Document Text Contents
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Abstract--The development and testing of an innovative and
compact saturating-reactor High Temperature Superconductor
Fault Current Limiter (HTS FCL) is described. The
development includes an initial dry-type magnetic core design
with iron cores partially encircled by an HTS DC coil and a
recently completed oil-immersed design with magnetic cores
enclosed in a metallic tank placed inside the warm bore of a
rectangular HTS DC magnet. The first 15 kV HTS FCL was
installed in Southern California Edison’s grid in 2009 and the
first transmission-class 138 kV Compact HTS FCL is planned to
be in operation in American Electric Power’s grid in 2011.
Index Terms--HTS FCL, Fault Current Limiter,
Superconducting Coil, Prospective Fault Current, Limited Fault
Current, Distribution Class FCL, Transmission Class FCL,
Saturating Reactor, Saturated-Core FCL.
I. INTRODUCTION
Since 2006, Zenergy Power, Inc. (ZEN) has been
developing a type of high-temperature superconductor (HTS)
fault current limiter (FCL) for electric power grid applications.
The HTS FCL employs a magnetically saturating reactor
concept which acts as a variable inductor in an electric circuit.
The inductance of the HTS FCL changes instantly in real-time
in response to the current in the electrical circuit being
protected and varies from a low steady-state value of
inductance during normal operating conditions to a high value
of inductance during a fault condition that is sufficient to limit
the fault current to the desired maximum value. HTS fault
current limiting concepts have been extensively reported to
date [1-5].
II. BACKGROUND
Figure 1 is a simplified schematic that shows the basic
arrangement of a single-phase ZEN HTS FCL. Referring to
Figure 1, one can see that there are two rectangular iron cores
arranged side-by-side. The iron cores are surrounded by a
single HTS coil that encircles the adjacent inner limbs of the
iron cores in the middle. A small DC power supply energizes
the HTS coil with a DC bias current to create a very strong DC
magnetic field that magnetically biases and saturates the iron
cores. Because the DC bias coil is superconducting, very little
energy is used to magnetically saturate the iron cores.
Conventional copper AC coils are wound on the outer limbs of
the iron cores. The AC coils are connected in series to the
electrical circuit that is to be protected. These AC coils are
This work was supported in part by the California Energy Commission and
the U.S. Department of Energy.
F. Moriconi, F. de la Rosa, A. Singh, B. Chen, M. Levitskaya, and A. Nelson
are with Zenergy Power, Inc., South San Francisco, CA, USA.
wound in opposite magnetic “sense,” so that during any
particular one-half cycle of the AC line current, the AC amp-
turns from one of the coils are additive to the DC magnetic
bias field (boost the DC magnetic bias field), while the AC
amp-turns from the other coil are opposing the DC magnetic
bias field (buck the DC magnetic bias field). Using this
arrangement, a single-phase device can be made in which each
of the rectangular iron cores acts independently during each
positive and negative half-cycle of the AC line current.
Figure 1 – The Basic Saturating Reactor HTS FCL Concept Diagram
Figure 2 shows a typical B-H curve for the material used in
the iron cores (typically the iron cores are laminated from M-6
grain-oriented silicon magnetic steel using overlapping
mitered-joint construction techniques common in
transformers). Under typical operating conditions, when the
DC bias current is on and no AC line current is flowing, the
iron cores are magnetically saturated and very strongly biased
into the upper right-hand quadrant of the B-H curve. When
the AC circuit is energized and the AC line current is flowing
at normal values, the magnetic operating state of the HTS FCL
oscillates over a small range in the extreme upper right-hand
quadrant of the B-H curve. The AC magnetic flux from the
individual half-phase AC coils alternately “boosts” and
“bucks” the DC magnetic bias flux during each positive and
negative half-cycle of the AC line current, but the magnetic
flux variation and associated losses are very small. Figure 2
also shows a representative normal steady-state magnetic
operating point for the HTS FCL. Because the slope of the B-
H curve is very flat in this extremely magnetically biased
condition and the oscillations are very small, the impedance of
the AC coils is a very low value of inductance and
approximates that of an air-core reactor with only a few AC
turns (the nominal steady-state AC voltage drop of the HTS
FCL is typically 1% or less on a per unit basis).
When an AC fault occurs, the AC amp-turns generated by
the AC coils increase linearly with the fault current, and the
range of oscillation of the HTS FCL magnetic operating state
Franco Moriconi, Francisco De La Rosa, Senior Member, IEEE, Amandeep Singh, Member, IEEE,
Bill Chen, Marina Levitskaya, Albert Nelson, Member, IEEE
An Innovative Compact Saturable-Core HTS
Fault Current Limiter - Development, Testing
and Application to Transmission Class Networks
978-1-4244-8357-0/10/$26.00 ©2010 IEEE
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increases proportionally. Figure 2 also shows a representative
magnetic operating point for the HTS FCL during fault
conditions in which the magnetic state of the HTS FCL is
fluctuating from extreme saturation in the flat, upper right-
hand quadrant of the B-H curve down into the steep, nearly
vertical portion of the B-H curve and into lower left-hand
quadrant of the B-H curve. In this condition the iron cores are
alternately magnetically unsaturated by the large excursions in
AC magnetic flux, and because the slope of the B-H curve is
very steep and the oscillations in the HTS FCL magnetic
operating state are very large, the impedance of the AC coils is
a large value of inductance and approximates that of an iron
core reactor.
Figure 2– Transition of HTS FCL Magnetic Core States During Fault
Conditions
From the simple schematic in Figure 1, it is easy to envision
a three-phase HTS FCL using a single HTS DC bias coil.
Figure 3 shows an arrangement in which three single-phase
devices are arranged radially with their corresponding inner
core limbs inside a single cryostat (silver cylinder) containing
the HTS DC bias magnet. The copper AC coils (red
cylinders) are located on the outer limbs of the iron cores and
spaced equidistantly. This arrangement constituted the basic
design for the ZEN HTS FCL and was used to construct the
first two full-scale test devices.
Figure 3 – A Three-Phase Saturating Reactor HTS FCL with a Single HTS
DC Bias Coil
The essential “technology” of the ZEN HTS FCL is creating
an integrated design that optimizes the performance of the iron
cores, the DC HTS magnetic coils and the AC copper coils so
that over the range of expected AC steady-state line currents
the iron cores remain magnetically saturated and the AC line
impedance is low, but over the range of expected potential AC
fault currents, the iron cores become partially or completely
magnetically unsaturated and the AC line impedance is
sufficiently high. Since 2006, ZEN has devoted extensive
resources to modeling, simulation, design, manufacture,
testing and experimental verification of the predicted
performance of the HTS FCL in order to be able to reliably
and accurately design a magnetically saturating reactor HTS
FCL for a specific AC circuit application. As a result of the
extensive modeling, simulation and testing (both full-scale and
sub-scale) that has been performed over the last three years,
ZEN is confident that its HTS FCL technology has been
proven and is ready for commercial deployment.
III. THE FIRST FULL-SCALE ZEN HTS FCL
This device was built and tested to verify the basic
operating principles and concepts of the ZEN HTS FCL. It
consisted of six rectangular iron cores arranged with a single
cryostat in the middle, the six AC coils arranged peripherally
around the structure, along with the supporting structure and
AC electrical bus-work. This device was nominally rated at
15 kV and 1,250 amperes RMS (root-mean-square), and was
designed to limit an AC fault current by about 15%-20%. The
HTS FCL was manufactured using conventional dry-type (air-
insulated) transformer construction techniques for a 110 kV
BIL (basic insulation level) rating. The cryostat was an open-
loop system using liquid nitrogen, which was replenished as
necessary to compensate for boil-off, and the HTS coil was
constructed on a G-10 glass reinforced composite structure
using 800 turns of 4-ply BSSCO 1G wire which was supplied
by American Superconductor.
The HTS FCL was subjected to full-scale testing first at
Pacific Gas and Electric’s High-Voltage Test Facility in San
Ramon, California in October 2007 and later at British
Columbia Hydro’s Powertech Laboratories in Surrey, British
Columbia, Canada in December 2007. The HTS FCL was
subjected to a full-range of testing to determine dielectric
performance, steady-state AC voltage drop (insertion
impedance) under normal operating conditions, and fault
limiting performance, as well as to characterize steady-state
heat loads on the HTS DC coil and in the cryostat, coupling
during steady-state and fault conditions between the AC coils
and the DC coil, and the effects of faults on the HTS coil and
the DC power supplies.
Figure 4 shows the typical performance of the first HTS
FCL during a fault. During testing of the first FCL at
Powertech Laboratories, a total of 54 tests were performed,
including 12 AC fault tests.
Figure 4 – Typical 16 kA Symmetrical, 37 kA First Peak Fault Test for the
First Full-Scale HTS FCL. Red is Prospective, Black is Limited Fault Current.
100 200 300 400 500 600ms
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10
20
30
40
kA
Li
ne
C
ur
re
nt
[k
A
]
-s033ia
s036ia
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IV. THE SECOND FULL-SCALE FCL – THE CEC HTS FCL
The test results from the first HTS FCL encouraged ZEN to
build a second full-scale HTS FCL with the support of the
California Energy Commission (CEC) and the U.S.
Department of Energy (DOE). This device, known as the
CEC HTS FCL, became the first HTS FCL in commercial
service in the United States on March 6, 2009 when it was
placed in the Avanti Circuit (otherwise known as the “Circuit
of the Future”) in the Southern California Edison (SCE)
Company’s Shandin substation in San Bernardino, California.
The “Circuit of the Future” is an actual commercial 12.47 kV
distribution circuit with real residential, commercial and light-
industrial customers that has been established by SCE, CEC
and DOE to demonstrate innovative technologies of potential
value in the modern electric grid.
Figure 5 is a graphic representation of the CEC HTS FCL.
The same central HTS DC magnet and radial AC coil general
arrangement was used in the CEC HTS FCL as in the first
full-scale HTS FCL. There were major differences, however,
between the first HTS FCL and the CEC HTS FCL. Among
other things, the CEC HTS FCL employed cast-epoxy AC
coils instead of built-up wound copper coils. The CEC HTS
FCL also employed a closed-loop cryogenic cooling system
that used sub-cooled liquid nitrogen at approximately 68K to
increase the IC and the working current of the DC HTS bias
magnet coil to increase the available DC amp-turns and the
range of DC magnetic bias flux. The cryogenic cooling
system employs two Cryomech® AL300-CP970
cryorefrigerators with cold heads located at the top of drip-
tubes connected to the liquid nitrogen space of the cryostat.
Nitrogen vapor from the liquid nitrogen condenses on the
cold-heads, is sub-cooled, and drips back into the liquid
nitrogen volume. This recycles the liquid nitrogen and
eliminates the need to periodically resupply the CEC HTS
FCL with cryogen. The basic design parameters of the CEC
HTS FCL are shown in Table 1. Because the Avanti Circuit is
a newly constructed distribution circuit with a low duty-cycle
and no expected fault issues, the CEC HTS FCL was designed
for only modest fault current limiting capabilities and was
intended to limit a 23 kA RMS potential steady-state fault
current by about 20%. Instead of fault limiting performance,
emphasis was placed on accurately modeling and predicting
the performance of the HTS FCL and its associated electrical
waveforms.
Figure 5 – The CEC HTS FCL Graphic Representation
Table 1 – The CEC FCL Basic Design Parameters
The CEC HTS FCL underwent extensive testing at
Powertech Laboratories in October 2008. In the absence of an
industry standard for HTS FCL testing, a comprehensive test
plan that incorporated IEEE standards [6-8] for series reactors
and transformers was prepared with input from SCE and the
National Electric Energy Testing, Research and Applications
Center (NEETRAC), a member-financed, non-profit research
laboratory of the Georgia Technical University (Georgia Tech)
in Atlanta, Georgia. Special emphasis was placed on
comparing the performance of the CEC HTS FCL predicted
by ZEN’s design protocol with the measured performance of
the CEC HTS FCL, including AC steady-state current voltage
drop (insertion impedance), steady-state AC current
temperature rise, AC fault current limiting, and AC coil and
DC HTS electromagnetic coupling. The dielectric
performance of the CEC HTS FCL was also tested including
BIL, DC withstand voltage, lightning impulse and chopped-
wave testing as required by the applicable IEEE standards [6-
8]. Dielectric testing was performed before fault testing, and
then repeated upon the conclusion of fault testing by SCE at
their Westminster, California test facility before installation in
the Avanti Circuit.
In all more than 65 separate test events were performed on
the CEC HTS FCL, including 32 fault tests. A typical fault
test sequence involved the application of full-load steady-state
current and voltage (1,250 amperes RMS at 13.1 kV), the
application of 30-cycles or more of fault current up to nearly
60 kA first-peak, and returning to the full-load conditions
upon clearance of the fault. The CEC HTS FCL performed
extremely well and exceeded expectations by withstanding
more than an expected lifetime of actual faults during a week
of testing. Figure 6 shows a typical insertion impedance test
for the CEC HTS FCL. Notice the excellent match between
the predicted and the measured voltage drop as a function of
AC steady-state current. Figure 7 shows a typical fault
sequence test in which the AC fault current is limited by
approximately the targeted 20% reduction level. Figure 8 is
an endurance test of the CEC HTS FCL in which it was
subjected to an 82-cycle fault, and Figure 9 is a double-fault
sequence test, which was performed to measure the CEC HTS
FCL performance under an automatic re-closer scenario.
Figure 10 shows the CEC HTS FCL in the Avanti Circuit at
SCE’s Shandin substation, where it remained as of November
2009.
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Figure 6 – Measured versus Predicted Voltage Drop (Insertion Impedance)
Figure 7 – Design Performance Verification Test for the CEC FCL
Figure 8 – 82-Cycle Endurance Fault Test of the CEC FCL
Figure 9 – A Double-Fault Sequence Simulating Re-Closer Operation on the
CEC FCL
Figure 10 – The CEC FCL Installed at the SCE Shandin Substation in San
Bernardino, California
V. THE INNOVATIVE COMPACT HTS FCL
In the course of building and testing the CEC HTS FCL,
ZEN conceived a new concept for saturating reactor HTS FLC
design that had the potential to considerably reduce the size
and weight of the device, while allowing the dielectric rating
of the HTS FCL to be increased to transmission voltages of
100 kV and higher. This concept became known as the
“Compact HTS FCL,” and in order to test the concept and
evaluate alternative methods for implementing it, ZEN, with
financial support from the U.S. Dept. of Energy, built and
tested four full-scale prototypes using different internal
designs.
All of the Compact HTS FCL prototypes were built using
standard “oil-filled” liquid dielectric transformer construction
techniques. This allowed the minimum required dielectric
offset distances within the HTS FCL to be minimized, greatly
reducing the HTS FCL prototypes’ size and weight for
equivalent performance. Table 2 shows a comparison between
a “dry-type” HTS FCL using the original radial AC coil
design and an “oil-filled” Compact HTS FCL of equivalent
designed performance. Both of the HTS FCLs are 26 kV, 2
kA steady-state current devices designed to limit a prospective
30 kA symmetrical fault with a 1.6 asymmetry factor by 50%.
The Compact HTS FCL requires only 28.4% of the volume
and has only 26.6% of the iron core mass of the original
design. Another important design innovation was the use of
“dry-type” cryogenics to conductively cool the HTS coil
without the use of liquid cryogens. This allowed the operating
temperature of the HTS coils to be reduced below the freezing
temperature of liquid nitrogen, enabling further increases in
the IC and working current of the 1G HTS wire used in the DC
bias magnet system and correspondingly higher DC amp-turns
to magnetically saturate the iron cores. The use of conduction
cooling also removes potential utility concerns about having
large volumes of liquid cryogens in confined spaces and
potential pressure vessel over-pressurization, rupture and
venting concerns.
Parameter Old Design New Design
Iron Core Weight
(lbs)
252K 67K
Cost of Iron
@ $3/lb
$ 756K $ 201K
FCL Size (core iron +
AC coils
19' x 19' 10' x 7'
Table 2 – Comparison of Radial AC Coil (Old Design) and Compact (New
Design) HTS FCLs
0.5 1 1.5 2
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TEST 77 - 1.25s - 80 cycles FAULT - 20kA X/R=22, FCL IN
Time [sec]
L
in
e
C
u
rr
e
n
t [
kA
]
Phase A
Phase B
Phase C
0.5 1 1.5 2 2.5 3 3.5 4
-50
-40
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-20
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30
40
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TEST 77 - DOUBLE FAULT SEQUENCE - 20kA X/R=22, FCL IN
Time [sec]
L
in
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C
u
rr
e
n
t [
kA
]
Phase A
Phase B
Phase C
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Table 3 shows all four of the Compact HTS FCL prototypes
that were built and tested. These prototypes had the same
nominal 15 kV design voltage and 110 BIL rating, but differed
in their steady-state AC current ratings and targeted AC
steady-state current insertion impedance and AC fault current
limiting performance. The designed AC steady-state current
levels ranged from 1,250 amperes RMS to 2,500 amperes
RMS, and the targeted AC fault current reduction levels
ranged from about 30% up to more than 50% of a 25 kA RMS
potential steady-state fault current with an asymmetry factor
yielding a first-peak fault current approaching 50 kA.
The Compact HTS FCL prototypes underwent full-power
load and fault testing at Powertech Laboratories in July 2009
using essentially the same comprehensive test plan that was
employed for the CEC HTS FCL. In all 118 separate tests
were performed on the four Compact HTS FCL prototypes,
including 55 calibration tests, 12 load current only tests, and
51 fault tests. In many cases, the measured performance
exceeded expectations, and the test program completely
validated both the performance potential of the Compact HTS
FCL design and the efficacy of ZEN’s design protocol. Figure
11 shows an illustration of one of the compact HTS FCL
prototypes.
Figure 12 shows the results of a typical AC load current
voltage drop or insertion impedance test which displays good
agreement between the predicted and the measured
performance. Figure 13 shows a fault current test in which the
Compact HTS FCL prototype reduced a prospective 25 kA
RMS fault current with a 1.6 asymmetry factor by about 46%.
Parameter Units FCL #
1
FCL #
2
FCL #
3
FCL #
4
Line-to-Line Voltage kV 12.47 12.47 12.47 13.8
Number of Phases # 3 3 1 1
Line Frequency Hz 60 60 60 60
Prospective Fault
Current
kA 35 46 80 25
Limited Peak Fault kA 27 30 40 18
Prospective Fault
Current RMS
Symmetrical
kA 20 20 40 11
Limited Symmetric
Fault Current
kA 15 11.5 18 6.5
Load Current Steady-
State RMS
kA 1.25 1.25 1.25 2.5 –
4.0
Voltage Drop Steady-
State Maximum
% 1 1 1 2
Line-to-Ground
Voltage
kV 6.9 6.9 6.9 8.0
Asymmetry Factor # 1.2 1.6 1.4 1.6
Source Fault
Impedance
Ohms 0.346 0.346 0.173 0.724
Fault Reduction % 25 43 55 41
Table 3 – The Four Full-Scale Compact HTS FCL Devices Tested at
Powertech Laboratories July 2009
Figure 11 – Compact ZEN 12 kV HTS FCL undergoing testing at Powertech
High Power Laboratory
Figure 12 – Typical AC Steady-State Load Current Voltage Drop (Insertion
Impedance) Measurements
Figure 13 – Compact FCL Fault Test at Powertech Laboratories July 2009.
The black curve is the prospective fault current, the red curve is the limited
fault current, and the blue curve is the voltage measured at the FCL terminals
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Figures 14-16 portray a comparison between calculated and
measured fault current waveforms for one of the compact
prototypes under a 15kA symmetric fault to ground condition.
Figure 14 - Measured vs. Calculated 15kA Prospective and Limited Fault
Current
Figure 15 - Measured vs. Calculated Back EMF for 15kA Fault Level
Figure 16 - Measured vs. Calculated Voltage Drop for 1.1kA Load Current
A particularly important result from the Compact HTS FCL
testing program was the fact that the AC coils and the DC
HTS Coil exhibited very little electromagnetic coupling.
Figure 17 shows that the DC current in the HTS bias coil
varied only about 5% as the Compact HTS FCL was subjected
to up to a 30 kA peak fault current. These results were very
typical for all of the Compact HTS FCL devices during fault
current testing. The steady-state voltage drop (insertion
impedance) of the Compact HTS FCL typically remained low
with increasing AC currents and also exhibited very “clean”
AC power characteristics with Total Harmonic Distortion
levels well within the requirements of IEEE 519-1992 [9].
Figure 17 – AC Coil and DC HTS Coil Electromagnetic Coupling during AC
Fault Current Testing
VI. A COMPACT HTS FCL DESIGN FOR TRANSMISSION CLASS
APPLICATIONS
As a result of the successful testing of the Compact HTS
FCL prototype, ZEN has initiated the commercial sale of the
Compact HTS FCL for medium-voltage applications. Also,
ZEN has entered into an agreement with American Electric
Power (AEP), Columbus, Ohio, to partner for the
demonstration of a 138 kV three-phase Compact HTS FCL as
a part of ZEN’s ongoing DOE-sponsored HTS FCL
development program. A single-phase 138 kV Compact HTS
FCL prototype will be built and tested in 2010, and a three-
phase Compact HTS FCL demonstration unit will be built,
tested and installed in AEP’s Tidd substation located near
Steubenville, Ohio in 2011.
ZEN has considered a potential application for a “typical”
154 kV transmission application in an Asian electric power
grid. The design approach taken was for a device with a
relatively modest level of fault current reduction and a low
value of steady-state voltage drop (insertion impedance).
Figure 18 shows the simplified transmission line one-line
diagram PSCAD model that ZEN created to represent a
“typical” 154 kV transmission line. The voltage source
parameters with the corresponding line impedances are shown
on the left-hand side of the diagram, and a single lumped load
is shown on the right-hand side of the diagram along with the
“Timed Fault Logic.” The FCL is located in the middle of the
diagram, and the graphical representation of the HTS FCL
model that is inserted into the circuit is shown in Figure 19.
Figure 20 shows the prospective fault current with the FCL
bypassed and a 2,000 amp load current bypassing the FCL. In
this scenario, the prospective first peak asymmetric fault
current is 103 kA and the prospective symmetrical fault
current is 40 kA. Figure 21 shows the resulting limited fault
current under the same scenario as Figure 18, but with the
HTS FCL in the circuit instead of being bypassed. In this
scenario, the limited first peak of the fault current is 75 kA (a
28% reduction) and the limited symmetrical fault current is
24.8 kA (a 38% reduction), and the normal steady-state
voltage drop (insertion impedance) with a 2,000 amp load
current through the HTS FCL is 1.0% or about 890 volts (this
voltage drop is proportional to the load current and is less
under lighter loads).
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75
-20
-15
-10
-5
0
5
10
15
20
25
30
Test 97 - ZENERGY POWER Compact FCL - 15kA Prospective Fault - 120A DC Bias
Time [sec]
L
in
e
C
u
rr
e
n
t [
kA
]
MEASURED LIMITED
MEASURED PROSPECTIVE
MODEL LIMITED
0.53 0.54 0.55 0.56 0.57 0.58 0.59 0.6 0.61 0.62
-5
-4
-3
-2
-1
0
1
2
3
4
5
Test 97 - ZENERGY POWER Compact FCL - 15kA Prospective Fault - 120A DC Bias
Time [sec]
F
C
L
B
A
C
K
E
M
F
[k
V
]
MEASURED
MODEL
0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
Test 97 - ZENERGY POWER Compact FCL - 15kA Prospective Fault - 120A DC Bias
Time [sec]
F
C
L
B
A
C
K
E
M
F
[k
V
]
MEASURED
MODEL
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Figure 18 – The Simplified 154 KV Transmission Line PSCAD Model
A summary of a possible design of the modeled HTS FCL
is presented in Table 4. Each phase of the three-phase HTS
FCL would be about 1.5 meters in diameter and about 7
meters long. Using a horizontal orientation, it would fit in a
footprint about 5 m x 7 m x 4 m.
Figure 19– The 154 kV HTS FCL Model for PSCAD Analysis
Figure 20 – The Prospective Fault Current in the 154 kV Circuit without the
HTS FCL
Figure 21– The Fault Currents in the 154 kV Circuit with the HTS FCL
Again, it is important to understand that while this is an
HTS FCL design that could be manufactured today and which
ZEN is confident would work as modeled, it is not the only
possible design and other potential HTS FCL devices of
different sizes, orientations and performance can also be
designed and manufactured. For example, an HTS FCL with a
lower steady-state voltage drop could be built, if a longer
device were acceptable. If desired, the fault limiting
performance of the HTS FCL could also be increased by
increasing the diameter and length of the device.
154 kV Single-Phase FCL Parameters Units Value
Line-to Line Voltage kV 154
Line Frequency Hz 60
Rated Current Amperes 2,000
Asymmetry Factor # 2
Base Power MVA 100
Maximum Allowable Voltage Drop Percent of
Line Voltage
% 2
Line-to-Ground Voltage kV 89
FCL Fault Impedance Ohms 2
Steady-State FCL Allowable Inductance µH 1,698
Maximum Induced EMF for Desired Fault Current
Limiting
kV 44
Maximum De-Saturation Flux Change Tesla 4
Steady-State FCL Maximum Allowable Impedance Ohms 1
Coil Height Meters 5
Core Height Meters 7
Core Weight Kg 48,912
HTS Wire Length Meters 37,762
NI HTS Coil Amp-
Turns
730,000
Overall FCL Width Oriented Horizontally (three,
single-phases in array)
Meters 5
Overall FCL Length Oriented Horizontally (three,
single-phases in array)
Meters 7
Overall FCL Height Oriented Horizontally (three,
single-phases in array)
Meters 4
Table 4 – The 154 kV HTS FCL Basic Design Parameters
R=0
Line LoadFCL
0.12485 [ohm]
5.8868e-3 [H]
BRK1
293.6 [MVAR]
485.4 [MW]
154 kV AC
Source
453 [MW] 281 [MVAR]
Ea
ABC->G
Timed
Fault
Logic
1
Abstract--The development and testing of an innovative and
compact saturating-reactor High Temperature Superconductor
Fault Current Limiter (HTS FCL) is described. The
development includes an initial dry-type magnetic core design
with iron cores partially encircled by an HTS DC coil and a
recently completed oil-immersed design with magnetic cores
enclosed in a metallic tank placed inside the warm bore of a
rectangular HTS DC magnet. The first 15 kV HTS FCL was
installed in Southern California Edison’s grid in 2009 and the
first transmission-class 138 kV Compact HTS FCL is planned to
be in operation in American Electric Power’s grid in 2011.
Index Terms--HTS FCL, Fault Current Limiter,
Superconducting Coil, Prospective Fault Current, Limited Fault
Current, Distribution Class FCL, Transmission Class FCL,
Saturating Reactor, Saturated-Core FCL.
I. INTRODUCTION
Since 2006, Zenergy Power, Inc. (ZEN) has been
developing a type of high-temperature superconductor (HTS)
fault current limiter (FCL) for electric power grid applications.
The HTS FCL employs a magnetically saturating reactor
concept which acts as a variable inductor in an electric circuit.
The inductance of the HTS FCL changes instantly in real-time
in response to the current in the electrical circuit being
protected and varies from a low steady-state value of
inductance during normal operating conditions to a high value
of inductance during a fault condition that is sufficient to limit
the fault current to the desired maximum value. HTS fault
current limiting concepts have been extensively reported to
date [1-5].
II. BACKGROUND
Figure 1 is a simplified schematic that shows the basic
arrangement of a single-phase ZEN HTS FCL. Referring to
Figure 1, one can see that there are two rectangular iron cores
arranged side-by-side. The iron cores are surrounded by a
single HTS coil that encircles the adjacent inner limbs of the
iron cores in the middle. A small DC power supply energizes
the HTS coil with a DC bias current to create a very strong DC
magnetic field that magnetically biases and saturates the iron
cores. Because the DC bias coil is superconducting, very little
energy is used to magnetically saturate the iron cores.
Conventional copper AC coils are wound on the outer limbs of
the iron cores. The AC coils are connected in series to the
electrical circuit that is to be protected. These AC coils are
This work was supported in part by the California Energy Commission and
the U.S. Department of Energy.
F. Moriconi, F. de la Rosa, A. Singh, B. Chen, M. Levitskaya, and A. Nelson
are with Zenergy Power, Inc., South San Francisco, CA, USA.
wound in opposite magnetic “sense,” so that during any
particular one-half cycle of the AC line current, the AC amp-
turns from one of the coils are additive to the DC magnetic
bias field (boost the DC magnetic bias field), while the AC
amp-turns from the other coil are opposing the DC magnetic
bias field (buck the DC magnetic bias field). Using this
arrangement, a single-phase device can be made in which each
of the rectangular iron cores acts independently during each
positive and negative half-cycle of the AC line current.
Figure 1 – The Basic Saturating Reactor HTS FCL Concept Diagram
Figure 2 shows a typical B-H curve for the material used in
the iron cores (typically the iron cores are laminated from M-6
grain-oriented silicon magnetic steel using overlapping
mitered-joint construction techniques common in
transformers). Under typical operating conditions, when the
DC bias current is on and no AC line current is flowing, the
iron cores are magnetically saturated and very strongly biased
into the upper right-hand quadrant of the B-H curve. When
the AC circuit is energized and the AC line current is flowing
at normal values, the magnetic operating state of the HTS FCL
oscillates over a small range in the extreme upper right-hand
quadrant of the B-H curve. The AC magnetic flux from the
individual half-phase AC coils alternately “boosts” and
“bucks” the DC magnetic bias flux during each positive and
negative half-cycle of the AC line current, but the magnetic
flux variation and associated losses are very small. Figure 2
also shows a representative normal steady-state magnetic
operating point for the HTS FCL. Because the slope of the B-
H curve is very flat in this extremely magnetically biased
condition and the oscillations are very small, the impedance of
the AC coils is a very low value of inductance and
approximates that of an air-core reactor with only a few AC
turns (the nominal steady-state AC voltage drop of the HTS
FCL is typically 1% or less on a per unit basis).
When an AC fault occurs, the AC amp-turns generated by
the AC coils increase linearly with the fault current, and the
range of oscillation of the HTS FCL magnetic operating state
Franco Moriconi, Francisco De La Rosa, Senior Member, IEEE, Amandeep Singh, Member, IEEE,
Bill Chen, Marina Levitskaya, Albert Nelson, Member, IEEE
An Innovative Compact Saturable-Core HTS
Fault Current Limiter - Development, Testing
and Application to Transmission Class Networks
978-1-4244-8357-0/10/$26.00 ©2010 IEEE
Page 2
2
increases proportionally. Figure 2 also shows a representative
magnetic operating point for the HTS FCL during fault
conditions in which the magnetic state of the HTS FCL is
fluctuating from extreme saturation in the flat, upper right-
hand quadrant of the B-H curve down into the steep, nearly
vertical portion of the B-H curve and into lower left-hand
quadrant of the B-H curve. In this condition the iron cores are
alternately magnetically unsaturated by the large excursions in
AC magnetic flux, and because the slope of the B-H curve is
very steep and the oscillations in the HTS FCL magnetic
operating state are very large, the impedance of the AC coils is
a large value of inductance and approximates that of an iron
core reactor.
Figure 2– Transition of HTS FCL Magnetic Core States During Fault
Conditions
From the simple schematic in Figure 1, it is easy to envision
a three-phase HTS FCL using a single HTS DC bias coil.
Figure 3 shows an arrangement in which three single-phase
devices are arranged radially with their corresponding inner
core limbs inside a single cryostat (silver cylinder) containing
the HTS DC bias magnet. The copper AC coils (red
cylinders) are located on the outer limbs of the iron cores and
spaced equidistantly. This arrangement constituted the basic
design for the ZEN HTS FCL and was used to construct the
first two full-scale test devices.
Figure 3 – A Three-Phase Saturating Reactor HTS FCL with a Single HTS
DC Bias Coil
The essential “technology” of the ZEN HTS FCL is creating
an integrated design that optimizes the performance of the iron
cores, the DC HTS magnetic coils and the AC copper coils so
that over the range of expected AC steady-state line currents
the iron cores remain magnetically saturated and the AC line
impedance is low, but over the range of expected potential AC
fault currents, the iron cores become partially or completely
magnetically unsaturated and the AC line impedance is
sufficiently high. Since 2006, ZEN has devoted extensive
resources to modeling, simulation, design, manufacture,
testing and experimental verification of the predicted
performance of the HTS FCL in order to be able to reliably
and accurately design a magnetically saturating reactor HTS
FCL for a specific AC circuit application. As a result of the
extensive modeling, simulation and testing (both full-scale and
sub-scale) that has been performed over the last three years,
ZEN is confident that its HTS FCL technology has been
proven and is ready for commercial deployment.
III. THE FIRST FULL-SCALE ZEN HTS FCL
This device was built and tested to verify the basic
operating principles and concepts of the ZEN HTS FCL. It
consisted of six rectangular iron cores arranged with a single
cryostat in the middle, the six AC coils arranged peripherally
around the structure, along with the supporting structure and
AC electrical bus-work. This device was nominally rated at
15 kV and 1,250 amperes RMS (root-mean-square), and was
designed to limit an AC fault current by about 15%-20%. The
HTS FCL was manufactured using conventional dry-type (air-
insulated) transformer construction techniques for a 110 kV
BIL (basic insulation level) rating. The cryostat was an open-
loop system using liquid nitrogen, which was replenished as
necessary to compensate for boil-off, and the HTS coil was
constructed on a G-10 glass reinforced composite structure
using 800 turns of 4-ply BSSCO 1G wire which was supplied
by American Superconductor.
The HTS FCL was subjected to full-scale testing first at
Pacific Gas and Electric’s High-Voltage Test Facility in San
Ramon, California in October 2007 and later at British
Columbia Hydro’s Powertech Laboratories in Surrey, British
Columbia, Canada in December 2007. The HTS FCL was
subjected to a full-range of testing to determine dielectric
performance, steady-state AC voltage drop (insertion
impedance) under normal operating conditions, and fault
limiting performance, as well as to characterize steady-state
heat loads on the HTS DC coil and in the cryostat, coupling
during steady-state and fault conditions between the AC coils
and the DC coil, and the effects of faults on the HTS coil and
the DC power supplies.
Figure 4 shows the typical performance of the first HTS
FCL during a fault. During testing of the first FCL at
Powertech Laboratories, a total of 54 tests were performed,
including 12 AC fault tests.
Figure 4 – Typical 16 kA Symmetrical, 37 kA First Peak Fault Test for the
First Full-Scale HTS FCL. Red is Prospective, Black is Limited Fault Current.
100 200 300 400 500 600ms
-30
-20
-10
0
10
20
30
40
kA
Li
ne
C
ur
re
nt
[k
A
]
-s033ia
s036ia
Page 3
3
IV. THE SECOND FULL-SCALE FCL – THE CEC HTS FCL
The test results from the first HTS FCL encouraged ZEN to
build a second full-scale HTS FCL with the support of the
California Energy Commission (CEC) and the U.S.
Department of Energy (DOE). This device, known as the
CEC HTS FCL, became the first HTS FCL in commercial
service in the United States on March 6, 2009 when it was
placed in the Avanti Circuit (otherwise known as the “Circuit
of the Future”) in the Southern California Edison (SCE)
Company’s Shandin substation in San Bernardino, California.
The “Circuit of the Future” is an actual commercial 12.47 kV
distribution circuit with real residential, commercial and light-
industrial customers that has been established by SCE, CEC
and DOE to demonstrate innovative technologies of potential
value in the modern electric grid.
Figure 5 is a graphic representation of the CEC HTS FCL.
The same central HTS DC magnet and radial AC coil general
arrangement was used in the CEC HTS FCL as in the first
full-scale HTS FCL. There were major differences, however,
between the first HTS FCL and the CEC HTS FCL. Among
other things, the CEC HTS FCL employed cast-epoxy AC
coils instead of built-up wound copper coils. The CEC HTS
FCL also employed a closed-loop cryogenic cooling system
that used sub-cooled liquid nitrogen at approximately 68K to
increase the IC and the working current of the DC HTS bias
magnet coil to increase the available DC amp-turns and the
range of DC magnetic bias flux. The cryogenic cooling
system employs two Cryomech® AL300-CP970
cryorefrigerators with cold heads located at the top of drip-
tubes connected to the liquid nitrogen space of the cryostat.
Nitrogen vapor from the liquid nitrogen condenses on the
cold-heads, is sub-cooled, and drips back into the liquid
nitrogen volume. This recycles the liquid nitrogen and
eliminates the need to periodically resupply the CEC HTS
FCL with cryogen. The basic design parameters of the CEC
HTS FCL are shown in Table 1. Because the Avanti Circuit is
a newly constructed distribution circuit with a low duty-cycle
and no expected fault issues, the CEC HTS FCL was designed
for only modest fault current limiting capabilities and was
intended to limit a 23 kA RMS potential steady-state fault
current by about 20%. Instead of fault limiting performance,
emphasis was placed on accurately modeling and predicting
the performance of the HTS FCL and its associated electrical
waveforms.
Figure 5 – The CEC HTS FCL Graphic Representation
Table 1 – The CEC FCL Basic Design Parameters
The CEC HTS FCL underwent extensive testing at
Powertech Laboratories in October 2008. In the absence of an
industry standard for HTS FCL testing, a comprehensive test
plan that incorporated IEEE standards [6-8] for series reactors
and transformers was prepared with input from SCE and the
National Electric Energy Testing, Research and Applications
Center (NEETRAC), a member-financed, non-profit research
laboratory of the Georgia Technical University (Georgia Tech)
in Atlanta, Georgia. Special emphasis was placed on
comparing the performance of the CEC HTS FCL predicted
by ZEN’s design protocol with the measured performance of
the CEC HTS FCL, including AC steady-state current voltage
drop (insertion impedance), steady-state AC current
temperature rise, AC fault current limiting, and AC coil and
DC HTS electromagnetic coupling. The dielectric
performance of the CEC HTS FCL was also tested including
BIL, DC withstand voltage, lightning impulse and chopped-
wave testing as required by the applicable IEEE standards [6-
8]. Dielectric testing was performed before fault testing, and
then repeated upon the conclusion of fault testing by SCE at
their Westminster, California test facility before installation in
the Avanti Circuit.
In all more than 65 separate test events were performed on
the CEC HTS FCL, including 32 fault tests. A typical fault
test sequence involved the application of full-load steady-state
current and voltage (1,250 amperes RMS at 13.1 kV), the
application of 30-cycles or more of fault current up to nearly
60 kA first-peak, and returning to the full-load conditions
upon clearance of the fault. The CEC HTS FCL performed
extremely well and exceeded expectations by withstanding
more than an expected lifetime of actual faults during a week
of testing. Figure 6 shows a typical insertion impedance test
for the CEC HTS FCL. Notice the excellent match between
the predicted and the measured voltage drop as a function of
AC steady-state current. Figure 7 shows a typical fault
sequence test in which the AC fault current is limited by
approximately the targeted 20% reduction level. Figure 8 is
an endurance test of the CEC HTS FCL in which it was
subjected to an 82-cycle fault, and Figure 9 is a double-fault
sequence test, which was performed to measure the CEC HTS
FCL performance under an automatic re-closer scenario.
Figure 10 shows the CEC HTS FCL in the Avanti Circuit at
SCE’s Shandin substation, where it remained as of November
2009.
Page 4
4
Figure 6 – Measured versus Predicted Voltage Drop (Insertion Impedance)
Figure 7 – Design Performance Verification Test for the CEC FCL
Figure 8 – 82-Cycle Endurance Fault Test of the CEC FCL
Figure 9 – A Double-Fault Sequence Simulating Re-Closer Operation on the
CEC FCL
Figure 10 – The CEC FCL Installed at the SCE Shandin Substation in San
Bernardino, California
V. THE INNOVATIVE COMPACT HTS FCL
In the course of building and testing the CEC HTS FCL,
ZEN conceived a new concept for saturating reactor HTS FLC
design that had the potential to considerably reduce the size
and weight of the device, while allowing the dielectric rating
of the HTS FCL to be increased to transmission voltages of
100 kV and higher. This concept became known as the
“Compact HTS FCL,” and in order to test the concept and
evaluate alternative methods for implementing it, ZEN, with
financial support from the U.S. Dept. of Energy, built and
tested four full-scale prototypes using different internal
designs.
All of the Compact HTS FCL prototypes were built using
standard “oil-filled” liquid dielectric transformer construction
techniques. This allowed the minimum required dielectric
offset distances within the HTS FCL to be minimized, greatly
reducing the HTS FCL prototypes’ size and weight for
equivalent performance. Table 2 shows a comparison between
a “dry-type” HTS FCL using the original radial AC coil
design and an “oil-filled” Compact HTS FCL of equivalent
designed performance. Both of the HTS FCLs are 26 kV, 2
kA steady-state current devices designed to limit a prospective
30 kA symmetrical fault with a 1.6 asymmetry factor by 50%.
The Compact HTS FCL requires only 28.4% of the volume
and has only 26.6% of the iron core mass of the original
design. Another important design innovation was the use of
“dry-type” cryogenics to conductively cool the HTS coil
without the use of liquid cryogens. This allowed the operating
temperature of the HTS coils to be reduced below the freezing
temperature of liquid nitrogen, enabling further increases in
the IC and working current of the 1G HTS wire used in the DC
bias magnet system and correspondingly higher DC amp-turns
to magnetically saturate the iron cores. The use of conduction
cooling also removes potential utility concerns about having
large volumes of liquid cryogens in confined spaces and
potential pressure vessel over-pressurization, rupture and
venting concerns.
Parameter Old Design New Design
Iron Core Weight
(lbs)
252K 67K
Cost of Iron
@ $3/lb
$ 756K $ 201K
FCL Size (core iron +
AC coils
19' x 19' 10' x 7'
Table 2 – Comparison of Radial AC Coil (Old Design) and Compact (New
Design) HTS FCLs
0.5 1 1.5 2
-50
-40
-30
-20
-10
0
10
20
30
40
50
TEST 77 - 1.25s - 80 cycles FAULT - 20kA X/R=22, FCL IN
Time [sec]
L
in
e
C
u
rr
e
n
t [
kA
]
Phase A
Phase B
Phase C
0.5 1 1.5 2 2.5 3 3.5 4
-50
-40
-30
-20
-10
0
10
20
30
40
50
TEST 77 - DOUBLE FAULT SEQUENCE - 20kA X/R=22, FCL IN
Time [sec]
L
in
e
C
u
rr
e
n
t [
kA
]
Phase A
Phase B
Phase C
Page 5
5
Table 3 shows all four of the Compact HTS FCL prototypes
that were built and tested. These prototypes had the same
nominal 15 kV design voltage and 110 BIL rating, but differed
in their steady-state AC current ratings and targeted AC
steady-state current insertion impedance and AC fault current
limiting performance. The designed AC steady-state current
levels ranged from 1,250 amperes RMS to 2,500 amperes
RMS, and the targeted AC fault current reduction levels
ranged from about 30% up to more than 50% of a 25 kA RMS
potential steady-state fault current with an asymmetry factor
yielding a first-peak fault current approaching 50 kA.
The Compact HTS FCL prototypes underwent full-power
load and fault testing at Powertech Laboratories in July 2009
using essentially the same comprehensive test plan that was
employed for the CEC HTS FCL. In all 118 separate tests
were performed on the four Compact HTS FCL prototypes,
including 55 calibration tests, 12 load current only tests, and
51 fault tests. In many cases, the measured performance
exceeded expectations, and the test program completely
validated both the performance potential of the Compact HTS
FCL design and the efficacy of ZEN’s design protocol. Figure
11 shows an illustration of one of the compact HTS FCL
prototypes.
Figure 12 shows the results of a typical AC load current
voltage drop or insertion impedance test which displays good
agreement between the predicted and the measured
performance. Figure 13 shows a fault current test in which the
Compact HTS FCL prototype reduced a prospective 25 kA
RMS fault current with a 1.6 asymmetry factor by about 46%.
Parameter Units FCL #
1
FCL #
2
FCL #
3
FCL #
4
Line-to-Line Voltage kV 12.47 12.47 12.47 13.8
Number of Phases # 3 3 1 1
Line Frequency Hz 60 60 60 60
Prospective Fault
Current
kA 35 46 80 25
Limited Peak Fault kA 27 30 40 18
Prospective Fault
Current RMS
Symmetrical
kA 20 20 40 11
Limited Symmetric
Fault Current
kA 15 11.5 18 6.5
Load Current Steady-
State RMS
kA 1.25 1.25 1.25 2.5 –
4.0
Voltage Drop Steady-
State Maximum
% 1 1 1 2
Line-to-Ground
Voltage
kV 6.9 6.9 6.9 8.0
Asymmetry Factor # 1.2 1.6 1.4 1.6
Source Fault
Impedance
Ohms 0.346 0.346 0.173 0.724
Fault Reduction % 25 43 55 41
Table 3 – The Four Full-Scale Compact HTS FCL Devices Tested at
Powertech Laboratories July 2009
Figure 11 – Compact ZEN 12 kV HTS FCL undergoing testing at Powertech
High Power Laboratory
Figure 12 – Typical AC Steady-State Load Current Voltage Drop (Insertion
Impedance) Measurements
Figure 13 – Compact FCL Fault Test at Powertech Laboratories July 2009.
The black curve is the prospective fault current, the red curve is the limited
fault current, and the blue curve is the voltage measured at the FCL terminals
Page 6
6
Figures 14-16 portray a comparison between calculated and
measured fault current waveforms for one of the compact
prototypes under a 15kA symmetric fault to ground condition.
Figure 14 - Measured vs. Calculated 15kA Prospective and Limited Fault
Current
Figure 15 - Measured vs. Calculated Back EMF for 15kA Fault Level
Figure 16 - Measured vs. Calculated Voltage Drop for 1.1kA Load Current
A particularly important result from the Compact HTS FCL
testing program was the fact that the AC coils and the DC
HTS Coil exhibited very little electromagnetic coupling.
Figure 17 shows that the DC current in the HTS bias coil
varied only about 5% as the Compact HTS FCL was subjected
to up to a 30 kA peak fault current. These results were very
typical for all of the Compact HTS FCL devices during fault
current testing. The steady-state voltage drop (insertion
impedance) of the Compact HTS FCL typically remained low
with increasing AC currents and also exhibited very “clean”
AC power characteristics with Total Harmonic Distortion
levels well within the requirements of IEEE 519-1992 [9].
Figure 17 – AC Coil and DC HTS Coil Electromagnetic Coupling during AC
Fault Current Testing
VI. A COMPACT HTS FCL DESIGN FOR TRANSMISSION CLASS
APPLICATIONS
As a result of the successful testing of the Compact HTS
FCL prototype, ZEN has initiated the commercial sale of the
Compact HTS FCL for medium-voltage applications. Also,
ZEN has entered into an agreement with American Electric
Power (AEP), Columbus, Ohio, to partner for the
demonstration of a 138 kV three-phase Compact HTS FCL as
a part of ZEN’s ongoing DOE-sponsored HTS FCL
development program. A single-phase 138 kV Compact HTS
FCL prototype will be built and tested in 2010, and a three-
phase Compact HTS FCL demonstration unit will be built,
tested and installed in AEP’s Tidd substation located near
Steubenville, Ohio in 2011.
ZEN has considered a potential application for a “typical”
154 kV transmission application in an Asian electric power
grid. The design approach taken was for a device with a
relatively modest level of fault current reduction and a low
value of steady-state voltage drop (insertion impedance).
Figure 18 shows the simplified transmission line one-line
diagram PSCAD model that ZEN created to represent a
“typical” 154 kV transmission line. The voltage source
parameters with the corresponding line impedances are shown
on the left-hand side of the diagram, and a single lumped load
is shown on the right-hand side of the diagram along with the
“Timed Fault Logic.” The FCL is located in the middle of the
diagram, and the graphical representation of the HTS FCL
model that is inserted into the circuit is shown in Figure 19.
Figure 20 shows the prospective fault current with the FCL
bypassed and a 2,000 amp load current bypassing the FCL. In
this scenario, the prospective first peak asymmetric fault
current is 103 kA and the prospective symmetrical fault
current is 40 kA. Figure 21 shows the resulting limited fault
current under the same scenario as Figure 18, but with the
HTS FCL in the circuit instead of being bypassed. In this
scenario, the limited first peak of the fault current is 75 kA (a
28% reduction) and the limited symmetrical fault current is
24.8 kA (a 38% reduction), and the normal steady-state
voltage drop (insertion impedance) with a 2,000 amp load
current through the HTS FCL is 1.0% or about 890 volts (this
voltage drop is proportional to the load current and is less
under lighter loads).
0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75
-20
-15
-10
-5
0
5
10
15
20
25
30
Test 97 - ZENERGY POWER Compact FCL - 15kA Prospective Fault - 120A DC Bias
Time [sec]
L
in
e
C
u
rr
e
n
t [
kA
]
MEASURED LIMITED
MEASURED PROSPECTIVE
MODEL LIMITED
0.53 0.54 0.55 0.56 0.57 0.58 0.59 0.6 0.61 0.62
-5
-4
-3
-2
-1
0
1
2
3
4
5
Test 97 - ZENERGY POWER Compact FCL - 15kA Prospective Fault - 120A DC Bias
Time [sec]
F
C
L
B
A
C
K
E
M
F
[k
V
]
MEASURED
MODEL
0.18 0.2 0.22 0.24 0.26 0.28 0.3 0.32
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
Test 97 - ZENERGY POWER Compact FCL - 15kA Prospective Fault - 120A DC Bias
Time [sec]
F
C
L
B
A
C
K
E
M
F
[k
V
]
MEASURED
MODEL
Page 7
7
Figure 18 – The Simplified 154 KV Transmission Line PSCAD Model
A summary of a possible design of the modeled HTS FCL
is presented in Table 4. Each phase of the three-phase HTS
FCL would be about 1.5 meters in diameter and about 7
meters long. Using a horizontal orientation, it would fit in a
footprint about 5 m x 7 m x 4 m.
Figure 19– The 154 kV HTS FCL Model for PSCAD Analysis
Figure 20 – The Prospective Fault Current in the 154 kV Circuit without the
HTS FCL
Figure 21– The Fault Currents in the 154 kV Circuit with the HTS FCL
Again, it is important to understand that while this is an
HTS FCL design that could be manufactured today and which
ZEN is confident would work as modeled, it is not the only
possible design and other potential HTS FCL devices of
different sizes, orientations and performance can also be
designed and manufactured. For example, an HTS FCL with a
lower steady-state voltage drop could be built, if a longer
device were acceptable. If desired, the fault limiting
performance of the HTS FCL could also be increased by
increasing the diameter and length of the device.
154 kV Single-Phase FCL Parameters Units Value
Line-to Line Voltage kV 154
Line Frequency Hz 60
Rated Current Amperes 2,000
Asymmetry Factor # 2
Base Power MVA 100
Maximum Allowable Voltage Drop Percent of
Line Voltage
% 2
Line-to-Ground Voltage kV 89
FCL Fault Impedance Ohms 2
Steady-State FCL Allowable Inductance µH 1,698
Maximum Induced EMF for Desired Fault Current
Limiting
kV 44
Maximum De-Saturation Flux Change Tesla 4
Steady-State FCL Maximum Allowable Impedance Ohms 1
Coil Height Meters 5
Core Height Meters 7
Core Weight Kg 48,912
HTS Wire Length Meters 37,762
NI HTS Coil Amp-
Turns
730,000
Overall FCL Width Oriented Horizontally (three,
single-phases in array)
Meters 5
Overall FCL Length Oriented Horizontally (three,
single-phases in array)
Meters 7
Overall FCL Height Oriented Horizontally (three,
single-phases in array)
Meters 4
Table 4 – The 154 kV HTS FCL Basic Design Parameters
R=0
Line LoadFCL
0.12485 [ohm]
5.8868e-3 [H]
BRK1
293.6 [MVAR]
485.4 [MW]
154 kV AC
Source
453 [MW] 281 [MVAR]
Ea
ABC->G
Timed
Fault
Logic
