Transmission Facilities Rating Methodology for Florida

Document title Transmission Facilities Rating Methodology for Florida Document number EGR-TRMF-00001 Applies to: Transmission Engineering, Transmission System Operations, and Transmission Planning Duke Energy Florida Keywords: engineering; transmission engineering standards; transmission engineering line; transmission - system standards; rating methodology NERC Compliance Related This document is NERC-compliance related. Changes to this document could impact compliance to FAC 008-3. All proposed changes to this document must be reviewed by Transmission System Standards. References to the NERC FAC-008 requirements are included in the left margin. 1.0 Purpose R3 The purpose of this document is to describe the criteria, or methodology, for determination of the ampacity rating of the transmission system facilities on the Duke Energy Florida s (DEF) and jointly owned systems. Facility Ratings include Normal Ratings and Emergency Ratings for the following Facilities as applicable: 1.1 Transmission Line Facilities 1.2 Transformer Facilities 1.3 Series and Shunt Compensation Facilities 1.3.1 Shunt Capacitor Facilities 1.3.2 Shunt Reactor Facilities 1.3.3 Series Reactor Facilities 1.3.4 Static VAR Compensator Facilities R3.4 R3.4.1 The process by which the Rating of equipment that comprises a Facility is determined in ADM- TRMF-00009, Duke Energy Florida Facility Ratings Procedure document. The scope of equipment addressed in determining ratings of the Bulk Electric System (BES) shall include, but not be limited to transmission conductors, transformers, relay protective devices, terminal equipment, and series and shunt compensation devices (shunt capacitors, shunt reactors, static VAR compensators, series reactors). It should be noted that no primary fuses are utilized as terminal equipment in the DEF transmission BES. EGR-TRMF-00001 Rev. 10 (03/14) Page 1 of 18

R3.4.2 R3.1 R3.2 R3.2.2 R3.2.1 R3.2.3 The scope of Ratings addressed shall include, as a minimum, both Normal and Emergency Ratings. DEF has two emergency facility ratings, Rate B which is a two hour rating, and Rate C which is a 15 minute rating. The following considerations will be utilized in the Facilities ratings methodology for the various equipment ratings (reference Attachment A): ratings provided by equipment manufacturers design criteria (industry practices, industry standards, etc), ambient temperature (the temperature of the surrounding medium such as air, earth, liquid, etc.) operating conditions other assumptions (solar, wind, etc) Operations and Planning will implement changes to winter and summer Rate A and Rate B ratings by December 31, 2013. Operations will implement winter and summer rate C by December 31, 2013. Planning will implement winter and summer Rate C during the 2014 Databank process (spring, 2014). 1.4 Operating Conditions Operating conditions can affect facility ratings in regards to normal versus emergency ratings of equipment, switching arrangements, and when operational concerns exist. In the case of normal versus emergency ratings, an underground high voltage cable may be the limiting element for continuous ratings, but a disconnect switch may be the limiting element for a two-hour emergency rating. When a transmission line is terminated with two breakers, and the facility rating is based on both breakers being closed, switching can result in a lower facility rating. When one of the breakers is opened and the remaining breaker has an ampacity lower than the established Facility Rating when both breakers are closed, the facility rating must be reduced to the rating of the closed breaker. Protective device settings can be utilized to limit facility ratings when operational concerns exist that require the facility s rating to be lower than what is dictated by the equipment comprising the facility. In those cases, the protective device setting becomes the facility rating. When there are concerns associated with a rating determined by this methodology and the facility must remain in service due to grid reliability or customer load, an engineering analysis shall be used to determine an interim facility rating until the issue is resolved. In these cases, the basis for the interim rating will be documented and maintained for the duration of the limitation. EGR-TRMF-00001 Rev. 10 (03/14) Page 2 of 18

2.0 Terms and Definitions 2.1 Facility - A set of electrical equipment that operates as a single Bulk Electric System Element (e.g., a line, a generator, a shunt compensator, transformer, etc.) 2.2 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. 2.3 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. 2.4 Equipment Rating - The maximum and 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. 2.5 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. 2.6 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. 2.7 Bulk Electric System - As defined by the Regional Reliability Organization, the electrical generation resources, transmission lines, interconnections with neighboring systems, and associated equipment, generally operated at voltages of 100 kv or higher. Radial transmission facilities serving only load with one transmission source are generally not included in this definition. 2.8 Shunt Compensation Device - Capacitor, Reactor, Static Var Compensator 2.9 Series Compensation Device Capacitor, Reactor 2.10 Rate A Normal continuous rating for facilities. 2.11 Rate B 2 hour emergency rating for facilities. 2.12 Rate C 15 minute emergency rating for facilities. 2.13 MCR3 - Normal continuous rating criteria used for some line conductors designed from 1995 to 2006. 2.14 EMR3-2 hour emergency rating criteria used for some line conductors designed from 1995 to 2006. EGR-TRMF-00001 Rev. 10 (03/14) Page 3 of 18

3.0 Roles and Responsibilities 3.1 Transmission Standards 3.1.1 Develop rating methodology to be used to determine facility ratings. 3.1.2 Communicate ratings methodology and respond to comments regarding rating methodology. 4.0 Rating Criteria and Methodology 4.1 Overhead Conductors Transmission Lines and Substation Flexible (Strain and Jumper) Bus IEEE Std 738-2006 IEEE Standard for Calculating the Current-erature of Bare Overhead Conductors is referenced for the methodology used to establish overhead conductor ratings. Table 4.1a specifies the maximum continuous and emergency conductor ampacity rating criteria for DEF overhead conductors. DEF transmission lines are designed to meet or exceed the requirements of the National Electrical Safety Code (NESC), federal regulation, state codes, and local codes. For substation applications, conductors (strain bus and jumpers) are rated based on Table 4.1a. Conductor ratings are based on Rate A, Rate B, and Rate C criteria except as stated in subsection 4.1.1. Rate A criteria are used for maximum (normal) continuous ratings. Rate B criteria are used for two (2) hour emergency ratings. Rate C criteria are used for 15 minute emergency ratings. For 500kV line conductors, Rate B and Rate C ratings are equal to Rate A ratings. EGR-TRMF-00001 Rev. 10 (03/14) Page 4 of 18

Table 4.1a Overhead Conductor Rating Criteria Criteria unit Rate A Rate B Rate C Wind Speed Summer Winter Wind Angle to Conductor emissivity, Al (Cu) absorptivity, Al (Cu) MPH (fps) 1.7 (2.5) 1.7 (2.5) 1.7 (2.5) C ( F) 35 (95) 35 (95) 35 (95) C ( F) 4.44 (40) 4.44 (40) 4.44 (40) degree 60 60 60 (0.85) (0.85) (0.85) (0.85) (0.85) (0.85) With Sun Line Direction N-S or E-W Line Latitude N Time of Day Atmosphere Solar Radiation Elevation (from MSL) Pre-Loading Duration Annual Maximums clear or industrial w/sq m (w/sq ft) 950 (88.26) 950 (88.26) 950 (88.26) ft 50 50 50 % of Rate A Daily Hours 50 24 2 15 minutes Hours 500 10 10 4.1.1 Overhead Conductors Rated using MCR3/EMR3 Criteria Historically, some conductors between 1995 and 2006 used MCR3 criteria to calculate Rate A ratings and EMR3 criteria to calculate Rate B ratings. Table 4.1b specifies the criteria used for the MCR3 and EMR3 ratings. EGR-TRMF-00001 Rev. 10 (03/14) Page 5 of 18

Table 4.1b MCR3/EMR3 Overhead Conductor Criteria Criteria unit MCR3 EMR3 Wind Speed Summer Winter Wind Angle to Conductor emissivity, Al (Cu) absorptivity, Al (Cu) MPH (fps) 3.0 (4.4) 3.0 (4.4) C ( F) 40 (104) 40 (104) C ( F) 4.44 (40) 4.44 (40) degree 90 90 () () () () With Sun Yes Yes Line Direction N-S or E-W E-W E-W Line Latitude N 28 28 Time of Day noon noon Atmosphere Solar Radiation Elevation (from MSL) Duration Annual Maximums clear or industrial w/sq m (w/sq ft) clear maximum clear maximum ft 50 50 Daily Hours 24 2 Hours 500 10 4.1.2 Overhead Conductor erature Rating Criteria Table 4.1c specifies the maximum conductor temperatures that cannot be exceeded in determining overhead conductor ratings. This table is also used for conductors in substation applications. EGR-TRMF-00001 Rev. 10 (03/14) Page 6 of 18

Table 4.1c Overhead Conductor Maximum Operating eratures CONDUCTOR TEMPERATURES CONDUCTOR Rate A Rate B/Rate C (including (including ratings ratings based based on EMR3) on MCR3) C ( F) C ( F) AAC/AAAC 100 (212) 130 (266) ACSR 105 (221) 140 (284) ACSR (500kV) 71 (160) HDB COPPER 70 (158) 80 (176) HDB COPPER (Substation) 80 (176) 90 (194) HYT COPPER 115 (239) 135 (275) Cu/CWLD 70 (158) 80 (176) AlWLD 100 (212) 130 (266) ACAR 105 (221) 130 (266) ACAR (500kV) 90 (194) ACSS/TW (prior to 2006) 140 (284) 180 (356) ACSS/TW (2006 - present) 180 (356) 200 (392) 4.2 Underground Transmission Cables DEF has multiple types of underground transmission cable in its system. They are: Pipe Type - 2500 MCM Cu High Pressure Oil Filled - 2000 MCM Cu High Pressure Oil Filled - 2000 MCM Cu High Pressure Gas Filled - 750 MCM Cu High Pressure Gas Filled - 650 MCM Cu High Pressure Gas Filled Direct Buried - 2500 MCM Cu XLPE - 2000 MCM Cu XLPE Duct Bank - 2500 MCM Cu XLPE - 5000 MCM Cu XLPE All pipe cables were installed in the late 50 s and 60 s with Rate A, Rate B, and Rate C ratings based on cable manufacturer or subsequent engineering ampacity studies. EGR-TRMF-00001 Rev. 10 (03/14) Page 7 of 18

XLPE cable systems use the temperature parameters and guidance stated in AEIC CS7 (Crosslinked Polyethylene Insulated Shielded Power Cable rated 69 through 138kV) and AEIC CS9 (Specification for Extruded Insulation Power Cables and their Accessories rated above 46kV through 345kV) for Rate A, Rate B, and Rate C rating calculations. Only the 230kV XLPE Bartow-Northeast cables have Rate C rating. 4.3 Rigid Bus Rigid bus conductor ampacity ratings are based on IEEE 605-2008 IEEE Guide for Bus Design in Air Insulated Substations and taken directly from Annex B Rigid Bus Ampacity Tables applied to both summer and winter temperatures. Bus conductor values not in the tables are calculated per the IEEE 605 criteria (listed in Table 4.3 below) and IEEE 605 formulas. Table 4.3 IEEE 605-2008 Rigid Bus Conductor Ampacity Criteria RIGID BUS AMPACITY CRITERIA unit Rate A Rate B and Rate C Wind Speed mps (fps) 0.6 (2) 0.6 (2) erature C ( F) 40 (104) 40 (104) Conductor erature (1) Al Cu C ( F) C ( F) 90 (194) 80 (176) 100 (212) 90 (194) Wind Angle to Conductor degree 90 90 emissivity, Al (Cu) (0.85) (0.85) absorptivity, Al (Cu) (0.85) (0.85) With Sun Yes Yes Bus Direction N-S or E-W E-W E-W Bus Latitude N 40 40 Time of Day noon noon Atmosphere clear or industrial clear clear Solar Radiation w/sq m (w/sq ft) maximum maximum Elevation (from MSL) ft 0 0 EGR-TRMF-00001 Rev. 10 (03/14) Page 8 of 18

4.4 Limiting Facilities R3.3 R8.1.1 R8.1.2 R8.2.1 R8.2.2 R3.1 R3.2.4 The Facility Rating Methodology in this document holds to the principle that the Facility Rating shall respect the most limiting applicable Equipment Rating 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 amperes or MVA. The Facility Rating Methodology also supports the ability to identify the existing next most limiting equipment of the Facility. 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 in an engineering analysis and with good utility practice. DEF 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 operating limitations due to equipment failure or malfunction, temporary Facility Ratings are established. DEF 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 with good utility practice 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 in an engineering analysis. 4.5 Equipment Rating (Substations and Transmission Lines) Terminal equipment at substations and equipment within line sections are specified, designed, and applied for the full range of system voltage conditions and ranges to which they will be subjected. Emergency overload current ratings (Rate B and Rate C) of substation equipment are equivalent to normal continuous current ratings (Rate A) except as noted in this section. Equipment is rated per the manufacturer s nameplate rating in accordance with industry standards, as follows, or as specified in subsections of this section: Equipment Industry Standard Circuit Breakers, Circuit Switchers and Disconnect Switches IEEE Std C37 Transformers, Reactors, Current Transformers (CT s) IEEE Std C57 Capacitors IEEE Std 18/NEMA CP1 Line Switches IEEE Std C37 Line Traps ANSI C93.3-1995 Protective Relays IEEE std C37.90 EGR-TRMF-00001 Rev. 10 (03/14) Page 9 of 18

4.5.1 Power Transformers Transformer normal ratings are rated per the manufacturer s nameplate rating in accordance with industry standards such as IEEE C57.12.00. Transformers are required to be capable of carrying rated load continuously at five per cent (5%) above rated secondary voltage without exceeding an average winding temperature rise of 55ºC above a 40ºC maximum ambient and a 30ºC average ambient over a 24 hour period for normal ratings. For newer transformers that have a 55ºC/65ºC average winding temperature rise design rating, two (2) nameplate ratings are provided; a 55ºC winding temperature rise rating and a 65ºC winding temperature rise rating. By design, the 65ºC rise ratings are one hundred and twelve per cent (112%) of the 55ºC rise ratings and can be used for normal ratings (Rate A). Bushings and load tap changers are considered a part of the transformer, and as such are subject to the same load rating criteria of the transformer. If emergency ratings (Rate B) are needed for transformers, they will be determined using one of two methods. Not all transformers will have an emergency rating (Rate B). When emergency ratings are implemented, the emergency summer rating and emergency winter rating will be the same. The first method is for transformers purchased starting in 2005. Due to transformer design specification requirements implemented in 2005 which required the manufacturer to perform a 4 hour overload heat run at 125% of nameplate rating, a 2 hour emergency rating of 125% can be applied to these units pending a review of the factory test data. For transformers purchased prior to 2005, the PT-Load computer program developed by Electric Power Research Institute (EPRI) is to be used along with a typical 24 hour loading profile and 24 hour ambient temperature cycle for the rating period. This program utilizes the algorithms in the IEEE Std C57. The PT-Load program can be used in conjunction with condition assessments to determine emergency ratings. There is no Rate C rating for transformers. 4.5.2 Potential Transformers (PTs) and Coupling Capacitor Voltage Transformers (CCVTs) PTs and CCVTs are not thermal in line devices and as such do not affect Facility Ratings. Therefore, these devices are not included in specific details of the ratings for Transmission Line facilities, Transformer Facilities, or Series and Shunt Compensation Facilities. EGR-TRMF-00001 Rev. 10 (03/14) Page 10 of 18

4.5.3 Current Transformers (CTs) There are four types of construction used for CTs: Wound, Bar-primary, Window, and Bushing. The Wound and Bar-primary types include the primary in the construction of the CT such that they are in line devices with thermal ratings. The Window and Bushing types have circular cores that contain the secondary windings and are designed in such a way that a primary conductor is inserted through the window of the CT. In the case of the Bushing type, they are designed to fit on bushings. Window and Bushing CTs that are solely for metering have no primary, and as such do not affect facility thermal ratings. Therefore, these devices are not included in specific details of the ratings for Transmission Line facilities, Transformer Facilities, or Series and Shunt Compensation Facilities. Bushing CTs that are integral part of a power transformer shall have normal continuous ratings equivalent to the connected tap of the CTs. If emergency ratings have been established on the power transformer, the CTs shall have ratings equivalent to the emergency ratings of the power transformer. Bushing CTs that are integral parts of circuit breakers shall have ratings corresponding to the loadability factor (LF) of the breaker times the connected tap and the CTs thermal current rating factor (RF). If the RF is unknown, a value of 1.0 shall be assumed. Free-standing CTs shall be analyzed for temperature rise to determine the appropriate Rate A winter, Rate B, and Rate C ratings. Rate A summer rating is the same as the nameplate rating or connected tap ratio of the CT. IEEE C57.13-2008, IEEE Standard Requirements for Instrument Transformers, provides guidance to rating adjustment of CTs with known designed classes, RFs, and temperature rises. 4.5.4 Line Traps The design criteria for line traps are based on ANSI C93.3-1995, Requirements for Power-Line Carrier Traps. Rating Methodology The determination of adjusted normal continuous current ratings (Rate A) is based on the temperature rise proportional to an exponential value of the current. The exponential value of 1/2.0 (typically, between 1/1.6 to 1/2.0) is used per utility design practice. The Rate B ratings are from ANSI C93.3-1995 Table A1 and interpolated values from the same table. Rate C rating is the least percentage calculated value (most conservative) of the various types of line traps in the DEF system based on the maximum allowable temperatures of line traps and ambient temperature. EGR-TRMF-00001 Rev. 10 (03/14) Page 11 of 18

Normal continuous current rating Rate A (normal continuous current rating) of line traps is per manufacturer s nameplate and based at 40 C ambient temperature. This current rating can be adjusted for specific ambient temperature without exceeding the normal allowable maximum temperature a line trap can withstand. Table 4.5.4 shows the percentage values of the nameplate rating for the calculation of adjusted normal continuous current ratings at summer and winter. Emergency overload current rating It should be realized that overload conditions will result in some loss of life on line traps. The emergency overload values should not be applied frequently. This accelerates aging of the unit resulting in shortening of life expectancy. If a frequent overload is to occur, it is recommended to upgrade the unit. Table 4.5.4 shows the Rate B and Rate C ratings in percentage values of continuous current (nameplate) ratings. Table 4.5.4 Line Trap Normal Continuous and Emergency Overload Current Ratings Timeframe C F Rate A (% of continuous current rating) Rate B (% of continuous current rating) Rate C (% of continuous current rating) SUMMER 40 104 100 110 130 WINTER 4.4 40 114.2 118.9 142 4.5.5 Disconnect Switches (including Line Switches) Duke Energy Florida utilized the industry standards referenced below as guidelines when creating the allowable disconnect switch normal and emergency load current ratings. IEEE C37.30 Standard Requirements for High Voltage Switches. IEEE C37.32 American National Standard for High Voltage Switches, Bus Supports, and Accessories Schedules of Preferred Ratings, Construction Guidelines, and Specifications. IEEE C37.37 Loading Guide for AC High-Voltage Air Switches (in Excess of 1000V) EGR-TRMF-00001 Rev. 10 (03/14) Page 12 of 18

Rating Methodology In developing the normal and emergency ratings for air disconnect switches, Duke Energy Florida utilizes the guidelines provided in clauses 5 & 6 of IEEE Std C37.37-1996. These guidelines utilize the ACCC (Allowable Continuous Current Class) code designation as defined in subclause 5.3 of IEEE Std C37.37-1996. The ACCC designation identifies the composite curve relating the loadability factor of the switch to the ambient temperature, as determined by the limiting switch part class designations. The IEEE Std C37.37 has established curves or an Emergency Load Current Formula to determine switch normal and emergency current ratings. As stated in Annex A background information of IEEE Std 37.34: This standard recognizes that air switches can be operated at allowable continuous currents in excess of rated continuous currents when reduced ambient temperatures prevail. Indoor and outdoor air switches built prior to 1971 in accordance with standards were allowed a 30 C temperature rise over a maximum ambient of 40 C. In this way, they were allowed to operate at a maximum temperature of 70 C. With a 25 C ambient, these switches could operate at 1.22 times rated current without exceeding the 70 C maximum temperature. To determine the normal and emergency rating, the loadability factor is multiplied by the rated continuous current of the air disconnect switch (nameplate value). Application Considerations NOTE: If a disconnect switch (or line switch) is equipped with a load-break device or interrupter, it may not successfully interrupt currents above the nameplate rating of the interrupter. Switches carrying loads and being subjected to outdoor environmental conditions for several years rely upon adequate maintenance for satisfactory performance. A switch not properly aligned, with poor or dirty contact condition, or without proper contact pressure will not carry rated current without excessive temperatures or resistance. Per IEEE C37.37-1996, the guidelines for emergency ratings assume that the allowable maximum temperatures of the switch parts were not exceeded during the 2 hours prior to an emergency. The limits of total temperature for switches stated in IEEE C37.37-1996 will be exceeded under emergency overload currents, and these higher temperatures may cause a reduction in the operating life of the switch. EGR-TRMF-00001 Rev. 10 (03/14) Page 13 of 18

Allowable Continuous Current Capability Ratings (Normal) Allowable continuous current capability ratings for switches under different ambient temperatures are not provided by the manufacturer. The loadability of each switch part class at various temperatures is determined by utilizing the formula in 5.4.1 of IEEE Std C37.30-1997 and Table 1 of C37.37-1996. Per IEEE C37.37-1996, subclause 5.1, The allowable continuous current is a function of maximum allowable total temperature of the switch parts and the ambient temperature. Normal allowable continuous current (Rate A ratings) loadability factors are determined from Figure 1 of IEEE Std C37.37-1996. See Table 4.5.5 below. Emergency Ratings Emergency Ratings for switches are not provided by the manufacturer. They are based on the methodology defined in IEEE Std C37.37. Rate B and C ratings are approved for ambient temperatures of 40 F/4.4 C (Winter Ratings) and 104 F/40 C (Summer Ratings). See Table 4.5.5 below. Rate B ratings are determined from Figure 3 of IEEE Std C37.37-1996. Rate C ratings are determined from subclause 6.2 of IEEE Std C37.37-1996. Note: It is at DEF s discretion to utilize the most conservative loadability factors in Table 4.5.5 when establishing facility ratings. Table 4.5.5 Switch Loadability Factor for Normal Continuous and Emergency Overload Current Capability Air Disconnect Switches Default ACCC designation AO1 (switch manufactured before 1971) DO6 (switch manufactured on and after 1971) Summer 104 F (40 C) Rate A Rate B Rate C Winter 40 F (4.4 C) Summer 104 F (40 C) Winter 40 F (4.4 C) Summer 104 F (40 C) Winter 40 F (4.4 C) 1.00 1.48 1.29 1.68 1.64 2.00 1.08 1.38 1.27 1.51 1.61 2.00 EGR-TRMF-00001 Rev. 10 (03/14) Page 14 of 18

4.5.6 Circuit Breakers Duke Energy Florida utilized the industry standards referenced below as guidelines when creating the allowable circuit breakers normal and emergency load current ratings. IEEE Std C37.010-1999, Application Guide for AC High- Voltage Breakers Rated on a Symmetrical Current Basis. IEEE Std C37.04-1999, Standard Rating Structure for AC High- Voltage Breakers. Rating Methodology The determination of adjusted normal continuous current ratings is based on the temperature rise proportional to an exponential value of the current. The exponential value of 1/1.8 (typically, between 1/1.6 to 1/2.0) is used per utility design practice and IEEE Std C37.010. Emergency overload current ratings are based on IEEE Std C37.010-1999 subclause 5.4.4. Ratings are based upon pre-loading equal to the circuit breakers rated continuous current. Normal continuous current rating The normal continuous current rating of circuit breakers is per manufacturer s nameplate and based on a 40 C ambient temperature. This current rating can be adjusted for specific ambient temperature without exceeding the normal allowable maximum temperature a circuit breaker can withstand. Table 4.5.6 shows the loadability factor of the nameplate rating for the calculation of adjusted normal continuous current ratings on different ambient temperatures. Emergency overload current rating Table 4.5.6 specifies the maximum loadability factor that may be applied to circuit breaker nameplate ratings for emergency overload current applications. The limits of total temperature for the circuit breaker will be exceeded under the specified emergency load currents, and these higher temperatures may cause a reduction in operating life of the circuit breaker. Note: It is at DEF s discretion to utilize the most conservative loadability factors in Table 4.5.6 when establishing facility ratings. EGR-TRMF-00001 Rev. 10 (03/14) Page 15 of 18

Table 4.5.6 Circuit Breaker Loadability Factor for Normal Continuous and Emergency Overload Current Ratings Rate A Rate B Rate C Circuit Breaker Type Summer 104 F (40 C) Winter 40 F (4.4 C) Summer 104 F (40 C) Winter 40 F (4.4 C) Summer 104 F (40 C) Winter 40 F (4.4 C) Oil 1.00 1.27 1.12 1.37 1.29 1.52 Gas 1.00 1.24 1.10 1.33 1.25 1.46 4.6 Relay Protective Devices A relay protective device as defined in IEEE std 100 as: Protective relay (power operations) - A device whose function is to detect defective lines or apparatus or other power system conditions of an abnormal or dangerous nature and to initiate appropriate control action. Protective relays are rated in accordance with IEEE standard C37.90, industry practices, and manufacturers recommendations. Components within the secondary circuits of current transformers (CT) (transducers, meters, DFRs, etc.) are rated in accordance with industry practices and manufacturers recommendations. Established Rate A, Rate B, and Rate C of the above devices are applicable to both summer and winter temperatures. Protective device settings can be utilized to limit facility ratings when operational situations, equipment concerns, or interim conditions exist, that require the facility s rating to be lower than what is dictated by the equipment comprising the facility. In those cases, the protective device setting becomes the facility rating. 4.7 Joint Facilities For joint facilities, DEF coordinates facility ratings with neighboring systems. EGR-TRMF-00001 Rev. 10 (03/14) Page 16 of 18

5.0 References 5.1 ANSI C93.3-1995 5.2 ANSI CS2 5.3 IEEE Standard 605-2008 5.4 IEEE Standard 738-2006 5.5 IEEE Standard C37 5.6 IEEE Standard C57 5.7 IEEE Standard C62 5.8 IEEE Standard C18 5.9 AEIC CS2 5.10 AEIC CS7 5.11 AEIC CS9 5.12 NEMA Standard CP1 5.13 National Electrical Safety Code (NESC) 5.14 NERC Standard FAC-008 5.15 NERC Glossary of Terms Used in Reliability Standards 5.16 ADM-TRMF-00009, Duke Energy Florida Facility Ratings Procedure EGR-TRMF-00001 Rev. 10 (03/14) Page 17 of 18

R3.1 R3.2 Equipment Overhead Transmission Line Conductor Manufacturer Rating or Data 6.0 Attachment A Rating Methodology Considerations Design/Industry Standards erature Operating Conditions Other Assumptions Yes 1 IEEE Std 738 Section 4.1 Section 1.0 Wind, Sun, Line Sag Underground Transmission Cables - Pipe Cables - XLPE Cables Substation Conductors Yes 1 AEIC CS2 AEIC CS7 and CS9 Yes 1 IEEE Std 605 IEEE Std 738 Yes Section 1.0 Section 4.3 Section 4.1 Section 1.0 Circuit Breakers Yes IEEE Std C37 Yes 2 Section 1.0 Circuit Switchers, Air Disconnect Switches, Line Switches Soil Thermal Properties, no. of circuits, Load Factor Wind, Solar erature rise, precontingency loading, thermal time constant 3 Yes IEEE Std C37 Yes 4 Section 1.0 Wind velocity, Altitude 4 Line Traps Yes IEEE Std C57 Yes 2 Section 1.0 Altitude 3 Power Transformers Yes IEEE Std C57 Section 4.5 Section 1.0 Wind Loading, Altitude 3 Current Transformers Yes IEEE Std C57 Yes 2 Section 1.0 Wind Loading, Altitude 3 Reactors Yes IEEE Std C57 Yes 2 Section 1.0 Average, Altitude 3 Capacitors Yes IEEE Std 18/NEMA CP1 Yes 2 Section 1.0 Average, Altitude 3 Relay Protective Devices Yes IEEE Std C37.90 Yes 2 Section 1.0 Altitude, Relative Humidity 3 Notes: 1 Manufacturer provided data for calculation of rating 2 temperature appropriate to the region as specified in the equipment specification 3 Specified in the equipment purchase specifications 4, wind velocity, and altitude are specified in IEEE Std C37 EGR-TRMF-00001 Rev. 10 (03/14) Page 18 of 18