Guidance
Constructing Aggregation Rules – Central Volume
Allocation
This document covers:
1.
Why is an Aggregation Rule Required?
2.
What is an Aggregation Rule?
3.
How Aggregation Rules Work
4.
BSCP Form Associations
5.
How to Construct Aggregation Rules
6.
GSP Group Take
7.
CDCA Constraints & System Parameters for Aggregation Rules
8.
Appendix A – Definitions
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1.
Why is an Aggregation Rule required?
Section R of the Balancing & Settlement Code (BSC) sets out the rules for determining Metered
Volumes for Central Volume Allocation (CVA) purposes for all Balancing Mechanism Units (BMUs)
(other than Interconnector BMUs and Supplier BMUs), Distribution System Connection Points (DSCP),
Interconnectors, Grid Supply Points (GSP), and GSP Groups. Collectively, these are referred to as
Volume Allocation Units (VAU). This document should be read alongside the BSC Simple Guide Section
R: Collection and Aggregation of Meter Data from CVA Metering Systems.
The Central Data Collection Agent (CDCA) is responsible for collecting and validating metered data
from CVA registered Metering Systems, aggregating the metered data to determine the Metered
Volumes for each registered VAU and for submitting the Metered Volumes to the Settlement
Administration Agent (SAA). The CDCA also calculates the GSP Group Take for each GSP Group and
submits to the Supplier Volume Allocation Agent (SVAA).
In order for the CDCA to aggregate metered data to the appropriate Metered Volume for a VAU, the
Party responsible for the VAU must submit Aggregation Rules to the CDCA in accordance with
BSCP75.
Section R defines the Metered Volume for a VAU, in a Settlement Period, as the net aggregate volume
of Active Energy (determined at the Transmission System Boundary) which flowed in that Settlement
Period to or from the VAU.
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2.
What is an Aggregation Rule?
An Aggregation Rule is algebraic equations, which the CDCA uses in its system to determine the
Metered Volumes for VAUs. CVA Metering Systems can be complex with many Meters and Meter
registers. Aggregation Rules define how Meter readings need to be combined.
For CVA Settlement to be accurately monitored, all energy generated onto, or demand taken from, the
Transmission System is allocated to VAUs.
VAUs fall under the following categories;
●
BMU – other than Supplier or Interconnector BMU
●
GSP
●
DSCP – often known as an Internal Interconnector
●
GSP Group
●
External Interconnector (e.g. FRANCE, MOYLE)
CVA Metering Systems measure and record Active (Energy) Export (AE) and Active Import (AI) in
Megawatt-hours, Reactive (Energy) Export (RE) and Reactive Import (RI,) in Megavolt-ampere
reactive hours (Mvarh) for each Settlement Period. Each VAU requires metering at each CVA Boundary
Point and Systems Connection Point. Aggregation Rules are required to allow the CDCA to aggregate
ONLY the AE and AI Meter readings to determine the Metered Volume associated with the Active
Energy for each VAU (Figure 1 - Simplified Transmission/Distribution System). Under the Balancing
and Settlement Code (BSC), the CDCA is not required to aggregate Reactive Energy Meter readings.
Figure 1 - Simplified Transmission/Distribution System
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3.
How Aggregation Rules work
Using the Aggregation Rule for each registered VAU, the CDCA collects metered data and uses active
energy metered data to calculate the Metered Volume for a VAU. This value is the net energy flow
(i.e. Active Export minus Active Import) in the Half Hourly Settlement Period at the Transmission
System Boundary.
Transmission System
Period X
MSID 1234
AE
AE
AI
M1
CR097457
M1
200 MWh
0 MWh
M2
0 MWh
10 MWh
Unit Transformer
STARUT1
AI
AE
M2
CR097458
AI
Generator
STARM1
Figure 2 - Generation Plant BM Unit Aggregation example
In Figure 2 - Generation Plant BM Unit Aggregation example, a generator and the flows to its unit
transformer are considered to be a single BMU. The net energy flow at the Transmission System
Boundary Point flowing to/from the BMU is the value derived by taking the energy reading for the
Generator (STARM1), Active Export Meter from the Active Import Meter and adding it to the energy
reading for the Unit transformer (STARUT1), Active Export Meter minus the Active Import Meter. The
Aggregation Rule is used for capturing the Import and Export energy flow through a boundary point
or System Connection Point, and is used in the CDCA systems.

BM Unit = (1234.STARM1.AE – 1234.STARM1.AI) +

(1234.STARUT1.AE – 1234.STARUT1.AI)

= (200 – 0) + (0 – 10)

= (200) + (-10)
= 190 MWh
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4.
BSCP Form Associations
During the registration of the Aggregation Rule process, the following information must be submitted;
BSCP Form & Associated
Forms
Details
Submitted By
BSCP20/4.3 – Meter Technical
Details (MTDs)
Registration of the MTDs with the
CDCA
CVA Meter Operator
Agent (MOA)
BSCP75/4.2 – Aggregation Rules
Registration of Meter Aggregation
Rules for VAUs.
Licensed Distribution
System Operators
(LDSO)/Transmission
Company/Lead Party, as
appropriate
Single Line Diagrams
Submission of a single line diagram(s) LDSO/Transmission
showing the location of the Metering
Company/Lead Party, as
Equipment: in particular the
appropriate
Settlement current and voltage
transformers (CTs/VTs) and CT/VT
ratios, and all existing and proposed
Boundary Points (BP) and any System
Connection Points (SCP) at the site;
Table 1 - BSCP Forms and Associated Information
The BSCP20/4.3 (b & c) and the BSCP75/4.2 link together to capture the necessary metering details
to ensure the Aggregation Rules are comprehensible.
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BSCP20/4.3 (b and c)
A Metering Subsystem is the basic unit in the aggregation process and Registrants will need to supply
Metering Subsystem Identifiers, both to the CVA MOA for use in the BSCP20/4.3 form, and for use in
the BSCP75/4.2 Form.

Metering Subsystem IDs should have some reference to the actual site e.g. site name
abbreviation (STAR POWER = STAR).

The Meter Technical Details (BSCP20/4.3b) have Measurement Quantity IDs and are directly
associated to the Aggregation Rules.
Table 2 - BSCP20/4.3b Meter Register Details
In Table 2 BSCP20/4.3b the highlighted sections indicate the information which will be essential in
forming a complete set of data which flows through the associated forms.

The Metering System ID (MSID) is a four digit identifier used in Central Meter Registration
Service (CMRS). In table 2 above 1234 has been used as an example.

Measurement Quantity IDs are reference points, which indicate which Meter register is Active
Import or Active Export. This information is vital in Aggregation Rules.
Table 3 - BSCP20/4.3c Outstation Channel Details
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Outstation ID is a unique identifier (up to 20 characters). It includes the MSID as the first four digits,
(in this case 1234), then a series of alphanumeric characters (in this case 0001). In the example in
Table 3 BSCP20/4.3c, 12340001 has been used.

Channel 1 of Outstation ID 12340001 is linked to Meter Serial Number CR097457 and its
Meter Register ID T1. The Outstation is designated as a main Meter Outstation (or an integral
Outstation Meter) or a Primary Outstation where the Outstation is separate from the Meter
(there may be a secondary Outstation).

In the Meter Register Details form in Table 2 BSCP20/4.3b, we can see that this Meter
Register ID is associated with an AI register for the STARM1 Metering Subsystem ID and the
Meter is the main Meter i.e. the data in Channel 01 of the main (or Primary) Outstation is
associated with the Active Import of the generating unit’s main Meter.
BSCP75/4.2
In an Aggregation Rule, the identifier for a specific string consists of the MSID, the Metering
Subsystem ID and the Measurement Quantity ID. The first line(s) of an Aggregation Rule should use
the Expression Reference numbers to highlight which lines are going to be used i.e. as illustrated in
the table below.
Table 4 - BSCP75/4.2 Aggregation Rules

In table 4 BSCP75/4.2, the form captures specific information held within BSCP20/4.3b i.e.
MSID, Metering Subsystem ID and the Measurement Quantity ID (MSID.MSSID.MQ, where
MSSID = Metering Subsystem ID, and MQ = AE or AI (Example MSQ = 1234.STARM1.AE).

The MSID in the Aggregation Rule should align with the MSID in the MTDs.
These key areas are vital for an Aggregation Rule to function correctly within the CDCA system. For
more details on system constraints, go to section 7 CDCA Constraints & System Parameters for
Aggregation Rules.
The standard for constructing an Aggregation Rule should be kept as simple as possible. If you look at
the BSCP75 example above, it’s turning a sequence of characters into a mathematical expression.
Effectively taking a set of numbers (Metered Volumes) for a given settlement period, aggregating
these and then assigning this to a specific VAU. Table 4 BSCP75/4.2 above should read as follows:

Expression Reference (Line) 1 = ER 2 (Net metered data) + ER 3 (Net metered data)

Expression Reference (Line) 2 = Active Export – Active Import (200 - 0) for Meter (M1)
total values.

Expression Reference (Line) 3 = Active Export – Active Import (0 - 10) for Meter (UT1)
total values.
Example (200 – 0) + (0 – 10) = (200) + (-10) = 190 MWh
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5.
How to construct Aggregation Rules
A.
Power Station with auxiliary Generation (T_BMU)
Transmission System
BM Unit 3
Station
Transformer
STARST1
BM Unit 1
Generator
STARM1
M4
STARUT1
M1
M2
M3
BM Unit 2
Auxiliary
Generator
STARG1
Figure 3 - Power Station (Transmission Connected)
The above example shows three BMUs (VAUs) registered as a power station that is directly connected
to the Transmission System. The power station in this instance is operated by Star Power. Star Power
has configured the power station into three BMUs (VAUs).

BM Unit 1 – Consists of the main Generating Unit with its Meter (M1) and associated
demand for that Generating Unit (Unit transformer UT1) with its Meter (M2)

BM Unit 2 – Consists of an auxiliary Generating Unit (G1) and associated meter (M3) and
has different costs in comparison to the main Generating Unit. Registering it separately
means that the Party can submit 1Bids and Offers for each generator independently.

BM Unit 3 – Is the station demand for the power plant (Station Load ST1) and is
associated with meter (M4).
1
The Balancing Mechanism allows BSC Parties (if they wish) to submit Offers to sell energy (by increasing generation or
decreasing consumption) to the system and Bids to buy energy (by decreasing generation or increasing consumption) from the
system, at prices of the BSC Party’s choosing
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The Aggregation Rule example is based on the above scenario. To calculate the Metered Volume for
BM Unit 1, the volumes (i.e. net active energy metered data) recorded by Meter M1 and M2 are added
together. However, because BM Unit 2 (auxiliary Generating Unit) volumes flow via BM Unit 1 through
Meter 2 to the Transmission System. the volumes from the auxiliary Generating Unit (G1) via its
associated Meter 3 (STAR3), must be subtracted from that sum.
Example equation 1

BM Unit 1 = Meter 1 + Meter 2 – Meter 3
BSCP75/4.2 Aggregation Rule – T_BMU
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Assumption 1 – BM Unit 1 Main Generator generates 200 MWh (in a Settlement Period), demand
taken from the Unit Transformer board for the main generator is 10 MWh, BM Unit 2 Auxiliary
Generator G1 NOT generating or importing (if possible). BM Unit 3 Station Transformer is NOT taking
Station Load. Using Equation 1 we get:

BM Unit 1 = (1234.STARM1.AE – 1234.STAR1M1.AI) +
(1234.STARUT1.AE – 1234.STARUT1.AI) –
(1234.STARG1.AE – 1234.STARG1.AI)
= (200 – 0) + (0 – 10) – (0 – 0)
= (200) + (-10) – (0)
= 190 MWh

BM Unit 2 = (1234.STARG1.AE – 1234.STARG1.AI)
= (0 – 0)
= 0 MWh

BM Unit 3 = (1234.STARST1.AE – 1234.STARST1.AI)
= (0 – 0)
= 0 MWh
Assumption 2 – BM Unit 1 Main Generator generates 200 MWh, Unit Transformer board is taking
10 MWh demand for the main generator, BM Unit 2 Auxiliary Generator G1 generating 100 MWh,
which flows through Unit Transformer M2 meter, so Meter M2 will record 100 Export -10 Import = 90
Export. BM Unit 3 Station Transformer is NOT taking Station Load

BM Unit 1 = (1234.STARM1.AE – 1234.STAR1M1.AI) +
(1234.STARUT1.AE – 1234.STARUT1.AI) –
(1234.STARG1.AE – 1234.STARG1.AI)
= (200 – 0) + (90 – 0) – (100 – 0)
= (200) + (90) – (100)
= 190 MWh
NB – The Unit board is taking 10 MWh demand for the main generator so Meter M2 would
only see 90 MWh Export.

BM Unit 2 = (1234.STARG1.AE – 1234.STARG1.AI)
= (100 – 0)
= 100 MWh

BM Unit 3 = (1234.STARST1.AE – 1234.STARST1.AI)
= (0 – 0)
= 0 MWh
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B.
Offshore Wind Farm
OnshoreTransmission System
Onshore
Offshore
Offshore
Transmission
System Boundary
LV Supplies
M1
M2
M3
LV Supplies
M4
BM Unit 1
T_STARWF-1
BM Unit 2
T_STARWF-2
Figure 4 - Offshore Wind Farm
The above offshore windfarm has two separated electrical busbars, which constitutes two Power Park
Modules (PPM) and two BMUs. The example above has the additional factors of low voltage (LV)
metered supplies for the generator, which will need to be accounted for within the Aggregation Rules.
The generator has applied for two non-standard BMUs in order to add in the LV supplies to the
respective PPM BMUs and the application has been approved by the BSC Panel.
BSCP75/4.2 Aggregation Rule - T_BMU (Offshore Wind Farm)
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Information
The above example has two BMUs, consisting of multiple Generating Units (wind turbines) and
associated generator LV supplies. Each BMU is generating 100 MWh of energy, and each has an LV
supply taking 0.1 MWh. So within each Aggregation Rule, this Low Voltage (LV) supply is, in effect,
subtracted from the generation.

BM Unit 1 = (1234.STARWFM1.AE – 1234.STARWMF1.AI) + (1234.STARLVM3.AE –
1234.STARLVM3.AI)
= (100 – 0) + (0 – 0.1)
= (100 – 0.1)
= 99.9 MWh

BM Unit 2 = (1234.STARWFM2.AE – 1234.STARWFM2.AI) ) + (1234.STARLVM3.AE –
1234.STARLVM3.AI)
= (100 – 0) + (0 – 0.1)
= (100 – 0.1)
= 99.9 MWh
C.
Embedded BM Unit (E_BMU) – Licensable Generator CVA Imports/Exports
SGT1 400kV/132kV
SGT2 400kV/132kV
Transmission System
Assets
Ownership and
Control Boundary
M1
M2
GSP_LDSO-1
LDSO Assets
132kV Distribution
Sub Station
M3
BM Unit
E_STAREM-1
Ownership and
Control Boundary
Generation Assets
Figure 5 - Embedded BMUs
Embedded Generator BMUs are directly connected to the Distribution System. Embedded BMUs
require Line Loss Factors (LLFs), these are accounted for within the Aggregation Rules (below).
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LLFs are multipliers, which are used to scale energy consumed or generated in order to account for
losses on the UK’s Distribution Networks. LLFs are applied to embedded CVA Metering Systems and all
Supplier Volume Allocation (SVA) Metering Systems (as these are always associated with Distribution
System Boundary Points).
CVA metering: LLFs are multipliers used to scale Meter readings taken at an embedded site to an
equivalent value at the Transmission System Boundary, so the LLFs account for the losses on the
Distribution System. CVA LLFs are applied at a MSID level via site Aggregation Rules.
LDSOs submit all SVA and CVA LLFs in accordance with BSCP128 – Production, Submission, Audit and
Approval of Line Loss Factors and should be contacted during the initial Registration process in
accordance with BSCP15 – BM Unit Registration.
BSCP75/4.2 Aggregation Rule – E_BMU & LLFs (Line Loss Factors)
Information
The above example (figure 5) is an embedded CVA generator directly connected to a Distribution
System busbar, and due to losses between the generating plant and the Transmission System
Boundary, LLFs need to be applied to account for them. The BM Unit is generating 100 MWh, but
losses scaling factors (0.996 Export and 1.004 Import) need to be applied to the metered data.
In this example the registrant requires two LLFs for one for Import and Export. This requires two
MSIDs from the CDCA (1234 and 1235). An applicant can also have a single LLF be applied to both
Export and Import, which requires one MSID.

BM Unit 1 = ((1234.STAREM1.AE X LLF1) –
(1235.STAREM1.AI X LLF2))
= (100 * 0.996) - (0 * 1.004)
= (99.6) – (0)
= 99.6 MWh
NB If the LDSO wishes to apply different LLFs to the Import and Export, the Registrant will require
two different MSIDs due to the CDCA system constraints (detailed in section 7).
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D.
GSP – Grid Supply Point 1 (Typical Code of Practice)
SGT1 400kV/132kV
SGT2 400kV/132kV
M1
M2
132kV
Transmission
System
GSP_STAR
Figure 6 - Grid Supply Point 1 (Single LDSO connects to GSP)
A Grid Supply Point is a connection between the Transmission System and a Distribution System and
can often contain one or more circuits, which feed from the Transmission System busbar onto
different types of VAU.
The submission of the Aggregation Rules for GSPs and GSP Groups are the responsibility of the
Distribution System Operator. The CDCA is responsible for completing the GSP Group Take
Aggregation Rules.
In Figure 6 Grid Supply Point 1, the Codes of Practice (CoPs) allow the metering to be located on the
SGT circuits, altering how the Aggregations Rules on the BSCP75/4.2 are written. Figure 7 Grid Supply
Point 2 (shown below) represents two GSPs and the CoPs require metering on the feeders to each
LDSO.
BSCP75/4.2 Aggregation Rule – Grid Supply Point 2

GSP_STAR = (1234.STARSGT1.AE – 1234.STARSGT1.AI) +
(1234.STARSGT2.AE – 1234.STARSGT2.AI)
= (0 – 100) + (0 – 100)
= - 200 MWh (i.e. Importing 200 MWh)
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E.
GSP – Grid Supply Point 2
SGT1 400kV/132kV
SGT2 400kV/132kV
132kV
Transmission
System
M1
1234.STARF1
M2
1234.STARF2
GSP_STAR
M1
1235.ELEXF1
M2
1235.ELEXF2
GSP_ELEX
Figure 7 - Grid Supply Point 2 (shared GSP)
Figure 7 has four feeders with individual metering for each feeder coming from the Transmission
System; these are split into two GSPs, and are shared by two LDSOs. This would be reflected in GSP
Aggregation Rules (below).
The submission of the Aggregation Rules for GSPs and GSP Groups are the responsibility of the
Distribution System Operator. The CDCA are responsible for completing the GSP Group Take
Aggregation Rules.
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BSCP75/4.2 Aggregation Rules – GSP 2
GSP_STAR = (1234.STARF1.AE – 1234.STARF1.AI) + (1234.STARF2.AE –
1234.STARF2.AI)

= (0 – 100) + (0 – 100)
= - 200 MWh (i.e. Importing 200 MWh)

GSP_ELEX = (1235.ELEXF1.AE – 1235.ELEXF1.AI) + (1235.ELEXF2.AE – 1235.ELEXF2.AI)
= (0 – 100) + (0 – 30)
= - 130 MWh (i.e. Importing 130 MWh)
F.
Distribution System Connection Point - DSCP
SGT1 400kV/132kV
SGT2 400kV/132kV
132kV
Transmission
System
GSP Group 2
GSP Group 1
< AI
DSCP
1234.STARF1
M1
M2
1234.STARF2
M3
1236.ELEX5
GSP2_ELEX
AE >
GSP1_STAR
Figure 8 – DCSP
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The Distribution System Connection Point (DSCP) in the example above is being metered at ‘M3’
(Metering System ‘1236’) and is registered by ELEX. The LDSOs are required at the first instance to
agree who registers the Metering System. In this case (AI is toward ELEX) the Registrant of M3 is
ELEX and the Aggregation Rule for the DSCP is added to the GSP Group Take for GSP Group 2 and
subtracted from GSP Group Take for GSP Group 1. The Registering Party (ELEX) would in this example
be responsible for submitting an Aggregation Rule for the DSCP. The CDCA would be responsible for
completing the GSP Group Take Aggregation Rules for GSP Groups 1 & 2. The LDSO of the GSP Group
which is acting as Registrant would be required to assign a LLF to account for losses between Meter
M3 and the Transmission System.
BSCP75/4.2 Aggregation Rules – DSCP
In the example below, the Registrant has used the same LLF for both Export and Import and would
only require one MSID.

DSCP (NAME) = ((1236.ELEX5.AE X LLF) –
(1236.ELEX5.AI X LLF))
= (0 * 0.996) - (100 * 0.996)
= (0) – (99.6) = - 99.6 MWh
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6.
GSP Group Take Aggregation Rules
For every GSP Group, the GSP Group Take Aggregation Rule details the amount of energy going into
(or out of) the Distribution System of that GSP Group, either from the Transmission System (via
GSPs), from another connected Distribution System (via DSCPs) or from a Distribution System
Connected (embedded) BM Unit.
The GSP Group Take metered volume of a GSP Group is predominantly a large negative quantity, but
this is not always the case.
Transmission connected BMUs do not affect GSP Group Take because their Import and Export goes
straight onto the Transmission System.
The CDCA is responsible for completing the BSCP75/4.2 GSP Group Take Aggregation Rules, and the
LDSO for authorising them.
There are certain parameters that can affect a GSP Group Take Aggregation Rule, these are:

The registration or de-registration of a GSP (note that this does not include the
registration or de-registration of individual circuits at the GSP)

The registration or de-registration of an Embedded BM Unit or part of an M_ cascade
hydro BM Unit

The registration or de-registration of a DSCP (note that this does not include the
registration or de-registration of individual circuits at the DSCP). This will require
changes to two sets of GSP Group Take Aggregation Rules for the two GSP Groups that
the DSCP is connecting.
Below is an example of a GSP Group Take Aggregation Rule for GSP Group ELEXON.
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BSC Section X: Annex X-2 Definition (GSP Group Take):
In relation to any GSP Group and any Settlement Period, shall be determined as follows:

GSPGT = GMV + I – E

where:

GSPGT means the GSP Group Take for that GSP Group and that Settlement Period;

GMV means the GSP Group Metered Volume for that GSP Group and that Settlement Period;

I - means the magnitude of the quantities of Imports at CVA Boundary Points in that GSP
Group (as at the Transmission Boundary) for that Settlement Period; and

E - means the magnitude of the quantities of Exports at CVA Boundary Points in that GSP
Group (as at the Transmission Boundary for that Settlement Period).
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7.
CDCA Constraints & System Parameters for Aggregation Rules
The CDCA system has a finite set of rules for how the data from the BSCP75/4.2 Form is entered.
Below is a list of set requirements which the end user should consider when completing
forms/documents associated to Aggregation Rules and Meter Technical Details.

CDCA system rounds all Metered Volumes in the CDCA database to 4 decimal places only
(i.e. 0.00009 or smaller will not be output as a result of a mathematical calculation),
using the normal rounding rules. Constants (CST) can be up to 5 decimal places, but are
still subject to the above rounding.

Each Expression Reference Line must be completed.

Make the Expression References (ER) as sequential as possible (ELEX_1 example DO
NOT use ER 1 + ER 9, ER 2 + ER 8 etc. instead use sequential numbering ER 1 + ER 2,
ER 3 + ER 4 etc.) This allows the Aggregation Rule to be entered into CDCA more
logically.

CDCA does not support the expression of a negative first term in an Aggregation Rule, so
where IMPORT ONLY is being aggregated, it should be written as either as CST 0 – MSQ
1234.STARSGT1.AI, or MSQ 1234.STARSGT1.AI * CST -1. CST represents a constant.

All Meter readings received by the CDCA are positive values, whether reported as AE or
AI. In Settlements terms, Exports are treated as positive, and Imports as negative. This
means that if the Plant/Apparatus is exporting, the aggregated Metered Volume will be
positive, and if the Plant/Apparatus is importing, the aggregated Metered Volume will be
negative.
Export: AE > AI, therefore AE –AI is positive.
Import: AI > AE, therefore AE –AI is negative.

Aggregation Rules should be constructed as the AE measurement minus the AI
measurement for each Metering Subsystem.

The reference for an MSQ is in the form of MSID.MSSID.MQ, where MSID is the Metering
System ID, MSSID = Metering Subsystem ID, and MQ = AE or AI (Example MSQ
reference = 1234.STARGT1.AI)

The MSSID in the Agg rule should align with the MSSID in the MTDs, as stated in Section
4 BSCP Form Associations.

For Embedded BMUs (E_) or DSCPs, reference MUST be made to LLFs.

In the case of Aggregation Rules which relate to a Metering System connected to a
Distribution System, the relevant LLF must be applied to metered data before any
combination of import and export active energy metered data i.e. Active Export * LLF,
Active Import * LLF is allowed, however Active Export – Active Import * LLF is not
allowed.

A LLF can only be applied in CDCA at the MSID level, NOT at the channel level. Because
of this, the same LLF would be applied to both the AE & AI metered data. If this is not
correct, then an additional LLF is required, which would require an additional MSID.
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
Parameters for Aggregation Rules (BSCP75/4.2):
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8.
Appendix A – Definitions
Code and Document Definitions
This section expands on some of the acronyms and terms used within this document and the
Balancing and Settlement Code.
Balancing Mechanism
This is one of the tools National Grid uses to balance electricity supply and demand close to real time.
It is needed because electricity cannot be stored and must be manufactured at the time of demand.
Where National Grid predicts that there will be a discrepancy between the amount of electricity
produced and that which will be in demand during a certain time period, they may accept a ‘bid’ or
‘offer’ to either increase or decrease generation (or consumption). The balancing mechanism is used
to balance supply and demand in each half hour trading period of every day
BM Unit (BMU)
A Balancing Mechanism Unit (BMU) is defined in the BSC as a unit of Plant and/or Apparatus
established and registered in accordance with section K3 of the Code.
The main attributes of a BM Unit are that:

A single party is responsible for the Exports/Imports to or from the Plant or Apparatus
comprising the BM Unit;

The Exports/Imports are capable of being controlled independently from any other BM
Unit; and

The quantities of electricity Exported and Imported from each BM Unit can be determined
and submitted to SAA for Settlement.
Boundary Point
A point at which any Plant or Apparatus not forming part of the Total System is connected to the Total
System
Boundary Point Metering System
A Metering System which measures Exports or Imports at a Boundary Point.
Central Data Collection Agent (CDCA)
The Central Data Collection Agent (CDCA) collects metered data from power stations and large
industrial consumers. It collects this data by polling the Meters of these Units via different
communication methods.
The CDCA calculates the Metered Volumes which are passed to the Settlement Administration Agent
(SAA). The CDCA also calculates the GSP Group Take for each GSP Group and submits to the Supplier
Volume Allocation Agent (SVAA).
Central Meter Registration Service (CMRS)
The service for registration of data relating to CVA Metering Systems maintained (for the purposes of
the Code) by the Central Data Collection Agent.
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Central Registration Agent (CRA)
When a Party registers with the BSC, its details will be stored in a database managed by the Central
Registration Agent (CRA).
The CRA database holds information such as:

Party IDs (each Party that signs with the BSC will be given its own unique Party ID);

Party roles (for example, Supplier or Generator);

Authorised Signatories (these are the people who are allowed to submit BSC forms on
behalf of a BSC Party); and

Balancing Mechanism Units (these are the generation or demand Units against which
Metered Volumes are stored in the central systems).
Central Volume Allocation (CVA)
The determination of quantities of Active Energy to be taken into account for the purposes of
Settlement in respect of Volume Allocation Units.
Code of Practice (CoPs)
Codes of Practice (CoPs) detail the technical requirements for Metering Systems. These versions are
not time limited in the same way as other documents.
When Metering Equipment is first registered in Settlement, it must comply with the requirements
which are set out in the relevant Code of Practice in place at that time.
CVA Boundary Point
Is a Boundary Point where the Exports and Imports at which are or are to be measured by CVA
Metering System(s).
Distribution System
Means: (i) all or part of a distribution system in Great Britain operated by a Licensed Distribution
System Operator; and (ii) all or part of any other distribution system in Great Britain for which the
condition is satisfied that all entry/exit points are subject to registration in SMRS pursuant to the
provisions of the MRA; provided that: (a) such distribution system or part thereof is connected to the
Transmission System at Grid Supply Points which fall within only one Group of GSPs, and (b) where
part only of a distribution system is comprised in a Distribution System, each other part thereof must
be comprised in one or more other Distribution Systems; where: (1) ‘distribution system’ has the
meaning given to that term in section 4(4) of the Act, following amendment of the Act by section 28
of the Utilities Act 2000; (2) ‘entry/exit point’ means a point at which electricity may flow on to or off
such distribution system other than from or to the Transmission System or another such system or a
distribution system referred to in paragraph (i) above; Except that prior to the BETTA Effective Date
every use of the words Great Britain in such meaning shall be deemed to be a reference to England
and Wales
Distribution System Connection Point (DSCP)
A Systems Connection Point at which two Distribution Systems are connected.
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External System
means an electricity Transmission System or electricity Distribution System which is outside the area
specified in Schedule 1 of the Transmission Licence and is electrically linked to a System; except that
during the Transition Period: means an electricity Transmission System or electricity Distribution
System which is outside the area covered by the Total System and is electrically linked to a System.
Generating Plant
An installation comprising one or more Generating Units (even where sited separately), other than an
Interconnector, owned and/or controlled by the same person, which may reasonably be considered as
being managed as one power station.
Grid Supply Point (GSP)
A Systems Connection Point at which the Transmission System is connected to a Distribution System.
GSP Group
A distinct electrical system, consisting of: (i) the Distribution System(s) which are connected to the
Transmission System at (and only at) Grid Supply Point(s) which fall within one Group of GSPs, and
(ii) any Distribution System which: (1) is connected to a Distribution System in paragraph (i), or to
any other Distribution System under this paragraph (ii), (2) is not connected to the Transmission
System at any Grid Supply Point and the total supply into which is determined by metering for each
half hour.
GSP Group Take
In relation to any GSP Group and any Settlement Period, shall be determined as follows: GSPGT =
GMV + I – E, where: GSPGT means the GSP Group Take for that GSP Group and that Settlement
Period; GMV means the GSP Group Metered Volume for that GSP Group and that Settlement Period; I
means the magnitude of the quantities of Imports at CVA Boundary Points in that GSP Group (as at
the Transmission Boundary) for that Settlement Period; and E means the magnitude of the quantities
of Exports at CVA Boundary Points in that GSP Group (as at the Transmission Boundary for that
Settlement Period).
GSP Group Metered Volume
In relation to any GSP Group and any Settlement Period, a Metered Volume representing the algebraic
sum of:
(i)
the quantity of Active Energy flowing into a GSP Group at Grid Supply Points connected to that
GSP Group and at Distribution Systems Connections Points connected to that GSP Group, and
(ii)
the quantity of Active Energy flowing out of a GSP Group at Grid Supply Points connected to
that GSP Group and at Distribution Systems Connections Points connected to that GSP Group
but disregarding Exports and Imports at Boundary Points in that GSP Group.
Section ANNEX X-2: TECHNICAL GLOSSARY 2.4 details the sign convention for Active Energy and
Active Power.
Interconnector
Apparatus connected to a System, for the transfer of electricity to or from the Total System from or to
an External System.
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Line Loss Factor (LLF)
A multiplier which, when applied to data from a CVA Metering System connected to a Boundary Point
on a Distribution System, converts such data into an equivalent value at the Transmission System
Boundary.
Metered Volume
For the purposes of this Section R, in relation to a Volume Allocation Unit and a Settlement Period, the
net aggregate volume of Active Energy, determined as at the Transmission System Boundary, which
flowed in that Settlement Period to or from that Volume Allocation Unit.
Metering Dispensation
A dispensation (in relation to any Metering Equipment) from compliance with any requirement of a
Code of Practice, granted by the Panel in accordance with the BSC.
Meter Operator Agent (MOA)
A Party Agent appointed in accordance with Section L to install, commission, test and maintain, and
rectifies faults in respect of, CVA Metering Equipment and/or SVA Metering Equipment.
Meter
A Meter is a device which measures the quantities of energy which flows in a circuit.
Meter Register
A Meter register records a metering subsystem quantity. These are two characters long and must be
unique within a meter.
Metering System
Particular commissioned Metering Equipment installed for the purposes of measuring the quantities of
flows of electricity at Systems Connection Points.
Metering Equipment
Metering Equipment or a Metering System is "associated with" particular Plant and/or Apparatus
including any Generating Plant), or a BM Unit, where such Metering Equipment or the Metering
Equipment comprised in such Metering System measures Imports and/or Exports of such Plant and/or
Apparatus or (as the case may be) BM Unit.
Metering Subsystem
A metering subsystem is the set of meter registers required to uniquely and unambiguously measure a
flow of energy. Logically this includes the main and check meters, any readings through dual
outstations and both active and reactive energy readings. In practice however the current aggregation
rules use only the main active energy readings.
Metering Subsystem Quantity (MSQ)
Each of the values associated with a Metering Subsystem is termed a Metering Subsystem Quantity.
Described as the Measurement Quantity ID in BSCP20 - Meter Technical Details
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These are:

AI = Active Import;

AE= Active Export;

RI = Reactive Import; and

RE = Reactive Export.
Metering System Identifier (MSID)
Unique number for a Metering System. For SVA metering systems this is equivalent to the MRA’s
MPAN core.
Offshore Transmission Connection Point
A form of Grid Supply Point (GSP) where an Offshore Transmission System connects to a (onshore)
Distribution System.
Outstation
An Outstation is a device which receives and stores data from a Meter or Meters and then transfers
that data to the Central Data Collection Agent’s systems when polled.
Outstation Channel
This identifies the channel number on the Outstation which stores data related to a Meter Register on
a particular Meter, e.g. Channel 1 might be associated with the Active Import (AI) register on the
main Meter for a particular circuit.
Power Park Module (PPM)
A Power Park Module is defined as a Single BM Unit and consists of Generation Plant.
Settlement
The determination and settlement of amounts payable in respect of Trading Charges (including
Reconciliation Charges) in accordance with the Code (including where the context admits Volume
Allocation).
Super Grid Transformer (SGT)
Point where energy is taken from the Transmission System (normally at 400kV or 275kV) and stepped
down to a lower voltage for a distribution system.
Total System
The Transmission System and each Distribution System.
Transmission System Boundary Point (TSBP)
A Boundary Point on the Transmission System (including Remote Transmission Assets).
Volume Allocation Unit (VAU)
BMUs, GSPs, GSP Groups, DSCPs and Interconnectors are collectively referred to as Volume Allocation
Units.
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Need more information?
For more information please contact the BSC Service Desk at bscservicedesk@cgi.com or call 0870
010 6950.
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