GB Transmission System Performance Report

8/8/2019 GB Transmission System Performance Report

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Report to the

Gas & Electricity Markets Authority

GB Transmission System Performance Report

2006 - 2007


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Contents PageIntroduction 2

Section 1

GB System Availability 3

Monthly System Availability

Annual` System Availability

Annual Winter Peak System Availability

Monthly Planned & Unplanned Unavailability

Section 2

Interconnector Availability 7

Annual Availability

Monthly Unavailability

Section 3

GB System Security 9

Overall Reliability of Supply

Number of Incidents

Estimated Unsupplied Energy

Incident Details

Section 4

GB Quality of Service 17

Voltage

Frequency

Frequency Standard Deviation


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GB Transmission System Performance Report 2

GB Transmission System Performance Report

Introduction The electricity transmission networks in

Great Britain are owned by National

Grid Electricity Transmission (NGET) in

England and Wales, SP TransmissionLimited (SPTL) in south and central

Scotland and Scottish Hydro Electric

Transmission Limited (SHETL) in the

north of Scotland.

In addition to its role as the Transmission owner in

England and Wales, NGET became the Great Britain

System Operator (GBSO) on 1 April 2005 following

implementation of British Electricity Transmission &

Trading Arrangements (BETTA).

In accordance with Standard Licence Condition C17,

(transmission system security standard and quality of

service) of its transmission licence, NGET is required by

the Gas and Electricity Markets Authority, to report

electricity transmission system performance in terms of

availability, system security and quality of service for

the GB Transmission System.

The GB Transmission System broadly comprises

circuits operating at 400kV and 275kV and in Scotland

only, Transmission also includes the 132kV network.

The formal definition of the GB Transmission System is

contained in the Grid Code and the GB Security and

Quality of Supply Standard (GBSQSS).

Information relating to the SP Transmission Ltd (SPTL)

and Scottish Hydro Electric Transmission Ltd (SHETL)

transmission networks included in this report, has been

provided by each of these Transmission Owners in

accordance with Licence Condition D3 (transmission

system security standard and quality of service) of their

transmission licences.

When considering the performance of the Scottish

transmission networks it should be recognised that this

can be influenced by the Scottish Transmission

Owners and by the GBSO.


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Section 1

GB System AvailabilitySystem performance is monitoredby reporting monthly variations insystem availability, winter peak andannual system availability, togetherwith planned and unplannedsystem unavailability.

System Availabilityis defined by the formula:

The sum of hours available for all circuits x 100%(No. of circuits) x (No. of hours in period)

Availability is reduced whenever a circuit is taken out of operation, either for planned purposes or as a result of a fault.

Planned outages are required for system constructionand new user connections as well as the maintenancenecessary to retain a high level of system reliability to

ensure that licence standards of security are met.

A circuit is defined as the overhead line, transformer orcable or any combination of these that connects two

system bussing points together, or connects thesystem to a Users busbar. (A bussing point could be asubstation or a tee point on the system).

Annual System Availability of the GBTransmission System during 2006/7:

[ GB 95.25 % ]

[ NGET 95.02 % ]

[ SPTL 95.61 % ]

[ SHETL 95.70 % ]

3 GB Transmission System Performance Report


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% Monthly System Availability

10098

96

94

92

90

88

86APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR

NGET SPTL SHETL GB

% APR 93.41 95.52 98.45 94.6392.73 94.82 94.57 93.45

93.30 95.23 94.44 93.88

93.61 95.34 95.72 94.30

92.80 93.86 95.12 93.38

92.99 94.73 94.71 93.62

93.96 95.30 93.12 94.11

96.91 95.59 93.30 96.07

98.28 96.94 96.55 97.73

98.41 96.91 98.11 98.05

98.10 97.42 98.23 97.98

97.04 95.85 96.39 96.69

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

JAN

FEB

MAR

NGET SPTL SHETL GB

% Annual System Availability

98

97

96

95

94

93

922005 - 06 2006 - 07

NGET SPTL SHETL GB

% 2005 - 06 95.09 96.03 96.87 95.5795.02 95.61 95.70 95.252006 - 07

NGET SPTL SHETL GB

100

99

98

97

96

95

942005 - 06 2006 - 07

NGET SPTL SHETL GB

%2005 - 06 97.88 99.27 99.48 98.41

98.19 97.08 97.64 97.872006 - 07

NGET SPTL SHETL GB

% Winter Peak System Availability


Winter Peak System Availability is calculated for themonths of December, January and February.


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Section 1 - Continued...

Planned and Unplanned System UnavailabilityPlanned Unavailability

User Connection Outages are planned outages requiredto construct or modify assets which are provided tofacilitate connection for the exclusive benefit of specificsystem users.

System Construction Outages are planned outagesrequired to construct or modify assets which are notprovided for the exclusive benefit of the specific users.

Maintenance Outages are planned outages required formaintenance.

Unplanned Unavailability

Unplanned Unavailability is due to outages occurringas a result of plant or equipment failure, i.e. outagesrequired and taken at less than 24 hours notice.

Note:NGET, SPTL and SHETL have harmonised thereporting of Unplanned Unavailability to a commonbasis. This supersedes the transitional reportingarrangements of the 2005-06 report.

Unavailabilityis defined as:

(100 - Availability) %



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The charts and the tables show the monthly variation in planned and unplanned unavailability.

Planned & Unplanned Unavailability (%) for NGET Transmission System

8

7

6

5

4

3

2

10

APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR

User Connection MaintenanceSystem Construction Unplanned

%

Planned & Unplanned Unavailability (%) for SPTL Transmission System

7

6

5

4

3

2

1



%APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

JAN

FEB

MAR

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

UserConnection

3.66

4.23

3.89

3.43

3.89

3.07

1.89

1.81

1.06

0.50

0.53

0.87

SystemConstruction

0.80

0.92

0.61

0.83

0.88

0.24

0.69

0.43

0.07

0.25

0.63

0.46

Maintenance

0.02

0.03

0.27

0.40

1.37

1.96

2.12

2.17

1.93

2.34

1.42

2.82

Unplanned

4.48

5.18

4.77

4.66

6.14

5.27

4.70

4.41

3.06

3.09

2.58

4.15

TOTAL

APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

JAN

FEBMAR

0.00

0.00

0.05

0.07

0.00

0.03

0.11

0.62

0.03

0.05

0.150.82

UserConnection

0.67

1.68

2.31

1.70

2.19

3.62

4.99

3.92

1.68

1.04

1.001.78

SystemConstruction

0.83

3.70

2.86

2.07

1.66

1.24

1.78

1.87

1.67

0.72

0.621.01

Maintenance

0.05

0.05

0.34

0.44

1.03

0.40

0.00

0.29

0.07

0.08

0.000.00

Unplanned

1.55

5.43

5.56

4.28

4.88

5.29

6.88

6.70

3.45

1.89

1.773.61

TOTAL

Planned & Unplanned Unavailability (%) for SHETL Transmission System

8

7

6

5

4

3

2

1



%


APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

JANFEB

MAR

1.16

1.27

1.27

0.94

0.96

0.77

0.52

0.27

0.08

0.080.14

0.39

UserConnection

3.71

4.61

3.65

3.44

3.85

3.34

3.61

1.40

0.63

0.500.61

1.24

SystemConstruction

1.22

0.99

1.39

1.28

1.68

2.20

1.34

0.98

0.42

0.610.75

1.19

Maintenance

0.50

0.40

0.39

0.73

0.71

0.71

0.57

0.44

0.59

0.400.40

0.14

Unplanned

6.59

7.27

6.70

6.39

7.20

7.01

6.04

3.09

1.72

1.591.90

2.96

TOTAL


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Section 2

England France Interconnector Availability The NGET transmission system hasan interconnection with the Rseaude Transport Electricit (RTE)transmission system in France.

Until August 2006 the interconnector was owned andoperated by NGET and RTE. In August 2006 NationalGrid transferred its part of the ownership and operationalresponsibility to National Grid Interconnectors Limited(NGIL). The information in this report has beenprovided by NGIL.

Outages are co-ordinated, as far as practical, betweenNGIL and RTE to allow work to be undertaken by bothparties during an outage. Losses of availability areattributed on the basis of work being carried out by therespective parties.

Note:There is also an interconnection circuit betweenScotland and Northern Ireland which is owned byMoyle Interconnector Limited, operated by theNorthern Ireland system operator (SONI) andregulated by the Northern Ireland regulator (OFREG).Consequently its performance falls outside thescope of this report.

Annual Availabilityof England - France Interconnectorduring 2006/07:

93.02 %



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% Annual Availability The chart below shows the annual comparison of availability of the England France Interconnector.

% Monthly Unavailability

30

25

20

15

10

5


NGET RTE

%


9594.5

9493.5

9392.5

9291.5

9190.5

902005 - 06

94.6

93.02

2006 - 07

%

APR

MAY

JUN

JUL

AUGSEP

OCT

NOV

DEC

JAN

FEB

MAR

0.00

1.07

20.31

25.00

0.328.96

0.21

0.00

0.00

0.08

0.00

0.00

0.28

1.19

1.07

0.00

0.0015.58

0.21

1.07

0.00

0.43

8.23

0.49

NGET RTE


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Section 3

GB System Security


All Transmission System events thatresulted in a loss of supplies arereported individually giving informationabout the cause of the incident, itslocation, duration and an estimateof energy unsupplied. The totalnumber of incidents and the energyunsupplied for each incident alongwith the aggregate unsuppliedenergy are presented in this section.

Losses of supplies at 3 or less customer sites are

shown separately. The 3 or less customer category

covers locations where major industrial customers are

directly connected to the transmission system. The

customer could be a steelworks, refinery or other large

industrial processing site. Connection arrangements

are chosen by the customer and often have a level of

design and operational security below that normally

required to satisfy the GBSQSS. This may be reflected

in a reduced cost of the connection. In some cases,

customers have also chosen to secure their supplies

using their own generation to compensate for this

reduced level of transmission system security.

Distribution Network Operators (DNOs) and domestic

customers do not come within the 3 or less customer

category.

The GBSQSS defines the minimum level to which the

security of demand is planned. The planned security

level at a substation is a function of the amount of

demand connected to the substation and the level of

interconnection. The result is that the actual level of

demand security is higher for 400kV and 275kV

transmission voltages than for 132kV.


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The total Estimated Unsupplied Energy from the GB Transmission Systemduring 2006-07 :

[ GB 510.91MWh ]

[ NGET 313.52MWh ][ SPTL 20.81MWh ][ SHETL 176.58MWh ]

Performance is monitored by total estimated energy unsupplied from the GB System foreach incident.

During 2006-07 there were over 700 GB system events where transmission circuits weredisconnected either automatically, or by urgent manual switching.

The vast majority of these events had no impact on electricity users, only 25 resulting inloss of supplies to customers.

Overall Reliability of Supply

The Overall Reliability of Supplyis calculated on the basis of:

Estimated Unsupplied Energy

Total energy that would have been supplied by the transmission system[ ( )]1- *100%

The Overall Reliability of supply of GB System during 2006-07:

[ GB 99.99985% ]

[ NGET 99.99990% ][ SPTL 99.99991% ][ SHETL 99.99786% ]


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Section 3 - Continued...Number of Incidents

18

15

12

9

6

3

02005 - 06 2006 - 07

NGET SPTL SHETL

8

5 4

1

9

1

21

4

1

17

350

300

250

200

150

100

50

02005 - 06 2006 - 07

NGET SPTL SHETL

303.85 312.79

176.58

18.33 1.13

78.2

MWh

14001300

120100

8060

4020

02005 - 06

MWh

2006 - 07

NGET SPTL SHETL

113.58

0.73 01.519.68

1423.2

Estimated Unsupplied Energy - 3 or less customer sites

The graph shows the annual comparison of the numbers of loss of supply incidents that occurred within England, Walesand Scotland.

The number of incidents affecting 3 or less customer sitesare shown in lighter shade on the graph.

The graph shows annual comparison of estimated unsuppliedenergy excluding 3 or less customer sites.

The graph shows annual comparison of estimated unsuppliedenergy at 3 or less customer sites.

Estimated Unsupplied Energy - excluding3 or less customer sites


13/20



14/20


NGET Incidents excluding 3 or less customer sitesDuration MWh

Incident Date, Time & Location MW Lost Minutes Unsupplied

28 June 2006, 08:49hours at Kearsley 132kV substation 196.1 0.02 0.05Kearsley SGT2A and SGT2B tripped when a third party contractor damaged anLV cable resulting in the loss of 196.1MW of demand. All demand was restoredwithin 500ms by an auto-close scheme. The restoration time has been roundedto 1 second for reporting purposes.

04 July 2006, 17:06hours, Grendon 132kV substation 521 81 309.65Grendon SGT3 and SGT1 tripped within 2 minutes of each other during a severerainstorm. The remaining transformer SGT2 subsequently tripped on overloadresulting in a loss of 521MW of demand. Demand was restored in steps with allbeing restored at 18:27 hours.

25 August 2006, 14:53hours, Gloucester 132kV substation 14.6 6 0.55Gloucester SGT1 tripped following energisation of its tertiary connected capacitor

disconnecting 14.6MW of demand due to the inadvertent operation of the capacitorprotection. The demand was partially restored in less than 1 minute by operationof the DNOs auto-close scheme and the remainder was restored by a loadtransfer at 14:59hours.

7 December 2006, 11:46hours, Upper Boat 132kV substation 152.2 1 2.54During a severe lightning storm, three out of the four circuits connecting UpperBoat 275kV substation tripped disconnecting both in-feeds to Upper Boat 132kVsubstation resulting in a loss of 152.2MW of demand. The circuits were returnedby delayed auto-reclose successfully restoring all demand.

Total312.79

NGET Incidents affecting 3 or less customer sitesDuration MWh


9 November 2006, 14:58hours, Patford Bridge 25kV substation 14.6 3 0.73 The Enderby-East Claydon 1 circuit along with SGT1 at Patford Bridge trippedand auto-isolated due to the inadvertent operation of the back up protectionat Enderby. Network Rail had chosen to feed the full Long Buckby Wharf demand from SGT1, so that 14.6MW of demand was disconnected.Network Rail carried out internal switching to transfer all demand to SGT2 at 15:01.

Total

0.73


Incident Details


15/20


16/20


SHETL Incidents excluding 3 or less customer sitesDuration MWh


4 May 2006, 19:38 hours, Dunvegan 33 kV Substation 4.20 3 0.25 Transformer 33 kV circuit breaker tripped in lightning storm and was successfullyreclosed by telecontrol. This is a single transformer GSP.

4 May 2006, 22:05 hours, Fort Augustus 132 kV Substation 42.00 0.5 0.36 This is a double circuit 132 kV line from Fort Augustus to Fort William with a teedsingle circuit line to Skye and the Western Isles. The double circuit tripped andauto reclosed in a lightning storm.

16 June 2006, 04:23 hours, Sloy 132 kV Substation 2.17 0.4 0.01Sloy to Clachan / Inverary 132 kV circuit tripped and reclosed. Cause unknown.Clachan is a single transformer GSP teed from this line.

20 July 2006, 15:00 hours, Broadford 132 kV Substation 6.5 4 0.14Broadford to Dunvegan 132 kV circuit tripped owing to faulty SEF relay. Dunveganis a single transformer GSP. Customers restored from alternative DNO 33 kV supplies.

22 July 2006, 09:28 hours, Inverary 132 kV Substation 13.00 1.2 0.26

Inverary to Port Ann / Carradale 132 kV circuit tripped and autoreclosed.Unknown transient. The other circuit was out of service for construction works.

26 July 2006, 06:47 hours, Shin 132 kV Substation 34.00 0.3 0.14Shin to Dounreay 132 kV double circuit tripped and auto reclosed in lightning storm.

18 August 2006, 17:09 hours, Port Ann 33 kV Substation 7.00 6 0.69GT2 33 kV circuit breaker opened for unknown transient fault, successfully reclosedby telecontrol from Control Centre. GT1 transformer was out of service at the timefor construction works.

26 September 2006, 09:03 hours, Taynuilt Grid 33 kV Substation 15 223 31.62 Taynuilt Grid 132 / 33 kV transformer GT2 auto-isolated owing to faulty contacts onpressure relief device. Relay disconnected and transformer restored to service.

GT1 was out of service for transformer change at the time. Supplies were partlyrestored from DNO 33 and 11 kV alternative circuits, final restoration was fromrestoration of GT2. First restoration in 18 minutes.

28 October 2006, 21:49 hours, Sloy 132 kV Substation 45.00 5 3.75Sloy to Clachan / Inverary 132 kV circuit tripped due to coincident total of directlyconnected and embedded generation being in excess of protection setting butbelow line rating. Circuit restored by telecontrol from Control Centre and generationconstrained off until protection settings altered.

11 December 2006, 05:52 hours at Inverary 132 kV Substation 10.00 0.3 0.05Inverary to Port Ann / Carradale 132kV double circuit tripped and auto reclosed inlightning storm.


Incident Details


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Duration MWhIncident Date, Time & Location MW Lost Minutes Unsupplied

14 December 2006, 21:15 hours, Fort Augustus 132 kV Substation 48 36 18.68Fort Augustus to Fort William 132 kV single circuit supplying Skye and the WesternIsles tripped, auto reclosed and locked out in lightning storm. Supplies wererestored from DNO auto changeover scheme (30 seconds), alternative DNO 33 kV

circuits (16 minutes) and from DNO standby generation (starting in 19 minutes).132 kV circuit was successfully restored and island generation resynchronised andall remaining supplies restored.

11 January 2007, 10:27 hours, Fort Augustus 132 kV Substation 40.80 0.5 0.35Fort Augustus to Fort William 132 kV single circuit supplying Skye and the WesternIsles tripped and auto reclosed. Unknown transient in gale force winds.

11 January 2007, 11:19 hours, Inverary 132 kV Substation 25.00 2.3 0.63Inverary to Port Ann / Carradale 132kV double circuit tripped in lightning storm,auto reclosed at source end and reclosed by telecontrol at remote end.

12 January 2007, 15:35 hours, Harris 132 kV Substation 17.5 82 14.28Stornoway to Harris 132kV single circuit tripped to lock out owing to faulty 132 kV

surge diverter at Harris Grid. Supplies partly restored from alternative DNO 33 kVsupply and remainder from DNO standby diesel generation,first restoration in 16 minutes.

20 January 2007, 01:17 hours, Fort Augustus 33 kV Substation 4.00 0.5 0.03Fort Augustus GT1 tripped and autoreclosed in high winds and wintry showers.Fort Augustus is a single transformer GSP.

24 February 2007, 02:09 hours, Fort Augustus 132 kV Substation 42.8 385 101.44Fort Augustus to Fort William 132 kV circuit supplying Skye and the Western Islestripped due to a failed overhead line connection on the sea crossing from Kyle tothe Isle of Skye. Supplies were restored via DNO 33 kV alternative circuit to SouthSkye and the remainder of customers were restored from DNO standby dieselgeneration in Lewis, Uist and Barra. First restoration in 11 minutes.

19 March 2007, 07:49 hours, Charleston Grid 33 kV Substation 26.00 9 3.9Charleston Grid 132 / 33 kV substation. When Charleston GT1 was deloaded inpreparation for outage, Charleston 2T0 tripped due to unstable protection.Supplies restored from GT1.

Total176.58

SHETL Incidents affecting 3 or less customer sitesDuration MWh


NONE


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Section 4

GB Quality of ServiceQuality of service is measured with reference to system voltage and frequency.

Voltage

The Electricity Safety, Quality andContinuity Regulations 2002permit variations of voltage notexceeding 10% above and belowthe nominal at voltages of 132kVand above and not exceeding 6%at lower voltages.

The GB Grid Code reflects these limits, and imposes afurther constraint for the 400kV system in that voltages

can only exceed +5% for a maximum of 15 minutes.

Consumers may expect the voltage to remain withinthese limits, except under abnormal conditions e.g. asystem fault outside of planning and operating standards.

Normal operational limits are agreed and monitoredindividually at connection points with consumers toensure that voltage limits are not exceeded, followingthe specified fault events described in the GBSQSS.

The criterion for reportingvariations in excess of thosepermitted by the Electricity Safety,Quality and ContinuityRegulations 2002 is:

Voltage excursions formore than 15 minutes.

Voltage Excursions

During 2006-07 no reportablevoltage excursions occuredwithin England, Wales orScotland.


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The Electricity Safety, Quality andContinuity Regulations 2002 permitvariations in frequency notexceeding 1% above and below50Hz, a range of 49.5 to 50.5Hz.

The system is normally managed such that frequencyis maintained within operational limits of 49.8 and 50.2Hz.

Frequency may, however, move outside these limitsunder fault conditions, or when abnormal changes tooperating conditions occur. Losses of generationbetween 1000 and 1320MW are considered abnormaland a maximum frequency change of 0.8Hz may occur,although operation is managed so that the frequencyshould return within the lower statutory limit of 49.5Hzwithin 60 seconds.

Frequency StandardDeviationNGET aim to keep the frequency standard deviation

below 0.07Hz. For information, the recorded weeklystandard deviation during 2006/7 is presented in thefollowing chart.

The criterion for reportingvariations in excess of thosepermitted by the Electricity Safety,Quality and ContinuityRegulations 2002 is:

Frequency excursionsoutside 1% of 50Hz.

Frequency Excursions

During 2006-07 there wereno reportable frequencyexcursions.

0.10

0.09

0.08

0.07

0.06

0.05

0.04

0.03

0.02

0.01

0.000 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51

Hz

Weeks

Frequency


20/20

Registered Office:

National Grid1-3 StrandLondonWC2N 5EH

Registered in England & Wales No. 2366977

Printed on 50% Recycled Paper

Documents

GB Transmission System Performance Report