Download 2. Bulk Electric System Facilities

Bulk Electric System
Facility Rating Methodology
NHT
PAGE 1 OF 18
Rev 2: 11/02/09
Revisions
Rev.
No.
Date
Description
By
Approval
0
5/31/07
New Document
MEP
RAT
1
10/3/07
Revised section 5 stating that the Emergency
Rating is the same as Normal Rating
MEP
RAT
2
Complete rewrite of document based on
detailed study of existing and new station
11/02/09
equipment and to make consistent with ISONew England Planning Procedure No.7.
MBN
MDJ
3
6/1/10
Change Name references throughout to NHT
from FPL-NED
GLW
4
PAGE 2 OF 18
Rev 2: 11/02/09
Table of Contents
1. Introduction................................................................................................................4
2. Bulk Electric System Facilities ..................................................................................6
2.1 Transmission Line Facilities .................................................................................... 6
2.2 Transformer Facility ................................................................................................ 6
3. Equipment Ratings (Open Air) ..................................................................................7
3.1 Generator Step-Up Transformers (GSU’s) .............................................................. 7
3.2 Substation Buses ......................................................................................................8
3.4 Current Transformers.............................................................................................12
3.5 Voltage Transformers ............................................................................................13
3.6 Line Traps .............................................................................................................. 14
3.7 Current Transformer Circuit Components ............................................................. 15
3.7.1 Relay Protective Devices .................................................................................... 15
3.7.2 Meters and Transducers ...................................................................................... 16
4.0 Equipment Ratings (GIS and GIL) ........................................................................ 17
4.1 Substation Buses, Switches and Circuit Breakers .................................................17
4.2 Current Transformers.............................................................................................18
4.3 Voltage Transformers ............................................................................................18
PAGE 3 OF 18
Rev 2: 11/02/09
1. Introduction
This document describes the ratings methodology that Florida Power & Light Company- New England
Division (NHT) uses to determine the Facility Rating1 of its Bulk Electric System Facilities (BES
Facilities) as required by NERC Reliability Standard FAC-008-12 and consistent with ISO New
England Planning Procedure No.7 (PP7)3. The ratings methodology described herein covers BES
Facilities solely owned by NHT and BES Facilities jointly owned for which NHT has responsibility for
providing ratings.
This document describes the current NHT ratings methodology for the following BES Facilities4
identified in Section 2 of this document:
1. Transmission line facilities
2. Transformer facilities
NHT does not own any of the following BES Facilities and therefore no rating methodologies have
been established:
1. Shunt compensators which includes shunt capacitors and shunt reactors.
2. Series reactors
3. Generators
The BES Facilities addressed in this document are comprised of various types of electrical equipment.
For example, a transmission line Facility may include one or more of the following equipment types:
conductors, line traps, switches, and breakers. Protective relays for the line will also be included as part
of the transmission line Facility.
The Facility Ratings and Equipment Ratings5 are Normal, Short Time Emergency (STE), Long Time
Emergency (LTE) and Drastic Action Limit (DAL) for Winter and Summer. In accordance with PP7,
the Normal and Emergency Ratings durations are listed in Table 1 below and are utilized in this
methodology.
Glossary of Terms Used in Reliability Standards (NERC), 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
NERC Reliability Standard FAC-008-1 – Facility Ratings Methodology: Adopted by Board of Trustees February 7, 2006,
Effective date of August 7,2007 and approved by Federal Regulatory Energy Commission on March 16, 2007
3
ISO New England Planning Procedure No.7 (PP7), Procedure for Determining and Implementing Transmission Facility
Ratings in New England, Effective date of August 31, 2005, revised February 14, 2007 (http://isone.com/rules_proceds/isone_plan/pp7_ratings_rev2_021407.pdf).
4
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.)5
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.
1
PAGE 4 OF 18
Rev 2: 11/02/09
Table 1
Normal and Emergency Ratings Durations
Winter Ratings




Winter Normal Rating (W NOR)
Winter Long-Time
Emergency Rating (W LTE)
Winter Short-Time
Emergency Rating (W STE)
Winter Drastic
Action Limit (W DAL)
Time
-
Summer Ratings


4 hrs

15 mins.

5 mins.
Time
Summer Normal Rating (S NOR)
Summer Long-Time
Emergency Rating (S STE)
Summer Short-Time
Emergency Rating (S STE)
Summer Drastic
Action Limit (S DAL)
NHT BES has both open-air and gas insulated equipment.
12 hrs
15 mins.
5 mins.
The equipment includes the following:
1. Generator Step-Up Transformers (GSU) (Note: GSU in this instance, describes a piece of
equipment not a Facility)
2. Substation buses
3. Disconnect switches
4. Current transformers
5. Voltage transformers
6. Line traps (also known as wave traps)
7. Current transformer circuit components
8. Circuit breakers
NHT does not own any of the following equipment and therefore no rating methodologies have been
established:
1. Overhead transmission conductors
2. Underground transmission cable
3. Autotransformers
4. Shunt capacitors
5. Shunt reactors
6. Series capacitors
7. Series reactors
8. Circuit switchers
9. Volt-Ampere (VAR) compensators
10. High Voltage Direct Current (HVDC) systems
The rating methodology in this document holds to the principle that the “Facility Rating shall equal the
most limiting applicable Equipment Rating of the individual equipment that comprises that Facility”.
PAGE 5 OF 18
Rev 2: 11/02/09
For the purposes of this Rating Methodology, and in accordance with PP7, 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 Mega Volt
Ampere (MVA) or Mega Volt Ampere Reactive (MVAR).
NHT equipment is designed 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 of this document.
For operating limitations due to equipment failure, malfunction, or other unforeseen impact requiring
temporary rerating, temporary Facility Ratings are established. NHT 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 by NHT a minimum of three years or for the duration of the
limitation, which ever is greater.
2. Bulk Electric System Facilities
2.1 Transmission Line Facilities
Transmission line facilities are comprised of two main sets of equipment: (1) transmission substation
terminal equipment; and (2) transmission line conductors.
NHT substation terminal equipment includes Gas Insulated Substation (GIS) circuit breakers, switches,
bushings, buses, and current and voltage transformer circuits as well as open air switches, wave traps
and buses. NHT transmission line conductors are Gas Insulated Line (GIL).
Except where otherwise noted, open air equipment ratings are discussed in Section 3, and gas insulated
equipment ratings in Section 4.
2.2 Transformer Facility
The Transformer Facility includes the GSU transformer and associated equipment. Associated
equipment connected to the transformer typically includes circuit breakers, disconnect switches,
substation buses, bushings, cooling systems, and current and voltage transformer circuits. The facility
includes both open air and gas insulated equipment.
PAGE 6 OF 18
Rev 2: 11/02/09
3. Equipment Ratings (Open Air)
3.1 Generator Step-Up Transformer (GSU)
Introduction
NHT owns one GSU, consisting of three single-phase transformers. The GSU is specified, designed
and applied for the full range of system loading conditions and ranges to which it will be subjected.
The Normal Rating for the NHT GSU is provided by the manufacturer.
Design Criteria/Industry Standards




ANSI/IEEE 57.92, Guide for Loading Mineral-Oil-Immersed Transformers.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, February 14, 2007.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix D Power Transformers, March 21,
2006. (Note: Appendix D references ANSI/IEEE 57.91. The NHT GSU was designed under
57.92)
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix A General Rating Parameters, April
11, 2006.
Rating Methodology
NHT relies on the manufacturer to calculate GSU equipment ratings based on appropriate design
criteria, standards, and other considerations. NHT uses those manufacturer provided equipment ratings
in the calculation of associated Facility Ratings.
Considerations
The assumptions for the GSU 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 than -20 degrees C.
Altitude shall not exceed 3300 ft
Normal and Emergency Ratings
The Normal Rating for the GSU is provided by the manufacturer. The Emergency Rating is equal to
the Normal Rating, per Appendix D Power Transformers of PP7.
PAGE 7 OF 18
Rev 2: 11/02/09
3.2 Substation Buses
Introduction
NHT utilizes the rating assumptions and methodology described below to determine the Normal, STE,
LTE and DAL ratings for substation buses.
Design Criteria/Industry Standards
Ratings for bare, outdoor, non-enclosed buses and cables are in accordance with the following:






IEEE Standard 605-1998, “Guide for Design of Substation Rigid Bus Structures”
IEEE Standard 738-2006, “Guide for Calculating the Current-Temperature relationship of
Bare Overhead Conductors”.
ISO New England Planning Procedure No. 7, Procedures for Determining and
Implementing Transmission Facility Ratings in New England, February 14, 2007.
ISO New England Planning Procedure No. 7, Procedures for Determining and
Implementing Transmission Facility Ratings in New England, Appendix J Substation
Buses, May 8, 2006.
ISO New England Planning Procedure No. 7, Procedures for Determining and
Implementing Transmission Facility Ratings in New England, Appendix A General Rating
Parameters, April 11, 2006.
PLS –CADD Version 10.20L
Rating Methodology
Normal and Emergency Ratings for rigid conductors are determined by utilizing proprietary software
based on the formulas provided by IEEE Std. 605-1998.
Ratings for flexible conductors (buses) are determined using the PLS CADD Version 10.2L and IEEE
Std. 738-2006 method of calculation.
Note: IEEE Std. 738-2006 is a later standard than the IEEE Std. 738-1993 referenced in PP7.
Considerations
Rigid Bus: The ampacity rating calculations for the 4” rigid, Aluminum bus conductors involve
parameters such as ambient temperature, maximum conductor temperature limitations, wind speed,
wind direction, solar gain, emissivity, and absorptivity. These parameters are required in order to
determine the ratings of substation buses. The values used for these parameters are listed Table 2
below.
PAGE 8 OF 18
Rev 2: 11/02/09
Table 2
Parameters Used For Rigid Bus
Parameter
Ambient Temperatures
Wind Direction
Wind Speed
Bus Temp Limit For Normal
Bus Temp Limit For LTE
Bus Temp Limit For STE
Bus Temp Limit For DAL
Emissivity
Absorptivity
Summer/Winter
28°C/10°C
90° to conductor
3fps
80°C
100°C
100°C
100°C
0.5
0.5
Flexible Conductors: The ampacity rating calculations for the flexible conductors involve parameters
such as ambient temperature, maximum conductor temperature limitations, wind speed, wind direction,
solar gain, emissivity, and absorptivity. These parameters are required in order to determine the ratings
of substation buses. The values used for these parameters are listed in Table 3 below.
.
Table 3
Parameters Used For Flexible Conductors
Parameter
Ambient Temperatures
Wind Direction
Wind Speed
Bus Temp Limit For Normal
Bus Temp Limit For LTE
Bus Temp Limit For STE
Bus Temp Limit For DAL
Emissivity
Absorptivity
Summer/Winter
28°C/10°C
90° to conductor
3fps
100°C
120°C
140°C
140°C
0.75
0.7
PAGE 9 OF 18
Rev 2: 11/02/09
Normal and Emergency Ratings
The Normal and Emergency Ratings (STE, LTE and DAL) are determined by NHT based upon the
above methodology.
3.3 Disconnect Switches
Introduction
NHT utilizes the IEEE industry standards and the PP7 as guidelines in rating disconnect switches.
Specifically, the Allowable Continuous Current Class (ACCC) designation of the IEEE industry
standards is applicable. As stated in IEEE C37.30-1996: “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 disconnect switches that were designed in accordance with ANSI
C37.30-1962 and earlier standards, for which there were no ACCC designations. The most common
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.
Design Criteria/Industry Standards





IEEE Std C37.30-1997, IEEE Standard Requirements for High-Voltage Switches
IEEE Std C37.37-1996, IEEE Loading Guide for AC High-Voltage Air Switches (in Excess of
1000V)
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, February 14, 2007.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix G Disconnect Switches, March 21,
2006.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix A General Rating Parameters, April
11, 2006.
Rating Methodology
NHT utilizes the guidelines in the March 21, 2006 version of Appendix G Disconnect Switches from
PP7 in developing the rating methodology for disconnect switches.
In developing the Normal Ratings (allowable continuous current) for disconnect switches; NHT
utilizes the equation provided in section 5.4.1 of IEEE Std C37.30-1997. This follows the
methodology outlined for Continuous Load Current Capability in the above referenced Appendix G of
PP7.
PAGE 10 OF 18
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In developing the LTE ratings for disconnect switches; NHT utilizes the guidelines provided in section
6.2 of IEEE Std C37.37-1996. This follows the methodology outlined for Extended Period
Emergencies, section 3.1.1, in the above referenced Appendix G of PP7.
In developing the STE and DAL ratings for disconnect switches; NHT utilizes Equation (4) as
described for Short Time Emergencies, section 3.2.2, in the above referenced Appendix G of PP7.
Utilizing this methodology results in lower loadability factors than utilizing IEEE Std C37.37-1996,
and is therefore more conservative.
Considerations
In developing disconnect switch ratings; NHT utilizes the ambient temperatures provided in Table A 1
from the above referenced Appendix A General Rating Parameters of PP7. Specifically, 10 degrees-C
is assumed in Winter and 28 degrees-C is assumed in the Summer.
It is assumed that disconnect switches will have an ACCC designation of either AO1 or DO6. Unless
a specific switch ACCC designation is verified or if a switch is verified to be designed in accordance
with the IEEE C37.30-1962 or earlier standard, NHT assumes worst case between AO1 and DO6
switch part class designations and adopts the lowest resulting rating according to this Facility Rating
Methodology.
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, a pre-disturbance loading of 100% of the Normal Rating is
assumed prior to a LTE or STE. In order to coincide with the standard considerations of the Drastic
Action Limit of PP7, a pre-disturbance loading of 75% of the Normal Rating is assumed prior to a
DAL emergency.
Emergency ratings accept an increase of 20 degrees-C above the normal allowable maximum
temperatures for the duration of the emergency, as outlined in IEEE C37.37-1996.
A thermal time constant of 30 minutes is assumed for disconnect switches, as provided in IEEE
C37.37-1996.
Normal and Emergency Ratings
1. Normal Ratings
For open air disconnect switches, NHT considers the Normal Rating to be synonymous with the
“allowable continuous current” rating of the IEEE standards referenced above.
Depending on ambient temperature, the Normal Rating may be above the rated continuous current
(nameplate rating). To determine the Normal Ratings, the appropriate loadability factor is
multiplied by the rated continuous current of the disconnect switch (nameplate value).
PAGE 11 OF 18
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If the specific switch ACCC designation is unknown, NHT rates its disconnect switches on a worst
case scenario basis by calculating the loadability factors for switch part class designations AO1,
DO4, and FO6 and utilizing the lowest resulting loadability factor.
If a specific disconnect switch ACCC designation is verified or if a switch is verified to be
designed in accordance with the IEEE C37.30-1962 or earlier standard, then the appropriate
allowable continuous current rating for that disconnect switch can be developed based on this
Facility Rating Methodology.
The Normal Rating loadability factor is calculated by utilizing the equation in IEEE Std C37.301997, section 5.4.1.
2. Emergency Ratings
To determine the Emergency Ratings, the appropriate loadability factor is multiplied by the rated
continuous current of the disconnect switch (nameplate value).
If the specific switch ACCC designation is unknown, NHT rates its disconnect switches on a worst
case scenario basis by calculating the loadability factors for switch part class designations AO1,
DO4, and FO6 and utilizing the lowest resulting loadability factor.
If a specific disconnect switch ACCC designation is verified or if a switch is verified to be
designed in accordance with the IEEE C37.30-1962 or earlier standard, then the appropriate
emergency rating for that disconnect switch can be developed based on this Facility Rating
Methodology.
The LTE loadability factor is calculated by utilizing the equation in IEEE Std C37.37-1996, section
6.2.
The STE and DAL ratings are calculated by utilizing Equation (4) in the above referenced
Appendix G of PP7. The loadability factor is the term multiplied by Ir in Equation (4).
3.4 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.
PAGE 12 OF 18
Rev 2: 11/02/09



ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, February 14, 2007.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix H Current transformers, December
30, 2005.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix A General Rating Parameters, April
11, 2006.
Rating Methodology
The Normal and Emergency Ratings (STE, LTE and DAL) methodology follow the guidelines of PP7.
Considerations
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 average 24hr ambient temperature is less than 30°C and the maximum
temperature is less than 40°C
 Alternately, air cooled CTs may be rated when the average 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 developed in accordance with PP7,
Appendix H.
3.5 Voltage Transformers
Introduction
Protection and metering devices are supplied voltages from Potential Transformers (PTs or VTs),
Coupling Capacitor Voltage Transformers (CVTs or CCVTs), or combined Metering Units (MUs). No
MUs are utilized by NHT. 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.
PAGE 13 OF 18
Rev 2: 11/02/09
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
NHT relies on the manufacturer to calculate PTs and CCVTs equipment ratings based on appropriate
design criteria, standards, and other considerations. NHT uses those manufacturer provided equipment
ratings in the calculation of associated Facility Ratings.
Considerations
The assumptions/considerations for the ratings are:
 Elevation is less than 1000m
 Temperature range for CVTs is from -40°C to 45°C (ANSI C93.1) , and for VTs (ANSI
C57.13) is from -30°C to 40°C
 Alternately, air cooled VTs may be rated when the average 24hr ambient temperature is less
than 55°C and the maximum temperature is less than 65°C
Normal and Emergency Ratings
The Normal Ratings for PTs and CCVTs are provided by the manufacturer. The Emergency Rating is
equal to the Normal Rating.
3.6 Line Traps
Introduction
The section includes line traps, sometimes referred to as wave traps, which are series connected
devices usually in one or more phases of the high voltage power system.
Design Criteria/Industry Standards




ANSI C93.3, Standard Requirements for Powerline Carrier Line Traps.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, February 14, 2007.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix I Line Traps, April 11, 2006.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix A General Rating Parameters, April
11, 2006.
PAGE 14 OF 18
Rev 2: 11/02/09
Rating Methodology
NHT relies on the manufacturer to calculate line trap equipment ratings based on appropriate design
criteria, standards, and other considerations. NHT uses those manufacturer provided equipment ratings
in the calculation of associated Facility Ratings. Additional criteria and parameters for the ratings are
defined through past studies in PP7.
Considerations
The assumptions/considerations for the ratings are:




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.
PP7 has classified though past history studies that summer will be defined as 28oC, and that
winter will be defined as 10oC as the average ambient temperatures with 3fps average wind
speed.
Normal and Emergency Ratings
The Normal and Emergency Ratings for line traps are developed in accordance with PP7, Appendix I.
3.7 Current Transformer Circuit Components
3.7.1 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.”
Design Criteria/Industry Standards



IEEE C37.90-2005 - Standard for Relays and Relay Systems Associated with Electric Power
Apparatus
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, February 14, 2007.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix K Current Transformer Circuit
Components, May 8, 2006.
PAGE 15 OF 18
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

ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix A General Rating Parameters, April
11, 2006
ISO-PP7-Attachment 4- Capacity Rating Procedures by the SDTF, Oct 2004, CT Relaying
Circuits
Rating Methodology
NHT relies on the manufacturer to calculate relay equipment ratings based on appropriate design
criteria, standards, and other considerations. NHT uses those manufacturer provided equipment ratings
in the calculation of associated Facility Ratings. The ratings are restated in PP7, Attachment 4.
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
The Normal and Emergency Ratings for relay protective devices are provided by the manufacturer, and
the ratings are restated in PP7, Attachment 4.
3.7.2 Meters and Transducers
Introduction
This section refers to control panel indicating meters and transducers. These may be independent
indicating meters and transducers, or they may be combined meter-transducer units, or the function
may be incorporated into a modern microprocessor relay using the front panel display unit.
Design Criteria/Industry Standards




ANSI Standard C39.1- 1964 in accordance with limitations/descriptions in PP7.
ISO-PP7-Attachment 4- Capacity Rating Procedures by the SDTF, Oct 2004, Metering and
Transducers
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, February 14, 2007.
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix K Current Transformer Circuit
Components, May 8, 2006.
PAGE 16 OF 18
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
ISO New England Planning Procedure No. 7, Procedures for Determining and Implementing
Transmission Facility Ratings in New England, Appendix A General Rating Parameters, April
11, 2006
Rating Methodology
NHT relies on the manufacturer to calculate meter and transducer equipment ratings based on
appropriate design criteria, standards, and other considerations. NHT uses those manufacturer
provided equipment ratings in the calculation of associated Facility Ratings. The ratings are restated in
PP7, Attachment 4.
Considerations
Meters and transducers 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
The Normal and Emergency Ratings for meters and transducers are provided by the manufacturer, and
the ratings are restated in PP7, Attachment 4.
4.0 Equipment Ratings (GIS and GIL)
PP7 does not specifically address gas insulated equipment so NHT utilizes the ratings provided by the
manufacturer for such equipment.
4.1 Substation Buses, Switches and Circuit Breakers
Introduction
This section includes GIL, GIS bus, and associated breakers, switches and gas to air bushings.
Design Criteria/Industry Standards
GIS and GIL equipment was specified and governed by applicable standards and practices at the time
of procurement of the equipment.
Rating Methodology
PAGE 17 OF 18
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NHT relies on the manufacturer to calculate gas insulated equipment ratings based on appropriate
design criteria, standards, and other considerations. NHT uses those manufacturer provided equipment
ratings in the calculation of associated Facility Ratings.
Considerations
Station Environmental Design Criteria
Elevation Above Sea Level
20 ft
Maximum Ambient Temperature 102 deg F
Minimum Ambient Temperature
-23 deg F
Maximum Wind Velocity
110 miles/hour
Maximum Ice Loading
1” radial
Maximum Snow Loading
50lbs./sq.ft
Humidity
100%
Subject to Salt water vapors
Normal and Emergency Ratings
The Normal and Emergency Ratings are provided by the manufacturer.
4.2 Current Transformers
Current transformer rating methodology for the gas insulated equipment is the same as for the open air
equipment. See Section 3.5 of this Facility Rating Methodology.
4.3 Voltage Transformers
Voltage transformer rating methodology for the gas insulated equipment is the same as for the open
air equipment. See Section 3.6 of this Facility Rating Methodology.
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