Download Justifying Exclusion of Local Networks from Bulk Electric System and more Exercises Topology in PDF only on Docsity!
Page 1 of 16
Local Network Exclusion
Introduction
The purpose of this document is to provide the justification for the definitional exclusion of local
networks (LN) from the definition of the Bulk Electric System (BES) as proposed in NERC Standards
Development Project 2010-17. Presented herein are technical, logical, and practical considerations that
provide such justification for exclusion of these facilities from the Bulk Electric System.
Summary of Justification
The local network exclusion proposal is shown to be justified through the following facts:
1. In accordance with Commission Orders 743 and 743a on the matter of the revision of the
Definition of the Bulk Electric System, the facilities used in the local distribution of electric
energy are to be excluded;
2. The exclusion for local networks, as provided in the revised definition of the BES, ensures that a
candidate for local network exclusion must satisfy all of the exclusion principles thus
demonstrating that the candidate facilities are not performing a transmission function;
3. The limit on connected generation within the local network is consistent with the existing
threshold above which a generating plant in aggregate becomes subject to owner and operator
registration in the ERO Statement of Compliance Registry Criteria;
4. The voltage cap applied to the qualifications for a local network is established at 300 kV, which
is consistent with the distinction being made between Extra High Voltage and High Voltage in
the NERC Board of Trustees-approved Reliability Standard on transmission planning, TPL-001-2;
5. The power flow “shifts” that would occur on the elements of a local network are but a
negligible fraction of that which distributes upon the BES elements for a given power transfer
and is fully eclipsed by the Load in the local network; and
6. The interaction of the local network with the BES is similar in character to that of a radial facility.
Description of Local Network
Local networks are defined in the draft BES Definition as:
A group of contiguous transmission Elements operated at or above 100 kV but less than 300 kV that
distribute power to Load rather than transfer bulk power across the interconnected system. LN’s
emanate from multiple points of connection at 100 kV or higher to improve the level of service to retail
customer Load and not to accommodate bulk power transfer across the interconnected system. The LN
is characterized by all of the following:
Page 2 of 16
a) Limits on connected generation: The LN and its underlying Elements do not include
generation resources identified in Inclusion I3 and do not have an aggregate capacity of
non-retail generation greater than 75 MVA (gross nameplate rating) ;
b) Power flows only into the LN: The LN does not transfer energy originating outside the LN for
delivery through the LN; and
c) Not part of a Flowgate or transfer path: The LN does not contain a monitored Facility of a
permanent Flowgate in the Eastern Interconnection, a major transfer path within the
Western Interconnection, or a comparable monitored Facility in the ERCOT or Quebec
Interconnections, and is not a monitored Facility included in an Interconnection Reliability
Operating Limit (IROL).
Local networks are present to provide local electrical distribution service and are not planned, designed,
nor operated to benefit or support the balance of the interconnected electrical transmission network.
Their purpose is to provide local distribution service, not to provide transfer capacity for the
interconnected electric transmission network. Their design and operation is such that at the point of
connection with the interconnected electric transmission network, their effect on that network is similar
to that of a radial facility, particularly in that flow always moves in a direction that is from the BES into
the facility. Any distribution of parallel flows into the local network from the BES, as governed by the
fundamentals of parallel electric circuits, is negligible, and, more importantly, is overcome by the Load
served by the local network, thereby ensuring that the net actual power flow direction will always be
into the local network at all interface points. The presence of a local network is not for the operability of
the interconnected electric transmission network; neither will the local network’s separation or
retirement diminish the reliability of the interconnected electric transmission network.
Commission Determination on Exclusion of Local Distribution – Relation
to Local Network
In Order 743a, the Commission made it clear that facilities that are used in the local distribution of
electric energy will be excluded from the Bulk Electric System. Such clarification was provided in both
paragraphs 22 and 25 of the Order. The Commission agreed with certain commenters that facilities
used in the local distribution of energy should be excluded from the revised Bulk Electric System
definition.
In response to this facet of the Order, in developing the BES definition, the SDT has followed this
guidance. Exclusion E3 was specifically designed to capture for exclusion those high voltage non-radial
facilities being used for the local distribution of energy.
The exclusion characteristics in items a, b, and c above are further explained in the next section. These
exclusion principles serve to ensure that facilities excluded under the local network exclusion (E3) are
not necessary for the reliable operation of the interconnected electric transmission network and are
instead used in the local distribution of energy.
Page 4 of 16
case basis, but will necessarily be the points, below 300 kV, at which all of the qualifying exclusion
principles are satisfied. As an example, see Appendix 1 to this document, which provides, among other
things, a single line diagram depicting a local network and its interface with the BES.
C. Third Exclusion Principle: Flowgates and Transfer Paths
Not part of a Flowgate or transfer path: The LN does not contain a monitored Facility of a
permanent Flowgate in the Eastern Interconnection, a major transfer path within the Western
Interconnection, or a comparable monitored Facility in the ERCOT or the Quebec
Interconnections, and is not a monitored Facility included in an Interconnection Reliability
Operating Limit (IROL).
This characteristic further ensures that the candidate local network facilities do not contain nor
comprise facilities of well-established flowgates and transfer paths throughout the Interconnections of
North America. These transfer paths are customarily used to provide bulk power transfers within the
Interconnections, and therefore, the function and purpose of any candidate facilities included in or
among such paths extends beyond the distribution function. A number of interchange coordination
Reliability Standards apply to these transfer paths and flowgates. The SDT feels that such facilities are
necessary for the reliable operation of an interconnected electric transmission network and would not
be excluded from the definition of the BES.
The Use of a 300 kV Cap is Appropriate for Local Network Exclusion
The selection of a 300 kV cap for the applicability of an exclusion for a local network was based upon
recent NERC Standards Development work in Project 2006-02 “Assess Transmission Future Needs and
Develop Transmission Plans.” As conveyed in its work product, TPL-001-2, the Project 2006-02 SDT sets
a voltage level of 300 kV to differentiate Extra High Voltage (EHV) facilities from High Voltage facilities
acting as a threshold to distinguish between expected system performance criteria.
1
There is Minimal Effect to Flow in the Local Network due to BES Power
Transfer
The Project 2010-
17 SDT seeks to establish consistency in the limitations placed on the exclusion applicability for local
network facilities, and has therefore adopted this 300 kV level to ensure that EHV facilities, which under
the TPL-001-2 Standard are held to a higher standard of performance, are not subject to this exclusion.
Similar to the character of a radial facility, and in order to qualify for exclusion from the BES under
Exclusion E3.b,a local network must only have power flow into the network at all connection points to
the BES. As demonstrated below, while this flow at the connection points is always into the local
1 Per footnote #3 in TPL-001-2, “ Bulk Electric System (BES) level references include extra-high voltage (EHV) Facilities defined as greater than 300 kV and high voltage (HV) Facilities defined as the 300 kV and lower voltage Systems. The designation of EHV and HV is used to distinguish between stated performance criteria allowances for interruption of Firm Transmission Service and Non-Consequential Load Loss.”
Page 5 of 16
network, the magnitude of the flow at these connection points will exhibit very slight shifts as bulk
power transactions are implemented on neighboring BES facilities. This occurs because local network
facilities are electrically parallel to Elements comprising the BES, and hence, the local network will
experience a small effect due to changes in power angle across the parallel network as BES dispatch and
flow patterns change. However, such flow shift is shown to be minimal, and the resultant power flow at
all BES interface points is dominated by the superimposed load flow serving the distribution Load
connected within the local network. Again, Exclusion E3.b ensures that flow shall always be from the
BES into the local network in order to qualify for exclusion.
In order to provide a realistic example of the electrical interaction between a typical local network and
the BES, an electric system in the western United States was examined from a power transfer
distribution factor (PTDF) perspective. In a PTDF analysis, the branch elements of an electrical network
are examined on the basis of the percentage split of a given power flow as it propagates through the
network. In the simplest example of two identical lines operated at the same voltage, arranged in
parallel between a given sending bus and receiving bus, the total power transfer will divide equally
among the two parallel line elements, and hence, each element would be found to have a 50% PTDF. In
a more complicated network, the line elements will carry a portion of the total flow in a manner that is
inversely proportional to their impedance; i.e., the lower the impedance of the network branch, the
higher portion of the flow that will distribute along that branch.
The electric system in question is depicted in Appendix 1. The station name identifiers and the network
topology (but not electrical connectivity) have been changed to respect the confidentiality of the
information. In the represented system, a bulk power transfer was simulated, with a point of receipt
(injection) at BES bus T9 and a point of delivery at the other end of the system at BES bus T10. With this
simulated power transfer, power flow analysis tools were used to determine the distribution of this
simulated transfer as it propagates across the various parallel branches of the network. As depicted in
Appendix 1, the facilities that are presumed to be excluded via the local network exclusion (E3) are
shown to carry negligible flow, with the largest PTDF at a mere 0.23% of the total transfer. Note that a
PTDF analysis shows only the incremental shift in power flow and does not imply that this 0.23% actually
flows in and then back out of the network. The power flow results demonstrate that the flow measured
at the interface points of the BES continues to flow into the local network, and is essentially unchanged,
as it is only shifted in magnitude by a mere 0.23% of the modeled transaction amount.
In addition to the PTDF analysis, another analysis of Line Outage Distribution Factors (LODF), examines
the re-distribution of flow that occurs on parallel elements after a subject element is removed from
service. For example, if a BES element is carrying 500 MW, and is taken out of service, LODF describes
how that flow re-distributes among all parallel paths in a given network. LODF factors are measured in
percent of the pre-outage flow on the outaged element. Conducting this analysis on the example
network and modeling the worst case outage, which is the loss of the line element between BES buses
T9 and T10, shows that the net shift in flow for the local network is 4.0% of the pre-outage flow, and the
largest shift in flow on any of the individual local network elements is 2.7%. The flow direction at the
interface points between the local network and the BES continues to be into the local network.
Page 7 of 16
Appendix 1
Local Network Technical Justification
Power Transfer Distribution Factor Analysis
This appendix provides Power Transfer Distribution Factor (PTDF) and Line Outage Distribution Factor
(LODF) analyses and assessments using a relevant power flow case used in actual operating studies in
the Western Interconnection to assess reliable Operating Transfer Capability on a rated path in the
Western Electricity Coordinating Council ("WECC"). The electrical system representation is accurate;
however, the bus names and topology have been graphically rearranged to address any Critical Energy
Infrastructure Information (“CEII”) concerns.
Although linear analyses, such as these, are relatively independent of actual power transfer levels, the
modeled system conditions represented peak load demand and high power transfer conditions. The
PTDF analyzes the injection of power from BES electrical bus T9 and delivering it to BES bus T10, which is
consistent with the use of the BES transfer path. Based on the PTDF assessment, 92% of the power flow
is transferred over the 500 kV line that directly connects BES buses T9 and T10. The remaining flow
appears on the underlying 230 kV lines and adjacent 345 kV and 500 kV lines. The largest PTDF on any
local network is 0.23 percent.
The LODF analysis considers the “worst-case” outage of the strongest (lowest impedance) transmission
element, the line between BES buses T9 and T10. The LODF values that are computed represent the
percentage of the pre-outage T9-T10 flow that re-distributes on each of the remaining branches. The
analysis shows that the net shift in flow for the local network is 4.0% of the pre-outage flow, and the
largest shift in flow on any of the individual local network elements is 2.7%. The 2.7% shift occurs on the
local network branch between buses LN19 and LN28, and a 1.3% shift occurs on the branch between
LN27 and LN33. The flow direction at the interface points between the local network and the BES
continues to be into the local network.
Below are three single line diagrams, which depict the 1) powerflow, 2) percentage distribution of flows
for the PTDF analysis, and 3) the percent of flow distribution for the LODF analysis. In these diagrams,
the local network elements are indicated by a green line color, and the local network station buses are
indicated with an “LN” designation, for example, “LN23”.
Following the single line diagrams are two tables: Table 1 - a tabulation of the PTDF values for the
network, and Table 2 - depicting the LODF values for the T9-T10 line outage case.
The Powerflow Single Line
To generation Local Network
Local Network
Red lines are 345 kV to 500 kV
Orange lines are 230 kV
Green lines are 115 kV
The size of the arrow is proportional to the magnitude of powerflow in MWs
The Line Outage Distribution Factors ("LODF") Single Line identifying the revised PTDF values of the transmission line from T9 to T10 is opened For the LODF assessment the transmission line from bus T9 to bus T10 is opened and the PTDF are recalculated (See the LODF table for additional details) To generation Local Network Local Network Red lines are 345 kV to 500 kV Orange lines are 230 kV Green lines are 115 kV The size of the arrow is proportional to the magnitude of PTDF 3% PTDF
22% PTDF
22%
PTDF
- Page 8 of
- LN Arrows do not appear when the level of powerflow is very low - LN - LN - LN
- LN - LN - LN - T23 T - T - T - T - T - T - T9 T - T6 T - T - T - T29 T - LN - LN - LN - T28 T - T - T - T - T - T - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN39 LN - LN - LN - LN - LN - LN19 LN - LN29 LN - LN - LN - LN - LN - T - LN - LN - LN - T - T - T - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - T - LN - LN - Page 9 of
- LN Arrows do not appear when the level of PTDF is very low - LN - LN - LN
- LN - LN - LN - T23 T - T - T - T - T - T - T9 T - T6 T - T - T - T29 T - LN - LN - LN - T28 T - T - T - T - T - T - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN39 LN - LN - LN - LN - LN - LN19 LN - LN29 LN - LN - LN - LN - LN - T - LN - LN - LN - T - T - T - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - T - LN - LN - Page 10 of
- LN Arrows do not appear when the level of PTDF is very low - LN - LN - LN
- LN - LN - LN - T23 T - T - T - T - T - T - T9 T - T6 T - T - T - T29 T - LN - LN - LN - T28 T - T - T - T - T - T - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN39 LN - LN - LN - LN - LN - LN19 LN - LN29 LN - LN - LN - LN - LN - T - LN - LN - LN - T - T - T - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - LN - T - LN - LN
Table 1 - Power Flow Transfer Distribution Factor Results
Line PTDF Records
From Name
To Name
PTDF
From
PTDF
To
Nom kV (Max)
T10 T9 - 91.61 91.61 500 T10 T11 - 5.4 5.4 500 T5 T9 - 4.77 4.77 500 T11 T36 - 4.13 4.13 230
T36 T35 - 3.08 3.08 230 T12 T11 - 2.4 2.4 500 T19 T20 - 1.84 1.84 230 T19 T22 - 1.81 1.81 230
T22 T21 - 1.74 1.74 230 T34 T30 - 1.3 1.3 230 T34 T30 - 1.29 1.29 230 T41 T40 - 0.57 0.57 230
T40 T39 - 0.55 0.55 230 T37 T38 - 0.49 0.49 230 LN16 LN8 - 0.23 0.23 115 LN28 LN19 - 0.23 0.23 115
LN19 LN18 - 0.23 0.23 115 T30 T33 - 0.11 0.11 115 LN50 LN36 - 0.11 0.11 115 LN32 LN33 - 0.11 0.11 115
LN31 LN32 - 0.11 0.11 115 LN20 LN17 - 0.11 0.11 115 LN12 LN11 - 0.11 0.11 115 LN11 LN10 - 0.11 0.11 115
LN3 LN2 - 0.1 0.1 115 T29 T32 - 0.09 0.09 115 T29 T17 - 0.09 0.09 230 LN30 LN29 - 0.09 0.09 115
LN9 T23 - 0.08 0.08 115 LN5 LN7 - 0.08 0.08 115 T28 T31 - 0.07 0.07 115 T32 T31 - 0.07 0.07 115
LN50 LN49 - 0.07 0.07 115 LN53 T33 - 0.06 0.06 115 LN55 LN54 - 0.06 0.06 115 LN41 LN43 - 0.06 0.06 115
T33 T32 - 0.05 0.05 115 LN39 LN41 - 0.05 0.05 115 T42 T39 - 0.04 0.04 230 LN47 T32 - 0.04 0.04 115
LN1 T23 - 0.04 0.04 115 LN41 LN42 - 0.04 0.04 115 LN25 LN23 - 0.04 0.04 115
Line PTDF Records
From Name
To Name
PTDF
From
PTDF
To
Nom kV (Max) LN50 T31 0.11 - 0.11 115 T22 T25 0.11 - 0.11 115
LN57 LN58 0.11 - 0.11 115 LN12 LN57 0.11 - 0.11 115 LN31 LN36 0.11 - 0.11 115
LN27 LN33 0.11 - 0.11 115 LN20 LN27 0.11 -0.11 115 LN58 LN17 0.11 -0.11 115 T25 LN10 0.11 -0.11 115 LN50 T33 0.12 -0.12 115
T21 T24 0.12 -0.12 115 T19 T18 0.13 -0.13 230 LN5 LN8 0.23 -0.23 115 LN28 LN29 0.23 -0.23 115
LN16 LN18 0.23 -0.23 115 T2 T7 0.3 -0.3 500 T2 T7 0.34 -0.34 500
T37 T34 0.49 -0.49 230 T13 T12 0.59 -0.59 500 T14 T11 0.71 -0.71 500 T38 T39 0.78 -0.78 230 T27 T28 0.94 -0.94 230
T28 T29 1.1 -1.1 230 T4 T3 1.15 -1.15 500 T19 T29 1.21 -1.21 230 T19 T27 1.22 -1.22 230
T19 T38 1.26 -1.26 230 T1 T7 1.28 -1.28 500 T4 T1 1.28 -1.28 500
T34 T35 1.54 -1.54 230 T34 T35 1.54 -1.54 230 T21 T20 1.77 -1.77 230 T6 T2 2.34 -2.34 500 T5 T6 2.37 -2.37 500
T5 T4 2.4 -2.4 500 T29 T30 2.48 -2.48 230 T15 T11 2.97 -2.97 500 T12 T10 3 -3 500
T9 T8 3.62 -3.62 500 T8 T21 3.62 -3.62 230
Table 2 - Line Outage Distribution Factor Results (Outage of T9-T10)
Line LODF Records From Name
To Name
LODF
MW
From
MW
To
CTG MW
From
CTG MW
To T10 T9 - 100 - 1482.1 1483.7 0 1. T9 T8 -43.2 217.9 -217.8 857.5 -857. T8 T21 -43.2 217.8 -217.5 857.4 -857.
T12 T10 -35.7 -937.2 937.2 -408.3 408. T15 T11 -35.4 1632.1 -
T29 T30 -29.5 404.1 -404.1 841.8 -841.
T5 T4 -28.6 -835.5 835.5 -411.4 411.
T5 T6 -28.2 -873.5 873.5 -455.2 455.
T6 T2 -27.8 -911.5 912.6 -499 500.
T21 T20 -21 69 -69 380.8 -380.
T34 T35 -18.3 29.2 -29.1 300.9 -300.
T34 T35 -18.3 29.2 -29.1 300.9 -300.
T4 T1 -15.3 -1783.5 1802.5 -1557.4 1576.
T1 T7 -15.3 -1802.5 1802.5 -1576.4 1576.
T19 T38 -15 107.3 -107 330.4 -
T19 T27 -14.5 -53.1 53.2 162.3 -162.
T19 T29 -14.4 -50.9 51 162.8 -162.
T4 T3 -13.8 986 -985 1189.8 -1188.
T28 T29 -13.1 155.8 -155.8 349.4 -349.
T27 T28 -11.2 -154.7 154.7 11.3 -11.
T38 T39 -9.2 326.8 -319.7 463.7 -456.
T14 T11 -8.4 -1656.8 1684.2 -1532.1 1559.
T13 T12 -7.1 -1308.7 1329.4 -1204.2 1224.
T37 T34 -5.8 -219.8 220.1 -133.7 133.
T2 T7 -4.1 -826.9 833.1 -766.2 772.
T2 T7 -3.5 -714.3 719.6 -661.9 667.
LN5 LN8 -2.7 21.8 -21.8 62.3 -62.
LN16 LN18 -2.7 21.1 -21.1 61.6 -61.
LN28 LN29 -2.7 -8.4 8.5 32.1 -32.
T19 T18 -1.5 203.2 -202.5 225.6 -224.
T22 T25 -1.4 83.1 -83 103.2 -103.
T21 T24 -1.4 78.4 -78.3 99.1 -
LN50 T33 -1.4 -38.6 38.7 -18.2 18.
T25 LN10 -1.3 35.7 -35.7 54.4 -54.
LN12 LN57 -1.3 22.3 -22.3 41 -
LN57 LN58 -1.3 12.4 -12.4 31.1 -31.
LN58 LN17 -1.3 0.1 -0.1 18.8 -18.
LN20 LN27 -1.3 0.1 -0.1 18.8 -18.
LN27 LN33 -1.3 0.1 -0.1 18.8 -18.
LN31 LN36 -1.3 -20.3 20.3 -1.6 1.
LN50 T31 -1.3 -36.7 36.7 -16.7 16.
T24 LN2 -1.2 80.3 -80.2 98.3 -98.
T20 T23 -1.2 77.4 -77.2 95.8 -95.
LN1 T23 0.5 - 64 64 - 71.9 71.
LN47 T32 0.5 -66.5 66.6 -74.4 74.
T33 T32 0.6 45.7 -45.7 36.4 -36.
LN39 LN41 0.6 -46.7 46.8 -55.3 55.
Line LODF Records From Name
To Name
LODF
MW
From
MW
To
CTG MW
From
CTG MW
To LN55 LN54 0.7 -50.6 50.7 -60.7 60.
LN41 LN43 0.7 -58.7 58.8 -69.2 69. LN53 T33 0.7 -62.8 63 -72.9 73 T32 T31 0.8 65.9 -65.9 54.4 -54.
T28 T31 0.9 125.9 -125.5 112.9 -112. LN50 LN49 0.9 61.9 -61.8 49.1 - T29 T32 1 136.8 -136.4 121.6 -121. LN30 LN29 1 -4.5 4.5 -19.7 19. LN5 LN7 1 -38.7 38.7 -53.4 53.
LN9 T23 1 -58.4 58.5 -73 73. T29 T17 1 -436.1 436.5 -451.3 451. LN3 LN2 1.2 -61.9 62 -79.9 80 T30 T33 1.3 125.6 -125.3 105.9 -105.
LN50 LN36 1.3 29.7 -29.7 11 - LN31 LN32 1.3 11.2 -11.2 -7.5 7. LN20 LN17 1.3 -0.1 0.1 -18.8 18.
LN32 LN33 1.3 -0.1 0.1 -18.8 18. LN11 LN10 1.3 -35.7 35.7 -54.4 54. LN12 LN11 1.3 -35.6 35.7 -54.3 54. LN28 LN19 2.7 -2.1 2.1 -42.6 42. LN19 LN18 2.7 -12.6 12.6 -53.1 53.
LN16 LN8 2.7 -21.7 21.8 -62.3 62. T37 T38 5.8 219.8 -219.8 133.7 -133. T40 T39 6.6 -221.1 222.8 -318.7 320. T41 T40 6.8 -308.2 309.9 -408.2 409.
T34 T30 15.4 -138.7 138.7 -366.6 366. T34 T30 15.5 -139.7 139.7 -369.2 369. T22 T21 20.7 -70.2 70.2 -377.3 377.
T19 T22 21.5 -90.4 90.7 -409.8 410 T19 T20 21.9 -91.6 91.9 -416.3 416. T12 T11 28.6 -392.2 392.2 -816.5 816. T36 T35 36.7 -58.2 58.2 -601.7 601. T11 T36 49.2 65.3 -64.8 -663.5 664
T5 T9 56.8 1709 -
T10 T11 64.3 544.9 -544.9 -408.3 408.