SULTANATE OF OMAN Security... · 2018. 3. 14. · SULTANATE OF OMAN LICENCE CONDITION (26)...

SULTANATE OF OMAN

LICENCE CONDITION (26)

TRANSMISSION SECURITY STANDARD

Second edition

As Approved by Authority for Electricity Regulation – July 2016

Transmission Security Standard Oman Electricity Transmission Company S.A.O.C

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CONTENTS

Page

1 Introduction to the OETC Transmission Security Standard 3

1.1 Roles and scope 3

1.2 Structure and reach of the TSS in the OETC licensed transmission system 4

2 System design and operational Values 7

2.1 Introduction 7

2.2 System parameters under various conditions 7

3 Design of the Main Interconnected Transmission System 9

3.1 Introduction 9

3.2 MITS design criteria 9

3.3 MITS – Intact System requirements at Peak Demand 10

3.4 MITS – Following a Restricted Period Fault Outage 11

3.5 MITS – Following a Maintenance Period Fault Outage 12

3.6 Variations to the MITS design criteria 12

4 Design of generation connections and GSO connections 13

4.1 Introduction 13

4.2 Generation connection design criteria 13

4.3 Generation & GSO connections – Intact System requirements at Peak Demand 14

4.4 Generation & GSO connections – Following a Restricted Period Fault Outage 15

4.5 Generation & GSO connections – Loss of Power Infeed constraints 16

4.6 Generation & GSO connections – Loss of Power Infeed during Planned Outages 17

4.7 Generation & GSO connections – Transmission Capacity & Loss of Power Infeed 18

4.8 GSO connections – Loss of Power Infeed constraints 18

4.9 Variations to generation connection design criteria or Table 4.6 19

5 Design of demand connections 20

5.1 Introduction 20

5.2 Demand connection design criteria 20

5.3 Demand connection capacity requirements 20

5.4 Demand connections – Intact System conditions at Peak Demand values 21

5.5 Demand connections – Following a Restricted Period Fault Outage 22

5.6 Demand connections – Following a Maintenance Period Fault Outage 23

5.7 Demand connections – Following a Restricted Period Unplanned Outage 24

5.8 Additional demand connection requirements 24


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5.9 Variations to demand connection design criteria 24

5.10 Demand Classes 25

6 OETC licensed transmission system operational criteria 27

6.1 Introduction 27

6.2 Operational security criteria 27

6.3 Operation – Prevailing System Conditions 28

6.4 Operation – Outcomes following a Fault Outage 29

6.5 Managing OETC licensed transmission system conditions and values 30

6.6 Conditional further operational security criteria 30

6.7 Restoration of OETC licensed transmission system following a Secured Event 31

6.8 Variations to operational security criteria 31

7 Definitions 33

List of figures

Figure 1.1 – Representation of the OETC licensed transmission system and other GSO systems ....... 5

Figure 1.2 – Generation connections, GSO connections and Grid Supply Points ................................. 6

Figure 5.1 – Demand Classes – Demand Group schematics ............................................................... 26

List of tables

Table 2.1 – OETC licensed transmission system – system parameter values ....................................... 8

Table 3.1 – MITS – Intact System requirements at Peak Demand values ........................................... 10

Table 3.2 – MITS – Following a Restricted Period Fault Outage.......................................................... 11

Table 3.3 – MITS – Following a Maintenance Period Fault Outage ..................................................... 12

Table 4.1 – Generation & GSO connections – Intact System requirements at Peak Demand ............ 14

Table 4.2 – Generation & GSO connections – Following a Restricted Period Fault Outage ............... 15

Table 4.3 – Generation & GSO connections – Loss of Power Infeed following a system outage ........ 16

Table 4.4 – Generation & GSO connections – Loss of Power Infeed during Planned Outages .......... 17

Table 4.5 – Generation & GSO connections – Following a Loss of Power Infeed ............................... 18

Table 4.6 – GSO connections – Loss of Power Infeed of following a system outage .......................... 19

Table 5.1 – Demand connections – Intact System requirements at Peak Demand ............................. 21

Table 5.2 – Demand connections – Following a Restricted Period Fault Outage ................................ 22

Table 5.3 – Demand connections – Following a Maintenance Period Fault Outage ............................ 23

Table 5.4 – Demand connections – Following a Restricted Period Unplanned Outage ....................... 24

Table 5.5 – Demand connections – Demand Class specification ......................................................... 25

Table 6.1 – Operational outcomes during Prevailing System Conditions ............................................. 28

Table 6.2 – Operational outcomes following a Fault Outage ................................................................ 29


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1 INTRODUCTION TO THE OETC TRANSMISSION SECURITY STANDARD

1.1 Roles and scope

1.1.1 This document sets out the Transmission Security Standard (the “Standard” or “TSS”)

that the Oman Electricity Transmission Company S.A.O.C (“OETC”) will implement for

the planning and operation of its licensed transmission system. The TSS has been

prepared in accordance with Condition 26 of OETC's Transmission and Dispatch

Licence.

1.1.2 The TSS contains technical terms and phrases specific to electricity transmission

systems and the electricity sector that may differ from their common usage. For this

reason ‘Definitions’ have been included in section 7. Throughout this document,

defined terms are shown in italics with capital initial letters. Other terms with an initial

capital letter and in normal font are defined in the Grid Code.

1.1.3 For ease of use, the component elements of the TSS are presented according to the

functional parts of the OETC licensed transmission system to which they primarily

apply, including, but not limited to:

a The Main Interconnected Transmission System (“MITS”) and the Dhofar Power System

b The generation connections at which a Production Facility feeds into the MITS and GSO connections both internal to Oman and internationally

c Demand connections, where demand is connected, including:

i Grid Supply Points, and

ii Demand Groups

d The operational security criteria

1.1.4 Taken together, each of elements described in sections 1.1.3a to 1.1.3c inclusive

make up the OETC licensed transmission system, as shown in Figure 1.1.

1.1.5 The criteria for radially connected generation, GSO connections and demand

connections are consistent with the criteria applied to the MITS. However, they are

conditioned by the criteria for the relevant generation connections, GSO connections

and/or demand connections.

1.1.6 The criteria presented in the TSS represent normal requirements for the planning and

operation of the OETC licensed transmission system. Any departure from the TSS

criteria shall be subject to detailed risk and economic studies. These shall include

consideration of the costs associated with the use and/or introduction of out-of-merit

generation as an alternative to network reinforcement. To the extent permitted and

required within the TSS, OETC shall seek derogations from the relevant provisions of

the TSS.


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1.1.7 Additional criteria, for example covering more detailed and other aspects of quality of

supply, are contained in the Grid Code and Distribution Code, which should be read in

conjunction with the TSS.

1.1.8 As described above and illustrated in Figure 1.2, there will be many parts of the

OETC licensed transmission system where more than one set of criteria apply. In

such parts, the requirements of all relevant criteria shall be met. Figure 1.1 provides

an overall view of the OETC licensed transmission system. Figure 1.2 shows the

more detailed reach and overlap of the TSS criteria. Thus Figure 1.2 governs in

terms of the application of TSS criteria.

1.1.9 While it is a requirement for Transmission Capacity to meet the TSS criteria, it does

not follow that Transmission Capacity should be reduced so that it only meets the

minimum requirement of those criteria.

1.2 Structure and reach of the TSS in the OETC licensed transmission system

1.2.1 Figure 1.1 below shows the relationship between the various elements of the OETC

licensed transmission system.

1.2.2 Figure 1.2 below shows the reach and overlap of the various design criteria specified

in the TSS.

1.2.3 Figure 1.2 governs over Figure 1.1.


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Figure 1.1 – Representation of the OETC licensed transmission system and

other GSO systems

GSO system

GCCIA system

MIT

S

Pro

duction F

acility

Pro

duction F

acility

Ge

ne

ratio

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Ge

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ratio

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ctio

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sed

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yste

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ctio

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MIT

S d

esig

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rite

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Genera

tion c

onnection d

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GSO system

PDO system

GS

O inte

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Future

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Dem

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roup

Dh

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roduction

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onnection d

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esig

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roup

De

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onnection

Ge

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onne

ctio

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Figure 1.2 – Generation connections, GSO connections and Grid Supply Points


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2 SYSTEM DESIGN AND OPERATIONAL VALUES

2.1 Introduction

2.1.1 The Grid Code specifies various parameters including frequency, voltage, harmonic

distortion and flicker. These parameters contribute to the quality of supply

experienced by Users.

2.2 System parameters under various conditions

2.2.1 For purposes of the TSS and in respect of frequency and voltage, four conditions are

identified for determining system parameter values, as follows:

a Normal conditions – being conditions that apply on a continuous basis; these are the preferred conditions of the OETC licensed transmission system

b Disturbed conditions – being conditions in which the voltages are the same as for normal conditions, but the frequency limits have been changed and include, as a lower limit, the Normal Infeed Loss Risk frequency limit

c Stretched Conditions – being conditions that have two parts:

i Continuous Stretched Conditions that are not time dependant

ii Time limited Stretched Conditions that may only be experienced for no more than sixty continuous seconds

d Unacceptable Conditions – being conditions that are never allowed in planning, design or operation

2.2.2 Transient frequency deviations that occur outside the limits of continuous operation

Stretched Conditions and last less than sixty seconds shall only occur at reasonably

infrequent intervals. This governs all relevant TSS criteria.

2.2.3 Table 2.1 sets out the required values for the system parameters.


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Table 2.1 – OETC licensed transmission system – system parameter values

Explanatory notes for Table 2.1:

a. The frequency values are derived from the Grid Code

b. The frequency value of 47.50 Hz is equal to the Infrequent Infeed Loss Risk frequency limit, also referred to as the “IILR frequency limit”

c. The frequency value of 49.50 Hz is equal to the Normal Infeed Loss Risk frequency limit, also referred to as the “NILR frequency limit”

d. Refer also to Unacceptable Frequency Conditions

Low High Low High Low High Low High Low High

˂ ≥ ˂ ≥ ˂ ≥ ≤ > ≤ > ≤ >

47.50 49.50 50.50 51.50

380 400 420

198 220 242

119 132 145

Quality of Supply – System Parameter values

Parameter

Unacceptable conditions

Stretched conditions

Target

Disturbed conditions

Normal conditions

Voltage

kV

49.95

390

209

125

51.5049.95 50.05 50.05 50.50

380

198

119

420

242

145

410

231

139

Less than

60 seconds

Less than

60 seconds

Frequency

Hz47.50 50.0049.50


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3 DESIGN OF THE MAIN INTERCONNECTED TRANSMISSION SYSTEM

3.1 Introduction

3.1.1 As at the approval date, the MITS and Dhofar Power System are connected via a

local GSO system owned and operated by PDO.

3.1.2 For the purposes of this section the MITS design criteria shall apply equally to the

MITS and the Dhofar Power System.

3.2 MITS design criteria

3.2.1 Collectively, sections 3.3, 3.4 and 3.5 set out the design criteria for the MITS (the

“MITS design criteria”).


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3.3 MITS – Intact System requirements at Peak Demand

3.3.1 The minimum Transmission Capacity of the MITS shall be planned and designed to

achieve the outcomes specified in Table 3.1 for the following Background Conditions:

i Peak Demand values;

ii The expected generation schedule;

iii Expected GSO connection transfers1 (if any), and

iv Prior to any Secured Event

Table 3.1 – MITS – Intact System requirements at Peak Demand values

MITS

Intact System design requirements for Peak Demand values

System Equipment loading

a) System Equipment shall not exceed Pre-Fault Rating levels

b) System Equipment shall be within the relevant Technical Limits

c) Circuit-breakers shall not be subjected to calculated fault current in excess of their Technical Limits

System parameters

For the OETC licensed transmission system there shall be:

a) No Unacceptable Frequency Conditions

b) Voltage levels within normal conditions

c) No Insufficient Performance Margins

System stability There shall be no System Instability

1 GSO connection transfers show power import or export for the OETC licensed transmission system


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3.4 MITS – Following a Restricted Period Fault Outage

3.4.1 Using Peak Demand values, the Background Conditions described in section 3.3 and

following a specified Fault Outage, the Transmission Capacity for the MITS shall be

planned and designed to achieve the outcomes specified in Table 3.2.

Table 3.2 – MITS – Following a Restricted Period Fault Outage

MITS

Outcomes following a Restricted Period Fault Outage at Peak Demand values

Following any one of the following: These outcomes shall be achieved:

1) A Fault Outage of a single Transmission Circuit

2) A Fault Outage of a single section of Busbar

3) A Fault Outage of a single GSO connection circuit

4) A Fault Outage of either: (i) a single Generation Unit; or (ii) a number of Generation Units, connected to the MITS through a single circuit-breaker

a) No loss of supply to Grid Supply Points except as provided for in Table 5.5

b) No loss of supply from a Production Facility or GSO system greater than the Normal Infeed Loss Risk

c) System Equipment shall be within the relevant Technical Limits

d) No Unacceptable Frequency

Conditions

e) No Unacceptable Voltage Conditions

f) No Insufficient Performance Margins

g) No System Instability


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3.5 MITS – Following a Maintenance Period Fault Outage

3.5.1 During the Maintenance Period, while using the expected OETC licensed

transmission system demand and the expected generation schedule but excluding

any forecast GSO connection import or export, with a Planned Outage of a single

Transmission Circuit or a single section of Busbar, and following the specified Fault

Outages, the MITS shall be designed to achieve the outcomes specified in Table 3.3.

Table 3.3 – MITS – Following a Maintenance Period Fault Outage

MITS

Outcomes following a Maintenance Period Fault Outage





4) A Fault Outage of either: (i) a single Generation Unit; or (ii) a number of Generation Units connected to the MITS through a single circuit-breaker

a) No loss of supply to Grid Supply

Points except as provided for in

Table 5.5

b) System Equipment shall be within

the relevant Technical Limits

c) No Unacceptable Frequency

Conditions

d) No Unacceptable Voltage

Conditions

e) No Insufficient Performance

Margins

f) No System Instability

3.5.2 Where necessary to satisfy the above MITS design criteria during the Maintenance

Period, and unless operational measures can be applied to ensure adequate

Transmission Capacity, investment analysis shall be applied.

3.6 Variations to the MITS design criteria

3.6.1 No variation to the MITS design criteria is permitted.


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4 DESIGN OF GENERATION CONNECTIONS AND GSO CONNECTIONS

4.1 Introduction

4.1.1 This section presents the criteria to be applied for the direct connection of one or

more Production Facilities or GSO systems to the OETC licensed transmission

system. The criteria in this section will also apply to the connections from a Grid

Supply Point or Demand Group to the OETC licensed transmission system by which

Generation Units embedded within a User’s network (e.g. a distribution network) are

connected to the OETC licensed transmission system.

4.1.2 In those parts of the OETC licensed transmission system where the criteria of any of

section 3 and section 5 also apply, then those criteria shall also be met.

4.2 Generation connection design criteria

4.2.1 Collectively, sections 4.3, 4.4, 4.5, 4.6 and 4.7 set out the design criteria for

connecting a Production Facility or GSO systems and any other Generation Units to

the OETC licensed transmission system (the “generation connection design criteria”).

4.2.2 The generation connection design criteria apply to GSO connections.

4.2.3 The generation connection design criteria apply to all forms of generation, such as but

not limited to:

a Synchronous machines

b Asynchronous machines, such as, for example, solar or wind powered generators

4.2.4 In designing generation connections or GSO connections to meet the TSS, the

following shall be considered:

a The Loss of Power Infeed resulting from a Fault Outage on the Generation Circuits or GSO connection circuits themselves; and

b The effects of a Fault Outage on the OETC licensed transmission system

4.2.5 When any new Production Facility, consisting of one or more Generation Units, or a

GSO connection, is proposed to be added to the OETC licensed transmission system,

then any system studies, planning, development and design shall consider the full

simultaneous power of all of the proposed Generation Units or GSO connections

operating together.


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4.3 Generation & GSO connections – Intact System requirements at Peak Demand


prior to any Secured Event, the minimum Transmission Capacity for generation

connections and GSO connections shall be planned and designed to achieve the

outcomes specified in Table 4.1.

Table 4.1 – Generation & GSO connections – Intact System requirements at

Peak Demand

Generation connections and GSO connections


Transmission and System Equipment loading



c) Circuit-breakers shall not be subjected to predicted fault current in excess of their Technical Limits

System parameters

On the OETC licensed transmission system there shall be:






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4.4 Generation & GSO connections – Following a Restricted Period Fault Outage


following the specified Secured Events, the Transmission Capacity for generation

connections and GSO connections shall be planned and designed to achieve the


Table 4.2 – Generation & GSO connections – Following a Restricted Period

Fault Outage

Generation connections and GSO connections Outcomes following a Restricted Period Fault Outage at Peak Demand values





4) An Unplanned Outage of a single Transmission Circuit followed by a Fault Outage of a further single Transmission Circuit

5) An Unplanned Outage of a Generation Circuit followed by a Fault Outage of a single Transmission Circuit

a) No loss of supply to a Grid Supply Point except as permitted in Table 5.5

b) No loss of supply from Production Facilities or GSO systems greater than the Infrequent Infeed Loss Risk

c) System Equipment shall be within the relevant Technical Limits

d) No Unacceptable Frequency

Conditions

e) No Unacceptable Voltage Conditions

f) No Insufficient Performance Margins

g) No System Instability


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4.5 Generation & GSO connections – Loss of Power Infeed constraints

4.5.1 Starting with an Intact System and including any forecast GSO connection import or

export, generation connections and GSO connections shall be planned, designed,

developed and constructed to achieve the outcomes specified in Table 4.3.

Table 4.3 – Generation & GSO connections – Loss of Power Infeed following a

system outage


Intact System

Requirements for Loss of Power Infeed following a system outage

Following the specified system outage

There shall be:

Planned Outage or fault on any single Transmission Circuit

No Loss of Power Infeed from Production Facilities

Planned Outage of any single section of Busbar on the MITS

Fault Outage of any single Generation

Circuit or single section of Busbar

Any Loss of Power Infeed from

Production Facilities shall not exceed

the Normal Infeed Loss Risk

Fault Outage of any single Busbar

coupler circuit-breaker or Busbar

section circuit-breaker on the MITS

Any Loss of Power Infeed from

Production Facilities shall not exceed

the Infrequent Infeed Loss Risk


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4.6 Generation & GSO connections – Loss of Power Infeed during Planned Outages

4.6.1 Generation connections and GSO connections shall be planned, designed, developed

and constructed such that, during the specified Planned Outages, any Loss of Power

Infeed shall achieve the outcomes specified in Table 4.4.

Table 4.4 – Generation & GSO connections – Loss of Power Infeed during

Planned Outages


Loss of Power Infeed during Planned Outages

During the

Planned Outage

of

If there is a

Fault Outage

on the MITS of:

Then:

A single Transmission

Circuit

a further single

Transmission Circuit;

or

a single section of

Busbar

Any Loss of Power

Infeed from Production

Facilities shall not

exceed the Infrequent

Infeed Loss Risk

a single Busbar coupler

circuit-breaker;

or

a single Busbar section

circuit-breaker

A single section of

Busbar on the MITS

a single Transmission

Circuit;

or

a further single section

of Busbar

a single Busbar coupler

circuit-breaker;

or

a single Busbar section

circuit-breaker


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4.7 Generation & GSO connections – Transmission Capacity & Loss of Power

Infeed

4.7.1 The Transmission Capacity for Generation connections and GSO connections shall

be planned such that, for all OETC licensed transmission system conditions, the Loss

of Power Infeed of the same magnitude as the Normal Infeed Loss Risk or Infrequent

Infeed Loss Risk respectively is secured as specified in Table 4.5.

Table 4.5 – Generation & GSO connections – Following a Loss of Power Infeed


Outcomes following a Loss of Power Infeed

Following: None of these outcomes shall occur:

Normal Infeed Loss Risk

a) Loss of supply to a Grid Supply Point except as permitted in Table 5.5

b) Loss of supply from any Production Facility or GSO system greater than the Normal Infeed Loss Risk

c) System Equipment exceeding the relevant Technical Limits

d) OETC licensed transmission system frequency falls below the NILR frequency limit

e) Unacceptable Voltage Conditions

f) Insufficient Performance Margins

g) System Instability

Infrequent Infeed Loss Risk

a) Cascade failure of the OETC licensed transmission system

b) OETC licensed transmission system frequency falls to below the IILR frequency limit

c) OETC licensed transmission system frequency remains below the NILR frequency limit for longer than 60 continuous seconds

d) Unacceptable Voltage Conditions

4.8 GSO connections – Loss of Power Infeed constraints

4.8.1 Starting with an Intact System, GSO connections shall be planned, designed,

developed and constructed to achieve the outcomes specified in Table 4.6.


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Table 4.6 – GSO connections – Loss of Power Infeed of following a system

outage

GSO connections

Intact System

Requirements for Loss of Power Infeed following a system outage

Following the specified system outage

There shall be:

On any single GSO connection circuit:

1) A Planned Outage, or

2) An Unplanned Outage, or

3) A Fault Outage

No Loss of Power Infeed

4.9 Variations to generation connection design criteria or Table 4.6

4.9.1 OETC may seek derogation for variation to the generation connection design criteria

and/or the requirements of Table 4.6, based on technical and economic analysis of

design options relative to the characteristics of the generation or GSO to be

connected.


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5 DESIGN OF DEMAND CONNECTIONS

5.1 Introduction

5.1.1 This section presents the planning and design criteria for the connection of Demand

Groups to the OETC licensed transmission system.

5.1.2 In those parts of the OETC licensed transmission system where the criteria of

sections 3 and 4 also apply, then those criteria must also be met.

5.2 Demand connection design criteria

5.2.1 All the criteria listed in this section 5 comprise the demand connection design criteria.

5.3 Demand connection capacity requirements

5.3.1 The connection of a particular Demand Group shall meet the criteria set out in

sections 5.4 through to and including 5.7 under the following Background Conditions:

a When there are neither Planned Outages nor Unplanned Outages, the Group Demand shall be set equal the value at the time of Peak Demand;

b When there is a Planned Outage local to the Demand Group, the Group Demand shall be set equal to the relevant Maintenance Period Demand;

c Any Transfer Capacity (i.e. the ability to transfer demand from one Demand Group to another) declared by Distribution Licensees shall be represented taking account of any restrictions on the timescales in which the Transfer Capacity applies. Any Transfer Capacity declared by the Distribution Licensees to be available for use in planning timescales must be available for use in such planning timescales; and

d Any generation available within a Demand Group shall be taken into account by considering its forecast generation as provided by the relevant Generation Unit owner


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5.4 Demand connections – Intact System conditions at Peak Demand values

5.4.1 For Peak Demand values and prior to any Secured Event, the minimum Transmission

Capacity of any demand connection, its relevant Transmission Circuits and Demand

Groups shall be planned and designed to achieve the outcomes specified in

Table 5.1.

Table 5.1 – Demand connections – Intact System requirements at Peak Demand

Demand connections

Demand Group





c) Circuit-breakers shall not be subjected to predicted fault current in excess of their Technical Limits

System parameters

For the OETC licensed transmission system there shall be:






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5.5 Demand connections – Following a Restricted Period Fault Outage


following a specified Fault Outage, the Transmission Capacity for the connection of a

Grid Supply Point to a Demand Group shall be planned and designed to achieve the


Table 5.2 – Demand connections – Following a Restricted Period Fault Outage

Demand connections

Demand Group

Outcomes following a Restricted Period Fault Outage at Peak Demand values

Following: These outcomes shall be met:

A Fault Outage of a single Transmission Circuit

a) No loss of supply to Grid Supply Points such that the provisions set out in Table 5.5 are not met



Conditions

d) Voltage levels within normal conditions

e) No Insufficient Performance Margins



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5.6 Demand connections – Following a Maintenance Period Fault Outage

5.6.1 During the Maintenance Period, using Maintenance Period Demand values, with the

Background Conditions described in section 5.3, the Transmission Capacity for the

connection of a Grid Supply Point to a Demand Group shall be planned to achieve the


Table 5.3 – Demand connections – Following a Maintenance Period Fault

Outage

Demand connections

Demand Group

Outcomes following a Maintenance Period Fault Outage

During the Planned Outage of either:

And following a further:

These outcomes shall be met:

A single Transmission Circuit;

or

A single Generation Unit

Fault Outage of a

single

Transmission

Circuit

a) No loss of supply to

Grid Supply Points

such that the

provisions set out in

Table 5.5 are not met

b) System Equipment

shall be within the

relevant Technical

Limits

c) No Unacceptable

Frequency Conditions

d) OETC licensed

transmission system

voltage levels within

normal conditions

e) No Insufficient

Performance Margins


5.6.2 Where necessary to satisfy the above demand connection design criteria during the

Maintenance Period, and unless operational measures can be applied to ensure

adequate Transmission Capacity, investment analysis shall be applied.


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5.7 Demand connections – Following a Restricted Period Unplanned Outage


following a specified Unplanned Outage, the Transmission Capacity for the

connection of a Grid Supply Point to a Demand Group shall be planned and designed

to achieve the outcomes specified in Table 5.4.

Table 5.4 – Demand connections – Following a Restricted Period Unplanned

Outage

Demand connections

Demand Groups

Outcomes following an Unplanned Outage at Peak Demand values

After any one of the following: These outcomes shall be met:

1) An Unplanned Outage of a single Transmission Circuit

2) An Unplanned Outage of a single section of Busbar

a) No loss of supply to Grid Supply Points for a Demand Group of greater than 2 MW



Conditions

d) OETC licensed transmission system voltage levels within normal conditions

e) No Insufficient Performance Margins


5.8 Additional demand connection requirements

5.8.1 In addition to the requirements of sections 5.4 through to and including 5.7 and for the

Background Conditions described in section 5.3, the system shall be planned such

that operational switching does not cause Unacceptable Voltage Conditions.

5.9 Variations to demand connection design criteria

5.9.1 OETC may seek derogation for variation to the demand connection design criteria in

this section 5, based on technical and economic analysis of design options relative to

the characteristics of the demand or embedded Generation Units to be connected.


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5.10 Demand Classes

5.10.1 The Demand Classes are set out in Table 5.5.

Table 5.5 – Demand connections – Demand Class specification

Demand connections

Demand Class definition and supply restoration times

Dem

and C

lass

Demand Class

boundaries

OETC licensed transmission system configuration

Following a system outage during the Restricted Period

A Planned Outage followed by

a single Fault Outage during the Maintenance Period

Low MW

>

High MW

≤

Required level of served

demand

MW

Time to restore served

demand

Required level of served

demand

MW

Time to restore served

demand

A 0 2

Total Group Demand

Repair time of faulted

circuit

Maintenance Period

Demand for the Demand

Group

No requirement

B 2 6 3 hours No

requirement

C 6 20 15 minutes Return time of Planned

Outage

D 20 115 Momentary Interruption

allowed

Return time of Planned

Outage

E 115 300 Momentary Interruption

allowed

Momentary Interruption

allowed

F 300 No loss of supply for the Secured Events described in

the MITS design criteria in section 3


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5.10.2 Figure 5.1 shows the Demand Classes as appropriate and the related Demand

Groups.

Figure 5.1 – Demand Classes – Demand Group schematics


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6 OETC LICENSED TRANSMISSION SYSTEM OPERATIONAL CRITERIA

6.1 Introduction

6.1.1 This section sets out the operational requirements, conditions, outcomes and system

states that should be achieved either through automatic control, operator intervention,

or any combination of these, as required by the circumstances.

6.1.2 The overall objective is always to maintain the values of system parameters within the

normal conditions as set out in section 2 and especially Table 2.1.

6.2 Operational security criteria

6.2.1 For the OETC licensed transmission system, sections 6.3 and 6.4 set out the normal

operational security criteria for its operation and maintenance, while section 6.6

provides for further conditional security criteria, together, the “operational security

criteria”.


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6.3 Operation – Prevailing System Conditions

6.3.1 At all times prior to any Secured Event, the OETC licensed transmission system shall

be operated so as to achieve the outcomes specified in Table 6.1.

Table 6.1 – Operational outcomes during Prevailing System Conditions

OETC licensed transmission system

Operational outcomes during Prevailing System Conditions




c) Circuit-breakers shall not be subjected to fault current in excess of their Technical Limits

System parameters

For the OETC licensed transmission system, there shall be:






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6.4 Operation – Outcomes following a Fault Outage

6.4.1 At all times during Prevailing System Conditions and following a specified Fault

Outage, the OETC licensed transmission system shall be operated to achieve the


Table 6.2 – Operational outcomes following a Fault Outage

OETC licensed transmission system

Required operational outcomes following a Fault Outage


1) A Fault Outage of a single

Transmission Circuit

2) A Fault Outage of a single section

of Busbar, where there are no

derogations to the design of the

relevant substation

3) A Fault Outage of a single GSO

connection circuit

4) A Fault Outage of either: (i) a

single Generation Unit; or (ii) a

number of Generation Units

connected to the MITS through a

single circuit-breaker

a) No loss of supply to Grid Supply

Points except as provided for in

Table 5.5

b) System Equipment shall be within

the relevant Technical Limits


Conditions

d) No Unacceptable Voltage

Conditions

e) No Insufficient Performance

Margins



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6.5 Managing OETC licensed transmission system conditions and values

6.5.1 If the any one of the outcomes set out in Table 6.1 and Table 6.2 cannot be achieved,

then the following actions should be taken, preferably in sequence, until the OETC

licensed transmission system has been secured such that the outcomes of Table 6.1

and Table 6.2 are met:

a Change the system voltage profile by:

i Adjusting tap changers

ii Adjusting reactive power compensation equipment

iii Adjusting excitation of any, or all, Generation Units

b Through operational switching, adjusting the OETC licensed transmission system configuration and topology

c Returning System Equipment from any Planned Outage

d Constraining Production Facilities through temporary disconnection

e Constraining generation

f Constraining load and demand

i Operator initiated load shedding

ii Automatic load shedding

6.5.2 Prior to constraining load and demand as contemplated in section 6.5.1f above, and

to the extent possible, OETC senior management shall be informed of the intended

operator action.

6.6 Conditional further operational security criteria

6.6.1 During Major Risk Periods, OETC shall implement measures to mitigate the

consequences of this risk. Such measures may include, but are not limited to:

a Providing additional reserve,

b Enhancing OETC licensed transmission system voltage prior to expected increases in demand,

c Securing, as far as possible, appropriate two-circuit combinations, or

d Reducing system transfers, for example through re-dispatching of Production Facilities or import or export over GSO connections

6.6.2 If, following a Fault Outage, any one of the outcomes required in section 6.4 is not

being met, it is acceptable to utilise short-term post-fault actions to avoid

Unacceptable Overloading of System Equipment which may include a requirement for

Group Demand reduction; however, this will not be used as a method of increasing

reserve to cover abnormal post-fault generation reduction. Where possible these


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post-fault actions shall be notified to the appropriate User. Normally the provisions of

the Grid Code will be applied. This may include emergency manual demand

disconnection and/or re-dispatching of Production Facilities. Additional post-fault

actions beyond the Grid Code provisions may be applied, but only where they have

been agreed in advance with the appropriate Distribution Licensee, Production

Facility or GSO.

6.7 Restoration of OETC licensed transmission system following a Secured Event

6.7.1 Following the occurrence of a Secured Event, measures shall be taken to re-secure

the system to the above operational security criteria as soon as reasonably

practicable. To achieve this, it is permissible to put operational measures in place

before the occurrence of a Secured Event to facilitate the subsequent restoration of

system security.

6.8 Variations to operational security criteria

6.8.1 OETC shall be permitted to submit a derogation application in relation to any

requirement of the operational security criteria, provided that such derogation

application is in accordance with the appropriate requirements of the demand

connection design criteria in section 5.

6.8.2 Provided it is in accordance with the appropriate requirements of the demand

connection design criteria, it is acceptable that there may be associated Loss of

Power Infeed due to a Secured Event, for example by virtue of the design of the

generation connections, GSO connections and/or the designed switching

arrangements at the substations concerned. Refer to Table 5.5.

6.8.3 The principles of the operational security criteria shall be applied at all times except in

special circumstances where OETC, following consultation with the appropriate User,

may need to give instructions to the contrary to preserve overall OETC licensed

transmission system integrity.


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7 DEFINITIONS

Term Meaning

Background Conditions For system study purposes, this will include, but not be limited to,

any parameters that are relevant to the behaviour and dynamics

of the OETC licensed transmission system, such as:

a) OETC licensed transmission system configuration

b) The electrical location and duration of Planned Outages

and/or Unplanned Outages

c) Voltage levels at Grid Supply Points

d) Forecast demand at Grid Supply Points

e) Transfer Capacity between Demand Groups that may not

make use of circuits within the OETC licensed transmission

system

f) Connected Production Facilities

g) Dispatched Generation Units

h) Available Generation Units which have not been dispatched

i) Energised GSO connection circuits

Specific Background Conditions required for particular Secured

Events are specified throughout the TSS

Busbar The common connection point of two or more Transmission

Circuits

Demand Class This is designated by a letter “A” through “F” for the relevant

Demand Group and the security of supply that should be

provided for the relevant Demand Group. Refer to Table 5.5 and

Figure 5.1

Demand Group A site or group of sites which collectively take power from the

remainder of the OETC licensed transmission system through a

Grid Supply Point. Refer to Table 5.5 and Figure 5.1

Dhofar Power System For the purpose of the TSS, the Dhofar Power System is that part

of the OETC licensed transmission system that is located in the

Dhofar Governorate, centred on Salalah, but does not include

radially connected Generation Units, GSO connections, and/or

radially connected Grid Supply Points.


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Term Meaning

Fault Initiation Event When any one of the following occurs:

a) Fault Outage of a single Transmission Circuit

b) Fault Outage of a single section of Busbar

c) Fault Outage of a single GSO connection circuit

d) Fault Outage of either: (i) a single Generation Unit; or (ii) a

number of Generation Units, connected to the MITS through

a single circuit-breaker

Fault Outage An outage of one or more items of System Equipment,

Generation Units and/or GSO connection circuits initiated by

automatic action, unplanned at that time, which may or may not

involve the passage of fault current

Generation Circuit The sole electrical connection between one or more Generation

Units at a Production Facility and the MITS; a radial circuit which,

if removed, would disconnect one or more Generation Units

Grid Supply Point

GSP

A point of supply from the OETC licensed transmission system to

any of, or any combination of:

a) Distribution Licensees

b) Non-embedded Customers

Group Demand Means the demand, expressed in MW or MVA, associated with

the relevant Demand Group

GSO Means a grid system operator and may mean either an

international connected party or an internal connected party, or

both of them, as required by the context.

A GSO is capable of importing power from and exporting power

to the OETC licensed transmission system

High Frequency Limits Means:

a) If above 50.50 Hz, then returning to be equal to, or below,

50.50 Hz within 60 seconds; and

b) Never above 51.50 Hz

Refer to Table 2.1

Refer to the Grid Code


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Term Meaning

Infrequent Infeed Loss Risk

IILR

That level of loss of power infeed risk which is covered over long

periods operationally by frequency response to: (i) avoid a

deviation of system frequency outside the range 49.50 Hz to

50.50 Hz for more than 60 seconds; and (ii) never below

47.50 Hz (Table 2.1).

As at the approval date, it has a value of:

For the MITS:

a) 1,200 MW.

b) The remaining GSO interconnection circuit rating less any

import from the GSO interconnection

For the Dhofar Power System:

c) 40 MW.

d) The remaining GSO interconnection circuit rating less any


Insufficient Performance Margins

For all time periods, and in particular the during Post-fault

Periods, there are Insufficient Performance Margins when the

voltage on any relevant portion of the OETC licensed

transmission system has values within the range of Unacceptable

Voltage Conditions and occurs under any one of the following

conditions:

a) Based on international best practise, a 5% increase in Group

Demand above the level prevailing prior to the occurrence of

the relevant Secured Event; or

b) The unavailability of any single reactive compensator or other

reactive power provider; or

c) The loss of any one automatic switching system or any

automatic voltage control system for on-load tap changing

Intact System This is the OETC licensed transmission system with no:

a) Planned Outages

b) Unplanned Outages

c) Fault Outages


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Term Meaning

Loss of Power Infeed Means the output of a Generation Unit or a group of Generation

Units or the import from GSO system(s) disconnected from the

OETC licensed transmission system by a Secured Event, less the

demand disconnected from the OETC licensed transmission

system by the same Secured Event.

For the avoidance of doubt if, following such a Secured Event,

demand associated with the normal operation of the affected

Generation Unit or Generation Units is automatically transferred

to a supply point which is not disconnected from the system, e.g.

the station board, then this shall not be deducted from the total

Loss of Power Infeed to the OETC licensed transmission system.

For the purpose of operational criteria, the Loss of Power Infeed

includes the output of a single Generation Unit, CCGT module, or

boiler lost as a result of such an event.

Low Frequency Limits Means:

a) If below 49.50 Hz, then returning to above 49.50 Hz within 60

seconds, and

b) Never below 47.50 Hz

Refer also to Table 2.1

Refer to the Grid Code

Main Interconnected Transmission System

MITS

For the purpose of the TSS, the Main Interconnected

Transmission System or MITS is that part of the OETC licensed

transmission system that is interconnected at 400 kV, 220 kV or

132 kV but does not include radially connected Generation Units,

GSO connections, and/or radially connected Grid Supply Points.

For purposes of the TSS, the MITS includes the Dhofar Power

System unless required otherwise by the context

Refer to section 3.1 for the Dhofar Power System

Maintenance Period For MITS: Means the period between 00:00 on 1st October and

24:00 on 31st March of the next following year.

For Dhofar: Means the period between 00:00 on 1st July and

24:00 on 31st March of the next following year.


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Term Meaning

Maintenance Period Demand

This is the highest demand during the Maintenance Period, taking

due account of the Group Demand. If no better forecast is

possible from the data available, Maintenance Period Demand

shall be estimated as the Group Demand multiplied by 67%.

Major Risk Period A Major Risk Period is one during which Secured Events are:

a) judged to be significantly more likely than under the

circumstances addressed by the normal TSS criteria, or

b) judged to have a significantly greater impact than normal, or

c) events not normally secured against which are judged to be

significantly more likely than normal such that measures

should be taken to mitigate their impact

An example would be country-wide extreme weather conditions

Momentary Interruption Means a loss of power that lasts for no more than one (1) minute

from the start of the relevant Fault Initiation Event, with the

restoration of power intended to be performed by automatic

equipment

Non-embedded Customer A customer, except for a Distribution Licensee, receiving

electricity direct from the OETC irrespective of from whom it is

supplied

Normal Infeed Loss Risk

NILR

Means that value of lost power infeed that would cause the OETC

licensed transmission system frequency to fall to a value equal to

but not below the NILR frequency limit (Table 2.1).

As at the approval date, and it has a value of:

For the MITS:

a) 600 MW

b) The remaining GSO interconnection circuit rating less any


For the Dhofar Power System:

c) 25 MW

d) The remaining GSO interconnection circuit rating less any



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Term Meaning

Operational Intertripping The automatic tripping of circuit-breakers to remove OETC

licensed transmission system Generation Units, GSO

connections and/or Demand Groups. It does not provide

additional Transmission Capacity and must not lead to

Unacceptable Frequency Conditions for any Secured Event

Peak Demand The estimated summer peak demand (expressed in MW and

MVar) on the OETC’s licensed transmission system. This

includes both transmission and distribution losses and represents

the demand to be met by Generation Units (directly connected or

embedded) which are connected to OETC’s licensed

transmission system and by electricity imported into the OETC

licensed system from GSO systems across GSO connections

Planned Outage An outage or one or more items of System Equipment,

Generation Units and/or GSO connections, initiated by manually

instructed action which:

a) Shall be confined to the Maintenance Period

b) Shall be planned at least seven (7) days in advance of the

event, or as prescribed by the Grid Code

Post-fault Period Means the period commencing with:

a) Automatic fault detection, followed by

b) Automatic fault clearance, followed by

c) Transient behaviour and

d) Subsequent recovery to Steady State conditions

Pre-Fault Rating The OETC specified pre-fault capability of transmission

equipment. Due allowance shall be made for specific conditions

(such as ambient or seasonal temperatures), agreed time-

dependent loading cycles of equipment and any additional

relevant procedures.

Refer also to Technical Limit

Prevailing System Conditions

These are conditions on the OETC licensed transmission system

prevailing at any given time and will therefore normally include

Planned Outages and Unplanned Outages, but excluding any

Fault Outage


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Term Meaning

Restricted Period For MITS: Means the period other than the Maintenance Period,

occurring between 00:00 on 1st April and 24:00 on 30th

September of any year.

For Dhofar: Means the period other than the Maintenance

Period, occurring between 00:00 on 1st April and 24:00 on 30th

June of any year.

The period is during which:

a) No Planned Outage shall occur

b) Unplanned Outages may only be permitted as prescribed in

the Grid Code

c) The summer Peak Demand will occur

Secured Event A contingency on the OETC licensed transmission system, or any

part thereof, which shall be considered for the purposes of

assessing system security and which, should it occur, must not

result in the remaining parts of the OETC licensed transmission

system being in breach of the TSS criteria. Secured Events are

individually specified throughout the TSS. More onerous

unsecured events may occur and additional operational

measures within the requirements of the Grid Code may be

utilised to maintain the overall integrity of the OETC licensed

transmission system.

A Secured Event may be caused by, it is not limited to, any of the

Fault Initiation Events

Steady State A condition of a power system in which all automatic and manual

corrective actions, such as, but not limited to, tap changing and

switching of circuits, have taken place and all of the operating

quantities that characterise it can be considered constant for the

purpose of analysis

Stretched Conditions In respect of either voltage or frequency, or both, when the

relevant system parameters have values that fall outside the

limits for disturbed conditions, but have not yet reached the

values for Unacceptable Conditions

Refer to Table 2.1


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Term Meaning

System Condition Has the meaning shown in Table 2.1 and addresses the following

conditions on the OETC licensed transmission system:

a) Normal conditions

b) Disturbed conditions

c) Stretched Conditions

d) Unacceptable Conditions

Refer to Table 2.1

System Equipment Any equipment installed on the OETC licensed transmission

system to enable the bulk transfer of electricity. This will include,

but is not limited to Transmission Circuits, Busbars, transformers,

reactors, capacitors, circuit-breakers, links, isolators and voltage

control and management equipment

System Instability System Instability may occur as a result of:

a) poor damping – where electromechanical oscillations of

Generation Units are such that the resultant peak deviations

in machine rotor angle and/or speed at the end of a 20

second period remain in excess of 15% of the peak

deviations at the outset (i.e. the time constant of the slowest

mode of oscillation exceeds 12 seconds); or

b) pole slipping – where one or more transmission connected

synchronous Generation Units lose synchronism with the

remainder of the system to which it is connected

For the purpose of assessing the existence of System Instability,

a Fault Outage is taken to include a solid three phase to earth

fault (or faults) anywhere on the transmission system with an

appropriate clearance time. Clearance times used should be

consistent with the fault location and appropriate to the actual

protection, signalling equipment, trip and interposing relays, and

circuit breakers involved in clearing the fault.


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Term Meaning

Technical Limit These represent the values of technical parameters usually

specified in type test certificates, which set out the manufacturer

specified rating for the relevant equipment, usually classified as:

a) ‘Continuous rating’

b) ‘Short duration’ or ‘peak rating’

Values may also be adjusted on the basis of environmental

conditions such as, but not limited to, ‘ambient temperature’ and

‘humidity’

Refer also to Pre-Fault Rating

Transfer Capacity That circuit capacity from adjacent Demand Groups which can be

made available within the times stated in Table 5.5

Transmission Capacity The ability of a network to transmit electricity. It does not include

the use of Operational Intertripping except in respect of

section 5.3.1c

Transmission Circuit Part of the OETC licensed transmission system between two or

more circuit-breakers which includes, for example, transformers,

reactors, cables and overhead lines but excludes Busbars,

Generation Circuits and GSO connection circuits

Unacceptable Conditions In respect of either voltage, or frequency, or both, when the

relevant system parameters have values that fall outside the

limits for Stretched Conditions.

Refer to:

Section 2.2.1d

Table 2.1

Unacceptable Frequency Conditions

These are conditions where the OETC licensed transmission

system frequency does not meet the criteria for either:

a) High Frequency Limits, or

b) Low Frequency Limits

Refer to:

Section 2.2.1d

Section 2.2.2

Table 2.1


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Term Meaning

Unacceptable Overloading The overloading of any System Equipment beyond its specified

time-related capability. Due allowance shall be made for specific

conditions (such as ambient or seasonal temperature), pre-fault

loading, agreed time-dependent loading cycles of equipment and

any additional relevant procedures

Refer to Pre-Fault Rating and Technical Limit

Unacceptable Voltage Conditions

Unacceptable Voltage Conditions occur when the values of

voltage fall in the Unacceptable Conditions range of values

Refer to:

Section 2.2.1d

Table 2.1

Unplanned Outage An outage or one or more items of System Equipment,

Generation Units and/or GSO connections by manually instructed

action which has not been subject to the recognised outage

planning process of the Grid Code

-o0o-

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