Bulk Electric System
Facility Rating Methodology
TRANSMISSION
PAGE 1 OF 26
Rev 8: 10/14/09
Revisions
Rev.
No.
0
Date
2/18/00
Description
New Document
DCS/JWS
Rev. for FRCC 2004 Compliance Program
with 2001 NERC Planning Standards; added
DCS/JWS
series and shunt reactive elements
Reformatted & added document number; rev
3.4 - added OPGW; rev 4.3 – added specific
DCS
criteria; added Appendix A – Generator rating.
1
11/1/04
2
8/25/05
3
10/14/05 Rev. 4.8 – Fault current methodology.
4
2/28/07
5
6
7
8
By
Approval
RDC
JJM
JJM
DCS
JJM
Reformatted & revised throughout, updated
conductor methodology, added GSU, updated
generator methodology.
DCS/JJM/
MCW/JAZ
JJM
7/01/08
Reformatted & revised throughout. Added
Emergency Ratings methodologies.
RAC/MDJ/
JJM/NCA
JJM
9/29/08
Deleted Appendix A. Generation Document
will be posted separately.
BJM
BJM
6/29/09
Reformatted and revised throughout.
Drawing number A-214381 is
voided/cancelled. This document will be
maintained in Documentum with a copy in the
Operational Model. It will also be posted on
FPL’s OASIS.
GJK
MDJ
10/14/09
 Added requirement to document unique cases
for temporary and permanent ratings that utilize
alternate rating methods.
 Recognized that some GSU’s may have an
Emergency Rating greater than the Normal Rating
 Inductors have the flexibility to be rated with
the Facility they support or as a separate stand
alone Facility.
GJK
 Added reference and equation for rating CTs on
partial tap setting. Recognized Supplier
obligation to provide bushing CTs with adequate
ratings when used in equipment such as breakers
and transformers
 Added FPL Contact information for written
questions or comments.
 Minor editorial changes
MDJ
PAGE 2 OF 26
Rev 8: 10/14/09
Table of Contents
1. Introduction................................................................................................................4
2. Bulk Electric System Facilities ..................................................................................5
2.1 Transmission Line Facilities .................................................................................... 5
2.2 Transformer Facilities .............................................................................................. 6
2.3 Series and Shunt Compensation Facilities ............................................................... 6
3. Major Equipment Ratings ..........................................................................................7
3.1 Underground Transmission Cable ........................................................................... 7
3.2 Overhead Transmission Conductors ........................................................................8
3.3 Autotransformers ...................................................................................................11
3.4 Generator Step-Up Transformers (GSU’s) ............................................................12
3.5 Shunt Capacitors .................................................................................................... 13
3.6 Shunt Reactors ....................................................................................................... 14
3.7 Series Capacitors ...................................................................................................14
3.8 Series Reactors....................................................................................................... 15
4. Terminal Equipment and Relay Protective Device Ratings ....................................15
4.1 Substation Conductors ........................................................................................... 15
4.2 Circuit Breakers ..................................................................................................... 17
4.3 Instrument Transformers .......................................................................................19
4.3.1 Current Transformers..........................................................................................19
4.3.2 Voltage Transformers .........................................................................................20
4.4 Air Disconnect Switches........................................................................................ 21
4.5 Circuit Switchers ................................................................................................... 22
4.6 Line Traps .............................................................................................................. 24
4.7 Relay Protective Devices ....................................................................................... 25
5. FPL Contact Information ......................................................................................... 26
PAGE 3 OF 26
Rev 8: 10/14/09
1. Introduction
This document describes the methodology that Florida Power & Light Company (FPL) uses to
determine the Facility Rating1 of certain Bulk Electric System (BES) Facilities2 (Facilities) as required
by NERC/FERC Reliability Standard FAC-008-13. The methodology described herein covers Facilities
solely owned by FPL and Facilities jointly owned for which FPL has responsibility for providing
ratings.
Facility Ratings include Normal Ratings4 and Emergency Ratings5 for the following Facilities6
identified in Section 2 of this document:
1. Transmission Line Facilities
2. Transformer Facilities
3. Series and Shunt Compensation Facilities
a. Shunt Capacitor Facilities
b. Shunt Reactor Facilities, and
c. Series Reactor Facilities
The Facilities addressed in this document are comprised of various electrical equipment or Elements7.
FPL Facilities may contain one or more Elements. For example, a Transmission Line Facility includes
conductors, line traps, switches, breakers, protective relays, etc. Section 3 of this document includes
the methodology for rating the major equipment of the Facility. Major equipment is the element of a
Facility that is unique to that type of facility. Major equipment includes the following:
1.
2.
3.
4.
Transmission Cables/Conductors
Transformers (Autotransformers and Generator Step-Up Transformers (GSU))
Reactors (series and shunt applications)
Capacitors (shunt only)
Section 4 of this document includes that methodology for rating the elements of a Facility that are
common to several facilities. These elements also referred to as Terminal Equipment or Associated
Equipment, include:
Glossary of Terms Used in Reliability Standards, February 12, 2008. Facility Rating – The maximum or minimum
voltage, current, frequency, or real or reactive power flow through a facility that does not violate the applicable equipment
rating of any equipment comprising the facility.
2
FPL has a separate Rating Methodology Document for Generation.
3
Standard FAC-008-1 – Facility Ratings Methodology: Adopted by Board of Trustees February 7, 2006, Effective date of
August 7,2007
4
Glossary of Terms Used in Reliability Standards, February 12, 2008. Normal Rating – The rating as defined by the
equipment owner that specifies the level of electrical loading, usually expressed in megawatts (MW) or other appropriate
units that a system, facility, or element can support or withstand through the daily demand cycles without loss of equipment
life.
5
Glossary of Terms Used in Reliability Standards, February 12, 2008. Emergency Rating – The rating as defined by the
equipment owner that specifies the level of electrical loading or output, usually expressed in megawatts (MW) or Mvar or
other appropriate units, that a system, facility or element can support, produce, or withstand for a finite period. The rating
assumes acceptable loss of equipment life or other physical or safety limitations for the equipment involved.
6
Glossary of Terms Used in Reliability Standards, February 12, 2008. Facility – A set of electrical equipment that operates
as a single Bulk Electrical System Element (e.g., a line, a generator, a shunt compensator, transformer, etc.)7
Glossary of Terms Used in Reliability Standards, February 12, 2008. Element - Any electrical device with terminals that
may be connected to other electrical devices such as a generator, transformer, circuit breaker, bus section, or transmission
line. An element may be comprised of one or more components.
1
PAGE 4 OF 26
Rev 8: 10/14/09
1.
2.
3.
4.
5.
6.
7.
Substation Conductors
Breakers
Instrument Transformers
Switches
Circuit Switchers
Line Traps (also known as Wave Traps), and
Relay Protective Devices
Note that FPL has no transmission level Series Capacitors, Flexible A/C Transmission Systems such as
SVC or STATCOM, High Voltage Direct Current or Electrical Energy Storage devices.
The Facility Rating Methodology in this document holds to the principle that the “Facility Rating shall
equal the most limiting applicable Equipment Rating8 of the individual equipment that comprises that
Facility”. For the purposes of this Facility Rating Methodology the equipment rating is the Normal
and Emergency “thermal” Rating of the equipment. The “thermal” rating is the amount of loading or
output that the equipment can support at 60HZ, typically measured in amps or MVA. The assigned
rating may deviate from the Facility Rating Methodology set forth herein where appropriate to do so
based on unique circumstances of a specific Facility or configuration of Facilities. In these unique
cases, the basis for the rating will be documented and maintained.
FPL designs and/or applies equipment to operate within the ranges of voltage, frequency, fault current
and transient conditions for which it is intended to function. This consideration of operating
limitations is applicable to all equipment on the BES. For considerations unique to the specific
equipment, refer to Sections 3 and 4.
For operating limitations due to equipment failure or malfunction, temporary Facility Ratings are
established. FPL follows the same methodology as described herein, however, due to the unique
situations that may be present when equipment or components fail to operate at design levels, the
engineer may use prudent alternative engineering methods to determine the Equipment Ratings if
appropriate. In these unique cases, the basis for the rating will be documented and maintained for the
duration of the limitation.
2. Bulk Electric System Facilities
2.1 Transmission Line Facilities
Transmission Line Facilities are comprised of four main sets of equipment: (1) transmission substation
terminal equipment; (2) distribution substation high-side terminal equipment; (3) transmission line
conductors and (4) relay protective devices. Line conductors may be underground cable or overhead
conductors. The transmission line terminal equipment includes breakers, switches, line traps,
substation conductors and instrument transformers. Switches and substation conductors also comprise
distribution substation high-side equipment.
Generally, the design intent for Transmission Line Facilities is to provide a Normal Rating
(continuous) and three Emergency Ratings: 100% continuous, 110% for 7 minutes, 120% for 7
minutes and 130% for 5 minutes. The Normal Rating is determined by identifying the most limiting
Glossary of Terms Used in Reliability Standards. Equipment Rating – The maximum or minimum voltage, current,
frequency, real and reactive power flows on individual equipment under steady state, short circuit and transient conditions,
as permitted or assigned by the equipment owner.
8
PAGE 5 OF 26
Rev 8: 10/14/09
applicable equipment associated with the Facility while operating at the rated current and under the
other conditions specified below. The Emergency Rating is established by calculating the maximum
allowable pre-existing current such that the Facility can be operated at the following overload
conditions: 110% for 7 minutes, 120% for 7 minutes or 130% for 5 minutes. Each Facility is
individually evaluated and rated based on the limiting applicable equipment rating. In some cases, an
adequate pre-existing current level can not be established. For these cases, the Emergency Rating
equals the Normal Rating.
In some cases the limiting element for a line may change with various switching arrangements. For
example, where a transmission line is terminated with two breakers in parallel, the Facility Rating may
be reduced when one of the breakers is open and the remaining breaker or other associated equipment
has an ampacity lower than the established Facility Rating when both breakers are closed. Such
situations are identified and handled in the FPL System Control Center with specific Energy
Management System (EMS) alarm logic.
For the purpose of this document an autotransformer in series with a transmission line is treated as a
separate Facility with its own ratings.
2.2 Transformer Facilities
A Transformer Facility includes a Generator Step-Up (GSU) transformer or autotransformer and
associated equipment. Associated equipment connected to the transformer typically includes breakers,
buswork, switches and relay protective devices.
Each Transformer Facility is individually evaluated and rated based on the limiting applicable
equipment rating.
GSU Transformer Facilities have Normal and Emergency Ratings that equal the Normal Rating, unless
otherwise stated.
Autotransformers Facilities have a Normal and two Emergency Ratings: summer and winter
Emergency Ratings. The summer rating is generally 150% of the Normal Rating for 3 hours and the
winter rating is generally 130% of the Normal Rating for 6 hours, unless otherwise stated.
In some cases the limiting element for a Transformer Facility may change with various switching
arrangements. For example, where a transformer is terminated with two breakers in parallel, the
Facility Rating may be reduced when one of the breakers is open and the remaining breaker or other
associated equipment has an ampacity lower than the established Facility Rating with both breakers
closed. Such situations are identified and handled in the FPL System Control Center with specific
EMS alarm logic.
2.3 Series and Shunt Compensation Facilities
FPL utilizes Series and Shunt Compensation Facilities. Shunt Compensation devices include Reactor
and Capacitor Facilities. Series Compensation devices include only Reactor Facilities. FPL does not
currently use series capacitors, Flexible A/C Transmission Systems such as SVC or STATCOM, High
Voltage Direct Current or Electrical Energy Storage devices.
Series and Shunt Compensation Facilities are comprised of a reactor or capacitor and associated
equipment. Associated equipment typically includes breakers, switches, substation conductors,
instrument transformers and relay protective devices. In some Transmission Line Facilities,
PAGE 6 OF 26
Rev 8: 10/14/09
Transformer Facilities, Capacitor Facilities or Bus applications, a reactor is included to limit or control
current flow. For these cases, the reactor may be considered part of the Facility it supports or it may be
considered as a stand alone Facility.
Compensation Facilities are individually evaluated and rated based on the limiting applicable
equipment rating.
3. Major Equipment Ratings
3.1 Underground Transmission Cable
Introduction
Normal and Emergency Ratings for underground transmission cables are determined using the rating
methodologies described below.
Design Criteria/Industry Standards



AEIC CS2 – 1997 - Specifications for Paper and Laminated Paper Polypropylene Insulated
Cable
AEIC CS7 – 1993 - Specifications for Crosslinked Polyethylene Insulated Shielded Power
Cables Rated 69 Through 138kV
IEC60287 2nd Edition – 1982 – Calculation of the Continuous Current Ratings of Cables (100%
Load Factor)
Rating Methodology
FPL uses two common algorithms for calculating the Normal Rating.
The FPL preferred method is the Neher-McGrath method outlined in "The Calculation of Temperature
Rise and Load Capability of Cable Systems," in AIEE Transactions on Power Apparatus and Systems,
vol. 76, October 1957.
An alternate and equally acceptable method is that outlined in the European IEC standard, "Calculation
of the Continuous Current Ratings of Cables, (100% Load Factor), Publication 287, 2nd Edition, 1982.
Considerations
The FPL inputs to the underground rating methodologies are as follows:
1. Earth Ambient Temperature: Normally assumed to be 30 degrees Celsius per Table 5-2 in the
EPRI Underground Transmission Systems Reference Book (1992 Edition, p. 209). A different
value may be used depending on field conditions.
2. Soil Thermal Resistivity: Measured at various locations along the route of a new underground
line. Typically measurements are made and soil samples are collected at intervals of 1000 ft at
the depth the cable(s) is to be placed
3. Soil Moisture Content: Measured at the same locations as the soil thermal resistivity.
PAGE 7 OF 26
Rev 8: 10/14/09
4. Load Factor of Proposed Underground Line: Normally based on the projected loading of the
proposed line. The minimum load factor used is 75%. The maximum load factor used is 100%.
5. Cable Depth: To be based on proposed route profile, local code restrictions and locations of
existing sub surface utilities.
6. Fault Current: Obtained from a system fault study for each proposed installation.
7. Adjacent Heat Sources: Type (i.e.: adjacent heat pipes, distribution lines, or transmission lines)
and location are obtained through field surveys of the proposed route of a new line.
8. Cable Characteristics: The cable's characteristics (conductor size, type, stranding, bonding
method, insulation thickness, etc.) are used to determine the cables thermal and electric losses.
9. Cable Maximum Operating Temperature: The maximum allowable cable temperature as
specified in the following industry standards:
AEIC CS2-1997 - Specifications for Paper and Laminated Paper Polypropylene Insulated
Cable
AEIC CS7 - 1993 – Specifications for Crosslinked Polyethylene Insulated Shielded Power
Cables Rated 69 through 138kV
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
Normal and Emergency Ratings for Underground Transmission Cable are not provided by the
manufacturer. The ratings are determined by FPL based upon this methodology.
The Normal Rating of underground transmission conductors at FPL is based on the steady state current
carrying capacity of the conductor. It is a continuous thermal rating based on a maximum rated
conductor temperature.
The Emergency Rating of underground transmission conductors at FPL is a short term thermal rating
based on an assumed fixed overload and time period. The rating represents the maximum load current
that can be applied to a cable operating at the specified initial conditions for the fixed time period
without causing thermal damage to the cable.
3.2 Overhead Transmission Conductors
Introduction
Normal and Emergency Ratings for overhead transmission conductors are determined using the rating
methodology and assumptions described below.
Design Criteria/Industry Standards

Alcoa Conductor Engineering Handbook, Section 6, Current-Temperature Characteristics of
Aluminum Conductors, copyright 1959.

IEEE Standard 738 –1993 - IEEE Standard for Calculating the Current-Temperature Relationship
of Bare Overhead Conductors
PAGE 8 OF 26
Rev 8: 10/14/09
Rating Methodology
Bare overhead transmission conductor ratings at FPL are consistent with and use the methodology
described in the Alcoa Conductor Engineering Handbook, Section 6, “Current-Temperature
Characteristics of Aluminum Conductors”, copyright 1959 and the IEEE Standard for Calculating the
Current-Temperature Relationship of Bare Overhead Conductors (IEEE Standard 738 –1993).
Considerations
Summarized below are the FPL inputs used in the methodology described in the Alcoa Conductor
Engineering Handbook, Section 6, “Current-Temperature Characteristics of Aluminum Conductors”,
copyright 1959 and the IEEE Standard for Calculating the Current-Temperature Relationship of Bare
Overhead Conductors (IEEE Standard 738 –1993).
1. Maximum Operating Temperature: The maximum temperature of the bare overhead conductor
when it is carrying normal rated current under the assumed parameters.
2. Ambient Air Temperature: The assumed temperature of the air surrounding the bare overhead
conductor.
3. Conductivity: The conductivity of the base material used to make the conductor. The
conductivity is used to calculate the resistance of the conductor.
4. Emissivity: The ratio (without units) comparing the emissive power of the bare overhead
conductor to the emissive power of a black body.
5. Absorbtivity: The ratio (without units) comparing the heat absorbing properties of the bare
overhead conductor with that of an ideal absorber.
6. Wind Speed Normal to Conductor: The velocity of the wind blowing in a direction
perpendicular to the path of the bare overhead conductor.
7. Solar Insolation: The total heat flux from the sun received by a surface normal to the sun’s rays
at sea level.
The assumed values used for these inputs are shown in the following tables.
1. Assumptions for rating ACSR overhead transmission conductors
Version
Maximum Operating Temperature (oC)
Ambient Temperature (oC)
Conductivity (% IACS)*
Emissivity
Absorbtivity
Wind speed normal to conductor (mph)
Solar insolation (W/ft2)
Prior to
1978
75
25
62
0.5
0.47
1.364
93
19781993
100
35
61
0.5
0.47
2
93
19942006
100
35
63
0.9
0.9
3
93
After 2006
115
35
62
0.9
0.9
2
93
PAGE 9 OF 26
Rev 8: 10/14/09
* International Annealed Copper Standard
2. Assumptions for rating AAAC overhead transmission conductors
Version
Maximum Operating Temperature (oC)
Ambient Temperature (oC)
Conductivity (% IACS)*
Emissivity
Absorbtivity
Wind speed normal to conductor (mph)
Solar insolation (W/ft2)
Prior to
1994
75
25
52.5
0.5
0.47
1.364
93
19942006
75
35
54
0.9
0.9
3
93
After
2006
85
35
53
0.9
0.9
2
93
* International Annealed Copper Standard
3. Assumptions for rating AAC overhead transmission conductors
Version
Maximum Operating Temperature (oC)
Ambient Temperature (oC)
Conductivity (% IACS)*
Emissivity
Absorbtivity
Wind speed normal to conductor (mph)
Prior to
1994
75
25
62
0.5
0.47
1.364
19942006
75
35
63
0.9
0.9
3
After
2006
85
35
62
0.9
0.9
2
93
93
93
Solar insolation (W/ft2)
* International Annealed Copper Standard
4. Assumptions for rating copper overhead transmission conductors
Version
Maximum Operating
Temperature (oC)
Ambient Temperature (oC)
Conductivity (% IACS)*
Emissivity
Absorbtivity
Wind speed normal to conductor
(mph)
Solar insolation (W/ft2)
Hard Drawn
Copper
75
High
Temperature
Copper Before
1994
100
High
Temperature
Copper 19942006
100
High
Temperature
Copper After
2006
115
25
97.5
0.5
0.47
1.364
25
97.5
.5
.47
1.364
35
98.5
.9
.9
3
35
97.5
0.9
0.9
2
93
93
93
93
* International Annealed Copper Standard
PAGE 10 OF 26
Rev 8: 10/14/09
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
Normal and Emergency Ratings for bare overhead conductor are not provided by the manufacturer.
The ratings are determined by FPL based upon this methodology.
The Normal Rating of bare overhead conductors at FPL is based on the steady state load current
carrying capacity of the conductor. It is a continuous thermal rating based on a maximum rated
conductor temperature.
The Emergency Rating of bare overhead conductors at FPL is based on a conductor’s response to a
step change in the steady state load current applied to the conductor. It is a short term thermal rating
based on a calculated maximum initial load current and an assumed fixed overload and time period.
The rating represents the maximum final load current that can be applied to a conductor operating at
the initial load current for the fixed time period without exceeding the conductor’s maximum rated
operating temperature. The Emergency Rating is expressed as a percentage of the Normal Rating.
The typical Emergency Ratings are:



110% of Normal Rating for 7 minutes
120% of Normal Rating for 7 minutes
130% of Normal Rating for 5 minutes
Other Emergency Ratings for overhead transmission conductors may be calculated on a case by case
basis, for specific conditions which may require a different percentage of Normal Rating and/or fixed
time period
3.3 Autotransformers
Introduction
Transmission system autotransformers on the BES are rated on an individual basis. Generally, the
autotransformers have a Normal and two Emergency Ratings: summer and winter Emergency Ratings.
The Emergency Ratings are developed from typical daily load and temperature profiles provided to the
manufacturer as part of the procurement specification.
Design Criteria/Industry Standards

ANSI/IEEE 57.91-1995 (R2004), Guide for Loading Mineral-Oil-Immersed Transformers
Rating Methodology
FPL uses manufacturer rating for normal and emergency conditions when available.
Where manufacturer ratings are not available, FPL uses the “PT-Load” computer program developed
by Electric Power Research Institute (EPRI). This program utilizes the algorithms in the above IEEE
standard.
In general, other transformer equipment such as bushings or tap changers should not limit auto
transformer ratings. However, should the rating of other transformer equipment be less than the
transformer, the transformer rating will equal the most limiting equipment rating.
PAGE 11 OF 26
Rev 8: 10/14/09
Considerations
The following criteria are currently used as the design basis to specify autotransformer Emergency
Rating capability. The transformer shall be capable of being loaded beyond its nameplate rating with
less than 1% loss- of-life, as calculated using the formula in ANSI/IEEE C57.91, over the 24-hour load
and temperature profiles in the procurement specification. Generally, the summer peak loading
capability is 1.3 per-unit for 6 hours and the winter peak loading capability is 1.5 per-unit for 3 hours.
Per-unit loading is defined for these purposes as the multiple of the transformer's nameplate rated
MVA output with all equipped pumps and fans operating.
The assumptions for the Normal Rating are:




Ambient temperature shall not exceed 40 degrees C and the average temperature of the cooling
air for any 24hr period shall not exceed 30 degrees C
The top liquid temperature of the transformer shall not be lower that -20 degrees C.
Altitude shall not exceed 3300 ft
Supply voltage and load current are approximately sinusoidal
The limiting assumptions under either summer or winter overloads are as follows:









Cumulative loss-of-life shall not exceed 1% over the 24-hour period.
Top oil temperature shall not exceed 110°C during the 24-hour period.
Winding hottest-spot temperature shall not exceed 140°C during the 24-hour period.
Temperature of any metallic part not in contact with paper insulation shall not exceed 150°C
during the 24-hour period. Metallic parts in contact with paper insulation shall not exceed
120°C
Free gas or dissolved acetylene shall not be generated during the 24-hour period.
The summer ratings are calculated using the ambient temperature cycle between 25°C and
35°C.
The winter ratings are calculated using the ambient temperature cycle between 2°C and 15°C.
Bushing nameplate rating (if limiting)
Tap Changer nameplate rating (if limiting)
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
The Normal and Emergency Ratings for an auto transformer are provided by the manufacturer. In
cases, where a manufacturer rating is not available, FPL calculates the ratings as described above.
3.4 Generator Step-Up Transformers (GSU’s)
Introduction
Transmission GSU’s are specified, designed and applied for the full range of system loading
conditions and ranges to which they will be subjected. The Normal Rating for FPL transmission GSU’s
are rated per the manufacturer’s nameplate. FPL does not normally specify ratings above the Normal
Rating for GSU’s therefore the Emergency Ratings are equal to the Normal Ratings, unless otherwise
stated.
Design Criteria/Industry Standards
PAGE 12 OF 26
Rev 8: 10/14/09

ANSI/IEEE 57.91-1995 (R2004), Guide for Loading Mineral-Oil-Immersed Transformers,
Rating Methodology
Rating algorithms are used by the manufacturer to establish the Normal and Emergency Ratings.
These algorithms are based on ANSI/IEEE 57.91.
Considerations
The assumptions for the ratings are:




Ambient temperature shall not exceed 40 degrees C and the average temperature of the cooling
air for any 24hr period shall not exceed 30 degrees C
The top liquid temperature of the transformer shall not be lower that -20 degrees C.
Altitude shall not exceed 3300 ft
Supply voltage and load current are approximately sinusoidal
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
Normal Ratings for the GSU are provided by the manufacturer. The Emergency Rating is equal to the
Normal Rating.
3.5 Shunt Capacitors
Introduction
Shunt capacitors, in support of the BES, are specified, designed, and applied for the full range of
system voltage conditions and ranges to which they will be subjected. Capacitors are static devices
with fixed loading based on operating voltage.
Other associated terminal equipment connected to the capacitors such as breakers, switches, substation
conductors and relay protective devices are generally designed not to be limiting elements for the
operation of the capacitor. Therefore, the capacitor is generally the limiting element of the Facility.
However, should the rating of other equipment be less than the capacitor, the Facility Rating will equal
the most limiting equipment rating.
Design Criteria/Industry Standards


IEEE 18 - 2002, IEEE Standard for Shunt Power Capacitors
IEEE 1036 - 1992, IEEE Guide for the Application of Shunt Power Capacitors
Rating Methodology
Shunt capacitor ratings are developed and provided by the manufacturer.
Considerations
The assumptions for the ratings are:

The minimum ambient temperature is -40°C.
PAGE 13 OF 26
Rev 8: 10/14/09


The average ambient temperature for any 24 h period does not exceed 40°C.
The altitude does not exceed 1800 m above sea level.
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
The Normal Rating for FPL shunt capacitors are provided by the manufacturer. As applied on the FPL
system, shunt capacitor Emergency Ratings are equal to the Normal Ratings.
3.6 Shunt Reactors
Introduction
Shunt reactors are specified, designed, and applied for the full range of system voltage conditions and
ranges to which they will be subjected. Shunt reactors are static devices with fixed loading based on
operating voltage.
Other associated equipment connected to the reactor such as breakers, switches, substation conductors
and relay protective devices are generally designed not to be limiting elements for the operation of the
Facility. Therefore the shunt reactor rating is usually the limiting element of the Facility. However,
should the rating of other equipment be less than the reactor, the Facility Rating will equal the most
limiting equipment rating.
Design Criteria/Industry Standards

IEEE C57.21-1990, IEEE Standard Requirements, Terminology, and Test Code for Shunt
Reactors Rated Over 500 kVA
Rating Methodology
Shunt reactor ratings are developed and provided by the manufacturer.
Considerations
The assumptions/considerations for the ratings are:
 The ambient temperature does not exceed 40°C, and the average temperature of the cooling air
for any 24 h period does not exceed 30°C.
 The altitude does not exceed 1000 m (3300 ft.).
 Under operation, the top liquid temperature of an oil-immersed shunt reactor is no lower than
minus 20°C.
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
The Normal Rating for FPL shunt reactors is provided by the manufacturer. As applied on the FPL
system, shunt reactor Emergency Ratings are equal to the Normal Ratings.
3.7 Series Capacitors
FPL has no transmission level series capacitors.
PAGE 14 OF 26
Rev 8: 10/14/09
3.8 Series Reactors
Introduction
FPL currently uses reactors in series with lines, autotransformers, bus sections and capacitor banks.
These reactors may be designed to control power flow, limit fault currents or limit capacitor discharge
currents. For all applications, the decision to include the reactor in the Facility it supports or treat it as
a stand alone Facility will be made on a case by case basis.
Design Criteria/Industry Standards

ANSI/IEEE C57.16-1996, IEEE Standard Requirements, Terminology, and Test Code for DryType Air-Core Series-Connected Reactors
 ANSI C57.99-1958, Guide for Loading Dry-Type and Oil-Immersed Current-Limiting
Reactors
Rating Methodology
Series reactor ratings are developed and provided by the manufacturer.
Considerations
The assumptions/considerations for the ratings are:


The ambient temperature does not exceed 40°C, and the average temperature of the cooling air
for any 24 h period does not exceed 30°C.
The altitude does not exceed 1000 m (3300 ft.).
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
The Normal and Emergency Ratings for FPL series reactors are provided by the manufacturer.
4. Terminal Equipment and Relay Protective Device Ratings
4.1 Substation Conductors
Introduction
Normal and Emergency Ratings for substation conductors are determined using the rating assumptions
and methodology described below.
Design Criteria/Industry Standards
Ampacities for rigid bus are taken directly from the Standard Ampacity Tables of IEEE Guide for
Design of Substation Rigid-Bus Structures, IEEE Standard 605-1998.
Bare overhead transmission conductor ratings at FPL are consistent with and use the methodology
described in the Alcoa Conductor Engineering Handbook, Section 6, Current-Temperature
Characteristics of Aluminum Conductors, copyright 1959 and the IEEE Standard for Calculating the
Current-Temperature Relationship of Bare Overhead Conductors, IEEE Standard 738 –1993.
PAGE 15 OF 26
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Rating Methodology
Rating algorithms used by IEEE for calculating the IEEE Standard Ampacity Tables used by FPL for
rigid bus are shown in IEEE Guide for Design of Substation Rigid-Bus Structures, IEEE Standard 6051998.
Rating algorithms used for calculating flexible transmission conductor ratings are shown in the Alcoa
Conductor Engineering Handbook, Section 6, “Current-Temperature Characteristics of Aluminum
Conductors”, copyright 1959 and the IEEE Standard for Calculating the Current-Temperature
Relationship of Bare Overhead Conductors, IEEE Standard 738 –1993.
Considerations
Rigid Bus: Ratings are not provided by the manufacturers. Ampacities for rigid bus are taken directly
from the Standard Ampacity Tables of IEEE Guide for Design of Substation Rigid-Bus Structures,
IEEE Standard 605-1998, Annex B. The assumptions and their basis used to derive the IEEE tables are
covered in pages 49 through 70 of the Standard in Annex C. The assumptions apply to both indoor and
outdoor facilities. The basic assumptions are 40ºC ambient temperature, with sun, wind velocity of 2
ft/sec, emissivity factors of 0.5 for aluminum and 0.35 for copper. No other operating limitations
apply.
Flexible Conductors: Ratings are not provided by the manufacturers. Ampacities for flexible bare
conductors used in substations are based on single conductors in free air, with sun, emissivity factor of
0.5 and 40º C ambient temperature for Normal and Summer Emergency and 20º C ambient
temperature for Winter Emergency. The wind velocity used for most conductors is 2 ft/sec. The wind
velocity used for ACSR conductors used for installations of outdoor transmission substations is 2
mi/hr. No other operating limitations apply.
By design it is assumed substation conductors will not limit static load devices such as shunt
compensators since their load is fixed and does not change during operation.
It is generally assumed substation conductors will not limit transmission line facilities by design and
based on the following assumptions:



The conductor in the pull-off tower down to the bus is rated under the same methodology as the
transmission line overhead conductors.
The current at the bus within the substation bay will split due to the parallel configuration
Within the substation bay, conductor sag is not a concern
However should the substation conductor rating be less than other equipment ratings the most limiting
rating will become the Facility Rating.
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
Normal and Emergency Ratings for substation conductors are not provided by the manufacturer. The
ratings are determined by FPL based upon this methodology.
The Normal Ratings of substation conductors at FPL are established based on a maximum conductor
temperature of 90º C with the assumptions stated above.
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For application with autotransformers a six hour summer Emergency Rating and three hour winter
Emergency Rating are established based on a maximum conductor temperature of 110º C with the
assumptions stated above.
For application with transmission lines a short time Emergency Rating equal to 130% of the Normal
Rating is established for substation conductors for up to 7 minutes based on the assumption and
methodology provided above.
4.2 Circuit Breakers
Introduction
AC High Voltage Circuit Breakers on the FPL BES are specified by operating voltage, continuous
current, interrupting current and operating time in accordance with ANSI/IEEE Standard C37 series.
ANSI/IEEE specifically addresses Circuit Breaker current loading in IEEE Standard C37.010-1999
section 5.4. This Standard is used as a guide in establishing continuous and emergency load current
capabilities.
Design Criteria/Industry Standards
The following standards are referenced in the breaker specifications and address thermal rating:


ANSI C37.04 - 1999, IEEE Standard Rating Structure
ANSI/IEEE C37.010 - 1999, AC High-Voltage Circuit Breakers Rated on a Symmetrical
Current Basis
Rating Methodology
General Continuous Load Current ratings are provided in IEEE C37.010-1999 Section 5.4.3.1
Allowable Continuous Load Current ratings based on Actual Ambient temperature are provided in
IEEE C37.010- 1999 Section 5.4.3.2.
Allowable Short-Time Load Current ratings based on actual pre-current operation below its allowable
continuous load current are provided in IEEE C37.010-1999, Section 5.4.3.3.
Allowable Emergency Load Current capability ratings are provided in IEEE C37.010-1999, Sections
5.4.4.1, 5.4.4.2, 5.4.4.3, and 5.4.4.4.
Under all conditions FPL internally determines its own inspection and maintenance policy following
emergency load current operation. In special applications FPL may apply criterion different than those
suggested by IEEE standard C37.010 based on Manufacturer recommendations and/or prudent internal
engineering evaluation.
Considerations
The assumptions/considerations for the ratings are:


20°C ambient temperature- winter.
40°C ambient temperature- summer
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




Temperature rise as function of the 1.8 power of the current (ANSI/IEEE C37.010, Section
4.4.3.2)
Thermal Time Constant t = .5
Temperature Rise and Total Temperature Limit of various circuit breaker components are
based on 65°C rise plus ambient
Accelerated deterioration limit of some circuit breaker parts under emergency conditions
Pre-contingency loading of (100%).
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
1. Normal Ratings are provided by the manufacturer but may be modified pursuant to IEEEC37.0101999 as described below
Continuous Load Current:
Outdoor Transmission Circuit Breakers are designed for normal application where sustained load
current does not exceed the rated continuous current at an altitude above sea level of 1000m (3300 ft),
or less, and an ambient temperature that does not exceed 40 deg C. -IEEE C37.010-1999 Section
5.4.3.1
Allowable Continuous Load Current:
When the actual applied ambient temperature is other than 40 deg C a conversion factor can be applied
to determine the actual allowable continuous load current. -IEEE C37.010- 1999 Section 5.4.3.2
Short Time Continuous Load Current:
Standard breaker design provides for 40 deg C ambient temperature, 65 deg C rise limit and 105 deg C
maximum temperature limit. When a circuit breaker has been operating at a current level below its
allowable continuous load current it is possible to increase the load current for a short time to a value
greater than the allowable current without exceeding the permissible temperature limitations. The
length of time that the short-time load current can be carried depends on these factors: - IEEE
C37.010-1999, Section 5.4.3.3.
- The magnitude of short time current to be carried
- The magnitude of initial current carried prior to the application of the short time current
- The thermal-time characteristics of the circuit breaker
- Typical design time constant t = 0.5 hr
- Typical design exponential temperature increases as 1.8 power as the current increases
2. Emergency Ratings are not provided by the manufacturer. They are calculated based on the
methodology herein.
Emergency Load Current Carrying Capability:
During emergency periods, operation may be required at higher load currents than permitted by the
ambient compensation procedures. Limits of the total temperature for the circuit breaker will be
exceeded under the specified emergency which may cause reduced operating life of the circuit breaker:
- IEEE C37.010-1999, Sections 5.4.4.1, 5.4.4.2, 5.4.4.3, and 5.4.4.4
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Under all conditions FPL internally determines its own inspection and maintenance policy following
emergency load current operation. In special applications FPL may apply criterion different than those
suggested by IEEE standard C37.010 based on Manufacturer recommendations and/or prudent internal
engineering evaluation. The IEEE standard is used as a Guide specific FPL criterion may differ in
special cases.
4.3 Instrument Transformers
4.3.1 Current Transformers
Introduction
Current transformers (CTs) may be supplied in the form of bushing CTs, slip-over CTs, or freestanding CTs for transmission facilities. Combined Metering Units (MUs), contain internal CTs along
with an internal potential voltage transformer (PT or VT).
Design Criteria/Industry Standards


IEEE-C57.13-2008 - Standard Requirements for Instrument Transformers
Westinghouse-8/18/1969- Memorandum on Thermal Current Characteristics of CTs Used With
Power Circuit Breakers and Power Transformers.
Rating Methodology
Bushing CTs mounted inside of breakers and transformers are assumed to have the same thermal
heating characteristics as the breaker (ANSI-IEEE C37.010)or transformer (ANSI-IEEE C57.91). In
addition to the normal Rating Factor of the CTs, there are also short time or emergency overload
ratings associated with the breaker or transformer. It is assumed that the CT installed inside of the
equipment is also designed to meet these overload conditions by inclusion within the equipment.
In the case where the bushing CT is being used at other than full ratio, the following formula defines
the partial ratio rating of the CT (see Westinghouse 8/18/69 reference above):
RFe = (Ib / Ict) ½
Where:
RFe = Continuous thermal rating factor
Ib = Breaker (or transformer) continuous current rating (Amps)
Ict = Primary current rating of bushing CT ratio to be used (Amps)
Where:
1. The maximum RFe does not exceed 2.0
2. The continuous current rating of the breaker or transformer is not exceeded
3. The resulting continuous thermal rating = RFe x In-service tap (Amps)
For free-standing and slip-over CTs, and free-standing MUs, the ratings are developed and provided by
the Manufacturer. These ratings typically include thermal rating factors and overload factors.
Considerations
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Overload ratings are assumed to start from full load from the point of the Rating Factor, less any
derating for ambient temperature as defined in IEEE-C57.13 - 2008.
The assumptions/considerations for the ratings are:
 Elevation is less than 1000m
 For air cooled CTs the 24hr ambient temperature is less than 30°C and the maximum
temperature is less than 40°C
 Alternately CTs may be rated with the 24hr ambient temperature is less than 55°C and the
maximum temperature is less than 65°C
 Bushing CTs mounted inside of breakers and transformers are assumed to have the same
thermal heating characteristics as the breaker (ANSI-IEEE C37.010) or transformer (ANSIIEEE C57.91).
Normal and Emergency Ratings
The Normal and Emergency Ratings for CTs and Metering Units are provided by the manufacturer but
may be modified as described above.
4.3.2 Voltage Transformers
Introduction
Protection and metering devices are supplied voltages from potential transformers (PTs or VTs),
coupling capacitor voltage transformers (CCVTs), or combined metering units (MUs, addressed
above). PTs and CCVTs, in support of the BES, are specified, designed, and applied for the full range
of system conditions to which they will be subjected and are static devices with fixed loading based on
operating voltage.
Design Criteria/Industry Standards


The requirements for PTs/VTs are defined by IEEE-C57.13-2008 - Standard Requirements for
Instrument Transformers
The standard for Coupling Capacitor Voltage Transformers (CCVTs) is ANSI C93.1.-1999 Requirements for Power-Line Carrier Coupling Capacitors and Coupling Capacitor Voltage
Transformers (CCVT)
Rating Methodology
PT and CCVT ratings are developed and provided by the Manufacturer.
Considerations
The assumptions/considerations for the ratings are:

Elevation is less than 1000m
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
The Normal Ratings for PTs and CCVTs are provided by the manufacturer. The Emergency Rating is
equal to the Normal Rating.
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4.4 Air Disconnect Switches
Introduction
FPL utilized the industry standards referenced below as guidelines in creating this Facility Rating
Methodology. Specifically applicable to this Facility Rating Methodology is the ACCC (Allowable
Continuous Current Class) designation of the industry standards. As stated in IEEE C37.30-1997:
“The ACCC designation of an air switch is a code that identifies the composite curve relating the
loadability factor, LF, of the switch to the ambient temperature, ΘA, as determined by the limiting
switch part class designations.”
An ACCC of AO1 is used for air disconnect switches that were designed in accordance with ANSI
C37.30-1962 and earlier standards, for which there was not an ACCC designation. The most common
air disconnect switches manufactured in accordance with the ANSI/IEEE C37.30 standards after the
1962 revision, up to the date of the current revision of this Facility Rating methodology, have an
ACCC of DO6. An ACCC designation of DO6 is the composite of the DO4 and FO6 switch part class
designations. There are two different switch parts that are given a switch part class designation of FO6
in IEEE C37.30-1997. These switch parts are: (a) silver, silver alloy, or equivalent contacts in air, and
(b) silver, silver alloy, or equivalent conducting mechanical joints. Although both are given an FO6
designation, these two switch parts have a different allowable maximum temperature, ΘA, and a
different limit of observable temperature rise at rated current, Θr.
Design Criteria/Industry Standards



IEEE C37.30-1997, IEEE Standard Requirements for High-Voltage Switches
ANSI C37.32-1996, High-Voltage Air Disconnect Switches Interrupter Switches, Fault
Initiating Switches, Grounding Switches, Bus Supports and Accessories Control Voltage
Ranges–Schedules of Preferred Ratings, Construction Guidelines and Specifications
IEEE C37.37-1996, IEEE Loading Guide for AC High-Voltage Air Switches (in Excess of
1000V)
Rating Methodology
In developing the Normal Ratings (allowable continuous current) for air disconnect switches; FPL
utilizes the equation provided in section 5.4.1 of IEEE Std C37.30-1997.
In developing the Emergency Ratings for air disconnect switches; FPL utilizes the guidelines provided
in section 6.2 of IEEE Std C37.37-1996.
Considerations
Air disconnect switches on the FPL transmission system have ACCC designations of either AO1 or
DO6. Unless a specific switch nameplate rating and ACCC designation is verified, FPL assumes worst
case, and adopts the lowest resulting rating according to this Facility Rating Methodology.
To allow for the creation of simplified guidelines, ambient temperatures are defined as 20 degrees-C
for winter, and 40 degrees-C for summer. For actual ambient temperatures above -10 degrees-C, up to
and including 20 degrees-C, the winter rating will be used. For actual temperatures above 20 degreesC, up to and including 40 degrees-C, the summer rating will be used. Temperatures outside of the -10
degrees-C to 40 degrees-C window are not expected within FPL Utility’s service territory.
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Per IEEE C37.37-1996, the guidelines for Emergency Ratings within this Facility Rating methodology
assume that “the allowable maximum temperatures of the switch parts were not exceeded during the 2
hours prior to an emergency.” Therefore, it is assumed that the pre-contingency loading of the
switches is 100% of the Normal Rating.
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
1. Normal Ratings
Within this document, FPL considers the Normal Rating to be synonymous with the “allowable
continuous current” rating of the industry standards referenced above. The Normal Rating for FPL
transmission air disconnect switches is provided by the manufacturer (i.e., rated continuous current
on the nameplate).
Depending on ambient temperature, the allowable continuous current rating may actually be above
the rated continuous current. FPL rates its air disconnect switches on a worst case scenario basis.
For Normal Ratings at 40 degrees-C, that would be an air disconnect switch with an AO1
designation, which provides an allowable continuous current equal to the rated continuous current.
For this case, the loadability factor is 1.00.
If a specific air disconnect switch nameplate rating and ACCC designation is verified, then a higher
allowable continuous current rating for that air disconnect switch can be developed.
2. Emergency Ratings
Emergency Ratings for switches are not provided by the manufacturer. They are calculated based
on the methodology herein.
To determine the Emergency Rating, the loadability factor is multiplied by the rated continuous
current of the air disconnect switch (nameplate value).
When calculating the emergency loadability factor for all air disconnect switches, the equations in
section 6.2 of IEEE 37.37 – 1996, are used to calculate all four values applicable to FPL switches:
(1) AO1, (2) DO4, (3) FO6 for contacts in air, and (4) FO6 for conducting mechanical joints, and
the lowest resulting loadability factor is selected. This will ensure safe utilization of Emergency
Ratings, regardless of whether the switch has an ACCC of AO1 or DO6.
For specific cases where the air disconnect switch nameplate rating and ACCC designation is
verified, it is allowable to use the loadability factor associated with that ACCC designation, rather
than the overall worst case scenario.
4.5 Circuit Switchers
Introduction
Circuit Switchers on the FPL BES are given current ratings based on the manufacturer’s
recommendations, which are based on industry standards. Circuit Switchers are not manufactured in
accordance with industry breaker standards; however the load current ratings are based on the industry
breaker standard listed below.
Design Criteria/Industry Standards
PAGE 22 OF 26
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
ANSI/IEEE C37.010 - 1999, IEEE Application Guide for AC High-Voltage Circuit-Breakers
Rated on a Symmetrical Current Basis.
Rating Methodology
Allowable continuous load current ratings are based on section 5.4.3.2 of IEEE C37.010- 1999.
Allowable short-time load current ratings are based on section 5.4.3.3 of IEEE C37.010-1999.
Allowable emergency load current capability ratings are based on in IEEE C37.010-1999, Section
5.4.4.
Considerations
To allow for the creation of simplified guidelines, ambient temperatures are defined as 20 degrees-C
for winter, and 40 degrees-C for summer. For actual ambient temperatures above -10 degrees-C, up to
and including 20 degrees-C, the winter rating will be used. For actual temperatures above 20 degreesC, up to and including 40 degrees-C, the summer rating will be used. Temperatures outside of the -10
degrees-C to 40 degrees-C window are not expected within FPL Utility’s service territory.
The calculations in ANSI/IEEE C37.010 allow for ratings to be based on the loading prior to the shorttime loading. FPL assumes the pre-loading to be 100% of the rated continuous current.
Temperature rise limit of various circuit switcher components is 65°C (149°F).
The switcher is at an altitude above sea level of 1000m (3300 ft), or less.
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
1. Normal Ratings are provided by the manufacturer but may be modified pursuant to IEEEC37.0101999 as described below.
Rated Load Current:
The equipment is designed for normal application where sustained load current does not exceed the
rated continuous current at an altitude above sea level of 1000m (3300 ft), or less, and an ambient
temperature that does not exceed 40 deg C. See IEEE C37.010-1999 Section 5.4.3.1
Allowable Continuous Load Current:
When the actual applied ambient temperature is other than 40 deg C a conversion factor can be applied
to determine the actual allowable continuous load current. See IEEE C37.010- 1999 Section 5.4.3.2
Short Time Continuous Load Current:
Standard equipment design provides for 40 deg C ambient temperature, 65 deg C rise limit and 105
deg C maximum temperature limit. When a circuit switcher has been operating at a current level below
its allowable continuous load current, it is possible to increase the load current for a short time to a
value greater than the allowable current without exceeding the permissible temperature limitations.
PAGE 23 OF 26
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The length of time that the short-time load current can be carried depends on these factors: (See IEEE
C37.010-1999, Section 5.4.3.3.)
- The magnitude of short time current to be carried
- The magnitude of initial current carried prior to the application of the short time current
- The thermal-time characteristics of the circuit breaker
- Typical design time constant t = 0.5 hr
- Typical design exponential temperature increases as 1.8 power as the current increases
2. Emergency Ratings are not provided by the manufacturer. They are calculated based on the
methodology below.
Emergency Load Current Carrying Capability:
During emergency periods, operation may be required at higher load currents than permitted by the
ambient compensation procedures. Limits of the total temperature for the circuit switcher will be
exceeded under the specified emergency which may cause reduced operating life of the circuit
switcher: - IEEE C37.010-1999, Section 5.4.4.
Under all conditions FPL internally determines its own inspection and maintenance policy following
emergency load current operation. In special applications FPL may apply criterion different than those
suggested by IEEE standard C37.010 based on manufacturer recommendations and/or prudent internal
engineering evaluation. The IEEE standard is used as a guide. Specific FPL criterion may differ in
special cases.
4.6 Line Traps
Introduction
Line Traps, sometimes referred to as wavetraps, are series connected devices usually in one or more
phases of the high voltage power system. These are used in conjunction with the power line carrier
system to block relay carrier such that the carrier signal is forced or trapped to all go into the coupling
capacitor where it is routed into the power line carrier transmitter/receiver. The current carrying
element consists of a large coil plus a tuning pack and internal arrestor, rated for a given ampacity.
The line trap is generally used at the ends of a transmission line; however, there are other applications
where it may be used in conjunction with capacitor banks or power transformers to block the carrier
signals from getting lost into the “remote” devices so that the carrier signal only goes down the
transmission line.
Design Criteria/Industry Standards

ANSI C93.3-1995, Standard Requirements for Powerline Carrier Line Traps.
Rating Methodology
Line trap ratings are developed and provided by the manufacturer.
Considerations
The assumptions/considerations for the ratings are:
PAGE 24 OF 26
Rev 8: 10/14/09



Ambient temperature is - 40°C to + 45°C
Altitude is less than 1000m
Any values of currents in excess of the rated current in this standard may cause the designed
temperature rise to be exceeded and may shorten the life expectancy of the line trap.
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
The Normal Rating for line traps are provided by the manufacturer. The Emergency Rating for line
traps are provided in ANSI C93.3 - 1995.
4.7 Relay Protective Devices
Introduction
For the purpose of this document relay protective devices will be defined by the term “Relay” from
IEEE C37.90-2005. “A relay is an electric device designed to respond to input conditions in a
prescribed manner and, after specified conditions are met, to cause contact operation or similar abrupt
change in associated electric control circuits.”
Relay protective devices are not directly connected to high voltage equipment but are connected
indirectly through instrument transformers.
Relay Protective Devices (Relays) have evolved from the electromechanical to the solid state to the
microprocessor protection packages. The ratings of these devices typically do not limit the
transmission facilities. However, should the rating of the relay protective device be less than other
equipment in the Facility, the Facility Rating will equal the most limiting equipment rating.
Design Criteria/Industry Standards

IEEE C37.90-2005 - Standard for Relays and Relay Systems Associated with Electric Power
Apparatus
Rating Methodology
Relay ratings are developed and provided by the Manufacturer.
Considerations
Relay protective devices are specified, designed and applied for the full range of expected system
conditions to which they will be subjected through the instrument transformers.
The assumptions/considerations for the ratings are:


Elevation is less than 1500m
Ambient temperature and humidity as specified for application
Normal and Emergency Ratings (Manufacturer/Industry Standard/Custom)
The Normal and Emergency Ratings for relay protective devices are provided by the manufacturer.
PAGE 25 OF 26
Rev 8: 10/14/09
5. FPL Contact Information
For questions or comments, please write to:
Manager of Technical Services
Florida Power & Light
Mailstop: SB/JB
PO Box 14000
Juno Beach, FL 33408
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