UDC - Association of Municipal Electricity Utilities SABS/NRS 048 Part 9 Loa… · WG draft 1A...
Transcript of UDC - Association of Municipal Electricity Utilities SABS/NRS 048 Part 9 Loa… · WG draft 1A...
WG draft 1A -17Feb 2009
ELECTRICITY SUPPLY —
QUALITY OF SUPPLY
Load Shedding Practices, System
Restoration Practices, and Critical &
Essential loads
WG draft 1A
This document is not a South African National Standard
N R S
NRS 048-9:2009
ISBN 978-0-626-21055-7 Edition 1
WG draft 1A -17Feb 2009
This specification is issued by
the Standardization Section, Eskom,
on behalf of the
User Group given in the foreword.
Table of changes
Change No. Date Text affected
Correspondence to be directed to Printed copies obtainable from
The NRS Projects Manager Standards South Africa
Industry Association Resources Centre
Eskom Private Bag X191
Private Bag X 13 Pretoria 0001
Halfway House 1685
Telephone: 012 428 7911
Fax : 011 651 6827 Fax : 012 344 1568
E-mail : [email protected] E-mail : [email protected]
Website: http://www.nrs.eskom.co.za Website : http://www.stansa.co.za
COPYRIGHT RESERVED
Printed in the Republic of South Africa
by Standards South Africa
1 Dr Lategan Road, Groenkloof, Pretoria
NRS 048-9:2007
WG draft 1A -17Feb 2009
Foreword
This specification 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 NERSA, Government, and customer representation - inter alia
representation of the Energy Intensive User Group (EIUG).
This specification specifies load shedding practices 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
load shedding practices.
This specification was prepared by a working group which, at the time of publication, comprised the
following members:
AJ Dold (Chairman) eThekwini Electricity
SA Adams Nelson Mandela Metropolitan Municipality
DK Bhana Eskom Holdings Limited (KSACS 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)
A Hepburn 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)
A Sayed 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, and C are for information only.
Introduction
The country’s infrastructure, of which the power system forms an essential part, is exposed to a
wide variety of threats (for example: storms 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 impact of such threats, South African
society has been relative unprepared for the associated disruptions – and therefore when these
occur the 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 frequency of
such threats materialising, implies the need for a country approach to enhancing 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.
NOTE: The load shedding undertaken in South Africa in January 2008 highlighted significant shortcomings in the preparedness of the country for load shedding, and in associated load shedding practices. Key concerns were: (i) safety - people, impact on the environment, and plant; (ii) the predictability of load shedding; (iii) the level of equitable participation of different customers in load reduction - i.e. when and how often customers were shed; (iv) social impact (e.g. traffic during peak hours) and; (v) economic impact on the country.
This code of practice is aimed at preparing the country for greater resilience in the event of threats
to the power system materialising (including national load shedding due to an imbalance in supply
and demand, blackouts extending of over a significant area of the country, and local supply
interruptions).
Although a low system reserve margin implies an increased likelihood that load reduction may be
required to balance supply and demand, the need for a robust set of emergency load shedding
protocols exists even under healthy reserve margin conditions. Load shedding is also not limited to
generation capacity shortages, but could arise due to regional or local 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.
An approach to dealing with critical loads that only addresses supply network considerations (e.g.
exclusion of these loads from load shedding schedules) may not be optimal - and in many cases
may be impractical. This brief therefore considers a more comprehensive approach to addressing
individual loads by addressing a range of interventions to make society in general more resilient to
possible load shedding, i.e.:
a) the time of day that loads should or should not be shed;
b) protocols for reacting when specific areas are shed;
c) the exclusion of some loads from load shedding schedules; and
d) load interventions 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 should be largely consistent on a
national level (i.e. the various supply authorities). It is the intention that a minimum set of critical
load sub-categories that should be addressed by the various supply authorities will be. Formalisation of the requirement for customers to provide the necessary essential load information
WG draft 1A NRS 048-2 17 eb 2009
WG draft 1A -17Feb 2009
required to the relevant electricity supply authorities. Ideally this could be legislated in terms of the
Occupational Health and Safety Act or the Factories 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, 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 striving for general fairness in the manner in which customers are required to participate in load reduction schemes. The nature of load shedding, customer types, and system characteristics, however does not allow for equal participation (complete fairness).
Drafting note – explain that ELS is itself a last resort
Keywords
load reduction, load shedding, load curtailment, critical loads, essential loads, schedules.
1 NRS 048-9:2009
Contents Page
1 Scope .............................................................................................................................. 3
2 Normative references ....................................................................................................... 5
3 Terms and definitions ...................................................................................................... 5
4 Requirements ................................................................................................................. 11
4.1 Application by licensees ........................................................................................... 11
4.2 Application by customers .......................................................................................... 11
4.3 Principles .................................................................................................................. 11
4.4 Development of schedules ......................................................................................... 11
4.5 Communication ......................................................................................................... 11
4.6 Reporting requirements ............................................................................................. 11
5 Requirements – essential loads ....................................................................................... 11
6 Requirements – critical loads ........................................................................................... 11
7 Requirements – specific types of loads ............................................................................ 11
Annex A (informative) Load shedding data for planning curtailment schedules ................. 25
Annex B (informative) Essential load data for system restoration planning and load shedding
.............................................................................................................................................. 26
Annex C (informative) Example of the calculation of schedules taking automatic under-frequency
load shedding into consideration ............................................................................................ 28
Annex D (informative) Example of a time-based load shedding schedule............................. 28
Bibliography ....................................................................................................................... 29
3 NRS 048-9:2009
ELECTRICITY SUPPLY — QUALITY OF SUPPLY
Load Reduction Practices and Critical and Essential Loads
1 Scope
This code of practice:
a) Provides electricity suppliers (licensees) with best practice for developing load shedding
practices; [ensure that this includes operational issues, real time info sharing]
b) Provides electricity suppliers (licensees) with best practice for prioritising load restoration after a
major system event;
c) Defines and categorises critical and essential loads;
d) Provides electricity suppliers (licensees), customers, and national and local government with
best practice on how to address these loads in the context of load shedding or system
restoration practices;
e) Identifies the responsibilities that all stakeholders have in relation to information sharing on
critical and essential loads,
f) Identifies the responsibilities that the licensee utility has in terms of information sharing related to
load shedding schedules.
g) Provides standard definitions related to load reduction principles in order to facilitate common
understanding between stakeholders.
h) Defines the roles, responsibilities, and limitations of licensees and customers in addressing
various aspects of load shedding.
Reporting formats are provided as annexes to facilitate the collection of essential load data.
[NOTE where will this doc be referred to in regulations so that all stakeholders can be called to
account/comply??]
2 Normative references
The following documents contain provisions which, through reference in this text, constitute
provisions of this specification. All documents are subject to revision and, since any reference to a
document is deemed to be a reference to the latest edition of that document, parties to agreements
based on this specification are encouraged to take steps to ensure the use of the most recent
editions of the documents listed below. Information on currently valid national and international
standards can be obtained from Standards South Africa.
(DRAFTING NOTE ..to be included).
NRS 048-9:2009 4
3 Terms, definitions and abbreviations
For the purposes of this specification, the following terms, definitions and abbreviations apply.
3.1 Definitions
load curtailment
load reduction obtained from customers who are able to reduce demand on instruction.
NOTE: This load reduction is typically effected within 6 hours of the instruction being issued.
load shedding
load reduction obtained by disconnecting load at selected points on the transmission or distribution
system.
automatic load shedding
load that is shed by automatic defence schemes in response to a sudden threat to the
system (e.g sudden trip of several generation units)
manual load shedding
load that is removed by a human operator
load reduction
the reduction in system load that can be achieved by load curtailment and/or load shedding.
NOTE: This may be required in order to: (i) balance system demand in relation to the available generation capacity at the time; and/or (ii) prevent overloading of transmission or distribution networks in the event of a network emergency.
national load reduction
load reduction interventions required on a national level in response to national generation
capacity shortages
regional/local load reduction
load reduction interventions required to address local power system capacity constraints.
NOTE: Although in some cases national schedules can be applied on a regional basis, the nature of the local event will determine what load should be reduced.
rotational load reduction
regular shedding and/or curtailment required to manage demand over an extended period of
time or for several load reduction events over a period of time, which spreads the requirement
to reduce load over a wider customer base.
emergency load reduction
load reduction in response to an unplanned event or series of unplanned events on the
system.
NOTE: These unplanned events could occur even when a healthy system reserve margin exists, and could be rotational should the event(s) last a few days
planned load reduction
rotational load shedding / curtailment undertaken over an extended period of time to manage
the system
NOTE Planned load reduction is a last resort, after alternative demand reduction or energy
saving measures have been exhausted
essential load requirement
5 NRS 048-9:2009
minimum customer load requirement (e.g. MW, notification time, and duration) to avoid a direct and
significant impact on the safety of people, the environment, and physical plant/equipment, and
which has been specifically notified as such by the customer to the licensee (See essential load
requirements data format in Annex B)
NOTE 1: The load required is generally part of the total load that a customer installation normally requires. A customer will be required to demonstrate the potential impact on safety, the environment, and physical
equipment when notifying the licensee. The essential load requirement may be subject to verification by
the licensee in terms of the criteria in this CoP ].
Drafting note - in requirements - customer to regularly update if any changes to
processes/plan/envirnoment , etc
NOTE 2: The load may be part of a larger installation that will still be required to participate in load shedding or curtailment schemes. NOTE 3: Not contracted (as no guarantee can be given).
NOTE 4: These loads should receive priority during restoration of the system (e.g. in the event of a major local interruption, or of a regional or national blackout) and should as far as possible be excluded from at least the initial stages of load shedding/curtailment.
NOTE 5: These loads that in the past were categorised as SATEPSA loads under the Republic of South Africa Telecommunications and Electrical Power Supply Authority.
critical loads
loads that should as far as possible be protected from the impact of load shedding or loss of supply
in order to either maintain the operational integrity of the power system, or to avoid a cascading
impact on public infrastructure. (e.g. refineries, fuel pipelines)
NOTE: Protection from the impact of load shedding includes measures such as excluding from load shedding schedules, installing back-up facilities, or implementing specific response protocols.
interruptible loads
loads where customers have signed long term contracts with a licensee, whereby the licensee may
interrupt a certain amount of load for a particular time period as a planned load intervention.
NOTE: These loads can specifically be used earlier in the merit order to reduce the possibility of a load reduction event.
customer
person or legal entity that has entered into an electricity supply agreement with a licensee
Demand market participation customers
customers who have signed a contract with their supplier or with Eskom to offer a portion of
their load at a price, for the purposes of load reduction.
NOTE: Depending on their participation parameters, these customers may be categorised as Instantaneous DMP (IDMP), Emergency DMP (EDMP) or Supplemental DMP (SDMP) customers (DRAFTING NOTE: CONSIDER REMOVING)
extra high voltage network
EHV network
set of nominal network voltage levels that are used in power systems for bulk transmission of
electricity in the range 220 kV Un 400 kV
[SANS 1019]
high-voltage network
HV network
NRS 048-9:2009 6
set of nominal network voltage levels that are used in power systems for bulk transmission of
electricity in the range 33 kV Un 220 kV
[SANS 1019, modified]
interruption
phenomenon that occurs when one or more phases of a supply to a customer or group of
customers are disconnected for a period exceeding 3 s
[NRS 047-1]
planned interruption
interruption that occurs when a component is deliberately taken out of service (by the licensee
or its agent) at a selected time, usually for the purposes of construction, preventative
maintenance or repair
[NRS 047-1]
unplanned interruption
interruption that occurs when a component is taken out of service immediately, either
automatically or as soon as switching operations can be performed, as a direct result of
emergency conditions, or an interruption that is caused by improper operation of equipment or
human error
[NRS 047-1]
licensee
body, licensed by the National Electricity Regulator, that generates, transmits or distributes
electricity
NOTE Such a body can be a direct licensee, or an agent (subdistributor) of the licensee.
low-voltage network
LV network
set of nominal network voltage levels that are used for the distribution of electricity, the upper limit of
which is generally accepted to be an a.c. voltage of 1 000 V or a d.c. voltage of 1 500 V
[SANS 1019, modified]
medium-voltage network
MV network
set of nominal network voltage levels that lie above low voltage and below high voltage in the range
1 kV Un 33 kV
[SANS 1019, modified]
major system event
define (needed?) NOT same as for reporting in part6
point of supply
point at which the electrical installation of a customer (on any premises) is connected to the
transmission or distribution system of the licensee (undertaker)
power system frequency
fundamental frequency
7 NRS 048-9:2009
frequency of alternating voltage generated by power system generators
[SANS 61000-4-30]
3.2 Abbreviations
NERSA: National Energy Regulator of South Africa
NRS 048-9:2009 8
4 Requirements – load shedding and curtailment
4.1 Application by licensees
Licensees are required to develop load shedding schedules that take into consideration the
practices in this document (including the manner in which identified categories of critical and
essential loads are addressed).
4.2 Application by customers
Customers should take appropriate precautions or protective measures to prevent, or at least limit,
threat to life, danger to environment, or damage to equipment in the event of load shedding, an
interruption, or load restoration.
4.3 Principles – load shedding
4.3.1 Stages of load shedding
Load shedding shall be undertaken in accordance with published schedules. These schedules
shall be designed to be rotational, should the need for protracted load reduction arise. The
schedules are prepared for the different system requirements (determined by the severity of the
capacity short-fall at the time).
These requirements are defined by the following stages:
Stage 1 (Scheduled): 1000 MW of national (Eskom Distribution and Municipal) load shall
be scheduled for shedding, with customers impacted for predefined intervals. Schedules
shall be prepared from 06:00 – 22:00 daily. Customer loads are assigned to specific time
slots.
Example : Published schedules may indicate that customers are impacted for 2h every 2nd day
(excl. Sunday). In practice, each time slot may overlap its adjacent time slot by an additional 0,5h
to facilitate smooth change over.
Stage 2 (Scheduled): 2000 MW of national (Eskom Distribution and Municipal) load is
scheduled to be shed at 2 hr intervals every day, for example by doubling the frequency of
first 1000MW block.
Stage 3 (Scheduled): Emergency schedules are prepared or an additional 2000 MW, on a
24 hour basis, but might not necessarily be published.
Stage 4 (Unscheduled): The amount of load required to be shed in Manual Load
Shedding Stage 4 is greater than 4000MW. The management of manual load shedding
for Stage 4 is handled in accordance with the situation prevalent at the time.
NOTE: The above includes limited curtailment of Dx customers …. t
Load curtailment in the case of key industrial customers (isolatable loads) – Eskom Key Industrial
Customers …
4.3.1 Principles
A coordinated approach to load reduction shall be developed for the first 3 stages based on the
following principles:
Principle 1: Automatic under-frequency load shedding shall take precedence over manual load-
shedding or curtailment (see note 1).
Principle 2: All customers shall be considered for emergency (manual) load reduction (see note 2).
9 NRS 048-9:2009
Principle 3: Critical and essential load requirements shall be addressed in accordance with this
code of practice.
Principle 4: Time-based manual load shedding shall be applied (see note 3).
Principle 5: Load shedding schedules shall be developed and made available to affected
customers.
Principle 6: Customer reduction due to ECS shall not be considered as emergency load reduction
(see note 4).
NOTE 1: Although both automatic and manual load shedding initiatives respond to supply constraint problems, the conditions that they respond to and the consequences of their failure to respond are very different. Manual load shedding is pro-active, whilst automatic load shedding is an automatic reactive response to an unplanned loss of generation. The consequences of an inadequate automatic response can be catastrophic and widespread, which includes the complete loss of supply to the entire network. For this reason, continuous load shedding beyond 4000MW is not scheduled – as the impact of this on under-frequency schemes places the system at significant risk. NOTE 2: Manual load reduction is an unavoidable event to prevent the power network sliding into an unstable state. The financial implications associated with a national blackout far outweigh the economic cost of manual load shedding. Economic reasons alone are therefore not sufficient to justify exclusion from the emergency load reduction. NOTE 3: Time-based manual load shedding is chosen for the following reasons : (i) Customers generally prefer to know when their supply will be interrupted so that they can better plan their operations / arrangements, (ii) the communication of load shedding schedules is less onerous; (iii) less confusion exists amongst customers about when their supply will be interrupted. NOTE 4: Customers not achieving Energy Conservation Scheme (ECS) targets are penalised in terms of the ECS scheme. Load reduction requirements are demand (MW) driven, whilst ECS targets are energy-based (MWh). Emergency load shedding will require an instantaneous demand reduction.
The management of manual load shedding for Stage 4 of manual load shedding is explicitly
excluded from these principles and will be handled in accordance with the situation prevalent at the
time (see note below)
NOTE 5: For Stage 4 of manual Load shedding to be activated, the implication is that the implementation of all other mitigation actions and initiatives has been exhausted. This means that the supply constraint is extremely serious and bordering on a total collapse of the entire network load. Under these conditions, the focus is entirely on managing the network from a technical point of view ie. to avoid a total loss of load on the entire network. The consequence of a total loss of load is that cold start sequences will have to be initiated which could take many hours before any load is restored. Therefore technical considerations take preference over customer considerations.
4.4 Development of schedules
4.4.1 Calculation of load shedding quotas per region
In determining load shedding quotas for the various licensees, the following methodology shall be
applied:
The total Distribution Load, excluding key industrial customer load under the control of a
specific Eskom Distribution Control Centre is determined.
From this total load, load set aside for national load management by the National System
Operator is subtracted to obtain the base load on which the required reduction for that
Eskom Distribution Control Centre is determined.
The revised load of each Eskom Distribution Control Centre is summed to obtain a revised
load for overall Distribution.
NRS 048-9:2009 10
Each Eskom Distribution Control Centre’s base load is divided by the overall Distribution
base load to calculate it’s required contribution (as a percentage).
Each Eskom Distribution Control Centre’s contribution to the total load shedding
requirement at any point in time is determined by this percentage.
The same method of allocation will be applied to municipal and metro licensees, when
allocating the percentage of the Eskom Distribution Control Centre load.
NOTE: The above is equivalent to the allocation of an individual licensee being determined by the National System Operator, based on the national load reduction requirement.
The above calculation determines the load to be shed continuously over the full period of load
shedding. An individual licensee may choose be completely shed in lieu of implementing its own
rotation. This shall be undertaken in consultation with the upstream licensee supplying this
licensee. The final arrangement shall not negatively impact the integrity of the load shedding
schedule.
4.4.2 Time-based load shedding schedules
A licensee shall develop a time-based load shedding schedule.
Where manual load shedding occurs repeatedly at the same time of the day for successive manual
load shedding events, the manual load shedding schedule that is in force (Schedule A) should be
replaced by another manual load shedding schedule (Schedule B) where the planned customer
loads in any time slot are different.
Both schedules shall comply with the principles laid out in this document. When allocating a
customer to a particular time slot in the schedule, the impact to the customer and / or other affected
parties should be considered. As far as is practical, all possible options should be explored and
taken into account to minimise the impact to those affected by the interruption of the electricity
supply e.g. trying to avoid interruptions to city centres during peak traffic times, etc
NOTE: The purpose of this hybrid approach is to assist with equity in supply interruptions amongst customers.
4.4.3 Addressing under-frequency protection requirements in schedules
The integrity of automatic under-frequency protection schemes shall be maintained during load
shedding/curtailment.
To address the implications of load being shed or curtailed also being required for under-frequency
load shedding during a particular Stage, the following procedure shall be applied:
For the first 10% of system load required for automatic under-frequency load shedding, a
percentage of this total requirement may be allocated to various time slots on the load
shedding schedule.
A proportionate increase in the available load for under-frequency load shedding scheme is
then implemented to address the load that may not be available in any given time slot.
An example of coordinating under-frequency load shedding scheme requirements with load
shedding schedules is provided in Annex C.
4.4.4 Catering for special events
In the case of a special event (such as a national sporting event involving large numbers of people),
certain loads may be temporarily protected from load shedding. It shall be the responsibility of the
licensee to revise the schedules whilst still ensuring that the required load to be shed is available.
In exceptional cases of national or regional interest, an agreement may be reached between two or
11 NRS 048-9:2009
more licensees to revise load shedding schedule in a manner that does not compromise the overall
load shedding requirement.
NOTE: The implication is that more load shedding will be required in other parts of the network.
4.4.5 Customer load curtailment option
A licensee may identify specific customers that, in lieu of being shed, can provide a pre-defined
amount of load to be curtailed on instruction from the licensee.
These customers will typically be larger customers, for which the following criteria shall apply:
The required load curtailment can be measured.
Protection of this customer from load shedding shall not exclude other customers from load
shedding due to network limitations.
The reduction can be effected within an agreed time frame.
The essential load requirement is met.
Actual load curtailment events meet the requirement agreed on with the licensee.
A licensee shall use load curtailment information provided by such customers to develop a
coordinated load curtailment plan. (Annex A provides an example of an information gathering
sheet). A licensee cannot guarantee that the notified requirements for load curtailment can be
accommodated.
A licensee shall ensure that such curtailment is coordinated with automatic under-frequency load
shedding requirements.
4.4.6 International customers
Cross-border load to other utilities supplied by South African generators shall be treated equitably
with South African customers in the event of national or regional load reduction. Cross-border load
reduction requirements shall be at least the same percentage as the load reduction required in
South Africa.
NOTE: This requirement implies that energy sales from South Africa be reduced. In the event that this power is wheeled from one country to another, the reduction requirement would not apply.
4.4.7 Exclusions based on participation in load reduction
Interruptible loads, which contribute to load reduction on a regular basis, are generally excluded
from manual load shedding schedules. Under emergency conditions, specific agreement may be
reached with these customers on further load curtailment.
Where it is technically feasible to isolate such customers, demand market participation customers
who participate with a minimum of 25% of their total load shall only be included in Stages 3 or 4.
Emergency DMP customers who participate with a minimum of 40% of their total load shall only be
included in Stages 3 or 4.
4.4.7 Changes to load shedding or curtailment schedules
The ability to adjust schedules is important to limit societal impact of load shedding. Such
adjustments may be:
Planned – for example in the case of a major sporting event, certain sites may be removed
from the schedules
Unplanned – for example in response to a concern raised during load shedding w.r.t. to a
critical load.
4.5 Communication
NRS 048-9:2009 12
4.5.1 Information related to load shedding schedules
Licensees shall make load shedding schedules available to their customers. Such schedules may
be published in print media, available on a website, and/or attached to electricity bills.
An appropriate mechanism for communicating changes to schedules shall be implemented.
4.5.2 Prior notice of load shedding
Customers shall be notified when there is a high degree of certainty that load shedding may occur.
4.6 Reporting requirements
For a given load shedding event, a licensee shall be in a position to report:
The actual load shed in each time period
The time for which specific feeders / customers were shed.
NOTE: NRS 048-6 requires that load shedding events be removed from interruption performance reporting.
Use of contracted ILS and DMP customers to manage load shall not be reported as part of load
shedding or curtailment.
5 Requirements – essential loads
5.1 Application by licensees
Licensees are required to collect essential load data and to appropriately address customer
essential load requirements.
A licensee shall provide its upstream electricity supplier with the power supply requirements to meet
its essential load requirements (i.e. its own essential loads and that of its customers).
NOTE: A licensee cannot guarantee that these can be met for all supply emergencies.
5.2 Application by customers
Customers shall notify their licensee of their essential load requirements.
5.3 Identification
Essential loads are identified by customers within their own business environment. Ideally,
customers inform their supply authority of such essential loads by completing and submitting
standard forms designed for this purpose. The relevant supply authority shall collate such
information and compile a registry of essential loads within their area of supply.
Define three categories in detail
- requirements for load shedding vs restoration
- Add annexure
- Motivation required and
- what if customer does not have essential loads (do they need to )
- List responsibility re information
- Clear note on the legal limitation of liability
- Update requirements (every 2 years) or if customer aware of significant change
13 NRS 048-9:2009
- New customers and old customers with new plant
- Every “LPU” should provide
- Communication to customers – how do they know to fill in (one month a year on the
electricity bill)?
6 Requirements – critical loads
6.1 Application by licensees
Licensees are required to appropriately address critical load requirements as defined in section 7.
NOTE: A licensee cannot guarantee that these can be met for all supply emergencies.
6.2 Application by customers
Customers operating critical and essential loads should evaluate their level of preparedness in
terms of the practices in this code of practice (section 7).
4.8 General
All customers shall be entitled to provide licensees with essential load data. Customers in the
following categories shall be required to provide essential load details:
Deep level mines (life support systems)
Hospitals & medical centres with life support requirements
Sewerage
Prisons
Refineries
DRAFTING NOT ON Essential load requirements:
“Don’t know what is inside”
Restored first (before critical loads)
Must not be shed unless within agreed time-scales
Reduce to essential load requirement (in stage 4 – make safe)
The following loads shall be considered critical loads:
Public transport (e.g. rail, airports)
Water pumping (power station requirements)
Refineries
Fuel pipelines
Coal mines supplying power stations
Essential services (e.g. police, fire fighting)
Telecommunications infrastructure (exchanges)
Traffic lights
DRAFTING NOTE on Critical loads
House of cards / disproportionate impact on society / impact on power system
Do not shed or other measures
Do not have to restore
Keeping business as usual going
4.8 Requirements for specific types of loads
4.2.1 General
NRS 048-9:2009 14
The loads defined below are customers that should be specifically addressed to understand the
implications of load shedding.
NOTE – this information requires significant interaction with relevant stakeholders
NOTE – need to address relevant Regulators (civil aviation authority, road traffic authority, ICASA)
NOTE – set up meetings Eskom/AMEU joint
NOTE – drive each of these industries to develop dove-tail standards or regulations.
ACTIONS:
Pravind – Begin setting up meetings with customer groupings
Jose – EDNO staff nationally to identify “deal breakers”
All WG members: examples of critical loads and how they are dealt with in Metros’ etc.,
4.2.3 Airports
4.2.3.1 Category 1 – Airports
Look at requirements in Civil Aviation Act etc … Ciil Aviation Authority / ACSA
4.2.3.2 Category 2 – Metro Rail
Metro rail shall be excluded from schedules.
4.2.3 Rail
4.2.3.1 Category 1 – Metro Rail
Airports are …..
4.2.3.2 Category 2 – Goods Transport
Metro rail shall be excluded from schedules.
4.2.4 Traffic lights
The electricity supply infrastructure to traffic lights generally does not allow for isolation in the event
of load shedding.
All traffic light installations shall be fitted with reflective indicators in the event of an interruption in
supply during the night.
Three categories of traffic light installations shall be identified.
4.2.4.1 Category 1 – high impact intersections
These intersections are defined as those that would lead to significant congestion on major
highways, or in central business districts.
Backup systems shall be implemented at these intersections. These backup systems shall be able
to support supply for a minimum of 4 hrs following an interruption in supply.
Alternatively, contingency plans shall be implemented at tehse intersections to ensure that traffic
flow is maintained within 30 min of an interruption.
4.2.4.2 Category 2 – medium impact junctions
15 NRS 048-9:2009
Contingency plans shall be implemented at these intersections to ensure that traffic flow is
maintained. Plans may include the coordinated deployment of traffic officials, based on the
schedules.
4.2.4.1 Category 3 – low impact intersections
No specific interventions are required.
4.2.2 Water
4.2.4.1 Category 1 – supply to power stations
Water supply to power stations shall be excluded from load reduction requirements.
4.2.2 Sports Stadiums
4.2.4.1 Category 1 – supply to power stations
Sports stadiums.
4.2.2 Sewerage
x:
4.2.2 Refineries and fuel pipe lines
Refineries and fuel pipe lines shall be excluded from load shedding schedules.
4.2.2 Mines supplying power stations
Mines supplying power stations shall be excluded from load shedding schedules.
4.2.2 Educational facilities
Educational facilities shall be :
4.2.2 Essential services
Police fire fighting:
4.2.2 Telecommunications infrastructure
x:
4.2.2 Hospitals and medical centres
State and private hospitals shall be treated equitably.
4.2.2.1 Category 1 – tertiary hospitals
Hospitals shall be .
NRS 048-9:2009 16
Protocols shall be in place for hospitals to contact the local operations centre directly in the event of
an emergency.
4.2.2.1 Category 2 – secondary hospitals
d.
4.2.2.1 Category 3 – clinics and medical centres
d.
4.4.2 Category 1 – danger to life and safety
x
4.4.3 Category 2 - environmental or health hazard
Danger to life and safety
4.4.4 Category 3 – nationally critical product
Destruction or damage to plant, equipment, or facilities which would disrupt production of a
nationally critical product
17 NRS 048-9:2009
Annex A
Load shedding data for planning curtailment schedules
General information
Type of Plant e.g. Mining
(open cast) Mining (deep
level)Furnaces (open arc)
Max Power (in
MW)
Transmission Substation Distribution
Substation
Impact of opening breaker Supply Voltage
MW Category A load Comment
MW Category B load Comment
MW Category C load Comment
MW Category D load Comment
Section 1: Emergency reduction possible if required ―immediately‖
Please indicate amount of load
to be reduced, and how much of
this forms part of the UFLS
scheme
MW UFLS
CVA stage
UFLS
Mandatory stage
Load that can
be reduced
in:
10 min
20 min
30 min
1 hr
2 hrs
4 hrs
6 hrs
Section 2(a): ―Preferred load reduction time frame‖
Provide profile for 10% and 20% reduction
Minimum notification period
MW that can be reduced and time it can be reduced for
MW1 T1
MW2 T2
MW3 T3
Section 2(b): Restoration requirements – provide profile of ramp up
Provide profile for restoration of 10% and 20% reduction
MW1 T1
MW2 T2
MW3 T3
Conditions for restoration (e.g. no
interruption for 24 hours)
Section 2(c): Time between reductions
Time between interruptions
Section 3: ―Safe Mode‖ operation
Minimum MW required for operating
in ―safe mode‖
Notification (hours) required to get
into this mode of operation
Duration that plant can be run in this
19 NRS 048-9:2009
Annex B
Essential load data for system restoration planning and load shedding
ESSENTIAL LOADS IN CASE OF NETWORK COLLAPSE AND RESTORATION Details regarding requirements for return of electrical power supply & priority of restoration after a
national or regional large-scale network collapse to be recorded in this appendix. Typically, there would be a total loss of power and the details submitted are required to determine the
duration before which and extent of power that should be returned to the customers site. All production would be shut down, and minimal power will be made available for the purposes of
o Avoiding danger to life & safety of persons o Avoiding a potential hazardous condition from developing o Shutting plant down safely.
No provision to be made to continue with normal or reduced production until after the emergency has been concluded.
CATEGORY 1A: RETURN POWER TO PREVENT DANGER TO LIFE AND SAFETY
HOURS MVA Please describe plant in
the space below General comments
Maximum
permissible
duration of power
interruption before
dangerous
condition/s develop
(Explanation − the amount of time before conditions become life threatening)
Survival Load required
once power has been
returned after the
above interruption
(Explanation − the amount of load required torequired to effectively remove personnel or prevent the dangerous condition from developing. (Not intended for continuous use, but for purposes of a controlled and safe shutdown/ evacuation etc)
Details of
plant/equipment/facilitie
s which will be operated
by the power detailed
herein. (For example, Winders, vent fans, dewatering pumps, etc.)
CATEGORY 2A: RETURN POWER TO PREVENT A POTENTIAL ENVIRONMENTAL OR
HEALTH HAZARD
Maximum
permissible
duration of power
interruption before
potential hazard
develops
(Explanation − length of time before an outage (complete interruption) causes
damage to a resource
or results in a
legislated limit ( eg
environmental or
occupational hygiene
limits) to be
exceeded
Survival Load required
once power has been
returned after the
above interruption
(Explanation − the amount of load needed to bring the limits back to acceptable levels. If the load needs to be continuous, please indicate this ) (Not intended for continuous use, but for purposes of a controlled and safe shutdown if possible)
Details of
plant/equipment/facilities
which will be operated by
the power detailed herein.
(For example dust control plants, oil water separation units, sewer pumps etc.)
HOURS MVA Please describe in the space below
General commentsHow is it required?
NRS 048-9:2009 20
CATEGORY 3A: RETURN POWERTO PREVENT THE DESTRUCTION OF, OR DAMAGE TO,
PLANT/EQUIPMENT OR FACILITIES WHICH WOULD DISRUPT PRODUCTION OF A NATIONALLY CRITICAL PRODUCT.
Maximum
permissible
duration of power
interruption before
damage or
destruction occurs
(Explanation − the amount of time before plant/equipment/facilities will incur damage. This applies only to plant/equipment or facilities and not the product itself. If the plant/equipment/facility will be instantly damaged or incur irreversible damage, please describe in field provided)
Survival Load required (Explanation − the amount of power following an interruption that will be needed to prevent damage to the plant/equipment/facility. This may imply the need for continuous load but ideally should be the amount of load needed to ramp down the plant/facility in a non-damaging way. Please describe the load ( continuous or ramp-down) in the field provided)
Details of
plant/equipment/facilities
which will be operated by
the power detailed herein.
(For example smelters,, silting of pipelines, freezing of charge or chutes etc)
HOURS MVA Please describe in the space below
If the plant/equipment/facility will be instantly damaged or incur irreversible damage, please
describe in field belowGeneral comments
SUMMARY FOR ALL THREE CATEGORIES
Category
Time (hours) Survival Load (MVA)
1A1
2A2
3A3
TOTAL
NOTE: Categories 1, 2, and 3 should be mutually exclusive of each other.
21 NRS 048-9:2009
ESSENTIAL LOADS IN CASE OF CONTINUOUS LOAD-REDUCTION/LOAD-SHEDDING/CURTAILMENT Details regarding application forthe electrical power requirements during emergency situation where
load is curtailed to customers without an interruption are to be recorded in this appendix.. This is the power required to sustain life, prevent violation of legislated limits and prevent damage to
equipment/plant/facilities for a limited period during a limited emergency. Typically, the outage reduction would last a few hours, generally according to a schedule. Customers
to also supply details where extended durations could cause further damage, which may not be realised if the durations where confined to a few hours.
The numbers here refer to load needed to maintain the plant in stasis without a complete shutdown. No power will be available for production requirements, just for temporarily sustaining life until the
load shedding has been switched to another location. s, just for temporarily sustaining life until the load-reduction (load-shedding) has been switched to another location.
CATEGORY 3B: REDUCE POWER TO A LEVEL THAT PREVENTS THE DESTRUCTION OR
DAMAGE TO PLANT/EQUIPMENT/FACILITIES WHICH WOULD DISRUPT PRODUCTION OF A NATIONALLY CRITICAL PRODUCT
Minimum Notification
period required before a
reduction of power
supply
(Explanation − the amount of time required to ensure that plant/equipment or facilities can be shutdown or ramped down so that no destruction or damage occurs)
Minimum Load
required
(Explanation − the amount of power required to continuously operate plant/equipment/facilities such that damage or destruction does not occur – i.e after ramp down period – Amount of power required to maintain the status of the plant/equipment/facility
) (i.e. reduce to include CAT 1B and 2B)
Details of
plant/equipment/fa
cilities which will be
operated by the
power detailed
herein. (Please describe what plant will be run by the power required)
In the event of being
shed without being
reduced , is the amount
of load needed different?
(Explanation − Sometimes the amount of load needed to restart critical equipment-processes is greater than the running load – Please supply details.)
HOURS MVA Description of
minimum load MVA Please
give
details.
CATEGORY 2B: REDUCE POWER TO A LEVEL TO PREVENT A POTENTIAL ENVIRONMENTAL OR HEALTH HAZARD
Minimum Notification
period required before a
reduction of power
supply (Explanation − of the amount of time required to ensure that all activities are completed to avoid damage to a resource and/or to avoid exceeding a legislated environmental or health limit .)
Minimum Load
required
(Explanation − the amount of power required to continuously to keep the system from exceeding legislated contamination limits for the period of the scheduled load-shedding)
Details of
plant/equipment/fa
cilities which will be
operated by the
power detailed
herein. (Please describe what plant will be run by the power required)
In the event of being
shed without being
reduced, is the amount of
load needed different? If
so, how much is it?
(Explanation − Sometimes the amount of load needed to restart critical equipment-processes is greater than the running load – Please supply details.)
HOURS MVA Description of
minimum load MVA Please
give
NRS 048-9:2009 22
details.
CATEGORY 1B: REDUCE POWER TO A LEVEL THAT DOES NOT ENDDANGER TO LIFE AND SAFETY
Minimum Notification
period required before a
reduction of power
supply
(Explanation − the amount of time required to ensure that all activities can be performed to ensure that no
dangerous condition can
develop).
Minimum Survival
Load required
(Explanation − the amount of load needed to keep the conditions in the plant/facility habitable without performing any actual work or production. People should be able to stay where they are safely for the duration of the load-reduction (load-shedding)0 and will not have to be moved. Therefore, power required for evacuating personnel should not be included. Please include power required to restart critical equipment)
Details of
plant/equipment/fa
cilities which will be
operated by the
power detailed
herein. (Please describe what plant will be run by the power required)
In the event of being
reduced without being
shed, is the amount of
load needed different?
If so, how much is it? (Explanation − often the amount of load needed to restart critical equipment is greater than the running load. If load critical to sustaining life needs a high start-up power, please put into the below field, while continuous running values can be placed here)
HOURS MVA Description of
minimum survival
demand
MVA Please
give
details.
SUMMARY FOR ALL THREE CATEGORIES
Category
Time (hours) Time (hours)Minimum Survival load (MVA)
Reduced Load (MVA)Demand (MVA)
3B1
Power to maintain Life & Safety
2B2
Power to prevent Environmental or Health Incident
1B3
Power to prevent damage to equipment etc
TOTAL
23 NRS 048-9:2009
3. Official(s) to be contacted during emergencies related to power supplies: OFFICIAL(S) TO BE CONTACTED DURING EMERGENCIES RELATED TO POWER SUPPLIES
Official 1: (Primary Contact) Name
Designation
Telephone
Fax
Cell phone
Official 2: (Secondary Contact) Name
Designation
Telephone
Fax
Cell phone
Official 3: (Alternativee 1) Name
Designation
Telephone
Fax
Cell phone
Official 4: (Senior Manager In charge – Last Resort Contact) Name
Designation
NRS 048-9:2009 24
Telephone
Fax
Cell phone
Details of generally manned station such as the Mine Rescue Team ( Proto Team) or main security offices: Name
Designation
Telephone
Fax
Cell phone
4 Do you have any other means by which the above persons may be contacted, for example , radio, satellite, etc? Give details: ……………………………………………………………………...............................................
5 REMARKS
Can you offer any further information or motivation that not captured elsewhere in this questionnaire that will be useful in identifying and evaluating your requirements during emergencies related to power supplies?
…………………………………………………………………………………………………………………
25 NRS 048-9:2009
Annex C
Example of the calculation of schedules taking automatic under-
frequency load shedding into consideration.
Given a UFLS 1st stage set of loads totalling 100MWs, 105% of the requirement, and a schedule of
10 time slots:
Time slot Manual
loadshedding
UFLS on
loadshedding
UFLS
available
UFLS %
available
6-8 200 11 89 93%
8-10 200 8 92 97%
10-12 200 12 88 92%
12-2 200 9 89 93%
2-4 200 10 90 95%
4-6 200 10 90 95%
6-8 200 11 89 93%
8-10 200 9 91 95%
10-12 200 10 90 95%
What can be seen is that the UFLS loads are split among all the various time slots. This means
that all the loads contribute to loadshedding, but the UFLS system is not materially affected. The
gap is only the amount of UFLS used at any one time, in this case the largest is 12MWs, which
reduces the scheme in the worst case to 92% of requirement. Therefore an additional installation of
12MWs of UFLS will cover the deficit.
The downside is a slight overshedding during a UFLS event, when not loadshedding, which is
likely.
Bibliography
NRS 048-4, Electricity supply – Quality of supply – Part 4: Application guidelines for utilities.
NRS 048-6, Electricity supply – Quality of supply – Part 6: Medium voltage network interruption
performance (In course of preparation.)
© Standards South Africa