IEEE Guide for the
Application of
Faulted Circuit Indicators
Discussion Group - B17D
March 2012
Seattle
Fran Angerer, Chair
Brieana Reed-Harmel, Vice-Chair
Frank DiGuglielmo
John Hans
Fred Koch
John Banting
Gene Weaver
Tim Robeson
Mark Boettcher
Brieana Reed Harmel
Farris Jibril
Agenda
March 26, 2012
Introductions
Call for essential patents
Approval of Minutes
Review modified Draft of P1610
Discuss Additional Changes for Application Guide
Actions and next meeting
Adjournment
Call for Essential Patents
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when a patent or patent application becomes known after initial approval of the standard).
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a) A general disclaimer to the effect that the patentee will not enforce any of its
present or future patent(s) whose use would be required to implement either mandatory or
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B17D – GUIDE FOR APPLICATION OF UNDERGROUD FAULT CURRENT INDICATORS
Fran Angerer, Chair – Jerry Harness, Vice-Chair
Location: Denver, CO
Date: October 24, 2011
Meeting was brought to order by Chairman Fran Angerer at 10:35 AM.
Approximately 12 in attendance
Introductions
Review of Agenda
Call for Patents
The DG Chair provided an opportunity for participants to identify patent claims, patent application claims, or patent application claims of which the participant is personally aware and that may be
essential for the use of this standard. No patent claims, patent application claims, or holders of patent claims or patent application claims have been identified at this time.
Approved Minutes from the Spring 2011 Meeting, May 2011 at St. Pete Beach, FL
Announced need for new group vice chair – Volunteer: Brieana Reed-Harmel
Application for PAR was dismissed due to IEEE 1216 was under the authority of T&D Committee. John Banting requested the authority to be changed to ICC so that B17D could re-apply for PAR.
Current Volunteers for Working Group
Fred Koch
John Hans
Eugene Weaver
Tim Robeson
Fran Angerer
Brieana Reed-Harmel
Mark Boettcher
Farris Jibril
Ken Lee
Discussed Additional Topics for Application Guide
Lightening Strokes
Multiple OH faults & Sequential Faults
Momentary Fault Display vs. Permanent Fault Display
Add Pictorials
Section on new application of FCI’s (Network Indicators, Data Collectors, Smart Sensors)
Discussed Section 5 of proposed draft guide document
Future Work (Action Items):
Group will apply for a PAR for the Application Guide to replace 1216 and 1610.
Next meeting group will review IEEE 495 to decide if it needs revision.
Next Meeting at Seattle, WA, March 25-28, 2012.
Meeting adjourned. 12:18 PM
Possible Additional Subject Topics for New Application Guide
FCI response to Sequential multiple faults on OH lines?
Lightning Strokes and FCIs.
FC I response on Phase to Phase faults.
(Other Suggestions?)
4. Application of FCIs
Underground and Overhead FCIs are applied to monitor conductors at switchgear, transformers,
junctions, and at cable dips, risers, etc. FCIs are attached to conductors, terminations or test points
to sense for abnormally high currents typically associated with faults. FCIs trip with a visual,
audible, radio or remote indication when they have sensed conditions that are determined to
indicate an overcurrent has passed its location. FCIs located along the fault current path will trip to
indicate a “FAULT” while those that do not determine a fault current has passed its location will
remain “NORMAL”. Operating personnel locate the faulted section between the last FCI displaying
“FAULT” and the first FCI displaying “NORMAL”.
Three-phase, residential distribution circuits can be radial or looped. Looped circuits typically have
an open point. When choosing the placement of FCIs, consideration between cost and customer
reliability should be made. FCIs could be placed on both the incoming and outgoing cables of each
transformer. This would provide the most knowledge on where the fault is located since information
would be available to differentiate between cable faults and faults on the high voltage bus in the
transformer.
Evidence has shown that primary cable faults are much more prevalent than high voltage bus faults
in the transformer. To address the problem of cable faults, FCIs need only be placed on the
outgoing cables of each transformer. Further reduction in the number of FCIs installed could be
realized by locating them at every other transformer or less. However, for each reduction in the
number of FCIs, the time to locate and isolate the faulted cable will increase. The customer outage
time will also increase.
Faulted circuit indicators are affected by many items including cold load pickup, inrush, switching
surges and power follow currents. Proper application is essential to proper operation. FCI’s should
avoid tripping on inrush, cold load pickup and switching surges and operate before protective
devices.
4.0 Types of FCIs
4.1 Manual Reset
Manual reset FCIs require an operator to check and reset each indicator after each fault event. The large
variety of system conditions that occur on a distribution system makes it very difficult to create generalized
application rules. Failure to reset the indicator can cause confusion for subsequent faults. Mechanical FCIs
do not employ inrush restraint
4.2 Automatic Reset
FCIs are available with a variety of resetting means that return a tripped unit to its normal state. Automatic
reset types include reset by voltage, current, time or combinations of each.
4.2.1 Current reset
Current reset FCIs will reset their indication when load current is sensed. Contact manufacturer for load
sensitivity.
4.2.2 Voltage Reset
Voltage resetting fault indicators are not affected by load current. Voltage resetting FCIs can be used on
overhead or underground systems. There are several types of voltage resetting devices. The high (primary)
voltage resetting devices depend on the electrostatic field surrounding a high voltage cable or a separable
connector’s capacitive test point for operating power. The electrostatic reset type requires that the cable be
unshielded and a test point reset type requires the use of a test point type separable connector. The low
(secondary) voltage resetting devices can only be applied wherever a secondary voltage is available and do
not require a “test point type separable connector”.
4.2.3 Time Reset
Time reset FCIs will reset after a period of time. When choosing the length of time before reset, the time
chosen should be long enough to allow operating personnel time to locate and isolate the fault. If some or
all of the units reset before this is accomplished, confusing information as to the location of the fault exists.
In contrast, choosing an excessively long time can also cause problems if there is a subsequent fault before
the units have had a chance to reset.
4.3 FCI Display
The basic function of an FCI is to detect fault currents and provide evidence that fault current
was detected. There are a variety of FCI display options available.
The first decision is the type of display. The display can be a mechanical flag, audible alarm,
light, or counter.
When choosing an FCI display, the second consideration is whether the display is to be remote
or
non-remote.
The non-remote display can be located on the primary cable immediately below the
termination or on an elbow test point.. This arrangement has the disadvantage of having to
open the enclosure or substructure to observe the display.
The remote display can be mounted so that it is visible without opening the enclosure. This
design requires a sensor on the cable termination or elbow test point that can be connected to
the remote display via cables, optics, or other means.
4.4 Self adjusting FCIs
Adaptive trip FCIs automatically adjust the trip point depending on sensed load. These devices
are “one size fits all” and can eliminate the need to have many different fixed trip levels.
5. Three-phase Distribution Circuit Considerations
5.1 Introduction
An example of a distribution system, with various components and line segments is illustrated in Figure 1. The figure shows a
600A underground three-phase circuit getaway from a distribution substation, and includes a combination of 3∅ overhead and
underground portions, and 1∅ overhead and underground looped laterals. A looped circuit is a common distribution system feeder
design and can be fully or partially fed by closing an open tie, should normal service be disrupted.
Distribution line voltages generally range from 5 kV to 46 kV and feeder circuit ratings are generally in the 600-amp range.
Available short circuit current at the feeder breaker depends upon the size of the substation transformer, circuit impedance and
system voltage, but generally range from 2,000 to 12,000 amps but may in some cases exceed these values.
Figure 1 – Example distribution circuit
5.2 Fault types
A fault is an abnormal condition where there is an electrical short circuit between an energized phase
conductor and ground or two or more dissimilar phase conductors. Faults can occur from a variety of
sources. Several examples are listed below:
• cable insulation, joint or termination failures
• digging into underground cables
• dielectric failures of electrical equipment
• tree limbs that fall onto overhead phase wires
• overhead wires contacting each other during high winds
• vehicle accidents with overhead poles or pad mounted distribution equipment
• wildlife contacting energized conductors
• contaminated insulators that flash-over
In order to properly apply Faulted Circuit Indicators (FCIs) and understand potential causes of operational
issues, one must consider the different types of faults, which can occur on an underground distribution
system. These faults are generally limited to two types: low impedance and high impedance. FCIs are
designed to detect low impedance faults and cannot respond reliably to high impedance faults. FCIs are
designed to detect high magnitude fault current that is typically sufficient to initiate breaker or recloser
tripping or fuse operation.
•The trip response should coordinate with all protective devices to ensure that the FCI will trip under most
low impedance fault conditions. The user should consider coordination with current-limiting fuses due to
their fast sub-cycle clearing time. Current Limiting Fuse protection may require FCIs to respond as fast as
¼ cycle.
5.2.1 Low impedance faults
Low impedance faults, or bolted faults can be either very high in current magnitude (10,000
amperes or above) or fairly low, e.g. 300 amperes at the end of a long feeder. Faults able to be
detected by high energy protective devices for solidly grounded systems are all considered low
impedance faults. The fault impedance of most detectable faults is close to 0 ohms. This
implies that the phase conductor either contacts the neutral wire or that the arc to the neutral
conductor has a very low impedance. The maximum fault impedance of a detectable fault is
approximately 2 ohms or less. As indicated in figure 2, 2 ohms of fault impedance decreases
the level of fault current for close-in faults, but has little effect for faults some distance away.
If values of 2 ohms or less are used in calculations considering low impedance detectable
faults, the result of those calculations will be very close to the actual fault levels present in the
distribution system. [B3]
5.2.2 High impedance faults
High impedance faults are not detectable by normal protection means. This implies that high
impedance faults do not contact the neutral, do not arc to the neutral, or there is not enough
voltage to establish a low impedance earth return path. As a result, these types of faults are
not detectable by conventional protection devices. Fault indicators sense over-current
conditions and as such, cannot be used to reliably detect high impedance faults.
5.2.1 Low impedance faults
Low impedance faults, or bolted faults can be either very high in current magnitude (10,000 amperes or
above) or fairly low, e.g. 50 amperes at the end of a long feeder. Faults able to be detected by high energy
protective devices for solidly grounded systems are all considered low impedance faults. The fault
impedance of most detectable faults is close to zero ohms. This implies that the phase conductor either
contacts the neutral wire or that the arc to the neutral conductor has a very low impedance. The maximum
fault impedance of a detectable fault is approximately two ohms or less. As indicated in Figure 2, two ohms
of fault impedance decreases the level of fault current for close-in faults, but has little effect for faults some
distance away. If values of two ohms or less are used in calculations considering low impedance detectable
faults, the result of those calculations will be very close to the actual fault levels present in the distribution
system. [B3]
5.3 Reclosing, re-fusing and inrush
For protected circuits, re-fusing or reclosing may result in inrush currents when the
equipment beyond the load is re-energized. The magnitude of this inrush current is
affected by the type of equipment, system impedance, load characteristic, and pointon-wave when the circuit is energized. See Figure 2. For a common protective
reclosing sequence, the inrush current on the reclose cycle may exceed the trip
level of the FCI on the un-faulted phases. The end user must be aware of the
possibility of high inrush currents resulting in the FCI tripping.
Inrush could be a problem on distribution circuits. If inrush is a concern (usually
because fault levels are very low, requiring FCIs with low trip), then precautions
must be taken to prevent operation of FCIs. A variety of inrush restraints are
available from manufacturers. Some use time/current response curves, while others
use inrush restraint logic.
Considering that the time/current characteristics of a fuse curve and an inrush curve
are similarly shaped with the inrush curve lying to the left of the fuse curve, as
shown in Figure 3. An FCI trip response must lie between the inrush curve and the
protection curve to assure coordination. If it is coordinated, the FCI will not trip on
inrush, but will trip before the protection clears.
25
0
P.U. of Connected Load
5
10
15
20
Transformers
Laterals
Feeders
Figure 2 – Typical magnitudes of inrush current
FCI Response
should be between
these curves
Protection
curve
Inrush
curve
Figure 3 - FCI Trip Response
5.3.1 Cold load pickup
Cold load pickup results from the re-energization of a circuit following a long outage. It is often the cause
of some protective device mis-operations, since there is no actual fault in the circuit. Figure 4 illustrates
several cold load pickup curves developed by various sources. These curves are normally considered to be
comprised of the following three components:
 Inrush – lasting a few cycles
 Motor starting – lasting a few seconds
 Loss of diversity – lasting many minutes
When a fuse operates as a result of cold load pickup, it is most likely due to a loss of diversity. Since fuses are
often sized for coordination, not load, this condition is rare on most laterals. Relay operation during cold load
pickup is generally the result of a trip on the instantaneous unit and probably results from high inrush. Likewise,
an FCI operation would not appear to be the result of loss of diversity but rather the high inrush currents.
Loss of Diversity
Figure 4 – Cold load inrush current characteristics for distribution circuits
5.4
Interference Energy
5.4.1 Backfeed Energy
Backfeed is caused by the release of energy stored in various components of the
distribution system, or the loads attached to it. If a fault occurs on the system, the
impedance of the circuit can fall to very low levels. In this case, the energy stored
in the capacitance or inductance of the circuit can result in relatively large current
flowing through the cable and into the fault. The backfeed energy flows in a
direction opposite of normal flow and can influence FCIs downstream from the
fault.
Sources of backfeed energy include:






Capacitor banks,
Cable discharge.
Rotating Machinery
Proximity Energy
Single-phase protection on three-phase loads
Distributed Generation
5.4
Interference Energy
5.4.1 Backfeed Energy
Backfeed is caused by the release of energy stored in various components of the distribution system, or the loads attached
to it. If a fault occurs on the system, the impedance of the circuit can fall to very low levels. In this case, the voltage stored
in the capacitance or inductance of the circuit can result in relatively large current flowing through the cable and into the
fault. The backfeed energy flows in a direction opposite of normal flow and can influence FCIs downstream from the fault.
Sources of backfeed energy include:





Capacitor banks,
Cable discharge.
Motors,
Proximity Energy
Single-phase protection on three-phase loads
5.4.1.1 Capacitor banks
A situation where backfeed energy could cause a false trip is on a single-phase
fault in three-phase circuits with three-phase capacitor banks and single-phase
tripping feature. When a single-phase fault occurs and opens the single-phase
protection, the two unfaulted phases will remain energized. The capacitors
connected to the faulted phase will discharge into the fault. If the circuit impedance
is low enough and if the capacitors were nearly charged to peak voltage at the time
of the fault, the FCI installed between the capacitors and the fault could be tripped.
The duration of this discharge is brief, but can be a concern as a cause for an FCI
to trip.
Capacitor Discharge to Fault
FCI
FCI
Figure 5
5.4.1.1 Capacitor banks
A situation where backfeed current could cause a false trip is on a single-phase fault in three-phase circuits with three-phase
capacitor banks and single-phase tripping feature. When a single-phase fault occurs and opens the single-phase protection,
the two unfaulted phases will remain energized. The capacitors connected to the faulted phase will discharge into the fault.
If the circuit impedance is low enough and if the capacitors were nearly charged to peak voltage at the time of the fault, the
FCI installed between the capacitors and the fault could be tripped. The duration of this discharge is brief, but can be a
concern as a cause for an FCI to trip.
5.4.1.2 Cable discharge
A similar discharge can result from cable discharge due to the capacitance
of the underground cable. The cable downstream from a fault will
discharge back to the fault, which could cause an FCI to false trip. The
length of the cable changes the frequency and duration of the discharge,
whereas the voltage and cable type will control the peak discharge current.
Need permission
from Cooper and
reference.
Figure 6
Figure 6 shows a simplified 25 kV distribution cable system
with a fault having a variable amount of cable behind it.
Assuming that the copper 1/0 cable has an L = 196.3 uH per
foot and C = 59 nF per foot, the discharge frequency can be
calculated:
f = 1/(2π√LC)
If there is 1000’ of cable behind the fault then f = 46.77 kHz
5.4.1.3 Rotating machinery (motors)
Rotating machinery after a fault can produce backfeed current that flows to the
fault from downstream sources that can trip or reset FCIs. The magnitude and
duration are typically very low, however, they can result in energy levels
sufficient to trip or reset FCIs, depending on the system impedance.
5.4.1.4 Proximity Energy
The influence of current or voltage from adjacent conductors or circuits on the operation of a
FCI is known as Proximity Effect. The effect can occur in a number of different ways.
Multi-phase circuit conductors could be very close together. The close proximity of the
conductors can make it difficult for FCIs to properly distinguish between the various
magnetic or voltage fields generated during a fault, reclose or reset condition. Conductors in
close proximity to one another (i.e., incoming and outgoing cables in a feed-thru transformer,
junctions, spacer cable, or underbuilt circuits) can influence the sensing ability of the FCI. In
addition, fault current in a phase conductor can be reduced by opposite flowing fault current
in the respective neutral conductor. Depending on the placement of the FCI, close proximity
could affect a proper trip or reset response.
Need Diagram
5.4.1.4 Proximity Energy
The influence of energy from adjacent conductors or circuits on the operation of a FCI is known as Proximity Effect.
The effect can occur in a number of different ways. Multi-phase circuit conductors could be very close together. The
close proximity of the conductors can make it difficult for FCIs to properly distinguish between the various energy
fields generated during a fault, reclose or reset condition. Conductors in close proximity to one another (i.e., incoming
and outgoing cables in a feed-thru transformer, junctions, spacer cable, or underbuilt circuits) can influence the sensing
ability of the FCI. In addition, fault current in a phase conductor can be reduced by opposite flowing fault current in the
respective neutral conductor. Depending on the placement of the FCI, close proximity could affect a proper trip or
reset response.
Need Diagram
typicalorientation
adjacentcable
distance
DEFINITION:
Proximity Energy
5.4.1.5 Delta connections
In other situations, such as isolated overhead circuits that serve three-phase
underground taps having single-phase protective devices, feedback current can be
generated through any delta connected load that remains connected to a grounded
wye-grounded wye transformer after a fault occurs. This current could be sufficient
to false trip or to incorrectly reset an FCI, which was previously tripped.
See Figure 7.
Figure 7 – Delta connected loads
“Electric Power Distribution Handbook”
Burke
“Electric Power Distribution Handbook
Burke”
Transformer Connection
Primary
Secondary
Load Connection
Possible Backfeed
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Yes
Backfeed can occur with these transformer/Load connections when used with single phase protection.
5.4.1.6
Multi-legged Transformers
In a similar situation, when FCIs are installed on multi-legged core transformers, circulating
current within the transformer may be of sufficient magnitude to reset a tripped FCI.
5.4.1.7 Installation of faulted circuit indicators on parallel cable circuits
FCIs that are installed on parallel feeder cables can give false indications of the fault
location. See Figure 6. When a fault occurs on a parallel cable run, fault current will
flow in both cables. Each FCI on both ends of the parallel cable run will trip
indicating a fault. This situation may lead to the conclusion that the fault occurred in
the next downstream cable run.
Flow of Fault Current
Figure 8 – Parallel Cable Circuits
FCIs Indicating Fault
5.4.1.6
Multi-legged Transformers
In a similar situation, when FCIs are installed on multi-legged core transformers, circulating
current within the transformer may be of sufficient magnitude to reset a tripped FCI.
5.4.1.8 Directional FCIs
Directional FCIs can be used to identify which cable of a parallel cable
circuit is faulted. See Figure 9. When each FCI at the source end of the
parallel cable circuit indicate a fault condition in the same direction the fault
is located beyond this point. If the FCIs located at the load end of the
parallel cable circuit indicate a fault in opposite directions, the fault is toward
the source.
Opposite Pointing
FCIs Indicate Fault
is on This
Cable Section
Source
Load
Flow of Fault Current
Figure 9– Directional FCIs
Opposite Pointing FCIs
Indicate Fault Is Toward
Source
5.4.1.9
Backfeed Voltage (This needs input and clarification)
Backfeed voltage can cause voltage resetting FCIs to incorrectly reset. FCIs
located on three-phase circuits with single-phase protection and delta-connected
loads are susceptible to this type of situation. Under these circuit conditions the
backfeed voltage could be sufficient to cause an FCI to reset.
5.4.1.10
Distributed Generation
Distributed generation can be a source of both current and voltage. When Distributed
Generation is connected to the circuit beyond the fault, they may provide sufficient current to
trip FCIs that are located between the fault and the generator. Generators that do not isolate
themselves from the faulted circuit quickly enough may also provide voltage sufficient to
reset a voltage reset FCI. The actual effects of distributed generators depend on the sizes of
the generator(s) and the interconnection/protection requirements of the utility.
6. Other considerations
Annex A
(informative)
Application Information
1. The typical application of FCIs to 200 / 600 A, distribution circuits is summarized as follows:
2. Pick a trip level of less than 50% of the available fault current or 500 amperes, whichever is less.
3. Ignore inrush, except on very long or heavily loaded laterals. In cases where inrush is a problem, use
inrush restraint.
4. Use a fault impedance of 0 to 2 ohms when calculating fault currents.
5. Ignore “high impedance” faults since they are undetectable with FCIs.
6. Ignore “cold load pickup” when using automatic resetting FCIs.
7. For current resettable devices, select the device with the lowest reset current available.
8. Use voltage reset or time reset where load currents are low (e.g., 25 kVA transformer on a 34.5 kV
system).
9. Select a display method that enhances operating practices.
10.Coordinate FCIs with inrush current and protective devices.
11.Place the FCIs on outgoing cables.
Annex B
(informative)
Bibliography
[B1] “Application of Fault Indicators on the Con Edison Electrical Distribution System”, J. P.
DiDonato, EEI T&D Meeting, May 17, 1989.
[B2] “Characteristics of Distribution Systems That May Affect Faulted Circuit Indicators,” J. J. Burke.
[B3] “Characteristics of Fault Currents on Distribution Systems”, J. J. Burke, D. J. Lawrence, IEEE
Transactions on Power Apparatus and Systems, Vol. PAS-103, No. 1. January 1984, pages 1-6.
[B4] Electric Power Research Institute Report EL-3085, Distribution Fault Current Analysis, May 1983
[B5] “Fault Indicator Applications at Virginia Power Company”, T. E. Royster, 1991 IEEE/PES T&D
Conference and Exposition.
[B6] “Fault Indicator Types, Strengths & Applications”, F. J. Muench, Jr., G. A. Wright, IEEE
Transactions on Power Apparatus & Systems, Vol. PAS-103, No. 12, December 1984, pages 36883693.
[B7] IEEE 100, “The Authoritative Dictionary of IEEE Standards Terms”, Seventh Edition.
Fall 20112 – St. Petersburg, FL November 11-14, 2012
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