Bulk Electric System
Facility Rating Methodology
TRANSMISSION
Revisions
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
5 / 7/01/08 / Reformatted & revised throughout. Added Emergency Ratings methodologies. / RAC/MDJ/
JJM/NCA / JJM
6 / 9/29/08 / Deleted Appendix A. Generation Document will be posted separately. / BJM / BJM
7 / 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
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 13
3.7 Series Capacitors 14
3.8 Series Reactors 14
4. Terminal Equipment and Relay Protective Device Ratings 15
4.1 Substation Conductors 15
4.2 Circuit Breakers 17
4.3 Instrument Transformers 18
4.3.1 Current Transformers 18
4.3.2 Voltage Transformers 19
4.4 Air Disconnect Switches 20
4.5 Circuit Switchers 22
4.6 Line Traps 23
4.7 Relay Protective Devices 24
1. Introduction
This document describes the methodology that Florida Power & Light Company (FPL) uses to determine the Facility Rating[1] of certain Bulk Electric System (BES) Facilities[2] (Facilities) as required by NERC/FERC Reliability Standard FAC-008-1[3]. 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 Ratings[4] and Emergency Ratings[5] for the following Facilities[6] identified in Section 2 of this document:
- Transmission Line Facilities
- Transformer Facilities
- Series and Shunt Compensation Facilities
- Shunt Capacitor Facilities
- Shunt Reactor Facilities, and
- Series Reactor Facilities
The Facilities addressed in this document are comprised of various electrical equipment or Elements[7]. 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. Transmission Cables/Conductors
2. Transformers (Autotransformers and Generator Step-Up Transformers (GSU))
3. Reactors (series and shunt applications)
4. 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:
1. Substation Conductors
2. Breakers
3. Instrument Transformers
4. Switches
5. Circuit Switchers
6. Line Traps (also known as Wave Traps), and
7. 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 Rating[8] 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.
FPL designs 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 temporary Facility Ratings, FPL follows the same methodology as described herein.
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.
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 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 allowable pre-existing current level greater than zero 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.
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.
Compensation Facilities are individually evaluated and rated based on the limiting applicable equipment rating.
In applications where a Compensation Facility is in series with a Facility whose Emergency Rating is equal to the Normal Rating, the Compensation Facility Emergency Rating may be set equal to the Normal Rating. An example is a reactor in series with a shunt capacitor. The Shunt Capacitor Facility Emergency Rating equals the Normal Rating; therefore, the Reactor Facility Emergency Rating may be set equal to its Normal 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.
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
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 / Prior to 1978 / 1978-1993 / 1994-2006 / After 2006Maximum Operating Temperature (oC) / 75 / 100 / 100 / 115
Ambient Temperature (oC) / 25 / 35 / 35 / 35
Conductivity (% IACS)* / 62 / 61 / 63 / 62
Emissivity / 0.5 / 0.5 / 0.9 / 0.9
Absorbtivity / 0.47 / 0.47 / 0.9 / 0.9
Wind speed normal to conductor (mph) / 1.364 / 2 / 3 / 2
Solar insolation (W/ft2) / 93 / 93 / 93 / 93
* International Annealed Copper Standard