ISBN 978-0-626-21055-7 / Edition 1
ELECTRICITY SUPPLY —
QUALITY OF SUPPLY
Emergency Load Shedding Reduction Practices, System Restoration Practices, and Critical Essential loads
Draft 2 - WG Draft 1bInterim draft Ffor working group input and information onlyconsultation
RGK comment on new draft – I have addressed the NRS 048 WG comments and reorganised the flow to better address Dx curtailment – look forward to your comments (I anticipate some good debate on some of the issues)
This document is not a South African National Standard
This specification is issued by
the Standardization Section, Eskom,
on behalf of the
User Group given in the foreword.
Table of changesChange No. / Date / Text affected
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Working GroupG Ddraft 12BE - 4158 May March 2009
WG draft 1BE NRS 048-9 MarchMay 2009
Foreword
This part of NRS 048specification was compiled by representatives of the South African Electricity Supply Industry (ESI), in a working group appointed by the Electricity Suppliers Liaison Committee (ESLC). The working group membership included a wide range of stakeholders, including representatives of the South African Electricity Supply Industry (ESI), NERSA, Government, and customer representation - - inter alia formal representation of the Energy Intensive User Group (EIUG).
This part of NRS 048 specifies emergency load reduction shedding practices (i.e. load shedding and load curtailment), load restoration practices after a local, regional, or national blackout, and associated practices for critical and essential loads. The working group was guided by the experiences of utilities, customers, and the public during the load shedding events of 2008, as well as subsequent measures taken to improve emergency load shedding reduction practices.
This part of NRS 048 was prepared by a working group which, at the time of publication, comprised the following members:
[DRAFTING NOTE: Compiler’s note : list to be inserted during final draft stage]
AJ Dold (Chairman) eThekwini Electricity
SA Adams Nelson Mandela Metropolitan Municipality
DK Bhana Eskom Holdings Limited (KSACS Division)
G Botha Eskom Holdings Limited (S &I, Corp Services Division)
BG Chatterton Eskom Holdings Limited (Distribution Division)
G de Beer Sasol
M Dekenah Marcus Dekenah Consulting cc
S Delport Ekurhuleni Metropolitan Municipality
GM Dindi City of Cape Town
HJ Geldenhuys (Dr) Eskom Holdings Limited (IARC, Corporate Services Division)
P van Niekerk Energy Intensive User Group (EIUG)
AC Kachelhoffer Tshwane Electricity
I Kekana Tshwane Electricity
M Kneen Glass Manufacturing Industry
RG Koch Eskom Holdings Limited (Corporate Services Division)
DA Kruger Chamber of Mines
J Maree Mondi Paper
RR McCurrach Eskom Holdings Limited (Transmission Division)
S Mda Department of Public Enterprises
M Mncube National Energy Regulator of South Africa (NERSA)
M Ngcamu Department of Public Enterprises
T Nortje Exxaro Resources
H Mostert Eskom Holding Limited (Distribution Division)
T Rangakile City Power Johannesburg (Pty) Ltd
V Shikoana Eskom (Distribution Division)
M Shozi National Energy Regulator of South Africa (NERSA)
I Sigwebela Eskom Holdings Limited (Transmission Division)
T Thenga National Energy Regulator of South Africa (NERSA)
S Zimu Eskom (Technical Audit, Corporate Services Division)
Annexes A, B, aand B are normative. Annexes C and D are are for information only.
Working GroupG Ddraft 12BE - 4158 May March 2009
WG Ddraft 2 1BE NRS 048-9: 15 Marchy 2009
Introduction
The country’s infrastructure, of which the power system forms an essential part, is exposed to a wide variety of threats - (for example: extreme weather, the impacts of climate change, wilful damage to infrastructure (including terrorism and vandalism), key network/plant failures, the impact of a sequence of unforeseen events, the potential failure of some barriers / protection systems, and sustained stresses due to generation and network infrastructure capacity shortagesextreme weather and the impacts of climate change, wilful damage to infrastructure, key network/plant failures, load shedding required in the event of capacity shortage). Unlike countries that are more regularly exposed to the impacts of some of thesesuch threats, South African society has been relatively unprepared for the associated disruptions – and therefore when these threats materialise occur the resulting impacts on society and the local/national economy can be significant. The increasing dependency of society on the power system, and the potential for an increase in the likelihood of frequency of such threats materialising from time to time, implies the need for a country approach to enhancing national societal resilience. From a power system perspective, a comprehensive approach to addressing the requirements of identified critical and essential loads needs to be developed so as to contain the impact from the perspectives of safety, environmental impact, society impact, economic impact etc. Similarly, individual customer installations need to be appropriately prepared for both notified and sudden load reduction events.
NOTE: The load shedding undertaken to protect the integrity of the power system in South Africa in January 2008 highlighted significant shortcomings in the preparedness of the country for such emergenciesload shedding, and in associated load shedding practices. Key concerns were: (i) the safety of- people;, (ii) the impact on the environment, and plant; (iii) the unpredictability of load shedding; (ivii) the level of equitable participation of different customers in load reduction - i.e. when and how often customers were shed; (viv) social impact (e.g. traffic during peak hours); (vi) the physical impact on plant (customer plant and the supply network) and; (vii) the direct and subsequent economic impact on the country; and (viii) the psychological impact on the nation.
This part of NRS 048 provides a code of practice is aimed at preparing the country for greater resilience in the event thatof threats to the power system materialise, giving rise toing – including: (i) a need for emergency reduction in system national load shedding due to an imbalance in electricity supply and demand;, (ii) sudden blackouts extending of over a significant area of the country;, and (iii) local supply interruptions.
NOTE: A blackout differs from emergency load reduction (as experienced by the country in 2008) in that the latter is a controlled (manual or automatic) intervention to protect the total system from collapse. Such emergency load reduction measures are implemented to protect the system from a blackout.
This document deals specifically with emergency load reduction, whilst recognising that other interventions may be implemented to manage longer-term system load during periods when system generation capacity is constrained in its ability to meet demand. The aim in implementing emergency load reduction measures is to protect the power system for the benefit of the safety of the country. Emergency load reduction (including load shedding) is a last resort to managing supply/demand and network constraints. The development a set of robust emergency load reduction practices (and the associated level of preparedness by stakeholders and the public), should therefore be seen in the context of overall measures that need to be undertaken to manage an imbalance in supply and demand - i.e. long-term supply-side interventions such as increased generating capacity, improved generation plant availability, and energy efficiency programmes, and medium term interventions such as energy conservation/rationing programmes.
Although a low system reserve margin (the margin between the system’s generation capacity and the peak load that this is expected to serve) implies an increased likelihood that emergency load reduction measures may need to be be required initiated to balance supply and demand, the need for a robust set of emergency load shedding protocols exists even under healthy reserve margin conditions. A sequence of unexpected events or a large significant event on an otherwise healthy power system can give rise to the need for emergency load shedding. Emergency load reduction Load shedding requirements are is also not limited to generation capacity shortages, but could arise due to regional or local transmission or distribution network constraints.
The aim of load shedding is to protect the network so as to ensure that the safety of the country as a whole is addressed. The development of a robust set of emergency load shedding practices and associated level of preparedness by stakeholders and the public, should be seen in the context of overall measures undertaken to manage an imbalance in supply and demand (i.e. supply-side interventions such as increased generating capacity and plant availability, as well as demand-side interventions such as demand side management (DSM) programmes and energy rationing programmed. Such imbalances are to be prevented as far as possible taking economics and practicality into account.
NOTE: The 2003 blackout in Northeast USA and Ontario (Canada) that affected 50 million people was caused by transmission network constraints. The event could have been avoided by load shedding in the 2 hours of the emerging system emergency before the final cascading loss of multiple transmission lines and generators occurred (this last sequence of events took 3 minutes).
The specific requirements of loads critical to safety, the environment, and to the prevention of an immediate and significant knock-on impact on society, need to be considered. An approach to dealing with critical loads that only addresses considers supply network considerations interventions (i.e.e.g. exclusion of suchthese loads from load shedding schedules) is may neitherot be optimal nor practical. This is largely because exclusion of these loads (and by implication loads on the same electricity supply circuit) will increase the frequency at which other customers on the networks are shed. - and in many cases may be impractical.
This brief code of practice theadopts arefore considers a more comprehensive approach to addressing various loads (including individual critical loads) by specifying a by addressing a range of interventions to make the countrysociety in general more resilient in the event of to possible a system emergency. Alternatives considered in this code of practice areload shedding, i.e.:
a) the time of day that loads should or should not be shed;a) the manner in which emergency load reduction is applied (i.e. time-based shedding vs. a reduction of load for the duration of the emergency);
b) the specific time of day that different types of loads are shed;
c) the exclusion of some specific loads from load shedding schedules;
cb) pprotocols for interaction between the customers operating critical loads and the electricity supply utilityreacting when specific areas are shed; and
c) the exclusion of some loads from load shedding schedules; and
d) load interventions in customer installations (e.g. the need for appropriate such as backup supplies).
A blanket exception of any customer from load shedding schedules is neither practical nor optimal.
Ideally the approach to addressing critical and essential loads during emergency load reduction or restoration should be largely consistent fromon a national level perspective (i.e. applied similarly by the various supply authorities). For this reason, this code of practice identifies It is the intention that a minimum set of critical load typessub-categories that should be addressed by the various supply authorities will be. In the case where specific critical loads exist within a customer installation, this information should be provided to a supply authority (termed an “essential load requirement” in this document). It proposesA fFormalisation of the requirement for customers to provide the necessary essential load information is specified. This information is particularly vital for a supply authority to establish priorities for power system restoration after a blackout. The format for submitting such information is also provided. required to the relevant electricity supply authorities.
NOTE: It is anticipated that the provision of essential load information IdeallyIdeally this couldwill at some stage be legislated – potentially in terms of the Occupational Health and Safety Act, and the Mine Health and Safety Act, and/or in and Mines Act – but may be more pragmatically implemented in terms of demand management legislation currently being developed.
The criteria considered in developing the code of practice are:
a) safety of people, the environment, and critical plant;
b) predictability of when and for how long a customer will be interrupted or required to reduce demand;
c) equitable participation by customers, and how load reduction requirements are allocated between various Eskom regions across the country, metros, municipalities, key industrial customers, and international customers (see note);
d) social impact of load shedding and/or curtailment;
e) economic impact on the country.
f) technical constraints on executing load shedding/curtailment or restoration (e.g. concerns about equipment failure, resources for manual restoration, availability of SCADA / telecontrol;
NOTE Equitable participation refers to a striving for general fairness in the manner in which customers are required to participate in load reduction schemes. Equal participation on the other hand is not possible given tThe nature of load shedding , customer types, and system characteristics. , however does not allow for equal participation (complete fairness).
Load shedding is a last resort to managing supply/demand and network constraints. This will generally follow a range of interventions to manage supply and demand (including the use of interruptible load agreements with customers). This document defines both emergency load shedding (a response to short-term system constraints) and planned load shedding (undertaken to manage a longer term shortage of generation capacity on the system). The focus of this Code of Practice is on emergency load shedding. It is the intention that other mechanisms will be in place to manager longer generation capacity constraints (i.e. the power conservation programme).
[DRAFTING DRAFTING NOTE: During the development of this document, discussions are being held with Government and NERSA on the most appropriate manner of promulgating the requirements]
Keywords
load reduction, load shedding, load curtailment, critical loads, essential loads, schedules.
Working GroupG Ddraft 12BE - 4158 May March 2009
13 WG Ddraft 1BE2 NRS 048-9 20 MarchMay 2009