Scope and Purpose


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Bulk Electric System

Facility Rating Methodology

Revisions



Rev.

No.


Date


Description


By


Approval

0

2/18/00

New Document

DCS/JWS

RDC

1

11/1/04

Rev. for FRCC 2004 Compliance Program with 2001 NERC Planning Standards; added series and shunt reactive elements

DCS/JWS

JJM

2

8/25/05

Reformatted & added document number; rev 3.4 - added OPGW; rev 4.3 – added specific criteria; added Appendix A – Generator rating.

DCS

JJM

3

10/14/05

Rev. 4.8 – Fault current methodology.

DCS

JJM

4

2/28/07

Reformatted & revised throughout, updated conductor methodology, added GSU, updated generator methodology.

DCS/JJM/MCW/JAZ

JJM

Table of Contents



Scope and Purpose 4

Transmission Facilities 5

Terminal Equipment 12



Scope and Purpose



This document describes the methodology FPL presently uses to rate its Bulk Electric System (BES) Facilities. The methodology described herein covers Facilities solely owned by FPL and Facilities jointly owned for which FPL has responsibility for providing ratings. It is intended to provide documentation in compliance with the NERC Reliability Standard FAC-008-1, approved by NERC Board of Trustees with an effective date of August 7, 2006. FPL bases its rating methodology on industry standards as discussed below. These standards have changed over the years and FPL modifies its rating methodology from time to time to keep pace with accepted industry practice. This document describes FPL current methodology and makes no assumptions as to the design criteria of legacy equipment and facilities.
This document describes the current FPL rating methodology for the following Bulk Electric System Facilities as defined in the NERC Glossary of Terms dated August 2, 2006:

  1. Transmission lines

  2. Transformers

  3. Shunt Compensators which includes Shunt Capacitors and Shunt Reactors.

  4. Series Reactors

  5. Generators


The Facilities addressed in this document are comprised of various electrical equipment or Elements (defined term by NERC). FPL Facilities may contain one or more Elements. For example, a transmission line includes conductors, line traps, switches, and breakers. Protective relays for the line will also be included as part of the transmission line Facility. All this equipment or Elements operate together with the limiting Facility ratings being derived from the individual equipment ratings. Thus the Facility ratings will be limited by the most limiting equipment rating. Likewise, the Facility rating will not exceed the most limiting rating of any equipment that comprises the Facility.
The scope of equipment or Elements addressed in this document includes the following:

  1. Transmission Conductors

  2. Transformers

  3. Series and Shunt Compensation Devices

  4. Generators

  5. Terminal Equipment


Terminal Equipment includes: circuit breakers, switches, substation conductors, instrument transformers, line traps and associated relay settings.
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.


Transmission Facilities



1Transmission Lines



FPL transmission lines are defined as those transmission circuits that terminate at fault interrupting circuit breakers. These lines may have one or more distribution (load serving) substations in the line between breakers. The lines between distribution stations are termed “transmission line sections.”
Transmission line Facilities are comprised of three main sets of equipment: transmission substation terminal equipment, distribution substation high-side equipment and transmission line conductors. Line conductors may be underground cable or overhead. The transmission terminal equipment includes breakers, switches, line traps, buswork, current transformers and protective relays. Switches and buswork also comprise distribution substation high-side equipment. Since all this associated transmission line equipment is also used in other Facilities besides transmission lines, the rating methodology for this equipment is shown under a separate section, “Terminal Equipment.” Each transmission line section of a line may have multiple conductor sizes, types, and ampacity ratings. A particular transmission line or line section is rated based on the most limiting rating of its associated equipment. In some cases the limiting element for a line may change with various switching arrangements. Where a line is terminated with two breakers in parallel the line rating may be reduced when one of the breakers is open and the remaining breaker has an ampacity lower than the line conductors. Such situations are handled in the System Control Center with specific 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.

1.1Underground Transmission Cable



Normal and Emergency Rating Criteria

Normal Ratings for underground transmission cables are determined using the below rating methodology. FPL does not have ratings above normal for these cables therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.
Industry Standards

FPL Underground Transmission Facilities are designed per the following applicable industry standards.
For pipe type cables and accessories, the industry standard used includes the Association of Edison Illuminating Companies specification CS2-90 (AEIC CS2-90 Specifications for Impregnated Paper and Laminated Paper Polypropylene Insulated Cable, High Pressure Pipe Type).
For Solid Dielectric Crosslinked Polyethylene (XLPE) cables and accessories, the industry standard used is AEIC CS7-93 (Specifications for Crosslinked Polyethylene Insulated Shielded Power Cables Rated 69 through 138kV).
Rating Algorithms

The AEIC cable standards listed above specify the allowable temperatures for various types and voltages of cable insulations which govern how much current may be transferred through the insulated conductor of the cable. FPL uses two common algorithms for calculating the predicted insulation temperature and thus the allowable operating ampacity.
The FPL preferred algorithm is that of 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.
Acceptable Rating Methods

FPL rates cables using the above algorithms in the following ways:


  1. CYMCAP for Windows by CTME International Inc. program or Power Delivery Consultants Inc., PCToolBox program. Both programs utilize the above algorithms.



  1. The cable manufacturer's cable calculations using the above algorithms and proprietary software.




  1. Certain conditions not adequately modeled by existing software may be rated using numerical methods, or other calculation techniques.


Input Criteria Assumptions

The FPL inputs to the underground rating algorithms are as follows:


  1. Earth Ambient Temperature: assumed to be 30 degrees Celsius per the EPRI Underground Transmission Systems Reference Book (1992 Edition, p. 209) unless can be proved otherwise.




  1. Soil Thermal Resistivity: Based on Moisture Content and is to be determined at each location an underground line is to be installed, in the form of a "Dry-Out Curve." Typically one soil sample location is required every 1000 ft or less at each depth the cable(s) is to be placed.




  1. Moisture Content: To be determined at each location an underground line is to be installed, based on the type of soil, the water level at that location, and the pipe depth.




  1. Load Factor of Proposed Underground Line: Obtained for each line but generally not to be less than 75%. For new lines, a 100% load factor is used.




  1. Cable Depth: To be based on proposed route profile and local code restrictions.




  1. Fault Current: Obtained from a system fault study for each proposed installation.




  1. Adjacent Heat Sources: (i.e.: adjacent heat pipes, distribution lines, or transmission lines) are to be taken into account as outlined in the EPRI Underground Transmission Systems Reference Book (1992 Edition).




  1. 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.



1.1Overhead Transmission Line



Normal and Emergency Rating Criteria

Normal Ratings for overhead transmission conductors are determined using the rating methodology described below. FPL does not have ratings above normal for these conductors therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.
The ampacity rating of bare overhead conductors at FPL is:


  • Based on the steady state load current carrying capacity of the conductor.




  • A continuous thermal rating based on a maximum rated conductor temperature. This rating serves as the “normal” or “full time” continuous rating for the line section it is in. There is no continuous “emergency” rating with a higher temperature associated with it for FPL Transmission lines.



Industry Standards

Bare overhead transmission conductor ratings at FPL are consistent with and use the methodology described in the IEEE Standard for Calculating the Current-Temperature Relationship of Bare Overhead Conductors (IEEE Standard 738 –1993).



Input Criteria Assumptions

Summarized in the following sections is the FPL criteria used in the methodology described in the IEEE Standard for Calculating the Current-Temperature Relationship of Bare Overhead Conductors (IEEE Standard 738 –1993).
1. Weather Conditions for rating overhead transmission conductors
Ambient Air Temperature

FPL’s current ampacity rating criteria uses a 95 degree-F (35 degree-C) ambient air temperature.
Wind Speed (Normal to Conductor)

FPL’s current ampacity rating criteria uses a 2 mile per hour wind (normal to conductor).
Solar Insulation (Full Sun, Clear Atmosphere)

FPL’s current ampacity rating criteria uses 93 watts per square-foot solar insulation level.
2. Maximum continuous conductor operating temperatures:
Summarized in the table below is the maximum continuous conductor operating temperatures used for the different transmission conductor types:


ACSR

Varies, up to 115 Deg-C (239 Deg-F)

AAAC

Varies, up to 85 Deg-C (185 Deg-F)

AAC

Varies, up to 85 Deg-C (185 Deg-F)

ACSS (SSAC)

Varies, to over 200 Deg-C

Copper Hard Drawn

75 Deg-C (167 Deg-F)

Copper, High Thermal

100 Deg-C (212 Deg-F)



3. Conductor properties:


Conductivity




ACSR

62% IACS*

AAAC

53% IACS*

AAC

62% IACS*

ACSS (SSAC)

63% IACS*

Copper

97% IACS*

Emissivity, absorptivity

Varies, up to 0.9


* International Annealed Copper Standard

2Transformers



Transformer Facilities include Generator Step-up (GSU) transformers, autotransformers and associated connected equipment. Associated equipment connected to the transformer such as breakers, buswork, switches and protective relays associated with Transformer Facilities are shown under section entitled “Terminal Equipment.” This other equipment is designed not to be limiting Elements for the operation of the transformer. Therefore the transformer ratings become the limiting ratings of the Facility.


2.1Autotransformers



Transmission system autotransformers on the Bulk Electric System are rated on an individual basis. These ratings are maintained on a list that includes the substation name, the FPL equipment company asset number or location within the substation, the autotransformer nameplate rating in MVA (megavolt-amperes), and the Summer Emergency and Winter Emergency ratings, also in MVA. The emergency ratings are determined by the following methods:


  1. Application of Standard IEEE C57.115, Guide for Loading Mineral-Oil Immersed Power Transformers Rated in Excess of 100 MVA (65° C Winding Rise).




  1. “PT-Load” computer program developed by Electric Power Research Institute (EPRI). This program utilizes the algorithms in the above IEEE C57.115 loading guide.




  1. Limitations of the transformer bushings as established and evaluated by the original bushing manufacturer or by bushing nameplate rating.


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 it's nameplate rating with less than 1% loss- of-life, as calculated using the formula in ANSI/IEEE C57.91, with 1.3 per-unit loading in Summer and 1.5 per-unit loading in Winter, over the 24-hour load and temperature cycles in Appendix 12.6. Per-unit loading shall be defined for these purposes as the multiple of the transformer's nameplate rated MVA output with all equipped pumps and fans operating.
For calculation purposes, the transformer loading shall change from normal operation to operation beyond nameplate rating at 12 PM and continue for 24 hours thereafter.
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 shall not exceed 150°C during the 24-hour period.

  • 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 transformers are loaded at 70% of nameplate rating, then at 13:00 they are overloaded to the maximum capacity for 6 hours, maintaining the temperature under the limits specified.

  • The winter ratings are calculated using the ambient temperature cycle between 2°C and 15°C. The transformers are loaded at 70% of nameplate rating, then at 06:00 they are overloaded to the maximum capacity for 3 hours, maintaining the temperature under the limits specified.

  • The maximum ratings in some cases are limited by the ampacity of the transformer bushings.



Unless otherwise specified the default rating for an autotransformer shall be nameplate for continuous loading, 1.5 times nameplate for winter emergency loading and 1.3 times nameplate for summer emergency loading.


2.2Generator Step-Up Transformers (GSU’s)



Transmission GSU’s at FPL are specified and rated according to:


  • IEEE C57.1200 , IEEE General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers, and IEEE C57.116 Guide for Transformers Directly Connected to Generation.


Transmission GSU’s are specified, designed and applied for the full range of normal 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 have ratings above normal for GSU’s therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.
Other associated power system equipment connected to the GSU such as breakers, switches, buswork, and relay settings are designed not to be limiting Elements for the operation of the GSU. Therefore the GSU ratings become the limiting ratings of the Facility. The rating methodology for these other devices is provided under section, “Terminal Equipment”.

3Shunt Capacitors



Transmission shunt capacitors at FPL are specified and rated according to:


  • IEEE 18, IEEE Standard for Shunt Power Capacitors

  • IEEE 1036, IEEE Guide for the Application of Shunt Power Capacitors

  • IEEE C37.99, IEEE Guide for the Protection of Shunt Power Capacitors


Transmission shunt capacitors are specified, designed and applied for the full range of normal system voltage conditions and ranges to which they will be subjected. The Normal Rating for FPL transmission shunt capacitors are rated per the manufacturer’s nameplate. FPL does not have ratings above normal for shunt capacitor banks therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.
Other associated power system equipment connected to the bank such as breakers, switches, buswork and relay settings are designed not to be limiting Elements for the operation of the bank. Therefore the shunt capacitor bank ratings become the limiting ratings of the Facility. The rating methodology for these other devices is provided under section, “Terminal Equipment”.


4Shunt Reactors



Shunt reactors in support of the Bulk Electric System are specified and rated according to:


  • IEEE C57.21, IEEE Standard Requirements, Terminology, and Test Code for Shunt Reactors Rated Over 500 kVA


Shunt reactors in support of the Bulk Electric System are specified, designed and applied for the full range of system voltage conditions and ranges to which they will be subjected. The Normal Rating for FPL shunt reactors are rated per the manufacturer’s nameplate. FPL does not have ratings above normal for shunt reactors therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.
Other associated power system equipment connected to the reactor such as breakers, switches, buswork and relay settings are designed not to be limiting Elements for the operation of the reactor. Therefore the reactor ratings become the limiting ratings of the Facility. The rating methodology for these other devices is provided under section “Terminal Equipment”.

5Series Reactors



Transmission series connected reactors are specified and rated according to:


  • ANSI/IEEE C57.16, IEEE Standard Requirements, Terminology, and Test Code for Dry-Type Air-Core Series-Connected Reactors




  • ANSI C57.99, Guide for Loading Dry-Type and Oil-Immersed Current-Limiting Reactors.


Transmission series reactors are rated per the manufacturer’s specifications. The Normal Rating for FPL transmission series reactors is given on the manufacturer’s nameplate. FPL does not provide ratings above normal for series reactors therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.
Other associated power system equipment connected to the series reactor such as breakers, switches, buswork and relay settings are designed not to be limiting Elements for the operation of the reactor. Therefore the reactor ratings become the limiting ratings of the Facility. The rating methodology for these other devices is provided under section “Terminal Equipment”.

Terminal Equipment



Substation Conductors


Ampacities for most conductors used in outdoor substations are based on single bus conductors in free air, 40º C ambient temperature, in the sun, emissivity factors of 0.35 for copper and 0.5 for aluminum, and a percent conductivity based on the International Annealed Copper Standard (IACS) conductivity. For new installations, the conductor sizes will normally be determined with conductor ampacities for a 30º C temperature rise above 40º C ambient. The 50º C rise over 40º C ambient ampacity will normally be used for existing substations, to determine if existing conductors should be replaced with higher ampacity conductors.
Aluminum and copper rigid bus conductors, including bar, angle, tube, and integral web, are rated with 2 ft/sec wind velocity. The rigid bus conductor ratings at FPL are consistent with and use the methodology described in the IEEE Guide for Design of Substation Rigid-Bus Structures, IEEE Std 605.
ACSR conductors are normally used at FPL substations in high voltage areas and are rated with 2 mph wind velocity. The ACSR conductor ratings at FPL are consistent with and use the methodology described in the IEEE Standard for Calculating the Current-Temperature of Bare Overhead Conductors, IEEE Std 738.
Bare copper cables are rated with 2 ft/sec wind velocity. Bare copper cable conductor ratings at FPL are consistent with the ratings listed in the Anderson Electrical Connectors – Technical Data booklet.
FPL’s philosophy is that conductors and connectors should be ampacity rated at or above the switches and equipment to which they are connected. For any given ampacity, the conductor should operate cooler than the switch or equipment, thus acting as a heat sink. FPL does not have ratings above normal for substation conductors therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.

Circuit Breakers


AC High-Voltage Circuit Breaker are specified by operating voltage, continuous current, interrupting current, and operating time in accordance with ANSI/IEEE Standards C37 series, “Symmetrical Current Basis.” These ratings are indicated on the individual Circuit Breaker nameplate. The following standards are referenced in the breaker specifications:


  • ANSI C37.04, IEEE Standard Rating Structure




  • ANSI C37.06, Standard for Switchgear- AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis- Preferred Ratings and Related Required Capabilities.




  • ANSI C37.09, IEEE Standard Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis.




  • IEEE C37.010b, Standard for Emergency Load Current-Carrying Capability




  • IEEE C37.010e, (Supplement to IEEE C37.010).


FPL rates transmission circuit breakers according to the manufacturer’s specifications. The Normal Rating for FPL transmission circuit breakers are rated as shown on the manufacturer’s nameplate. Nameplate interrupting ratings are adjusted for reclosing of oil circuit breakers per ANSI C37.04, IEEE Standard Rating Structure. FPL does not have ratings above normal for transmission circuit breakers therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.


Instrument Transformers


Free standing current transformers, metering units or voltage transformers, are rated according to:


  • IEEE C57.13, Standard Requirements for Instrument Transformers.


FPL rates transmission instrument transformers according to the manufacturer’s specifications. The Normal Rating for FPL transmission instrument transformers are rated as shown on the manufacturer’s nameplate. FPL does not have ratings above normal for transmission instrument transformers therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.


Switches


The following Standards are used to rate High-Voltage switches:


  • IEEE C37.30, Standard Requirements for High-Voltage Switches.




  • IEEE C37.37, Standard Loading Guide for AC High-Voltage Switches (in excess of 1000 volts).




  • IEEE C37.37a, Standard Loading Guide for AC High-Voltage Air Switches Under Emergency Conditions.


Transmission switches are rated according to the manufacturer’s specifications. The Normal Rating for FPL transmission switches are rated as shown on the manufacturer’s nameplate. FPL does not have ratings above normal for transmission switches therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.

Line Traps


Line traps are rated according to:


  • ANSI C93.3, Requirements for Power-line Carrier Line Traps.


Line traps are rated according to the manufacturer’s specifications. The Normal Rating for FPL line traps are rated as shown on the manufacturer’s nameplate. FPL does not have ratings above normal for line traps therefore no Emergency Ratings are provided as they would be equal to the Normal Ratings.


Relay Settings


FPL is currently following NERC System Protection Control Task Force applicable guidelines for relay loadability. It is FPL’s design philosophy that relay settings shall not be the limiting factor on transmission system transfer capability. Relays sensitive to system loading are being set to carry at least 150% of rated ampacity.




Appendix “A” - Generation Facilities






Rev.

No.


Date


Description


By


Approval

0

6/22/05

New Document

JAZ

FRO

1

2/22/07

Rev. for FAC-008-2 – Facility Ratings

Revised generation capability rating methodology to distinguish between commitment and long-term ratings.

Added reactive power capability methodology.

JAZ

FRO

















Document A-214381, rev.4 Page of 02/28/07

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