The U.S. Army Research Laboratory, Fort Monmouth, NJ, has developed and is installing two 3.3 MW high speed solid state circuit breakers at the Army's Pulse Power Center. These circuit breakers will interrupt 4160V three phase power mains in no more than 300 microseconds, two orders of magnitude faster than conventional mechanical contact type circuit breakers. These circuit breakers utilize Gate Turnoff Thyristors (GTO's) and are currently utility type devices using air cooling in an air conditioned enclosure. Future refinements include liquid cooling, either water or two phase organic coolant, and more advanced semiconductors. Each of these refinements promises a more compact, more reliable unit

Podlesak, Thomas F.

English

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HIGH SPEED SOLID STATE CIRCUIT BREAKER 
Thomas F. Podlesak 
Electronics Engineer 
U.S. Army Research Laboratory, Electronics and Power Sources 
Directorate 
Pulse Power Components Branch 
ATTN: AMSRL-EP-MC(Pod1esak) 
Fort Monmouth, NJ 07703-5601 
ABSTRACT 
The U.S. Army Research Laboratory, Fort Monmouth, NJ, has 
developed and is installing two 3.3 MW high speed solid state 
circuit breakers at the Army's Pulse Power Center. These circuit 
breakers will interrupt 4160V three phase power mains in no more 
than 300 microseconds, two orders of magnitude faster than 
conventional mechanical contact type circuit breakers. These 
circuit breakers utilize Gate Turnoff Thyristors (GTOs) and are 
currently utility type devices using air cooling in an air 
conditioned enclosure. Future refinements include liquid 
cooling, either water or two phase organic coolant, and more 
advanced semiconductors. Each of these refinements promises a 
more compact, more reliable unit. 
INTRODUCTION 
The U.S. Army Pulse Power Center, located at Fort Monmsuth, 
NJ, has the unique mission of performing research, development 
and benchmark testing of megawatt class power components and 
subsystems. The Center, shown in Figure 1, has an installed 
continuous capability of 30 MVA, continuous liquid cooling sf 10 
Megawatts and is shielded to the DoD TEMPEST standard. This 
facility is ideally suited to the stressing of high powered 
components to the limits of their ability. 
When subjected to the extreme conditions of benchmark 
testing, components and subsystems are very likely to undergo a 
fault condition. The amount of available power makes the 
destruction of the component under these conditions very 
probable. The incident rate of component destruction, which can 
be hazardous to equipment and personnel, is high. In the past, 
the component under test was protected by standard, mechanical, 
utility circuit breakers, which clear in tens of milliseconds, 
This length of time, although considered very short under normal 
conditions, can be an eternity under dangerous fault conditions, 
It was therefore determined that a faster fault protection device 
was needed. 
https://ntrs.nasa.gov/search.jsp?R=19930016409 2020-03-24T07:27:38+00:00Z
Figure 1: The U.S. Army Pulse Power Center at Fort Monmouth, NJ 
The decision was made to install a solid state based 
circuit breaker in the 4160 Volt utility mains leading into the 
Pulse Power Center's dual 3.3 Megawatt power supply. This supply 
consists of two independent 3.3 Megawatt power supplies, which 
may operated together to form one 6.6 Megawatt power supply. 
This a most versatile unit and is used extensively for 
experiments at the Pulse Power Center. As part of its ongoing 
mission in high power components, extensive work has be done at 
the Pulse Power Center in the area of high power solid state 
switching. A series of experiments established the applicability 
of operating Gate Turnoff Thyristors (GTOs) in series to produce 
a repetitive opening and closing switch, capable of operating at 
voltages that were much in excess of the rating of an individual 
device, Additional experimental work has been conducted 
utilizing more advanced semiconductors, which promise more 
efficient operation. The knowledge of the capabilities of these 
devices lead to the conception of a solid state circuit breaker 
for power applications, with the key requirement that the 
interrupt time be less than 300 microseconds, two orders of 
magnitude better than existing mechanical circuit breaker. There 
is also the advantage of no mechanical degradation of the solid 
state circuit breaker, since moving parts have been eliminated 
and arcing is not present. 
THE INSTALLATION OF THE SOLID STATE CIRCUIT BREAKERS 
The installation of the solid state circuit breaker and 
associated control circuitry was authorized in 1989, under the 
Productivity and Capital Improvement Program (PCIP). This is a 
program within the Department of Defense to improve productivity 
at its facilities by means of the installation of advanced 
equipment. The reasoning was that so much would be saved in time 
and material by preventing destruction of components under test 
that the project would easily justify the its expense, this pay 
back being a requirement of the program. 
The specifications for the solid state circuit breaker are 
presented in Table I. Upon release of the specifications, the 
Westinghouse Science and Technology Center, Pittsburgh, PA, bid 
and was awarded the contract to design and manufacture two such 
units, one for each of the two 3.3 Megawatt power supplies, The 
units are illustrated in Figure 2. Note the three individual 
structures, one for each phase of the power circuit. The units 
use four GTOs per polarity per phase, resulting in twenty-four 
GTOs per units. The Pulse Power Center is heavily committed to 
preserving the technical manufacturing base in the United States 
and, therefore insisted on domestic GTOs. The GTOs were 
manufactured to Westinghouse's specifications by the Static Power 
Control Operation of General Electric, located at Malvern, PA, 
The devices are a modification of an existing GE design for 4000 
V, 1 KA devices. The modification was to allow a more reliable 
turnon of the power, which was predicated by the control 
algorithm adopted by Westinghouse. The GTOs are symmetric, The 
devices stand approximately 4 feet (1.3 m) high, are 
approximately 6 feet (1.8 m) long and 2 feet (0.6 m) deep, and 
weigh approximately 1 ton (900 kg). They are utility units and 
air cooled, hence the large size and weight. 
Table 1 
Solid State Circuit Breaker Technical Requirements 
Withstand Voltage-Terminals 15 kV 
Withstand Voltage to Ground 15 kV 
BIL (Basic Impulse Level) 30 kV 
Continuous Current 600 A 
Maximum Interrupt Current 2 k A  
Surge Current (10 ms- 1 cycle) 10 kA 
Steady State Switch Impedance 50 mOhms 
Closing Time 50 microseconds 
Opening Time 300 microseconds 
Operating Temperature 0 C to 80 C 
Figure 2: Drawing of the solid state circuit breaker, showing 
the location of the line and load cables, the control enclosure 
(rectangular, lower center) and detail of the structure of one 
phase of the circuit breaker (at left). Specifically, the eight 
flattened rectangles to the left of the structure are the GTOs, 
the corresponding eight structures to the right are steering 
diodes and the components along the centerline constitute the 
snubbers for the GTO. The unit is approximately six feet long. 
The air cooling requirement necessitated a special 
enclosure for the units. Power handling equipment of this type 
is normally located outside in a switch yard. The solid state 
circ~it breakers are no exception. They have been installed in a 
climatically controlled NEMA Class 4 enclosure in the switchyard 
located behind the Pulse Power Center, in close proximity to the 
existing equipment that comprise the 6.6 MW power supply. A 
photograph of the installed units appears as Figure 3. A 
schematic of the installation is shown in Figure 4. Note the 
voltage arrestors on both line and load sides of the solid state 
circuit breaker in the schematic, and which are visible at the 
right of the photograph. These protect the GTOs from voltage 
transients, which may occur in closing and opening operations. 
Saturable core reactors in the line side protect the unit from 
damage due to the instantaneous application of current. 
Mechanical contactors are provided on the line side for 
isolation, Synchronization signals from the phases are detected 
from the auxiliary power circuit. This is present even if the 
prime power is not connected. To conclude the discussion on the 
circuit breaker, there are three control lines, two fiber optics 
and one twisted pair. The fiber optics are system enable and the 
on/off signal. The twisted pair is a relay closure, confirming 
circuit breaker closure. The signal leaves the circuit breaker 
over twisted pair, but is converted to fiber optic, as are all 
control signals on all power supplies at the Pulse Power Center, 
Figure 3. The solid state circuit breakers installed at Fort 
Monmouth. The phase section at the left clearly shows the 
snubber components along the vertical centerline, with the GTOs 
(white structures) to their left. One voltage arrestor is 
visible to the far right. 
Further on the subject of controls, the installation of the 
solid state circuit breakers into an existing system has prov ided  
the opportunity to upgrade the instrumentation of this system, 
System control, which formally consisted of mechanically driven 
contactors and transformer taps, has now been supplemented by a 
computer based control and measurement system. The computer is 
an Apple Macintosh IIx running the National Instruments LABVIEW 
instrumentation software package. The computer is interfaced to 
the existing control system via four plug in boards, which 
support various digital I/O, D to A and A to D function via new 
interface chasses, which have been installed in the existing 
control rack cabinets of the power supply. The computer also 
interface, via IEEE 488 bus, to two CAMAC systems, which, at the 
present are hosting seventy-six channels of data acquisition, 
GTO BREAKER CONTROLS 
Figure 4: Schematic of installation of the solid state circuit 
breaker, Note the saturable core reactors and mechanical 
disconnects in the line side, to the left, and the voltage 
arrestor in both line and load sides. Note also the voltage 
dividers, which measure phasing off the 208 V control power. 
Original plan had the voltage di~riders measuring off the 4160 V 
mains, but it is possible to have no voltage on the mains, due to 
the aforementioned mechanical disconnects, and still need to 
sense phase. A thirty degree phase shift between the 4160 V and 
208 V circuits is factored into the control algorithm. 
The desire to add, subtract and modify this data acquisition 
capability lead to the selection of the CAMAC standard for this 
purpose, The instrument suite is completed by a custom 
peakgfault detector, which records peak currents and fault 
occurrences and will trip the system if fault number or rate per 
specified unit time exceeds operator set limits. The system was 
designed and built by Maxwell Laboratories, San Diego, CA. 
STATUS OF PROGRAM 
The solid state circuit breakers were completed and 
installed in 1991. The high voltage wiring installation was done 
by the Army's 535th Combat Engineering Detachment, which has a 
contingent based at Fort Monmouth. This military unit 
specializes in the installation of electric generation and 
distribution on the battlefield, utilizing 1 MW all fuel turbine 
driven 4160 V generators mounted on trailers, palletized 
distribution transformers and all the associated cabling. An 
deployed Army division requires 5 MW of electric power 
generation. 
The new controls for the system were installed in 1 9 9 2 ,  A 
control problem delayed final testing of the system. However, 
preliminary results are available and are illustrated in Figure 
5. Note the bottom trace; it is the control signal. The abrupt 
end of this signal is the trip command. The top trace, the 
current, drops to zero within 300  microseconds, exclude some 
small ringing out which is attributable to load conditions, 
Figure 5. A test trip of one solid state circuit breaker, The 
top trace is the circuit breaker current and one vertical 
division is equal to 5 0  Amperes. One horizontal division is 
equal to 5 0 0  microseconds. The bottom trace is the 10 kHz 
control signal, one vertical division is equal to 5 volts, At 1 
millisecond into the event, an over current is induced into the 
system by shorting out a portion of the load resistance. At 
approximately 2 milliseconds into the event, the current exceeds 
the trip value. The control signal ceases at 2.8 milliseconds 
into the event and the solid state circuit breaker trips in 
approximately 300 microseconds. The circuitry producing the 
control signal cessation is one of the slower modes, in this 
case; faster responses for this signal drop are possible. 
FUTURE APPLICATIONS 
The present application was for a utility type device, in 
which size and weight is of little consequence. Future units 
should be made much smaller. There are military applications for 
units of this nature. These would be in connection with the 
previously mentioned 1 MW trailer mounted generators. A 1 1  three 
services use these systems. The Army, as previously mentioned, 
uses these for field power generation. The Navy uses them to 
power ships in port and the Air Force uses them to provide power 
to aircraft and associated equipment on the flight line. Since 
these operations must be portable on a worldwide basis, it is 
imperative that such units be lightweight, compact and rugged, 
The latter requirement makes the solid state circuit breaker 
ideally suitable, in that it will replace the present day system 
which is based on mechanical contactors, often housed in fragile 
glass vacuum envelops. 
Civilian applications are also foreseeable for this 
technology, including protection of utility lines, the 
realization of a nonmechanical reclosure, with remote, adjustable 
settings, the protection of valuable industrial equipment, the 
improvement of power quality and balancing, improved 
synchronization of capacitor banks for power correction, 
diverters for industrial loads, power brokerage from one utility 
to another and intelligent power control in industrial systems. 
Again, these may be done at the megawatt level. 
The solid state circuit breaker will achieve reduction in 
size and weight by several technical innovations. The first is 
the replacement of the current air cooling with one or two phase 
liquid cooling systems. Preliminary discussions with the builder 
of the current solid state circuit breaker indicates that size 
reduction, with incumbent weight reduction, to one or two cubic 
feet of volume for a unit rated similarly to the present units is 
quite conceivable. The second innovation will be a replacement 
of the GTOs with more advanced semiconductors. Recently 
developed devices have less demanding driver and snubber 
requirements, which will result in smaller auxiliary circuits. 
Further improvement may be obtained due to the more efficient 
nature of these devices, resulting in fewer thermal management 
requirements due to enhanced performance in conduction and 
switching. 
CONCLUSION 
The solid state circuit breaker is about to begin a new era 
in fault protection for power systems. Future more advanced 
systems will open up new applications both terrestrial and space 
based. Such devices will insure less damage due to the 
shortening of the time during which a fault condition exists and 
higher reliability due to the elimination of moving parts. 
ACKNOWLEDGMENTS 
The author would like to acknowledge the efforts of the two 
principals on this project, Dr. F. Owen Johnson of the 
Westinghouse Science and Technology Center and Dr. George 
Schofield of Maxwell Laboratories. A note of special thanks goes 
to Chief Warrant Officer Borst, Staff Sergeant K. Payne and 
Sergeants K. Chaney, C. Claxton, A. Potter, D. Brown, R. Simpson 
and J, Moss of the 535th Combat Engineering Detachment. 


High Speed Solid State Circuit Breaker

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