Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS00
Page 1 of 1
INDEX
SECTION WFS01: GENERAL DISTRIBUTION FUSING
GENERAL ....................................................................................... Page 1
TYPES OF OVERCURRENT DEVICES .................................... Page 1
DISTRIBUTION LINE PROTECTION .......................................................... Page 1
SECTION WFS02: GENERAL DISTRIBUTION FUSING
FUSE CUTOUTS .......................................................................... Page 1
FUSE LINKS .................................................................................. Page 4
CURRENT LIMITING FUSES ..................................................... Page 5
BAYONET FUSES ........................................................................ Page 10
SECTION WFS03: OVERHEAD TRANSFORMER FUSING
SECTION WFS04: PADMOUNT TRANSFORMER FUSING
OPERATING VOLTAGE TABLES FOR
PADMOUNT TRANSFORMERS ................................................... Page 1
SECTION WFS05: STEP-TIE TRANSFORMERS
SECTION WFS06: DISTRIBUTION CAPACITORS
SECTION WFS07: RECLOSERS
GENERAL ...................................................................................... Page 1
TYPES OF RECLOSERS ............................................................ Page 1
SEQUENCE AND OPTIONS ......................................................... Page 2
SECTION WFS08: SECTIONALIZERS
GENERAL ...................................................................................... Page 1
TYPES OF SECTIONALIZERS .................................................... Page 1
SECTION WFS09: CIRCUIT BREAKERS AND RELAYS
GENERAL - BREAKERS ............................................................. Page 1
GENERAL - RELAYS .................................................................. Page 1
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS01
Page 1 of 2
GENERAL DISTRIBUTION FUSING
1. GENERAL
The purpose of an overcurrent protective device is to isolate a fault or overloaded piece of
equipment from the electrical delivery system. An overcurrent protective device will not prevent a
fault, only isolate after it has occurred. Equipment that has a capacity rating (e.g. transformers)
should have an appropriately sized overcurrent protective device on the source side of the
equipment to provide overload protection.
2. TYPES OF OVERCURRENT DEVICES
Overcurrent protective devices that are in use on the electrical delivery system are: breakers,
reclosers, sectionalizers, and fuses. Each of the devices has their own operating characteristics and
applications. Some are single-phase devices, while others are three-phase. Some require
replacement parts after operating (fuses), while others just need to be reset (breakers, reclosers).
3. DISTRIBUTION LINE PROTECTION
a. Main Feeder Protection
The main feeder should be protected by a recloser (hydraulic or electronic) or a breaker with
relays in the distribution substation. The main line should be solid to the normal open point or
the end of the main feeder of a radial line if the zone of protection of the substation protective
device reaches to the end of the main feeder. If the substation protective device's zone of
protection does not reach to the end of the main feeder, another protective device should be
installed in the main line at one of the following points:
1) Transition point from urban to rural customer base.
2) Downstream from a large customer.
3) At the end of the substation protective device's zone protection.
The substation protective device can be single or three phase depending on the makeup of the
customers served by the feeder. When sizing the main feeder protective devices, consideration
should be given for backfeeding (if applicable).
b. Protection of Taps off of the Main Feeder
1) Three-Phase Taps
All three-phase taps greater than two spans should have an overcurrent protective device
installed on it to minimize the exposure to the main feeder. This device should be located as
close as possible to the tap point. Installing an overcurrent device on a tap may not be
possible due to load levels (normal and when backfeeding) or miscoordination with
upstream/downstream devices. The type of device used depends on the customer makeup,
amount of line to be protected, load (normal and backfeeding) and upstream/downstream
protective devices.
2) Single-Phase Taps
All single-phase taps greater than two spans should have an overcurrent device installed as
close as possible to the tap point. The type of device used depends on the customer
makeup, amount of line protected, load and upstream/downstream protective devices.
Section WFS01
Page 2 of 2
E.C.S.
INFORMATION SECTION
GENERAL DISTRIBUTION FUSING
Issued 06-01-07
FUSING
c. Protection of Taps Off of Taps
Engineering judgment needs to be used when determining whether or not to install overcurrent
protective devices on taps off of taps. Some items to consider when determining whether or not
to install a device are:
Outage exposure to customers.
Troubleshooting.
Providing locations to sectionalize.
Coordination with upstream/downstream devices.
Cost of the device.
Single-phase taps off three-phase taps that serve three-phase customers should have an
overcurrent device installed on the single-phase tap as close as possible to the tap point. This is
done to reduce the possibility of single phasing the three-phase customers.
d. Riser (Dip) Pole Fusing
1) Main Feeder
Overcurrent protection where the main feeder transitions from overhead to underground is
not required. It is recommended to install switches at the riser pole(s) that are compatible
for use with a loadbuster tool. This allows the underground section to be isolated from the
overhead portion of the main feeder, if so desired.
2) To a Single Transformer
Use the appropriate table to select the riser fuse size.
3) To Multiple Transformers
Use the appropriate table to determine the minimum size fuse that will coordinate with the
largest transformer's bayonet fuse downstream from the riser. When sizing this fuse,
consideration should be given to:
Load current (normal and backfeeding where applicable).
Upstream devices.
Future development.
Size and number of transformers fed from riser.
(END)
Issued 06-01-07
FUSING
E.C.S.
INFORMATION SECTION
Section WFS02
P a g e 1 o f 11
GENERAL DISTRIBUTION FUSING
1. FUSE CUTOUTS
a. General
Most fuse cutouts operate on the expulsion principle. They employ an arc confining tube with a
deionizing fiber liner and a fuse link.
To interrupt fault current, the fiber liner is heated when the fusible element of the fuse link melts,
emitting deionizing gases, which accumulate within the tube.
The arc is stretched, compressed, and cooled within the tube, and escaping gas at the tube
ends carry away a portion of arc-sustaining particles. Reestablishment of the fault current arc
after current passes through the zero point is prevented by the presence of the deionizing gases
and by extreme gas pressure and turbulence which increase the dielectric strength of the air
gap in the tube. High pressure gases then expel arc-supporting ions remaining in the tube.
b. Types
Enclosed, open, and open-link cutouts differ in their external appearance (See Figure 02-1 Fuse
Cutouts) and method of operation. Enclosed cutouts have terminals, fuse clips and fuseholders
mounted completely within an insulating enclosure. Open cutouts have these parts completely
exposed as the name indicates. Open-link cutouts have no integral fuseholder; the arc confining
tube for these cutouts is incorporated in the fuse link.
Source: Alliant Electrical Standards
Figure 02-1 Fuse Cutouts
E.C.S.
INFORMATION SECTION
Section WFS02
Page 2 of 11
Issued 06-01-07
GENERAL DISTRIBUTION FUSING
FUSING
c. Cutout Ratings
VOLTAGE
RATING
MAXIMUM
OPERATING
VOLTAGE
BIL
CONTINUOUS
CURRENT
15 kV
15 kV
95 kV
100A
10,000A
106667
15 kV
15 kV
95 kV
200A
12,000A
151129
15 kV
15 kV
95 kV
300A
12,000A
123342
15 kV
15 kV
95 kV
100A
16,000 A
102012
INTERRUPTING
CAPACITY*
ITEM ID
15 kV
15 kV
95 kV
100A
10,000A
121719**
15 kV
15 kV
95 kV
200A
22,400A
120790***
27 kV
24.9 kV
125 kV
100A
12,000A
120312
27 kV
24.9 kV
125 kV
200A
10,000A
121375
27 kV
24.9 kV
125 kV
300A
12,000A
104947
27 kV
24.9 kV
125 kV
100A
12,000A
120247**
* Asymmetrical Current Rating- Depending on the X/R Ratio the Symmetrical Rating for the 10,000 A. could be
as low as 7,100 A, 12,000 A could be as low as 8,000 A, 16,000 A could be as low as 10,600 A.
** Arc chute cutout for fixed capacitor banks.
*** This unit is for SMU-20 fuses.
Source: Alliant Electrical Standards
Chart 02-1 Cutout Ratings
d. Replacement Parts
ITEM
VOLTAGE
RATING
CURRENT
RATING
INTERRUPTING
RATING
ITEM ID
Fuseholder
15 kV
100A
10,000A
106793
Fuseholder
15 kV
200A
12,000A
Fuseholder
15 kV
100A
104799
--
Switchblade
15 kV
300A
16,000A
--
Fuseholder
27 kV
100A
12,000A
107487
Fuseholder
27 kV
27 kV
200A
10,000A
--
104799
Switchblade
300A
122582
102209
Source: Alliant Electrical Standards
Chart 02-2 Replacement Parts
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS02
P a g e 3 o f 11
GENERAL DISTRIBUTION FUSING
e. Current Rating Applications
The American National Standard Institute's (ANSI) C37.42-3.2.1 states:
1) "For all cutouts except as noted in 2), fuse link sizes shall be from one Ampere to the
rated continuous current of the cutout.
2) For cutouts rated above 100 Amperes, fuse link sizes shall be from above 100 Amperes
to the rated current of the cutout."
Even though a fuse link may fit, cutout fuseholders are designed for a specific fuse range.
Thus, the fuse range for a 100 Ampere cutout runs up to and includes the 100 Amp fuselink.
The fuse range for a 200 Ampere cutout is from 125 Amp up to and including the 200 Amp
fuselink. Misapplication may result in a cutout that will not operate properly.
DO NOT FUSE A 200 AMPERE CUTOUT WITH LESS THAN A 125 AMP FUSE LINK
NOR A 100 AMPERE CUTOUT WITH MORE THAN A 100 AMP FUSE LINK.
f.
Cutout Installation Guidelines
1) Don't mount a cutout in a vault or other enclosed area. The cutout operates by expelling
gases during interrution. Limiting the gas flow can result in insulator flashover.
2) Don't mount cutouts directly above transformers, capacitors, etc. Expelled gases and debris
can cause flashovers. This will also minimize any safety hazard to the operator in case of
equipment failure while opening or closing the cutout.
3) Always cut off any excess tail of the fuse link. Never stick excess fuse link cable (tail) into
the fuse tube or allow it to hang free where it could get in the way of the fuseholder swinging
open or cause a flashover.
4) Don't pull too hard on the pigtail of the fuse link. According to ANSI specifications, fuse links
are designed to withstand up to ten pounds of tension. Pulling in excess of ten pounds can
damage the fuse element, especially on small fuse links.
5) Do not remove or damage the small tube on the fuse link. This tube is not packaging. Low
fault currents which do not clear in the fuseholder tube of the cutout, are cleared in this
auxiliary fuse tube.
g. Fuse Link Installation
There have been some problems with fuse links pulling apart. This may be caused by not
pulling the tension setting mechanism (flipper) all the way back when installing a fuse in the
holder. If the tensioning device is not pulled all the way back, it will exert extra tension on the
fuse link when the holder is slammed in the cutout.
h. Cutouts in Open Position
Cutout doors (fuse holders)should not be left in the open position. Moisture can build up in the
fuse holder causing freezing and thawing action which can result in premature failure upon reenergization. Water in the fuse holder can also make the liner swell and trap the fuse link. In this
condition, the fuse holder may not drop open when subjected to fault current. When a cutout
must be disconnected from the line, hang the door on the pole by the hotstick ring with a nail so
the fuse tube or switch blade is in the upright position.
Section WFS02
Page 4 of 11
E.C.S.
INFORMATION SECTION
GENERAL DISTRIBUTION FUSING
i.
Issued 06-01-07
FUSING
Cutout Fuse Tubes With Exposed Fiberglass
Fuse tube paint coatings are expected to last approximately 20-25 years under normal
conditions (there may be a reduction in the useful life in areas of high chemical contamination).
However, the paint coating on cutout fuse tubes can become weathered to the point of exposing
the fiberglass. The exposed fiberglass presents a potential safety hazard to line personnel
during refusing of these cutouts. These same fuse tubes are also susceptible to the entrance of
moisture which can affect the electrical operation of the cutout. For these reasons, all cutout
fuse tubes with exposed fiberglass should be replaced.
j.
Cracking of Cutout Porcelain
Cutout porcelain bodies can break allowing the cutout door to fall free. Cutout porcelain bodies
were changed from brown to gray in about 1965. For these reasons, brown cutouts, whether in
inventory or in service, should be replaced and/or junked. Also, extreme care should be
maintained when handling and working around gray porcelain cutouts. To minimize the
possibility of damage, keep cutouts in the shipment box until they are to be installed at the job
site. Avoid accidental banging of the porcelain body during handling and installation. Inspect
new and existing cutouts for cracks. If cracks are seen in gray porcelain cutouts, they also
should be replaced.
2. FUSE LINKS
a. General
A distribution fuse link consists of three basic
parts - button, fusible element, and leader as
shown in Figure 02-2 Fuse Link. Various types
of links are available, designed under NEMA
specifications, to fit the several types of cutouts
mentioned previously.
A link with an element of given material, length,
and cross section is rated to carry a specific load
current and melt in a definite time when
subjected to a specific fault current.
When placed in a cutout and connected into a
distribution line, a fuse link is ready to function
as a protective device. When a fault occurs, the
fusible element is melted by the fault current.
Simultaneously, because of its high resistance,
the strain wire is heated and separates. At this
instant, an arc establishes itself across the
severed link. The arc is a conducting path of
ionized particles, among which are metallic ions
of the melted element and wire and ionized gas.
Because the arc provides a path for fault current
to flow, it must be extinguished rapidly in order
to prevent damage to the system and equipment.
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS02
P a g e 5 o f 11
GENERAL DISTRIBUTION FUSING
As shown in Figure 02-3 Expulsion Fuse Fault Interruption, the expulsion fuse is capable of
interrupting higher currents, but does not limit the current before the circuit is interrupted.
SOURCE: Alliant Electrical Standards
Figure 02-3 Expulsion Fuse Fault Interruption
b. Fuse Link Loading
Fuse links should not be loaded continuously above 100% of their current rating. Fuse links may
be overloaded for short, infrequent periods of time up to 140% of their rated current. Loading
fuse links beyond 100% of their current rating for long, frequent lengths of time can change their
time - current characteristics resulting in coordination problems, or may partially melt the fuse
link resulting in the malfunctioning of the fuse link and cutout during a fault.
c. Fuse Link Failures
A fuse link installed in a cutout with a loose buttonhead can cause overheating and result in
premature failure. Fuse link buttonheads are supposed to be properly installed at the factory,
however, they may become loose during handling and transportation. Therefore, be sure all
buttonheads are correctly secured (screwed all the way down - tight) before installing fuse links
in cutouts.
3. CURRENT LIMITING FUSES
a. General
Current limiting fuses have many features which make them ideally suitable as protective
devices. They primarily limit the fault current to a fraction of its damage potential within the first
one-half cycle of fault current (see Figure 02-4 Current Limiting Fuse Fault Interruption). They
do not expel any gases and are completely silent during operation. These characteristics are
particularly useful for protective devices in constricted areas such as indoor and underground
applications. By limiting the fault current, they greatly reduce the mechanical and thermal stress
imposed on system components.
Section WFS02
Page 6 of 11
E.C.S.
INFORMATION SECTION
Issued 06-01-07
GENERAL DISTRIBUTION FUSING
FUSING
Source: Alliant Electrical Standards
Figure 02-4 Current Limiting Fuse Fault Interruption
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS02
P a g e 7 o f 11
GENERAL DISTRIBUTION FUSING
The fusible element consists of one or more silver elements spirally wound and surrounded by a
high-purity silica sand and enclosed in a high-temperature resistant material tube.
Source: WP&L Electrical Standards
Figure 02-5 Current Limiting Fuse Element
When exposed to a high-current fault, the element melts almost instantaneously over its full
length. The resulting arc loses its heat energy rapidly into the surrounding sand. This energy
melts the sand to a glass-like substance. The rapid loss of heat energy and arc confinement by
the molten glass literally chokes off the current to a relatively small value known as the letthrough current.
b. Partial Range Current Limiting Fuses
1) General
The partial range current limiting (PRCL) fuse is similar to the full range current limiting
(FRCL) fuse in that it will limit high energy fault current to a fraction of its potential within the
first one-half cycle of fault current (see section on current limiting fuses).
However, the PRCL will not clear the low level faults and transformer overloads that the
FRCL fuse will. For this reason, it is used in series with a bayonet expulsion fuse in
padmount transformers and with an expulsion fuse on overhead transformers and capacitor
banks.
The PRCL fuse performs its function in a manner similar to the FRCL fuse does. In
padmount transformers, the PRCL fuse is permanently installed under oil. It operates only
on high energy faults due to transformer failure. Therefore, a padmount transformer with a
blown PRCL fuse must be changed out.
Where the current limiting fuse is mounted on the load side of the cutout, the manufacturers
recommend that the current limiting fuse be mounted well out of the expulsion-fuse venting
area of the cutout. Also, one foot of clearance must be maintained between the fuse and:
a) other phase conductors
b) grounded leads
c) primary conductor of the same phase
Section WFS02
Page 8 of 11
E.C.S.
INFORMATION SECTION
GENERAL DISTRIBUTION FUSING
Issued 06-01-07
FUSING
These recommendations will help prevent short-circuits from expulsion fuse gases during
cutout operations.
2) Application
Current limiting fuses are used to protect transformers from catastrophic failure during a high
fault current event. The available fault current levels which determine when current limiting
fuses are installed are as follows:
a. For 4kV systems, the threshold fault current is 7,100 amps, phase to ground.
b. For 12.5kV – 13.8kV, the threshold is 6,400 amps, phase to ground.
c. For 24kV and 24.9kV systems, the threshold is 4,500 amps, phase to ground.
There are two different styles of partial range current limiting fuses used at Alliant Energy.
K-Mate fuses are mounted to the bottom terminal of a cutout as shown in figure 2-6. The Kmate current limiting cartridge is provided in a 40 Amp rating and is used to protect the
following overhead transformers:
a. 4kV systems – 37.5 kVA and 50 kVA transformers.
b. 12.5kV, 13.2kV and 13.8kV systems – 100 kVA transformers.
c. 24 kV & 24.9 kV systems – 250 kVA transformers.
Figure 02-6 K-Mate Partial Range Current Limiting Fuse
ELF Tandem mount - The Cooper Power Systems Tandem ELF current-limiting fuse
combines the features of a series fuse link and a backup current-limiting fuse cartridge. The
Tandem ELF unit replaces an S&C, Chance, etc. standard cutout door/assembly as shown
in figure 2-6. The ELF has a 25 Amp current limiting fuse that coordinates with up to a 15T,
25K and 25 standard speed expulsion fuse links. This limits the size of transformer that can
be effectively protected without miss-coordination of overcurrent devices. Tandem ELF
devices are used as follows:
a. 4kV systems – all overhead transformers 25kVA and smaller.
b. 12.5kV, 13.2kV and 13.8kV systems – all overhead transformers 50kVA and smaller.
c. 24kV and 24.9kV systems – all overhead transformers 167kVA and smaller.
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS02
P a g e 9 o f 11
GENERAL DISTRIBUTION FUSING
The Cooper Tandem ELF Current-Limiting Dropout Fuse is a cost effective alternative to the
K-Mate current limiting fuse/fuse cutout combination. This unit combines a current limiting
fuse with a shortened expulsion fuse assembly and is designed to be interchangeable with
standard S&C type XS and Chance type C fuse cutouts doors/fuse tubes. This feature
makes the installation, removal and testing of the ELF units easier and safer than the KMate devices.
Figure 02-7 Tandem Mount Series Expulsion and Current Limiting Fuse Cutout
3)
Alliant Application Philosophy
The pressure generated by an arc in the transformer tank during a fault is a function of the
energy delivered to the fault by the electric delivery system. This energy is dependent
upon the available fault current, the arc resistance (or arc voltage), arc length and the
duration of current flow.
The utility industry has relied upon testing and operating experience to develop thresholds
for the application of current limiting fuses to minimize the risk of a pole-type transformer
tank failure. ANSI standard c57.12.20-1988, Requirements for Overhead-type Distribution
Transformers, 500 kVA and Smaller; High Voltage, 34,500 and Below; Low Voltage
7970/13,8090 Volts and Below specifies design tests to demonstrate the capability of a
transformer enclosure to withstand pressure changes due to specified faults. ANSI
standard C57 requires that transformer enclosures have the capability of withstanding
pressure changes due to an 8,000 amp fault at 7,200 volts for ½ cycle. The total clearing
time for a fuse cutout is 0.8 cycle. For this amount of time, a fault of approximately 6,400
amps will generate approximately the same amount of energy as the ANSI test at 8,000
amps. This fault current level is applicable for 12.5kV through 13.9kV delivery systems.
Based on this energy let-through capability, and assuming the transformer sees fault
current for 0.8 cycles, the fault current thresholds stated above were determined. The 0.8
cycle is more conservative than the ½ cycle standard and is based on the amount of time
a fuse link will take to clear higher current faults.
Limited information is available regarding 2.4kV transformer tank damage and failures due
to internal faults. At lower voltages, it is difficult to sustain a 1-inch arc. Shorter arc
lengths generate less energy. From Alliant Energy experience, very few, if any,
catastrophic transformer failures have occurred on our 2.4/4.16 kV systems. The fault
current interrupting rating of a 10,000-amp cutout is 7,100 amps. Therefore, on
2.4/4.16kV delivery systems at locations where the available fault current may exceed the
interrupting rating of the cutout, a current limiting fuse will be installed.
Section WFS02
P a g e 10 o f 1 1
E.C.S.
INFORMATION SECTION
GENERAL DISTRIBUTION FUSING
Issued 06-01-07
FUSING
At this time, WP&L has very few, if any, 2.4 kV single phase delivery systems. More
2.4/4.16 kV systems exist in IES & IPC service territories. Very few of these systems
have available fault current levels in excess of 7,100 amps.
4)
Failures
Back-up current limiting fuses (used on the overhead distribution system) that have
operated under low fault conditions will not normally withstand voltage for an extended
period of time and can breakdown resulting in the generation of an extreme amount of
heat. These failures are due to pre-conditioning of the PRCL fuse. A "window of exposure"
exists where the protection characteristics of the expulsion fuse and the PRCL fuse
overlap such that at low levels of fault current the expulsion fuse will not totally clear
before the PRCL fuse element begins to melt. This results in partial melting of the PRCL
fuse element.
In some cases, following a low current fault, the element of the PRCL fuse may be
damaged. Therefore, after replacing the expulsion fuse, voltage may not be restored. This
is the result of the PRCL fuse element burning open. The partially melted element of the
PRCL fuse then begins arcing over internally until the fuse burns itself up. Depending on
the extent of the partial melt and amount of load current, this internal arcing and burning
up may take a few days. Customer complaints of blinking lights are an indication of this
process.
Therefore, it is very important to check the continuity of the current limiting fuse before
refusing the fuse link in the cutout. Replace the current limiting fuse if it is found to be
open.
4. BAYONET FUSES
A bayonet fuse is an oil-immersed expulsion-type fuse used in both single-phase and three-phase
deadfront padmount transformers. This bayonet expulsion fuse is a part of the two fuse protection
scheme. This fuse is in series with a nonreplaceable, partial range current limiting (PRCL) fuse
which is placed under oil inside the transformer by the manufacturer. The two fuses are connected
in series between the high-voltage bushing and the transformer coil as shown in Figure 02-8
Bayonet Expulsion Fuse With PRCL Fuse on Page WFS02.11.
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS02
P a g e 11 o f 11
GENERAL DISTRIBUTION FUSING
Source: Alliant Electrical Standards
Figure 02-8 Bayonet Expulsion Fuse With PRCL Fuse
The bayonet expulsion fuse sits in a bayonet fuseholder. The main advantages of the bayonet
fuseholder are that it provides a loadbreak function and is externally removable. This allows positive
visual indication that load has been interrupted and enables the operator to inspect and replace the
fuse element. This fusing scheme also provides cost advantages in that it reduces both transformer
costs and replacement fuse costs.
The fuse characteristics of the bayonet expulsion fuse and PRCL fuse combine to form a
characteristic very similar to the full range drywell fuse. In this protection scheme, the expulsion
fuse is coordinated to clear low level faults and excessive load currents. The PRCL fuse is then
coordinated to clear the high energy faults due to transformer failure.
The bayonet expulsion fuse is a dual element link which is sensitive to both current and oil
temperature. The link is used to sense secondary faults and excessive load currents, but is also
affected by excessive transformer oil temperatures. This feature limits long time transformer heating
due to overloads or elevated temperature environments.
The High Ampere (HA) bayonet fuse has an integral fuse link and should not be disassembled. If
the HA fuse blows, the entire fuse cartridge should be replaced.
(END)
E.C.S.
INFORMATION SECTION
Issued 06-01-07
FUSING
Section WFS03
Page 1 of 6
OVERHEAD TRANSFORMER FUSING
2.4/4.16 KV OPERATING VOLTAGE
Table 03-1 - Overhead Transformer Fusing for 2400 Volt Single-Phase or 4160 Volt Three-Phase
KVA
1
3
5
7.5
10
15
25
37.5
50
75
100
167
250
333
TANK MOUNTED
ARRESTER
(NON-STANDARD)
STANDARD
(SPEED)
LINK
T
(SPEED)
Link
CURRENT
LIMITING
FUSE
SIZE
“CU”
SIZE
“CU”
SIZE
“CU”
SIZE
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
25STD
FUNIVSTSPD25A
30STD
FUNIVSTSPD30A
50STD
FUNIVSTSPD50A
65STD
FUNIVSTSPD65A
100STD
FUNIVSTSPD100A
150STD
FUNIVSTSPD150A
2STD
FLB20STD
2STD
FLB20STD
3STD
FLB3STD
5STD
FLB5STD
7STD
2STD
FLB20STD
2STD
FLB20STD
3STD
FLB3STD
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
25STD
FUNIVSTSPD25A
30STD
FUNIVSTSPD30A
50STD
FUNIVSTSPD50A
65STD
FUNIVSTSPD65A
100STD
FUNIVSTSPD100A
150STD
FUNIVSTSPD150A
--
--
-6T
FLB6T(W)
10T
FLB10T(W)
15T
FLB15T(W)
25T
FLB25T(W)
30T
FLB30T(W)
50T
FLB50T(W)
65T
FLB65T(W)
100T
FLB100T(W)
140T
FLB140T(W)
200T
FLB200T
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
40 KMATE
40 KMATE
40 KMATE
-----
Current Limiting Fuses should be installed where available fault current exceeds 7100 Amps
E.C.S.
INFORMATION SECTION
Section WFS03
Page 2 of 6
Issued 06-01-07
OVERHEAD TRANSFORMER FUSING
FUSING
7.2 KV, 7.6 KV, 7.9 KV SINGLE-PHASE AND
12.47 KV, 13.2 KV AND 13.8 KV
THREE-PHASE OPERATING VOLTAGE
Table 03-2
Overhead Transformer Fusing for 7200, 7600, and 7900 Volt Single-Phase
and 12470, 13200, and 13800 Volt Three-Phase.
TANK MOUNTED
ARRESTER
(NONSTANDARD)
STANDARD
(SPEED)
LINK
SIZE
“CU”
SIZE
“CU”
SIZE
“CU”
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
20STD
FUNIVSTSPD20A
30STD
FUNIVSTSPD30A
50STD
FUNIVSTSPD50A
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
3STD
FLB3STD
3STD
FLB3STD
5STD
FLB5STD
5STD
FLB5STD
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
20STD
FUNIVSTSPD20A
30STD
FUNIVSTSPD30A
50STD
FUNIVSTSPD50A
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
333
--
--
500
--
--
KVA
1
3
5
7.5
10
15
25
37.5
50
75
100
167
250
T
(SPEED)
Link
-3STD
FLB3STD
5STD
FLB5STD
6T
FLB6T(W)
8T
FLB8T(W)
10T
FLB10T(W)
15T
FLB15T(W)
20T
FLB20T(W)
30T
FLB30T(W)
50T
FLB50T(W)
65T
FLB65T(W)
100T
FLB100T(W)
CURRENT
LIMITING
FUSE
SIZE
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
40 KMATE
40 KMATE
---
Current Limiting Fuses should be installed where available fault current exceeds 6400 Amps.
E.C.S.
INFORMATION SECTION
Issued 06-01-07
FUSING
Section WFS03
Page 3 of 6
OVERHEAD TRANSFORMER FUSING
7 . 2 K V D E L T A T H R E E - PH A S E O P E R A T I N G V O L T A G E
Table 03-3 - Overhead Transformer Fusing for 7200 Volt Delta Three-Phase
KVA/PHASE
1
3
5
7.5
10
15
25
37.5
50
75
100
167
250
NOTE:
TANK MOUNTED
ARRESTER
(NON-STANDARD)
STANDARD
(SPEED)
LINK
SIZE
“CU”
SIZE
“CU”
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
20STD
FUNIVSTSPD20A
30STD
FUNIVSTSPD30A
40STD
FUNIVSTSPD40A
65STD
FUNIVSTSPD65A
100STD
FUNIVSTSPD100A
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
5STD
FLB5STD
5STD
FLB5STD
7STD
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
20STD
FUNIVSTSPD20A
30STD
FUNIVSTSPD30A
40STD
FUNIVSTSPD40A
65STD
FUNIVSTSPD65A
100STD
FUNIVSTSPD100A
For open delta banks, fuse each outside leg per single-phase transformer fusing recommendations. The middle leg should be fused for the largest connected transformer.
For closed banks of unequal size, fuse for the largest transformer connected to that leg.
E.C.S.
INFORMATION SECTION
Section WFS03
Page 4 of 6
OVERHEAD TRANSFORMER FUSING
Issued 06-01-07
FUSING
14.4 KV SINGLE-PHASE AND 24.9 KV
THREE-PHASE OPERATING VOLTAGE
Table 03-4 - Overhead Transformer Fusing for 14400 Volts Single-Phase and 24900 Volt ThreePhase
KVA
1
3
5
10
15
25
37.5
50
75
100
167
250
333
500
T
(SPEED)
Link
CURRENT
LIMITING
FUSE
SIZE
“CU”
SIZE
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
3STD
FLB3STD
6T
FLB6T(W)
6T
FLB6T(W)
8T
FLB8T(W)
10T
FLB10T(W)
15T
FLB15T(W)
25T
FLB25T(W)
30T
FLB30T(W)
50T
FLB50T(W)
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
TANDEM MOUNT
40 KMATE
--
Current Limiting Fuses should be installed where available fault current exceeds 4500 Amps.
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS03
Page 5 of 6
OVERHEAD TRANSFORMER FUSING
12.5 KV AND 13.8 KV DELTA
SINGLE-PHASE OPERATING VOLTAGE
Table 03-5 - Overhead Transformer Fusing for 12500 Volt and 13800 Volt Delta Single-Phase
TANK MOUNTED
ARRESTER
(NON-STANDARD)
STANDARD
(SPEED)
LINK
T
(SPEED)
Link
SIZE
“CU”
SIZE
“CU”
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
20STD
FUNIVSTSPD20A
30STD
FUNIVSTSPD30A
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
SIZE
“CU”
2STD
FLB20STD
2STD
FLB20STD
2STD
FLB20STD
--
--
2STD
FLB20STD
2STD
FLB20STD
3STD
FLB3STD
5STD
FLB5STD
7STD
10STD
FUNIVSTSPD10A
15STD
FUNIVSTSPD15A
20STD
FUNIVSTSPD20A
30STD
FUNIVSTSPD30A
333
--
--
500
--
--
2STD
FLB20STD
2STD
FLB20STD
3STD
FLB3STD
6T
FLB6T(W)
6T
FLB6T(W)
10T
FLB10T(W)
12T
FLB12T(W)
20T
FLB20T(W)
30T
FLB30T(W)
40T
FLB40T(W)
50T
FLB50T(W)
KVA
1
3
5
7.5
10
15
25
37.5
50
75
100
167
250
NOTE:
For open delta banks, fuse each outside leg per single phase transformer fusing
recommendations.
For closed banks of unequal size, fuse for the largest transformer connected to that leg.
E.C.S.
INFORMATION SECTION
Section WFS03
Page 6 of 6
Issued 06-01-07
OVERHEAD TRANSFORMER FUSING
Table 03-6 - Tandem Mount Series Expulsion and Current Limiting Fuse Cutouts
CUTOUT, TANDEM MOUNT, SERIES EXPULSION AND CURRENT LIMITING FUSE
OPERATING
VOLTAGE
CUTOUT
RATING
APPLICATION
CU CODE
4KV
15KV
1 TO 25KVA TRANSFORMER
CO15TECL
104728
15KV
15KV
1 TO 75KVA TRANSFORMER
CO15TECL
104728
15KV
25KV
1 TO 75KVA TRANSFORMER
CO1525TECL
101939
25KV
25KV
1 TO 167KVA TRANSFORMER
CO25TECL
102397
ITEM ID
Includes CL fuse and link holder. Order fuse link separately.
Table 03-7 - Tandem Mount Fuse Holders
HOLDER, TANDEM MOUNT, SERIES EXPULSION AND CURRENT LIMITING FUSE
OPERATING
VOLTAGE
CUTOUT RATING
CU CODE
ITEM ID
4-15KV
15KV
HF15TECL
125001
15KV
25KV
HF1525TECL
125002
25KV
25KV
HF25TECLL
125003
Holders can be installed in existing cutout bodies when CL protection must be added to existing
transformer installations. Fuse link must be ordered separately.
Figure 03-1 Tandem Mount Holder
(END)
FUSING
E.C.S.
INFORMATION SECTION
Issued 06-01-07
FUSING
Section WFS04
Page 1 of 12
PADMOUNT TRANSFORMER FUSING
1. OPERATING VOLTAGE TABLES FOR PADMOUNT TRANSFORMERS
7.2/12.47 kV OPERATING VOLTAGE
Table 04-1 -Padmount Transformer Full-Range Current Limiting Fusing for WP&L Territory
('Drywell' Fuses in Transformers Manufactured Prior to 1986)
TRANSFORMER kVA
FUSE VOLTAGE
FUSE AMPS
ITEM ID
15
8.3 kV
3
123102
25
8.3 kV
6
100022
50
8.3 kV
12
103384
100
8.3 kV
20
120257
167
8.3 kV
30
106844
Single-Phase 240/120 V
Three-Phase 480Y/277 V or 208Y/120 V
75
8.3 kV
6
100022
150
8.3 kV
12
103384
300
8.3 kV
20
120257
500
8.3 kV
30
120956
75
15 kV
6
101471
150
15 kV
12
106254
300
15 kV
20
103193
500
15 kV
30
105132
Three-Phase 240/120 V Delta
E.C.S.
INFORMATION SECTION
Section WFS04
Page 2 of 12
Issued 06-01-07
PADMOUNT TRANSFORMER FUSING
FUSING
2.4/4.16 kV OPERATING VOLTAGE
Table 04-2 -2.4/4.16 kV Padmount Transformer Bayonet-Type Expulsion Fusing
BAY-O-NET FUSING
FUSE SIZE
COOPER NUMBER
15
15DE
4038108C07B
121033
25
25DE
4038108C09B
108431
50
50DE
4038108C12B
101731
100
65HA
4038361C03CB
103191
167
100HA
4038361C04CB
101650
75
25DE
4038108C09B
108431
150
50DE
4038108C12B
101731
300
65HA
4038361C03CB
103191
500
100HA
4038361C04CB
101650
750
125HA
4038361C05CB
102292
kVA
ITEM ID
Single-Phase
Three-Phase
NOTE 1: Fuse Size with "DE" Suffix is a Dual Element Bay-O-Net
NOTE 2: Fuse Size with "HA" Suffix is a High Ampere Overload Bay-O-Net
NOTE 3: "HA" Type Fuses have an Integral Cartridge, and Should Not be Disassembled
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS04
Page 3 of 12
PADMOUNT TRANSFORMER FUSING
7.2/1 2.47 kV, 7.6/1 3.2 kV, 7.9/1 3.8 kV, and
7.2 kV DELTA OPERATING VOLTAGE
Table 04-3 -7.2/12.47 kV; 7.62/13.2 kV 7.96/13.8 kV, 7.2 kV Delta Padmount Transformer Bay-O-Net
Type Expulsion Fusing
BAY-O-NET FUSING
Single-Phase
COOPER
ITEM ID
NUMBER
5DE
4038108C03B
103225
15
6DE
4038108C04B
105712
25
15DE
4038108C07B
121033
50
25DE
4038108C09B
108431
100
50DE
4038108C12B
101731
167
Three-Phase 7.2 kV Delta, 7.2/12.47 kV Delta-Wye Switch on Primary Side
COOPER
ITEM ID
FUSE SIZE
KVA
NUMBER
12DE
4038108C06B
109930
75
25DE
4038108C09B
108431
150
50DE
4038108C12B
101731
300
65HA
4038361C03CB
103191
500
100HA
4308361C04CB
101650
750
125HA
4038361C05CB
102292
1000
125HA
4038361C05CB
102292
1500
Three-Phase 7.2/12.47 kV, 7.6/13.2 kV, 7.9/13.8 kV, 14.4 kV Delta With 4 Taps All Down
6DE
4038108C04B
105712
75
15DE
4038108C07B
121033
150
25DE
4038108C09B
108431
300
50DE
4038108C12B
101731
500
65DE
4038108C14B
109267
750
65HA
4038361C03CB
103191
1000
100HA
403836AC04CB
101650
1500
125HA
403836AC05CB
102292
2000
125HA
403836AC05CB
102292
2500
NOTE 1: Fuse Size with"DE" Suffix is a Dual Element Bay-O-Net
NOTE 2: Fuse Size with "HA" Suffix is a High Ampere Overload Bay-O-Net
NOTE 3: "HA" Type Fuses have an Integral Cartridge, and Should Not be Disassembled
KVA
FUSE SIZE
Section WFS04
Page 4 of 12
E.C.S.
INFORMATION SECTION
Issued 06-01-07
PADMOUNT TRANSFORMER FUSING
FUSING
14.4/24.9 kV OPERATING VOLTAGE
Table 04-4 -14.4/24.9 kV Padmount Transformer Bay-O-Net Type Expulsion Fusing
KVA
BAY-O-NET FUSING
COOPER
FUSE SIZE
NUMBER
ITEM ID
Single-Phase
5DE
4038108C03B
103225
15
5DE
4038108C03B
103225
25
8DE
4038108C05B
107270
50
15DE
4038108C07B
121033
100
25DE
4038108C09B
108431
167
Three-Phase
5DE
4038108C03B
103225
75
8DE
4038108C05B
107270
150
15DE
4038108C07B
121033
300
25DE
4038108C09B
108431
500
40DE
4308108C11B
102453
750
50DE
4038108C12B
101731
1000
65HA
4038361C03B
103191
1500
100HA
4038361C04B
101650
2000
100HA
4038361C04CB
101650
2500
NOTE 1: Fuse Size with"DE" Suffix is a Dual Element Bay-O-Net
NOTE 2: Fuse Size with "HA" Suffix is a High Ampere Overload Bay-O-Net
NOTE 3: "HA" Type Fuses have an Integral Cartridge, and Should Not be Disassembled
Issued 06-01-07
FUSING
E.C.S.
INFORMATION SECTION
Section WFS04
Page 5 of 12
PADMOUNT TRANSFORMER FUSING
GUIDELINES FOR USING FUSE TABLES 04-5, 04-6 AND 04-7
DETERMINE SECTIONALIZING FUSE FOR SINGLE PADMOUNT TRANSFORMER
BACKGROUND
The sectionalizing fuse identified in Table 04-5 - Used to Determine Sectionalizing Fuse Size for
Serving a Single Padmount Transformer on Page WFS04.6 Table 04-6 - Used to Determine
Sectionalizing Fuse Size for Serving a Single Padmount Transformer on Page WFS04.7, and
Table 04-7 - Used to Determine Sectionalizing Fuse Size for Serving a Single Padmount
Transformer on Page WFS04.8and is the recommended minimum size fuse capable of carrying
transformer full-load current, moderate overloads, inrush and cold-load pickup. The fuse sizes were
chosen by following utility industry transformer fusing guidelines.
In general, the size of the sectionalizing fuse in the aforementioned tables was minimized to aid in
coordination with upstream devices. As a result, the sectionalizing fuse does not coordinate with the
transformer internal bayonet or full range current limiting fuse. This miscoordination is not an important
factor since only one transformer is being served by the sectionalizing fuse. If desired, the
sectionalizing fuse size can be increased when serving transformers containing internal bayonet or fullrange current limiting fuse protection. Consult your Distribution Engineer on these applications.
EXAMPLE
Determine the recommended size sectionalizing fuse to serve the padmount transformer shown below:
Figure 04-1 - Sectionalizing Fuse, Single Padmount
a.
Step #1 - Refer to proper fusing chart. Since this example involves a single padmount
transformer on the 7.2/12.47 kV distribution system, use Table 04-6 - Used to Determine
Sectionalizing Fuse Size for Serving a Single Padmount Transformer on Page
WFS04.7. If the distribution system operating voltage had been 14.4/24.9 kV, you would
need to refer to Table 04-7 - Used to Determine Sectionalizing Fuse Size for Serving a
Single Padmount Transformer on Page WFS04.8.
b.
Step #2 - Locate the transformer size and type in the left column of the table.
c.
Step #3 - Follow the row across to the right to determine the recommended size
sectionalizing fuse. For this example in WPL territory, Table 04-6 - Used to Determine
Sectionalizing Fuse Size for Serving a Single Padmount Transformer on Page
WFS04.7 recommends that a 25T riser fuse or 30E SM-4 switchgear fuse be installed.
E.C.S.
INFORMATION SECTION
Section WFS04
Page 6 of 12
Issued 06-01-07
PADMOUNT TRANSFORMER FUSING
FUSING
2.4/4.16 KV OPERATING VOLTAGE SINGLE PADMOUNT
TRANSFORMER FUSING
Table 04-5 - Used to Determine Sectionalizing
Fuse Size for Serving a Single Padmount
Transformer
RISER FUSES
KVA
STANDARD
TCC 123-6
SWITCHGEAR FUSES
ITEM ID #
T SPEED
TCC 170-6
ITEM ID #
SMU-20
TCC 119-2
ITEM ID #
SMU-20
TCC 165-2
ITEM ID #
SINGLE-PHASE
15
10A
121831
8T
105380
10E
106919
10K
101003
25
15A
106996
12T
106362
15E
121728
15K
106528
50
25A
105571
25T
105891
25E
100809
25K
106214
100
50A
107456
50T
108986
50E
108672
50K
109355
167
80A
121942
80T
100063
80E
105834
80K
108663
THREE-PHASE
(2)
75
15A
106996
12T
106362
15E
121728
15K
106528
150
25A
105571
25T
105891
25E
100809
25K
106214
300
50A
107456
50T
108986
50E
108672
50K
109355
500
80A
121942
80T
100063
80E
105834
80K
108663
750
125A
100398
140T(2)
102029
125E
123256
140K
120889
These fuses coordinate with the Bay-O-Net above 400A
E.C.S.
INFORMATION SECTION
Issued 06-01-07
FUSING
Section WFS04
Page 7 of 12
PADMOUNT TRANSFORMER FUSING
7.2/12.47 KV, 7.6/13.2 KV, 7.9/13.8 KV, AND 14.4 DELTA OPERATING VOLTAGE
SINGLE PADMOUNT TRANSFORMER FUSING
Table 04-6 - Used to Determine Sectionalizing
Fuse Size for Serving a Single Padmount
Transformer
RISER FUSES
IES
STANDARD
KVA TCC 123-6
Single-Phase
SWITCHGEAR FUSES
IPW/WPL
IES/IPW/WPL
IES/IPW
ITEM ID #
T SPEED
TCC 170-6
ITEM ID #
SMU-20
TCC 119-2
ITEM ID #
SMU-20
TCC 165-2
ITEM ID #
WPL
SM-4
TCC 119-4
ITEM ID #
15
10A
121831
3A/2.5X(2)
104307
5E
102799
5E(1)
5E(1)
25
10A
121831
6T
107031
5E
102799
5E(1)
5E(1)
50
10a
121831
8T
121334
10E
106919
10K
101003
10E(1)
107947
100
15A
106996
15T
106953
15E
121728
15K
106528
20E
107527
167
25A
105571
25T
106050
25E
106919
25K
106214
30E
109160
Three-Phase 7.2 kV Delta and 7.2/12.47 kV Tranfsormers Equipped with a Delta/Wye Switch on Primary Side
75
10A
121831
8T
121334
10E
106919
10K
101003
10E(1)
107947
150
15A
106996
15T
106953
15E
121728
15K
106528
15E
122034
300
30A
101496
30T
102152
30E
106222
30K
107432
30E
109160
500
50A
107456
50T
123035
50E
108672
50K
109355
50E
122921
750
65A
102042
65T
120424
65E
100747
65K
101433
65E
106148
1000
100A
120363
100T
109005
100E
121395
100K
104648
100E
123298
1500
125A
100398
140T
121946
125E
123256
140K
120889
125E
108218
5E(1)
106645
Three-Phase 7.2/12.47 kV, 7.6/13.2 kV, 7.9/13.8 kV and 14.4 kV Delta W/4 Taps Down
75
10A
121831
6T
107031
5E
102799
5E(1)
(1)
150
10A
121831
8T
121334
10E
106919
10K
101003
300
15A
106996
15T
106953
15E
121728
15K
106528
20E
107527
500
25A
105571
25T
106050
25E
106919
25K
106214
30E
109160
750
40A
120109
40T
120518
40E
121728
40K
122214
50E
122921
1000
50A
107456
50T
123035
50E
108672
50K
109355
65E
106148
1500
80A
121942
80T
103087
80E
105834
80K
108663
80E
102049
2000
100A
120363
100T
109005
100E
121395
100K
104648
100E
128298
2500
125A
100398
140T
121946
125E
123256
140K
120889
125E
108218
(1)
This fuse is a standard speed TCC 153-2 for SMU-20 or 153-4 for SM-4.
(2)
Standard Speed TCC 123-6 (IPW) Kearney X-Link (WPL).
10E
107947
E.C.S.
INFORMATION SECTION
Section WFS04
Page 8 of 12
Issued 06-01-07
PADMOUNT TRANSFORMER FUSING
FUSING
14.4/24.9 KV OPERATING VOLTAGE SINGLE PADMOUNT TRANSFORMER
FUSING
Table 04-7 - Used to Determine Sectionalizing
Fuse Size for Serving a Single Padmount Transformer
RISER FUSES
SWITCHGEAR FUSES
IES
STANDARD
KVA TCC 123-6
Single-Phase
10A
15
25
10A
IPW/WPL
IE S/IP W/WPL
ITEM ID #
T SPEED
TCC 170-6
ITEM ID #
SMU-20
TCC 119-2
ITEM ID #
121831
2A/2X(2)
107236
5E(1)
106672
104307
(1)
106672
(1)
121831
3A/2.5X ( 2 )
5E
100
10A
10A
121831
121831
6T
10T
107031
121716
5E
10E(1)
106672
108026
167
15A
106996
12T
122617
15E
108943
Three-Phase
10A
75
121831
3A/2.5X(2)
104307
5E(1)
106672
50
150
10A
121831
6T
107031
(1)
108026
(1)
10E
500
10A
15A
121831
106996
10T
12T
121716
122617
10E
15E
108026
108943
750
20A
109718
20T
105936
25E
109982
1000
1500
25A
40A
105571
120109
25T
40T
106050
120518
30E
50E
103633
107111
2500
65A
102042
65T
120424
80E
107016
300
(1)
This fuse is a standard speed TCC 153-2.
(2)
Standard Speed TCC 123-6 (IPW) / Kearney X-Link (WPL)
Issued 06-01-07
FUSING
E.C.S.
INFORMATION SECTION
Section WFS04
Page 9 of 12
PADMOUNT TRANSFORMER FUSING
GUIDELINES FOR USING FUSE TABLES 04-8, 04-9 AND 04-10
DETERMINE SECTIONALIZING FUSE FOR MULTIPLE PADMOUNT TRANSFORMERS
BACKGROUND
The sectionalizing fuse identified in Table 04-8 Use to Coordinate Sectionalizing Fuse with Largest
Padmount Transformer Bayonet Fuse in a Multiple Transformer System on Page WFS04.10,
Table 04-9 - Use to Coordinate Sectionalizing Fuse with Largest Padmount Transformer Bayonet
Fuse in a Multiple Transformer System on Page WFS04.11 and Table 04-10 - Use to Coordinate
Sectionalizing Fuse with Largest Padmount Transfomer Bayonet Fuse in a Multiple Transformer
System on Page WFS04.12 is the minimum size fuse that will properly coordinate with the transformer
internal bayonet fuse under secondary fault conditions. The fuse sizes were chosen such that when a
transformer secondary fault occurs, the transformer internal bayonet fuse will open without affecting the
sectionalizing fuse. As a result, the other transformers served by the sectionalizing fuse will remain
energized.
The sectionalizing fuse size can be increased if more capacity is needed to serve the full load of the
tap. Consult your Distribution Engineer for these applications.
EXAMPLE
Determine the minimum size sectionalizing fuse for serving the multiple padmount transformers shown
below:
Figure 04-2 - Sectionalizing Fuse, Multiple Padmounts
a. Step #1 - Refer to proper fusing chart. Since this example involves multiple padmount
transformers on the 7.2/12.47 kV distribution system, use Table 04-9 - Use to Coordinate
Sectionalizing Fuse with Largest Padmount Transformer Bayonet Fuse in a Multiple
Transformer System on Page WFS04.11.
b. Step #2 - Identify the largest size transformer to be served. For this example, the largest
transformer is 500 kVA, 480/277 volt. Locate this transformer size and type in the left
column of the table.
c. Step #3 - Follow the row across to the right to determine the minimum size sectionalizing
fuse that will coordinate with the transformer internal bayonet or full-range current limiting
fuse. For this example in WPL territory, Table 04-9 - Use to Coordinate Sectionalizing
Fuse with Largest Padmount Transformer Bayonet Fuse in a Multiple Transformer
System on Page WFS04.11 identifies that the minimum size sectionalizing fuse should be
a 65T riser fuse or 80E SM-4 switchgear fuse.
E.C.S.
INFORMATION SECTION
Section WFS04
Page 10 of 12
Issued 06-01-07
PADMOUNT TRANSFORMER FUSING
FUSING
d. Step #4 - Estimate the diversified load on the tap and compare to the size of the
sectionalizing fuse. If appropriate, consult your Distribution
Engineer to increase the size of the sectionalizing fuse.
2.4/4.16 KV OPERATING VOLTAGE MULTIPLE
PADMOUNT TRANSFORMER FUSING
Table 04-8 Use to Coordinate Sectionalizing Fuse with
Largest Padmount Transformer Bayonet Fuse in a Multiple
Transformer System
RISER FUSES
IES
STANDARD
KVA TCC 123-6
SINGLE-PHASE
SWITCHGEAR FUSES
IPW/WPL
IES/IPW
ITEM ID #
T SPEED
TCC 170-6
ITEM ID #
SMU-20
TCC 119-2
ITEM ID #
SMU-20
TCC 165-2
ITEM ID #
15
15A
106996
12T
122617
15E
121728
20K
104456
25
20A
109718
15T
106953
20E
106896
25K
106214
50
65A
102042
40T
120518
50E
108672
65K
101438
100
100A
120363
65T
120424
80E
105834
100K
104648
167
125A
100398
140T
121946
125E
123256
140K
120889
40T
120518
50E
108672
65K
101438
THREE-PHASE
75
65A
102042
150
100A
120363
65T
120424
80E
105834
100K
104648
300
125A
100398
140T
121946
125E
123256
140K
120889
500
150A
103308
140T
121946
150E
105026
200K
101789
750
200A
104883
140T(1)
121946
175E
101419
200K
101789
(2)
These fuses coordinate with the Bay-O-Net above 400A
E.C.S.
INFORMATION SECTION
Issued 06-01-07
FUSING
Section WFS04
Page 11 of 12
PADMOUNT TRANSFORMER FUSING
7.2/1 2.47 KV, 7.6/13.2 KV, 7.9/1 3.8 KV AND 14.4 DELTA OPERATING VOLTAGE
MULTIPLE PADMOUNT TRANSFORMER FUSING
Table 04-9 - Use to Coordinate Sectionalizing Fuse
with Largest Padmount Transformer Bayonet Fuse in a Multiple
Transformer System
RISER FUSES
SWITCHGEAR FUSES
IES
STANDARD
KVA TCC 123-6
10A
15
IPW/WPL
IES/IPW/WPL
IES/IPW
WPL
ITEM ID #
121831
T SPEED
TCC 170-6
8T
ITEM ID #
121334
SMU-20
TCC 119-2
15E
ITEM ID #
106528
SMU-20
TCC 165-2
10K
ITEM ID #
101003
SM-4
TCC 119-4
10E(1)
ITEM ID #
107947
25
15A
106996
10T
121716
15E
106528
15K
106528
15E
122034
50
40A
120109
25T
106050
30E
107432
40K
122214
30E
109160
100
65A
102042
40T
120518
65E
101438
65K
101438
65E
106148
167
100A
120363
65T
120424
80E
108663
100K
104648
80E
102049
106214
20E
107527
Three-Phase 7.2 kV Delta and 7.2/12.47 kV Tranfsormers Equipped with a Delta/Wye Switch on Primary Side
75
20A
109718
15T
106953
20E
106896
25K
150
65A
102042
40T
120518
50E
108672
65K
101438
50E
122921
300
100A
120363
65T
120424
80E
105834
100K
104648
80E
102049
500
125A
100398
140T
121946
125E
123256
140K
120889
150E
102703
750
150A
103308
140T
121946
150E
105026
200K
101789
175E
109002
(2)
1000
200A
104883
140T
121946
175E
101419
200K
101789
200E
102499
1500
200A
104883
140T(2)
121946
175E
101419
200K
101789
200E
102499
Three-Phase 7.2/12.47 kV, 7.6/13.2 kV, 7.9/13.8 kV and 14.4 kV Delta W/4 Taps Down
75
15A
106996
10T
121716
15E
106528
15K
106528
15E
122034
150
40A
120109
25T
106050
30E
107432
40K
122214
30E
109160
300
65A
102042
40T
120518
50E
108672
65K
101438
50E
122921
500
100A
120363
65T
120424
80E
105834
100K
104648
80E
102049
750
125A
100398
80T
103087
100E
121395
140K
120889
100E
123298
1000
125A
100398
140T
121946
125E
123256
140K
120889
150E
102703
1500
150A
103308
140T
121946
150E
105026
200K
101789
175E
109002
(2)
2000
200A
104883
140T
121946
17TE
101419
200K
101789
200E
102499
2500
200A
104883
140T(2)
121946
175E
101419
200K
101789
200E
102499
(1)
This fuse is a standard speed TCC 153-4.
(2)
These fuses coordinate with the Bay-O-Net above 400A.
E.C.S.
INFORMATION SECTION
Section WFS04
Page 12 of 12
Issued 06-01-07
PADMOUNT TRANSFORMER FUSING
FUSING
14.4/24.9 KV OPERATING VOLTAGE
MULTIPLE PADMOUNT TRANSFORMER FUSING
Table 04-10 - Use to Coordinate Sectionalizing Fuse
with Largest Padmount Transfomer Bayonet Fuse in a
Multiple Transformer System
RISER FUSES
IES
SWITCHGEAR FUSES
IPW/WPL
IES/IPW/WPL
STANDARD
TCC 123-6
ITEM ID #
T SPEED
TCC 170-6
ITEM ID #
SMU-20
TCC 119-2
ITEM ID #
15
10A
121831
8T
105380
15E
108943
25
10A
121831
8T
105380
15E
108943
50
15A
106996
12T
106362
15E
108943
100
40A
120109
25T
105891
30E
103633
167
65A
102042
40T
102029
50E
107111
75
10A
121831
8T
105380
15E
108943
150
15A
106996
12T
106362
15E
108943
300
40A
120109
25T
105891
30E
103633
500
65A
102042
40T
102029
50E
107111
750
80A
121942
50T
108986
6TE
103586
1000
100A
120363
65T
121327
80E
107016
1500
2500
125A
150A
100398
103308
100T
140T
107536
102889
125E
150E
105031
102072
KVA
Single-Phase
Three-Phase
(END)
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS05
Page 1 of 4
STEP-TIE TRANSFORMERS
GUIDELINES FOR USING FUSE TABLE 05-1
STEP-TIE TRANSFORMER PROTECTION
SOURCE AND LOAD SIDE FUSING
BACKGROUND
The source and load side fuse combination identified in Figure 05-1 - Step-Tie Transformer Fuse is the
recommended method for fusing step-tie transformer applications. The load side fuse protects the steptie transformer from overloads and downstream faults. The source side fuse provides protection in the
event of a step-tie transformer failure. This fuse combination will coordinate throughout the entire range
of fault levels on the Alliant distribution system.
Since the load side fuse is the device protecting the step-tie transformer from overloads and down
stream faults, it must be located as close to the transformer as possible. In overhead step-tie
transformer applications, the load side fuse should be installed on the transformer pole. It is
recommended that the source side fuse be located one span away from the step-tie transformer to
provide a safe physical separation for line personnel in the event that a damaged transformer is refused.
There are other devices (i.e., reclosers) and protection schemes which can be used to protect step-tie
transformers, providing the transformer damage curve is not exceeded. Consult your Distribution
Engineer on these applications.
EXAMPLE
Determine the source and load side fuse sizes for protecting the step-tie transformer shown below.
Figure 05-1 - Step-Tie Transformer Fuse
a. Step #1 - Refer to proper fusing chart. Since this example involves fusing for both the source
and load side of the step-tie transformer, use Figure 05-1 - Step-Tie Transformer Fuse.
b. Step #2 - This example involves a 14.4/24.9 kV distribution source. Locate the 250 kVA step-tie
transformer in the 14.4/24.9 kV portion of the table.
c. Step #3 - Follow the row across to the right to determine the recommended size source and
load side fuse. For this example, Table 05-1 recommends that a 40T source side fuse and
a 40T load size fuse be installed.
E.C.S.
INFORMATION SECTION
Section WFS05
Page 2 of 4
Issued 06-01-07
STEP-TIE TRANSFORMERS
FUSING
STEP-TIE TRANSFORMER PROTECTION
(SOURCE AND LOAD SIDE FUSING)
Table 05-1
Use to determine maximum source side and load side fuse combination for protection of
overhead or padmount step-tie transformers. This fuse combination will protect the step-tie
transformer and coordinate throughout the entire range of fault levels on the WP&L distribution system.
This is the recommended method for fusing step-tie transformer applications. In situations where there
is no load side fuse, use Figure 05-2 - Step-Tie Transformer Fuse.
14.4/24.9 kV Distribution Source(Step-Down Applications)
kVA
PHASE
100
167
250
333
500
500
750
1000
1500
2500
5000
1-Phase
1-Phase
1-Phase
1-Phase
1-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
14.4/24.9kV
SOURCE SIDE T-LINK
10T
15T
25T
30T
40T
15T
25T
30T
40T
80T
140T
7.2/14.47 kV
LOAD SIDE T-LINK
12T
20T
30T
40T
50T
20T
30T
40T
50T
100T
140T
7.2/12.47 kV Distribution Source (Step-Up Applications)
kVA
PHASE
100
167
250
333
500
500
750
1000
1500
2500
5000
1-Phase
1-Phase
1-Phase
1-Phase
1-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
7.2/12.47 kV
SOURCE SIDE T-LINK
20T
30T
50T
65T
80T
30T
50T
65T
80T
140T
200T
14.4/24.9 kV
LOAD SIDE T-LINK
8T
10T
15T
20T
25T
10T
15T
20T
25T
50T
100T
Do not exceed the fuse size identified or transformer protection will be compromised.
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS05
Page 3 of 4
STEP-TIE TRANSFORMERS
GUIDELINES FOR USING FUSE TABLE 05-2
STEP-TIE TRANSFORMER PROTECTION
SOURCE SIDE FUSING ONLY
BACKGROUND
The source side only fuse protection scheme identified in Figure 05-2 - Step-Tie Transformer Fuse is
an alternative method for fusing step-tie transformer applications. This method should be used when a
load side fuse is not located at the transformer. The source side fuse protects the step-tie transformer
from overloads and down stream faults. It also provides protection in the event of a step-tie transformer
failure.
In overhead applications, it is recommended that the source side fuse be located one span away from
the step-tie transformer to provide a safe physical separation for line personnel in the event that a
damaged transformer is re-fused. It is also recommended that a disconnect device (cutout) be located
on the load side of the step-tie transformer to aid line personnel when troubleshooting outages.
There are other devices (i.e., reclosers) which can be used to protect step-tie transformers providing
the transformer damage curve is not exceeded. Consult your Distribution Engineer on these
applications.
EXAMPLE
Determine the source side fuse size for protecting the step-tie transformer shown below.
Figure 05-2 - Step-Tie Transformer Fuse
a. Step #1 - Refer to proper fusing chart. Since this example involves fusing only the source side
of the step-tie transformer, use Figure 05-2 - Step-Tie Transformer Fuse.
b. Step #2 - This example involves a 14.4/24.9 kV distribution source. Locate the 250 kVA step-tie
transformer in the 14.4/24.9 kV portion of the table.
c. Step #3 - Follow the row across to the right to determine the recommended size source side
fuse. For this example, Table 05-2 recommends that a 20T or 25E source side fuse be installed.
E.C.S.
INFORMATION SECTION
Section WFS05
Page 4 of 4
Issued 06-01-07
STEP-TIE TRANSFORMERS
FUSING
STEP-TIE TRANSFORMER PROTECTION
(SOURCE SIDE FUSING ONLY)
Table 05-2
Use to determine maximum source side fuse for protection of overhead or padmount step-tie
transformers. This method of fusing step-tie transformers should be followed when there is no load
side fuse.
14.4/24.9 kV Distribution Source(Step-Down Applications)
kVA
PHASE
100
167
250
333
500
500
750
1000
1500
2500
5000
1-Phase
1-Phase
1-Phase
1-Phase
1-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
MAXIMUM SOURCE SIDE FUSE
T-LINK
SMU-20
8T
10E
15T
20E
20T
25E
25T
30E
40T
50E
15T
20E
20T
25E
25T
30E
40T
50E
65T
80E
140T
150E
7.2/12.47 kV Distribution Source (Step-Up Applications)
kVA
PHASE
100
167
250
333
500
500
750
1000
1500
2500
5000
1-Phase
1-Phase
1-Phase
1-Phase
1-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
3-Phase
MAXIMUM SOURCE SIDE FUSE
T-LINK
15T
25T
40T
50T
80T
25T
40T
50T
80T
100T
200T
SM-4
20E
30E
50E
65E
100E
30E
50E
65E
100E
125E
200E
Do not exceed the maximum source side fuse identified or transformer protection will be compromised.
(END)
E.C.S.
INFORMATION SECTION
Issued 06-01-07
FUSING
Section WFS06
Page 1 of 1
DISTRIBUTION CAPACITORS
Table 06-1 - Distribution Capacitor Bank Fusing Chart
MAXIMUM COORDINATING FAULT CURRENT
COOPER TYPE EX
VOLTAGE
(KVLL)
4.16
BANK
SIZE
(KVAR)
150
STD LINK
FUSE
SIZE
25STD
K LINK
FUSE
SIZE
20K
T LINK
FUSE
SIZE
25T
50
KVAR
CELLS
100
KVAR
CELLS
200
KVAR
CELLS
GE
400
KVAR
CELLS
100
KVAR
CELLS
200
KVAR
CELLS
*
*
ABB
400
KVAR
CELLS
50
KVAR
CELLS
100
KVAR
CELLS
1000
*
520
300
50STD
40K
50T
4.16
450
65STD
65K
65T
4.16
600
100STD
80K
100T
12.47
150
7STD
6K
8T
*
12.47
300
15STD
15K
15T
*
*
4200
4200
5200
12.47
450
25STD
20K
25T
*
*
4200
3800
5200
12.47
600
30STD
30K
30T
*
*
4000
4800
5000
12.47
900
50STD
50K
50T
*
*
1000
3800
3500
12.47
1200
65STD
65K
65T
13.2
300
15STD
15K
15T
13.2
600
30STD
30K
25T
*
*
4200
4800
5200
13.2
900
50STD
50K
40T
*
*
3300
4400
4500
13.2
1200
65STD
65K
65T
13.8
150
7STD
6K
8T
*
13.8
300
15STD
15K
15T
*
*
4200
4200
5200
13.8
450
20STD
20K
20T
*
*
4200
4200
5200
13.8
600
25STD
30K
25T
*
*
4200
4800
5200
13.8
900
50STD
50K
40T
*
*
3300
4400
4500
13.8
1200
65STD
65K
65T
24.9
300
7STD
6K
8T
24.9
600
15STD
12K
15T
*
*
4200
4800
5200
24.9
900
25STD
20K
25T
*
*
4200
4800
5200
24.9
24.9
24.9
1200
1800
2400
30STD
50STD
65STD
25K
50K
65K
400
KVAR
CELLS
3800
*
4.16
*
400
3500
800
0
700
4200
*
*
200
KVAR
CELLS
2410
*
4200
*
*
*
*
6000
4200
5200
2400
*
*
6000
*
4200
*
2400
*
*
*
6000
4200
30T
*
*
50T
*
*
65T
*
*
2400
*
*
4800
*
*
3800
*
*
6000
* There is not a concern with tank rupture for these units for faults under 10,000 Amps.
For application using GE and ABB capacitor cells with fault currents greater than those listed contact a
Distribution Engineer for the possible application of a current limiting fuse.
This cell size is not applicable with bank size.
Note: A standard cutout should be used on all switched banks and an arc chute cutout should be
used on all fixed banks.
(END)
*
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS07
Page 1 of 2
RECLOSERS
1. GENERAL
Reclosers are utilized within many substations and on the distribution feeders or tap lines to protect
concentrated load areas from interruptions from downstream faults. Utilization of successively
smaller reclosers, going away from the substation, can also insure that a high resistance fault at the
end of a line will trip a recloser.
Three-phase reclosers are often used in a substation to prevent single-phasing of large three-phase
loads. Single-phase reclosers are usually preferred on rural feeder lines to limit an outage to the
least possible number of customers.
Most reclosers are equipped with a non-reclosing handle that can be used to prevent the recloser
from closing back into a fault. This "one shot" feature should be used when working on a line
downstream from the recloser. R, RX, W and WV reclosers are equipped with a closing coil on the
source side of the recloser. This coil has to be energized for the recloser to close after an operation.
When backfeeding through these reclosers, they will not close after the first operation because the
closing coil would be de-energized. To close the recloser, the source side needs to be re-energized.
2. TYPES OF RECLOSERS
a. Single-Phase Reclosers
Single-phase reclosers in use on the delivery system are: H, 3H, 4H, L and V4H. Each of these
reclosers have different applications, depending on load, sequence needed, interrupting rating
needed, and interrupting medium desired (oil or vacuum).
b. Three-Phase Reclosers
Three-phase reclosers in use on the delivery system are 6H, V6H, R, RX, W, WV, VW and
WVE. These reclosers differ in interrupting rating, interrupting medium, type of control (hydraulic
or electronic), voltage rating and trip style (single-phase or three-phase lockout). The 6H and
V6H reclosers are single-phase trip with three-phase lockout. The R, RX, W, WV, VW and WVE
are three-phase trip with three-phase lockout.
c. Three-Phase 15 kV Electronic Reclosers
The electronic reclosers are: RE, RXE, WE and VWE. These reclosers usually have their
control mounted on the recloser stand. The recloser is normally operated with the control switch
inside the control cabinet. Some reclosers may be controlled remotely. If the manual operating
handle is down, the electronic control cannot reclose the device until the manual operating
handle is returned to the closed position. If the yellow handle is pulled down manually, the
recloser will lockout. If the yellow handle is raised, the recloser may close. Normally the recloser
must be closed with the control switch, or remotely. These reclosers have closing coils and are
mostly used in substations.
d. Single-Phase 24.9 kV Hydraulic Reclosers
Single-phase reclosers that can be used on 24 kV systems are: E, 4E and V4E.
e. Three-Phase 24.9 kV Reclosers
The hydraulic recloser used on 24 kV systems is the WV. The electronic reclosers used
on 24 kV systems are RVE and WVE. These reclosers have closing coils.
Section WFS07
Page 2 of 2
E.C.S.
INFORMATION SECTION
RECLOSERS
Issued 06-01-07
FUSING
3. SEQUENCE AND OPTIONS
Reclosers can be set to operate on all delayed sequence or a combination of fast
(instantaneous) and delayed sequence. Another option that can be installed on reclosers is
ground trip. This option is most commonly used in substations. The most common
sequence used on a recloser installed outside of a substation is 2A2B. This is the
preferred sequence, but may not work in all applications.
(END)
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS08
Page 1 of 1
SECTIONALIZERS
1. GENERAL
Sectionalizers are used in conjunction with an upstream recloser to permit an additional automatic
sectionalizing device where overcurrent device coordination is tight. A sectionalizer does not
interrupt fault current. Sectionalizers sense an overcurrent condition and will open following a set
number of operations of the upstream recloser (at least one less operation than the number of
operations to lockout of the upstream recloser). These devices are usually sized for the same
current rating as the upstream recloser. The upstream recloser must be sized to be able to detect a
downstream fault, beyond the sectionalizer, to the next overcurrent device or the end of line.
2. TYPES OF SECTIONALIZERS
There are two types of sectionalizers in use on our delivery system: hydraulic and electronic.
Hydraulic sectionalizers look very much like a recloser and are capable of switching normal load
current. Counters in these devices are actuated when fault current drops below the actuating
current level of the device. To reset an open hydraulic sectionalizer, the operating handle needs to
be reset like a recloser.
Electronic sectionalizers fit into a cutout body. Electronic cutout-type sectionalizers are not
designed to interrupt normal load current. To open these devices under load, an S&C Loadbuster
tool must be used. The electronic sectionalizer opens after counting a preset number of loss of
voltages preceded by fault current. After they operate, an actuator located on the bottom of the
sectionalizer must be replaced before the electronic sectionalizer can be re-energized.
(END)
Issued 06-01-07
E.C.S.
INFORMATION SECTION
FUSING
Section WFS09
Page 1 of 1
CIRCUIT BREAKERS AND RELAYS
1. GENERAL - BREAKERS
Breakers are an interrupting device capable of multiple operations, much like a recloser. A breaker
receives an open and close signal from relays. The interrupting medium for a breaker varies. Some
options are vacuum, oil, air blast, air-magnetic, and SF6. The main application for circuit breakers
are in substations. The advantages of a circuit breaker over a recloser are higher interrupting
ratings and higher continuous current capacities. A breaker is used to open and break load or fault
current. Each breaker has an emergency trip lever, but operation is performed with an open/close
switch.
2. GENERAL - RELAYS
Relays provide the trip information to the circuit breakers, similar to the current coil in a recloser.
The most common relays used on our distribution system are the Westinghouse CO Type, G.E. IAC
Type, and Schweitzer (SEL). A relay has multiple settings available that allows its use in many
different scenarios. The settings depend on load current, available fault current, and
upstream/downstream devices. A reclosing relay is also needed with the Westinghouse Type RC
being the most common. This relay provides a signal to the circuit breaker to close in a preset
length of time after the circuit breaker has opened for a faulted condition. The relays, non-reclosing
switch, and breaker open/close control switch can be located in either a control house or a cabinet
mounted on the breaker.
(END)