covers both assemblies to protect personnel having access to the 
enclosure. The embodiment of enclosure 22B is supplied with power over two 
separate sets of power lines, power lines L1-L3 which supply power to 
using equipment through power control assembly 154a, and power lines L4-L6 
for the three-phase power supplied through power control assembly 154b. 
When used with industrial heating equipment, the power supplied through 
the controller is typically 480V three-phase power. The power lines 
terminate at one side of respective circuit breakers 172a, 172b which are 
again, 1200 A circuit breakers, for example. Each circuit breaker unit 
includes a power disconnect switch 174a, or 174b operable by control means 
20 of the respective firing package. The routing of power through the 
circuit breakers and the fuses is as previously described. Again, each of 
the respective fuse bars 92 can accommodate up to ten separate fuses F. 
Each power control assembly 154 includes a cooling means 26 having a fan 
88. Because the power controller assemblies are installed side-by-side, 
the fan 88 in one assembly is oppositely installed from that in the other 
assembly so the respective fans are located adjacent a side panel of the 
enclosure. The respective fans are enclosed in housings 196. The 
respective side panels 130, 132 of the enclosure each have openings 198 
formed therein, panel 130 having upper and lower openings 198a, 198b, and 
panel 132 openings 198c, 198d. Each opening is covered by a grating 200 
attached to the respective side panel. A circular opening 202 is also 
formed in each side panel 130, 132 adjacent the location of the fan 88 
when the respective power control assemblies are mounted in enclosure 22B. 
Housing 196 again has a circumferentially extending mounting flange 204 
which abuts against the inside wall of the side panels. In this 
embodiment, circulating air is drawn into the enclosure through the 
openings 198. The respective fans 88 draw the air over the heat sinks in 
each power control assembly 154 on which the respective SCR's are mounted. 
The forced air flow through the channel portion of each control assembly 
frame 56 extracts heat from the heat sinks and lowers the operating 
temperature for the SCR's. 
Referring to FIG. 7, the firing and control circuits comprising means 14 
and 20 are shown to include the master firing package 64, a step-down 
transformer ST for providing a single-phase 115Vac-120Vac input to the 
firing package, and switches and sensors for use by the control means to 
control operation of the power controller. Transformer ST is connected 
across input lines L2-L3. A status light LT1 is connected across lines L1 
and L2 to provide a visual indication of when power is supplied to 
controller 10. As shown in FIG. 1, status light LT1 is located on door 
panel 38 of enclosure 22A. Additional status lights LT2-LT4 are also 
installed on door panel 38 for easy visibility to one monitoring the 
status of the power controller's operation. Light LT2 is a status light 
indicating when the controller power is "ON". This light is connected 
across the secondary side of transformer ST. Light LT3 is a status light 
for the equipment powered using power controller 10. If the operating 
temperature of the equipment exceeds a preset temperature limit, this will 
trigger an equipment power-down. Light LT3 is illuminated if this occurs. 
Light LT4 is a status light indicating whether or not the temperature of 
the heat sinks 84 are within an acceptable limit. If, for example, a fan 
88 fails, or an air discharge opening from the enclosure becomes blocked, 
air circulation through the enclosure would cease, and the heat sink 
temperature would rise to unacceptable levels, possibly damaging the SCR's 
82. To prevent this, there is a shut-down of the controller if the heat 
sink temperature exceeds the limit; and, status light LT4 provides an 
indication if this happens. Both status lights LT3 and LT4 are connected 
between the secondary of transformer ST and firing package 64. A relay RY1 
is associated with the heat sink monitoring. If illuminating light LT4 is 
through the relay, status light LT3 is similarly controlled through a 
relay RY2. The shut-down sequence implemented using master firing package 
64 is described hereinafter. 
Temperature switches TS1-TS5 for a heater and other equipment to which 
power controller 10 is connected and whose operating condition is 
monitored are mounted on front panel 38 of the enclosure. Each temperature 
switch is connected in parallel across the secondary of transformer ST. 
Further, each switch is a relay type switch whose operation is controlled 
by the sensed temperature of the element monitored by the switch. All the 
switches are commonly grounded. Switch TS1 is, for example, an optional 
temperature indicating switch having an associated sensor S1 for sensing 
temperatures in a range between 0.degree. C.-500.degree. C. (32.degree. 
F.-932.degree. F.). The other four switches also have associated sensors 
S2-S5, and are capable of monitoring temperatures in a range of 0.degree. 
C.-1100.degree. C. (32.degree. F.-2012.degree. F.). Each of the 
temperature switches TS2-TS5 is independently set to an upper temperature 
limit above which the equipment may not operate. Further, each switch 
includes its own separate reset switch to reset the sensing unit back to 
its initial sensing condition after a shut-down. 
Temperature switch TS1 supplies an output to master firing package 64. The 
other temperature switches TS2-TS5 have a series connected path GP with 
the firing package. This common path is maintained by a set of electrical 
contacts within each switch. If an overtemperature condition is sensed by 
any of these elements, this path is opened by the contacts, an audible 
alarm 114 is sounded, and the power controller is shut down. After the 
over temperature condition which causes a shut-down is corrected, a manual 
push-button PB located on from panel 38 is pushed. This resets the sensor 
network and the contacts by which the common path is maintained back to 
their original position. An interlocking door switch 116 on front panel 38 
is operable by a user to turn the controller "ON", or "OFF", or lock the 
controller in a "RESET" condition. 
In FIG. 8, dual master firing packages 64a, 64b are supplied power through 
step-down transformer ST. Again, this transformer provides single-phase 
voltage to the firing packages, the switches and sensors used by the 
control means to control operation of the power controller. Transformer ST 
is connected across input lines L2-L3 for the one side of the controller. 
It will be understood it could also be connected across lines L5-L6, for 
example. Respective status lights LT5A and LT5B are connected across lines 
L1, L2 and L4, L5 to provide a visual indication when the disconnect 
switches are closed. Both status lights are located on door panel 138a of 
enclosure 22B, as is a power control indicator status light LT6. 
Additional status lights LT7-LT10 are also installed on panel 138a. Light 
LT6 is a status light indicating when the controller power is "ON". This 
light is connected across the secondary side of transformer ST. Light LT7 
is a status light for the heater or other equipment powered by the 
controller. Lights LT8 and LT9 are respective status lights for heat sink 
temperature. Light LT8 is for the heat sinks 84 of firing package 164a, 
and light LT9 is for the heat sinks of package 164b. Again, both status 
lights are connected between the secondary of transformer ST and their 
respective firing packages 164. Each firing package has an associated 
relay RY3a, RY3b associated with the heat sink monitoring to illuminate 
status light LT8 or LT9 if an over temperature condition occurs. Finally, 
a status light LT10 is similarly controlled through a relay RY4 of firing 
package 164a. This status light monitors whether or not a control signal 
of the controller remains within a defined upper or lower limit. 
Typically, the control signal used by the firing package is a 4 ma-20 ma 
signal. This signal can be monitored so that if the amplitude exceeds 25 
ma., for example, or falls below 1 ma., for example, status light LT 10 is 
illuminated and an alarm sounded. 
This embodiment of the controller further includes temperature switches 
TS6-TS7 for a heater and other equipment to which the power controller is 
connected and whose operating condition is monitored. Both temperature 
switches are connected in parallel across the secondary of transformer ST. 
As in the other embodiment, both switches are relay type switches each of 
whose operation is controlled by the sensed temperature of the element 
monitored by the switch. Switch TS6 is a temperature indicating switch 
having an associated sensor S6. Switch TS7 has an associated sensor S7. 
Switch TS7 is settable to an upper temperature limit above which the 
heater may not operate. Both switches are separately operable to reset the 
controller back to an initial condition after a shut-down. Temperature 
switch TS6 supplies its output to firing package 164a. The common path GP 
established by appropriate electrical contacts within temperature switch 
TS7 is a parallel ground path to both firing packages. Again, if an 
overtemperature condition is sensed an audible alarm can be sounded when 
an overtemperature condition is sensed. 
Operation of the firing package 64, and packages 164a, 164b is such that 
they gate the SCR's 82 associated with package on at an appropriate time. 
This conduction control allows current flow through lines L1 and L3, or L4 
and L6 to be in accordance with an established control scheme for the 
controller. Since there are no SCR's associated with lines L2 or L5, these 
two lines are constantly available for current flow. The control means 20 
portion of the firing package supplies control signals to the firing means 
14 portion thereof. Firing means 14, in response thereto, supplies gating 
signals to the gate input of the appropriate SCR, gating it into 
conduction. This gating signal is an intermittent signal because once 
gated into conduction, the SCR continues to conduct until the current flow 
goes to zero. It is a unique feature of the present invention to utilize a 
shut-down sequence by which operation of the power controller serves to 
extend the operating life of the circuit breakers. When an external alarm 
goes off; i.e., the ground path GP is interrupted by the contact opening 
in one of the switches TS2-TS5, or TS7, control means 20 ceases supplying 
control signals to firing means 14. In turn, firing means 14 ceases 
supplying gating signals to the SCR's. This almost immediately stops 
supply of power to a heater or other piece of using equipment. That is, 
the gating signals cease in approximately 8.3 msec. A few milliseconds 
thereafter, a control signal is supplied from the control means to the 
disconnect switch 74, or 174a, 174b, to trip the circuit breakers 72 and 
disconnect the power flow from the source to the using equipment. The 
disconnect switch includes a shunt trip solenoid (not shown) which 
provides this function. Since the SCR's are solid state power devices, 
they operate in an arcless manner. By timing the opening of the shunt trip 
solenoid, so there is no load on the controller, there is no arcing when 
the circuit breakers open. This extends the life of the circuit breakers. 
Since the shut-down sequence is initiated whenever a contact in the ground 
path circuit changes state, the sequence is initiated regardless of 
whether a heater overtemperature condition occurs, or a heat sink 
overtemperature condition, etc. This shut-down procedure is also initiated 
when an operator of the controller manually turns the controller "OFF" 
using switch 116. 
With respect to the wiring configuration of FIG. 8, the two firing packages 
64a, 64b are used when the industrial equipment, such as a heater, which 
is connected to the heater is so large as to require both power control 
assemblies to provide power to it. In this circumstance, one of the 
packages, package 64a functions as a master firing package; while the 
other firing package 64b operates as a slave package. Operation of the 
firing packages is such that supply of power to the using equipment is 
alternated between the two firing packages in a unique manner. 
Master firing package 64A first generates a triangular waveform as shown in 
FIG. 13A. The waveform has a peak amplitude, for example, of +10V or -10V 
with a period of approximately one second. As shown in FIG. 14A, the 
triangular waveform is used to generate a proportional control signal as 
shown in FIG. 14B. That is, the portion of the triangular waveform period 
the amplitude exceeds zero, represents an "ON" portion of the control 
signal, with the remainder of the period representing an "OFF" portion of 
the signal. In FIG. 14A, the triangular waveform represents a condition 
where approximately 50% of the available controller power needs to be 
supplied to the heater, for example, for it to maintain a desired 
temperature output. Accordingly, the triangular waveform exceeds 0V. 50% 
of the period. In FIG. 14B, a proportional control signal derived by the 
master firing package 64a from the triangular waveshape is shown to have a 
"1" or "ON" state 50% of each time interval and to be in a "0" or "OFF" 
state the remainder of the time. The proportional control signal is 
supplied by control means 20 to firing means 14. In response, the firing 
means develops the gating signals supplied to the respective SCR's to gate 
them into conduction. 
Conditioning of the triangular waveform to produce the control signal with 
the requisite ON/OFF ratio is shown in FIG. 15. Here, a comparator 200 of 
control means 20 is supplied the triangular waveform at its inverting 
input. The input to the non-inverting input of the comparator is a control 
input which has a range, for example of +1Vdc to -1Vdc. For the triangular 
waveshape input shown at the inverting input of the comparator, if the 
control input has a value of 0Vdc (12 ma), for example, the resulting 
binary or time proportional output from the comparator is a signal whose 
proportionality is 50% ON/50% OFF. If the control signal input is, for 
example, at a value of 5Vdc (16 ma), the proportionality may be 75% ON/25% 
OFF. Where, as shown in FIG. 8, both a master and slave firing package are 
used to provide power to using equipment, the triangular signal developed 
by master firing package 64a, and the resulting proportionality signal 
derived therefrom, are also supplied to slave firing package 64b. However, 
for firing control purposes, these signals are now inverted for use by the 
slave package by an inversion means indicated generally 190. This is shown 
in FIG. 14, where the triangular waveform and derived proportionality 
signal for package 64a are shown in FIGS. 14A and 14B, and the inverted 
waveform and proportionality signal for package 64b are shown in FIGS. 14C 
and 14D. This method of equipment power control is advantageous in that 
power usage is smoother than otherwise would be possible. The inversion of 
the control signals allows the firing packages to share the power control 
on an easy to implement basis which is readily tied to the equipment's 
power usage. Effecting this inverse proportionality involves inverting the 
triangular waveform generated in the master firing package and supplying 
it to the slave package; or, supplying the waveform from the master firing 
package to the slave package and inverting it there. In either 
circumstance, the inverted triangular waveform is supplied to a comparator 
200 within the slave package to produce the inverse proportionality 
signal. 
The time proportional signal developed in either the master or slave firing 
package is used with a synchronization or sync signal to drive a flip-flop 
202. The flip-flop, in turn, drives a transistor 204. The transistor 
output switches an optical coupler 206 "ON" and "OFF" to provide a gating 
input to an SCR 82. In FIG. 8, a simplified schematic illustrating this 
circuitry is shown with respect to master firing package 64a. Master 
firing package 64a, as shown in FIG. 7, and slave firing package 64b, have 
similar circuitry to that described. It will be understood that the 
circuitry as described is for only one phase of the three-phase input to 
the controller. The circuitry for the other two phases is similar to that 
described. A sync pulse generator indicated generally 208 in FIG. 16 is 
provided a 24Vac input from step-down transformer ST. The transformer 
output is provided through a first voltage divider network comprising 
resistors R1, R2, a 12V zener diode Z1 which regulates the input voltage, 
and an input resistor R3 to the non-inverting input of a comparator 210. 
Meanwhile, unregulated 24Vdc voltage is provided to the inverting input of 
the comparator through a second voltage divider network comprising 
resistors R4 and R5. These resistors provide a 3:1 division ratio so the 
comparator input is 6Vdc. The comparator also has a feedback resistor R6 
between its output and the non-inverting input. When the input voltage at 
the non-inverting input of the comparator reaches 6V, the comparator 
output switches states. This will occur approximately 30.degree. into the 
interval of the sine wave input to the comparator as shown in FIG. 17. 
The comparator output will remain in this state until the ac voltage input 
falls back below 6v. This occurs at a point 150.degree. into the interval. 
Thus, the comparator sync output signal has a period of 120.degree.. The 
30.degree. point is chosen because it represents the maximum crossover 
point for all three phases of the power input to controller 10. Also, the 
point occurs at a relatively steep portion of the sine wave curve. This is 
important because it provides a safety margin with respect to sequencing 
the respective phases through gating the various SCR's. Further in this 
regard, the unregulated dc voltage is used for input comparison with the 
ac input to comparator 210 because its magnitude will vary with that of 
the regulated ac input. This helps to maintain the 30.degree. firing point 
as much as possible. 
In FIG. 19, the time proportional control signal is supplied to the D input 
of the flip-flop 202. The sync signal output from sync signal generator 
208 is supplied to the clock or C input of the flip-flop. The positive 
going edge of the sync signal turns the Q output of the flip-flop "ON", if 
a signal element of the time proportional control signal is present at the 
flip-flop's D input at this time. If a control signal element is absent, 
the Q output is switched "OFF". As a result, only full cycles of power are 
supplied to the using equipment connected to controller 10. This is as 
shown with the signal composite in FIG. 18 which represents all three 
phases of the power input to the equipment. Zero crossover trigger 
circuits which include the optical coupler 206 gate the respective SCR's 
82 into conduction at the first zero crossover which occurs after the Q 
output of flip-flop 202 is switched "ON". After an SCR 82 is conducting, 
it remain in conduction until the current flow through the SCR reaches 
zero. Then, if there is no voltage at the gate input to the SCR, it 
switches to a non-conducting state. Thereafter, only a subsequent signal 
to its gate input will bring it back into conduction. 
What has been described is a controller for use in a power distribution 
network for supplying single-phase, or three-phase, as appropriate, to 
using equipment connected to the network. The controller has a compact 
design which makes it less costly to manufacture and assemble. It also 
requires less space when installed. To accomplish this, the controller 
employs bus bars rather than cabling for connecting between a power 
controller installed in the enclosure and circuit breakers or control 
switches which control power flow to the controller. Bus bars are cheaper 
than cables and require less labor to install. Further, the controller 
incorporates fuse bars on its distribution side rather than fuse blocks. 
Fuse bars are not only readily installed, but also cheaper than fuse 
blocks. Fuse bars require only 10%-15% as much space within the enclosure 
as conventional fuse blocks and the connecting wiring. Components 
installed within the enclosure are easily and readily cooled by a fan 
which is so situated that the last components over which air is drawn 
prior to being exhausted from the enclosure are those components which 
generate the most heat. There is a unique shutdown sequence provided for 
powering down the controller. This sequence enables the power controller 
to be rendered inactive prior to opening any circuit breakers so the 
circuit breakers are opened under no load conditions. This eliminates 
electrical arcing. Using the sequence prolongs the useful life of the 
circuit breakers. The controller senses the temperature of heat sinks on 
which SCR's of the power controller are mounted, and initiates the 
shutdown sequence if the sensed heat sink temperature exceeds a 
predetermined value. Shutdown is also initiated if control signals 
supplied to a firing package which gates the SCR's into conduction are 
found to be out of tolerance. An audible alarm sounds in the event of a 
shutdown. Finally, the controller incorporates two separate power 
distribution network controls and incorporates both a master and a slave 
firing package. 
In view of the foregoing, it will be seen that the several objects of the 
invention are achieved and other advantageous results are obtained. 
As various changes could be made in the above constructions without 
departing from the scope of the invention, it is intended that all the 
matter contained in the above description or shown in the accompanying 
drawings shall be interpreted as illustrative and not in a limiting sense.