Eskom Energy Emergency Preparedness - Tjaart van der Walt National Operations
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Eskom Energy Emergency Preparedness
Tjaart van der Walt
National OperationsLONG TERM CAPACITY SHORTAGES
• Eskom may face the possibility of generation inadequacy
• It is preferable to shed load in an emergency on the IPS for a
short period rather than risk system security by operating for
extended periods with low frequency and voltage
• Any operation at low frequency causes a slowing down or
electrically driven plant auxiliaries and may make it impossible
to increase or even maintain station generation
• All requests for load reductions/restoration are co-ordinated
through the Distribution NMCs by National Control
• This presentation highlights actions when such emergencies do
occur and does not show Eskom’s mitigation plans for such
emergencies not to occur
2DAILY GENERATION CAPACITY AND RESERVES
• Objective of daily operation
– Operate generation capacity as to deliver reasonable protection
against:
y load forecasting errors
y equipment failures
– Ensure adequate regulation of frequency and power flows on
transmission lines
• Interruptible load is a generation reserve
– Not part of the load shedding quota of the under-frequency load
shedding schemes
– Where possible, interruptible load should be used before UFLS and
manual load reduction
• Guidelines for the amount of spinning and operating reserves
required on the IPS are contained in Procedure OP16 and OP17
3SYSTEM CONTROL STRUCTURE
765 - 220 kV System Control
NC
TOC 132 - 66 kV Operating Control
Dx Controls
66 -11 kV
Reticulation Controls
Power Station Controls P.S. Auxiliaries
4CONTROL CENTRES
TOC
132 kV
NMC NMC
Witbank Central
66 kV 66 kV
Bloemfontein Mkondeni
132 kV NC 132 kV
765 kV
Legend:
System Control
Bellville Sunilaws
132 kV 132 kV TOC
Dx Control
Both
5RESPONSIBILITIES DURING EMERGENCIES
• NATIONAL CONTROL CENTRE
– Ultimate authority over and responsibility for operating the
Eskom IPS
– Advance Warning of Capacity Defects
y National Control shall give notice of a future generation deficit
by issuing the appropriate warning instruction, depending on the
severity of the emergency
y The warning will be issued to Distribution NMCs, directly or via
Distribution NMCs to the Power Station Control Rooms, SAPP
members and customers
6RESPONSIBILITIES DURING EMERGENCIES cont.
• DISTRIBUTION CONTROL CENTRES
– Load curtailment and/or load shedding after instructions by
National Control
– Restoration of load after instruction from NC
– Switching, generation dispatch and voltage control in the
event of a complete breakdown of all avenues of
communication with NC
– NOT Municipal generation assistance as this is requested by
NC
– NOT DMP requests as this is the function of NC
7COMMUNICATION
• Control to Control
– Warnings
– System/DMP changes
– Instructions
• Back office to Back office
– Other information
• Communications department to consumer
8FREQUENCY DECAY
• Rapid freq. decline
–Mainly due to incidents
–Generation reserves utilised
–Human action too slow
–Automatic emergency schemes utilised
• Gradual freq. decline
–Mainly due to load pickup
–Generation reserves utilised
–Controller action adequate
–Manual emergency schemes utilised
9SHORT TERM CAPACITY SHORTAGE
• Emergency Resource Merit Order (ERMO)
– Utilised to compensate for the shortage of generation
– The order in which the resources shall be utilised is also given in the ERMO
– The order of resources in this Memorandum is based on the energy bid
price (average over the past month) in increasing price order
– Once a resource is used it is moved to the bottom of the list (for one month)
so that the same resource is not used too often
– Gas turbines are normally included after interruptible load
• Emergency resources may also be called upon for transmission related
emergencies such as incipient voltage collapse or line overloads.
• The ERMO includes various resources to be utilised in a specific order
to recover the frequency to 50 Hz.
10Merit Order for Managing Energy Shortages
R equirem ents S ource of C apacity C riteria for U tilization
Em ergency reserves: at least to cover loss of largest pow er station (3600M W )
O peratio n al g u id elines for n o n-essential B ased on system secu rity & eq u itab le lo ad
M an dato ry L o ad sh ed d ing lo ad s sh ed d in g in ESK O M co n tro l area
G as G eneratio n M u nicipal/ Esko m If availab le
In terru p tible lo ads C o n tracts C ost o f su p p ly op tim izatio n .
All m ach in es th at are capable and
E L1: Eskom generatio n at M C R E sko m G en eratio n availab le.
E sko m g en eration : E n erg y co n strained w ater
reso u rces E sko m G en eratio n B ased o n W ater resou rces in S A.
D em an d M arket P articipation C o n tracts C o n tracts C o n tractual C o st o ptim izatio n .
O perational R eserves: 1900M W requirem ent
In tern atio nal & N atio nal (D M P) n on -firm C on tractu al co sts op tim izatio n &
S u p p lem ental reserves: D em an d + G en eratio n co n tracts & g en eration sup p ly g en eratio n p ro d uction cost op tim izatio n
G en eratio n su p p ly & co ntracted n atio nal C on tractu al co sts op tim izatio n &
10-m inu te reserves DM P g en eratio n p ro d uction cost op tim izatio n
reg u latin g reserv es G eneratio n su p ply G en eration p ro d u ction co st o ptim izatio n
G en eratio n su p p ly & N atio n n o n-firm C on tractu al co sts op tim izatio n &
Instan taneou s co n tracts (D M P) g en eratio n p ro d uction cost op tim izatio n
D em and: Variable M W from day to day
Peak lo ad G en eratio n su p p lies C o st o f p ro d u ctio n
B ase lo ad Im po rts & G en eratio n su p p lies C o st o f p ro d u ctio n
•YTD 4 times the entire emergency merit order has been used
•YTD 1 mandatory load shedding for an energy shortage (2 hours of 250MW on Jan 6 2006)
•Frequency has been allowed to decline to 49.6 Hz for a short period of time on a number of
occasions
11UNSCHEDULED PUMP STORAGE GENERATION
• Starting of units
– In order to prevent the IPS spinning reserve from falling below the
required level
y Units are available
y Sufficient water, should be started
– After a sudden loss of generation or during plant shortages
y Increase the system frequency above unacceptable low frequency
levels
− In order to provide National Control sufficient time to implement other
corrective actions
– Unscheduled Pump Storage generation will be limited to the
minimum time necessary for system security
– Operation procedures for Pump Storage generation will change as
the available water supply changes
12TYPES OF DMP
• Supplemental reserve
–Availability
–Market
• Emergency DMP
• Instantaneous DMP
–49.75 Hz
13SUPPLEMENTAL RESERVE (DMP)
• Communication
– NC to instruct
– NC to inform Regional Control
• Instructions
– As per individual contract
• Implementation
– Customer implemented as per instruction
• Cancellation
– As per instruction period
14Emergency DMP
• Short notice from NC
• Instructed according to ERMO
• Higher cost than Supplemental DMP
• Issued as per individual contract
15EMERGENCY LEVEL 1 WARNINGS
• Maximum Generation Warnings
– National Control shall issue an Emergency Level 1 Warning
y Expected shortfall of spinning reserves
– Sent to:
y Power Stations
y Dx Control centres
– Communicated via SMS
y Eskom staff
– Emergency Level 1 Warning will be cancelled as soon as the
required amount of Spinning Reserve is in hand
16EMERGENCY LEVEL 1 WARNINGS
• Generation Responsibility
– Power Station Control Room shall inform the Senior Shift
Supervisor who shall organise the internal activity of the
station such that, during the period of warning:
y Maximum/Emergency Generation output of the plant is readily
available
y The plant is operated in a manner that will allow rapid increase
to Maximum/Emergency Generation output
y All testing and maintenance on the control and protection
systems that may affect the output of the station and can be
deferred, is halted
17EL1 GENERATION INSTRUCTIONS
• Emergency Level 1 in force
– Instructed:
y Spinning reserve of 500 MW not met and load is still expected to increase
– Cancelled:
y Spinning reserve requirement is met
y Frequency has returned to 50.0 Hz and is expected to remain there for the next 30
minutes
• Units off AGC and go to MCR
• Limited to specific periods for the various power stations
• When EL1 is instructed to the power stations it must be
logged on the facility provided in the control room
18INTERRUPTIBLE LOAD
• Interruptible load shedding
– EL1 in force
AND
y Frequency gradually declines below 49.80 Hz and load is still picking up
or
y Frequency falls rapidly below 49.5 Hz and does not recover within one
minute
• Sufficient interruptible load shall be shed until the
frequency returns to 50 Hz
19GAS TURBINE GENERATION
• All gas turbines will be armed for under
frequency starting at all times
• Order for deployment of the gas turbines shall
be as per the ERMO
• Unit Starting
– Slow frequency decline
y Frequency gradually declines below 49.80 Hz and load is still picking up
– Fast frequency decline
y F < 49.4 Hz for a period longer than 20 seconds
– Only the number of gas turbines sufficient to return the frequency to
49.7 Hz should be started
• Shutdown
– When the frequency has returned to 50.0 Hz
– Gas turbines shall be taken to SCO mode
20MUNICIPAL ASSISTANCE
• Assistance from municipal gas turbines and municipal
operating oil fired stations will be requested when:
– Frequency is expected to fall below 49.6 Hz with all other
emergency measures introduced in the time available
• Purpose
– Prevent the frequency from falling below 49.5 Hz
• Termination
– When the frequency is restored to 49.7 Hz and is expected to
remain above 49.7 Hz for the next 30 minutes
21FREQUENCY RESPONSE
• Affected by:
–Spinning reserves
–Generator governor settings
–Load characteristic
• Eskom’s bias
–125 – 250 MW / 0.1 Hz
22LOAD REDUCTION FOR FREQUENCY CONTROL
• LOAD REDUCTION SCHEMES
–Under frequency
y Automatic
–Voltage / capacity shortage
y Manual
23AUTOMATIC SCHEMES
• Consumer voluntarily automatic under
frequency load shedding (CVA-U/F-LS)
– Arrest rapid frequency decline
– Operated by relays in consumers yards
– Protect the consumers connected to the MA-/F-LS scheme
– Three stages
y 49.2 Hz
y 49.1 Hz
y 49.0 Hz
– 10% of Distribution’s peak
24RESTORATION OF AUTOMATICALLY SHED LOADS
• CVA UFLS RESTORATION
• Only shed load that can be restored without
instruction from National Control
• Requirements
– May be restored by the customer without reference to either
Distributor Network Management or National Control
– F > 49.5 Hz (Relays will only be reset @ this frequency)
25AUTOMATIC SCHEMES cont.
• Mandatory automatic under frequency load
shedding (MA-U/F-LS)
– Operated by relays in Eskom’s yards
– Stabilise rapid declines in system frequency that are not corrected
by the CVA-U/F-LS scheme.
– A total of 40 % of the IPS load must be connected to U/F relays set
at four frequency stages (10 % each stage)
y 48.8 Hz
y 48.5 Hz
y 48.2 Hz
y 47.9 Hz
– The MA-U/F-LS scheme must be applied to every Distribution
network
– CVA-U/F-LS consumers should be omitted from this scheme or
connected at the lower frequency levels
26MANUAL REDUCTIONS
• Purpose
– Stabilise gradual declines in system frequency
y By reducing load on a pro rata basis in all Distribution networks
− Through curtailment or shedding
• Two categories
– Load curtailment
y Disconnected voluntarily by consumers
y Within a set time delay (1 hour)
y Following an instruction by National Control to reduce load
– Load shedding
y Shed manually at convenient points on the distribution system
y Within a set time delay (10 min)
y Following an instruction by National Control to shed load or reduce load
– Time delay for load shedding is appreciably less than the time delay
for load curtailment
27Load Reduction
MANUAL LOAD REDUCTION
MANUAL
LOAD CURTAILMENT
LOAD SHEDDING
Not selective Action taken Selective for
Short Notice Action by Eskom Longer notice
for consumer by customer consumer
Minimum 1 hour
Within 10 min
notification
28LOAD REDUCTION INSTRUCTION
• Instructed as far in advance as possible
– Time that the reduction is to commence
– Amount of load
– Expected duration
• If the load profile changes NCC will cancel the
instruction before the time
• Restoration only takes place on instruction from
NC
29LOAD REDUCTION ACTIONS
• Distribution
– Distribution networks may decide whether to approach consumers for load
curtailment or to shed load manually on a pro rata basis to achieve the
requested load reduction at the required time
– Consumers on curtailment must be notified and instructed to curtail desired
amount of load at specified time
y This must be verified
– Load reduction must take place at specified time
– Recording and reporting must take place
• Municipalities
– Own generation should be included in the group of consumers who form
part of the load curtailment scheme
– Should be requested to reduce their import when the load curtailment
instruction is given
– Required municipal reduction (in %) should not be less than the
municipalities’ percentage of the total Regional demand
30LOAD SHEDDING WARNING
• It will not always be possible to give
a load shedding warning
• As far in advance as possible
–Time of warning
–Amount of load expected
–NOT expected start time
–NOT expected duration
31WARNING ACTIONS
• Distribution actions
–Prepare for load shedding
–One hour after the warning
y Distribution NMCs shall be able to reduce the required
amount of load within 10 minutes by load shedding.
–This warning enables the Distribution NMCs to
prepare their plans for load shedding
–Preferably no action (i.e. contacting customers)
must be taken when the warning is received
32LOAD SHEDDING INSTRUCTION
• Indications
– Immediate load reduction is required
• Instruction
– Shed amount of required load
• Sufficient load shall be shed to return the
frequency to 49.7 Hz
33LOAD SHEDDING ACTIONS
• Distribution
–The requested load must be shed within 10 min
y If exact amount cannot be shed select the higher of the
two options
–Recording and reporting must take place
34RECORDING AND REPORTING
• Recording/logging
– Which loads were reduced
– Time breaker opened
– Time breaker closed
• Report back
– Amount of load reduced
– Time requested load reduced
35RESTORATION OF MANUALLY SHED LOADS
• RESTORATION
– Gradually restored on instruction from National
Control via the Distributor Network Management
Centres
y If the exact amount cannot be restored select the
lower of the two options
– Frequency is seen to be recovering to 50.0 Hz
AND
– F > 49.7 Hz
36ORDER OF RESTORATION OF ALL LOADS SHED
• Requirements
– Restoration of the majority of load shed by the mandatory automatic UFLS
scheme will have priority over loads shed by the manual UFLS scheme
• Restoration sequence
– Mandatory UFLS stage 4
– Mandatory UFLS stage 3
– Mandatory UFLS stage 2
– Mandatory UFLS stage 1
– CVA UFLS
– Manual LS
– Load curtailment
– Manual load shedding/curtailment may take place to replace load, which was
shed by the different stages of the Mandatory UFLS Scheme
37END THANK YOU
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