Transcript The black start procedures should contain the following

Important definitions
Total System Black Out
The system is said to be under total black out
when all Regional utility generation has ceased to
operate and there is no supply from external
interconnections to the Western grid and it is not
possible for the total system to function again without
black start.
Partial System Black out
Blackout of a particular sonstituent system
either partially or fully or of more than one
constituents’ systems.
System islands
In case, part of the system is separated from
the grid due to system splitting or through defence
schemes and operates independently, it is called
System Islanding.
Normal System Conditions
System will be declared to be normal when all
islands are re-connected, all emergency and essential
loads restored and adequate transmission restored
enabling States to draw their scheduled requirements
from ISGS.
1
The black start procedures should contain the
following minimum details.
1.
Generation Securing
2.
Generation build-up

Survival and Start-up Power of Power Plant(s).

Power Station(s) with Black-start facility.
3.
Build-up of islands
4.
List of black start facilities, interstate/regional ties, synchronizing points and essential
loads to be restored on priority
5.
Detailed State/Utility-wise Restoration
plans
2
SYSTEM RESTORATION APPROACHES
1. In systems with a fair dispersal of Generating stations with black start
facilities, those generating stations where black start facilities are available,
should be started up and islands formed around these generating stations by
connecting essential loads. These islands are then interconnected at predefined
locations where synchronizing facilities are available. The speed of restoration
enhances with increase in number of black start facilities and their dispersal.
Gujarat, Chhattisgarh and M.P have considerable number of black start facilities
while Maharashtra suffers from lack of adequate number of black start
generators. It is required to carefully monitor the operation of the island (reintegration with rest of the grid) due to small stiffness in islands. One engineer
shall be specifically assigned to monitor one island.
2.
While adding loads, care should be taken to ensure step by step
addition keeping in view load characteristics, ie., variation of load with respect
to voltage and frequency and stiffness of island. During cold load pick up
sudden starting of motor loads or power plant auxiliaries like BFP, PA fan etc.,
can cause voltage dips due to drawal of high starting currents. Essential loads
can be restarted in steps smaller than 5 MW. It is preferable to restore rotating
type loads which co~tributes to inertia of the island. In any case, load pick up
should not cause frequency excursions greater than 0.5 Hz in the island.
3.
The second approach could be followed in case self start facilities
are available at only a few power stations or the stqrt up power has to be
imported from neighbouring regions at one0or two points. In this approach, the
start up power required to be extended to all the generating stations on priority
basis while restoring few loads and transformers for voltage control. The start
up power available from neighbouring regions at various interconnections have
to be seriously explored since considerable assistance can be availed and the
restored system is connected to stable external systems. The procedures have to
be laid down for quickly harnessing these facilities.
The restoration through this approach could be delayed due to problems in
charging the lines, high voltage, lack of synchronising equipment at certain
substations etc. and may involve system disturbances during restoration.
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OPERATIONAL GUIDELINES.
1.
Each SLDC will coordinate synchronisation of
units and transmission lines in its system in consultation with
WRLDC. For ISGS power stations , WRLDC will be
coordinating for their synchronisation. WRLDC will
coordinate interstate/ inter-regional startup power availability
and also inter-state/inter-regionql synchronisation of the
system.
2.
Minimum 25 MW power flow from West to
North will be maintained on HVDC back to back link at
Vindhyachal during normal operating condition.
3.
Black start generation usage priorities:a)
provide startup power to hot units
b)
provide startup power to units that are cool; but capable
of rapid restart
c)
restore stations auxiliary service to generating
stations0and sub-stations.
d)
Pick up essential loads.
4.
Transmission corridors used for startup power
should be isolated from any damaged/faulty equipment and
are of minimum length and minimum voltage level to reduce
line charging.
5.
The constituent receiving assistance during
restoration process should restrict to the agreed quantum only
since this may have an adverse effect on healthy
system0rendering the assistance.
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GENERAL GUIDELINES
While each disturbance would be different and may require a different plan,
nevertheless it would be useful to formulate general guidelines for the benefit
of the load despatchers. These may be described as0below:
i. The operators at generating stations and substations should have the
knowledge of pre-planned synchronising locations and synchronising
procedures. Synchronising should be done preferably at generating stations.
ii. Switching procedures should be clearly laid down and periodically
reviewed.
iii. The part systems should be reintegrated only after adequate
stabilization.
iv. The transformer taps should be checked for desired settings to
minimise voltage difference.
v. The substation operators and load despatchers sxould make a check of
the capacitor banks and reactors in service and accordingly to carry out the
switching operations for voltage control.
vi. Energising long high voltage lines and cables should be avoided until
enough generating capacity is available.
vii. Provision of islanding schemes area-wise, power station-wise and unitwise would enhance the ability to restore faster. These should be fully
exploited.
viii. Some of the generating units might have been saved due to successful
islanding. Stabilization of such online generation is of top most priority.
ix. Provision of start up power to nuclear plants should be given priority as
poisoning of the reactors would delay restoration of nuclear units.
x. In case of failure of main communication channels, guidelines for
decision making should be given to all the major substations and generating
stations.
xi. Devising islands for power stations wherever small units could help in
faster restoration of the grid are available. One small unit at these power
stations can be islanded with radial loads and/or house load.
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REQUIREMENT OF SURVIVAL POWER /
AUXILIARY POWER
Survival power can be defined as the power
needed for avoiding the damage to the equipment
in case of supply failure. This power is required
for

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Turbine emergency oil pump
Jacking oil pumps
Barring gear of the turbines
Lubricating oil pumps
Compressors for ABCB operation
Emergency lighting
Battery chargers of units, station, and
communication and telemetry system
The survival power required by 120 MW units is
of the order of 250-350 kW while the requirement
of 210 MW units is of the order of 350-500 KW. As
a general rule, the survival power requirement
would be around 0.25-0.30% of the unit capacity.
Nuclear power plants should be supplied with
survival power on priority basis.
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REQUIREMENT OF START UP POWER
The start-up power is the power required for the
auxiliaries while the generating unit is restored. The
requirement of start-up power by various units is as
follows:Nuclear &
Thermal
:
7 to 8% of the unit capacity
Hydro
:
0.5 to 1% of the unit
capacity
Gas
:
1.5 to 2% of the unit
capacity.
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GUJARAT
Ukai (H)
4 x 75
Hydro
Diesel
500 KVA
Mini Hydro
2 x 2.5
Hydro
Diesel
50 KW
Kadana
4 x 60
Hydro
Diesel
500 KVA
Dhuvaran
1 x 27
+ 4 x 63.5
+ 2 x 140
Gas
Thermal
Any one
unit out of
the units
1,2,3 & 4
1 x 63.5
MW
Diesel
1600 KVA
x2
700 KVA
GIPCL
A.E.Co.
Stn. C
Stn. D,E,F
3 x 32
+ 1 x45
+ 1x104
+ 1x5
Gas
Steam
Gas
Steam
All units
141 MW
Diesel
500 KVA
4 x 15
2 x 30
3 x 110
Thermal
Thermal
Thermal
Stn-C
islands
30 MW
500 KVA
One 75 MW
gen. house set
Islanding of
any one units
out of units 1,
2, 3, & 4 on to
house load
Islanding of
all units
Islanding of
0ne 30 MW
unit
Diesel
GPEC
3x 138
Thermal
Diesel
3000 KVA
Kawas
4 x 106
2 x 116
Gas
Diesel
2700 KW
Gandhar
3 x 144
+ 1x225
Gas
Diesel
3120 KW
CCPP, Vatwa
3 x 39
+ 1 x 45
Gas
Essar
8
ower Station
Installed
Cap. (MW)
Survival
power
Auxiliary
Power
Diesel
Capacity
Synch. Facl.
Ukai (Hy)
4 x 75
100 KW
250 KW
500 KVA
Yes
Ukai LBCH
2 x 2.5
5 KW
20 KW
50 KW
Yes
Kadana (Hy)
4 x 60
7 KW
200 / 250 KW
500 KVA
Yes
Ukai (Th)
2 x 120
+ 1 x 200
+ 2 x 210
1.447
MW
4.5/ 8 MW
-
Yes
2 x 120
500 KW
12 MW
500 KW
Yes
Dhuvaran (Th)
1 x 27
+ 4x63.5
+ 2x140
500 KW
5 MW
500 KW
Yes
Gandhinagar
2 x 120
+ 3 x 210
175/350
KW P.U
7.2/10.7 MW
P.U
500 KVA
D.G.set
under
erection
Yes
Wanakbori
7 x 210
0.8 MW
13 MW P.U
3x400
KW
Yes
2 x70+1x75
360 KW
4.5 MW
1280 KW
& 500
KW
Yes
h. Stn. C
2 x 30
250 KVA
9 MW
1x500
KVA
Yes
h.D,E,F,
+ 3x110
GEB
ikka (Th)
anandro
A.E.Co
GT
+ 3x33
Gas
3 x 32
2 x 125
KVA
9
Nil
350 KVA
1x500
KVA
Yes
1.
REACTIVE POWER BALANCE
Objective
To keep system voltage within allowable range
Strategies
 Energising fewer high voltage lines
 Operating generators at minimum voltage
levels (logging p.f)
 Deactivate switchable capacity
 Connect shunt reactors and tertiary reactors
 Adjustment of transformer taps
 Pick up loads with lagging p.f
 Charge more transformers
 Charge shorter lines
 Operating synchronous condensers / SVCs
where available
 Avoid charging lines with series capacitors
Concerns
 Self excitation of generators and run away
voltage rise.
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2
LOAD AND GENERATION BALANCE
Objective
To maintain system frequency within allowable
limits
Strategies
 Restore loads in small increments (minimum &
essential)
 Smaller and radial loads to be restored prior to
larger and network loads
 Feeders with U/F relays are restored later (bypass
until frequency stabilizes)
 Load restoration based on load characteristics
 To get adequate inductive loading to compensate
capacitive effect while charging high voltage long line,
a concentrated load of large town/city should be
released along with that of Railways.
 Maintain frequency close to 50 Hz paying special
attention to traction and other fluctuating loads
Concerns
 Size of load pick up depends upon the rate of
response of prime movers
 Load pick up in large increments led to collapse of
the restored systems
Twice in Gujarat on 9.12.95
Twice in Maharashtra on 9.12.95
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Once in MP on 9.12.95
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LOAD AND GENERATION COORDINATION PRIORITIES
Restart Stage
 Priority to restore power supply to generating
stations and load dispatch centers.
 Priority to supply start up power to hydro and
gas units
 Priority for providing backup/survival/startup
power to nuclear power stations
 Several load and generation islands formed
 Black starting of small hydro or gas units
 In each island, the objective is to supply
station auxiliary power and start up power
 The number of islands limited by sources of
black start units
 Each island should preferably be monitored
by one load despatcher till reintegration.
Re-integration stage
Load restoration stage
v In small steps
v Observe frequency charges (< 0.5 Hz) with load
addition
v Preferable to restore rotating type loads if
possible
v Cold load pick up is the main concern
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4
MONITORING & CONTROL
 Location of the fault and extent of
collapse of the system should be
ascertained before restoration
 It is dangerous to restore a faulty line
or faulty equipment
 Ensure communication links between
control centers, power plants and substations
 SCADA system performance
Inadequate displays
Excessive alarms
Protection tele-metering
EMS
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5
Communications
¨ Establishing communication
between LDCs, Generating Stations
and major substations.
¨ All important substations only to be
kept in touch with and links with
unimportant substations to0be cut off
to avoid draining of batteries.
¨ All communication channels
required for restoration process shall
be used for operatyonal
communication only till grid normalcy
is restored (IEGC 6.8.e)
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6
PROTECTIVE SYSTEMS /
SYNCHRONISATION
 Check all interlocks
 Sort out problems in closing of breakers due
to low gas/air pressure
 Avoid paralleling islands through weak ties.
 Synchronizing facilities at sub-stations
 Standing phase angles to be checked and
difference reduced by generation control.
Synchronisation only through synchro-check
relays
 Try to synchronise islands or part systems,
near the generating stations requires less coordination and easier to control
 Operate generators on lagging p.f
 Generators supplying start up power should
not be loaded beyond 80%
 The capacity of the island to sustain the
starting current of BFPs should be checked
 If sub-systems are to be synchronized away
from generating stations, be extremely cautious
of standing phase angle differences (system
occurrence on 28.4.93 in Maharashtra)
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7
ENERGY STORAGE
Loss of back up power supplies like:
Batteries
Battery chargers
UPS
Diesel sets
Could affect
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Operation of circuit breakers
Motor operated isolators
Communication
SCADA
(one of the important causes of delays in
restoration)
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SWITCHING OVER VOLTAGES
Energise small sections of lines
Energise lower voltage lines
In case of parallel circuits, energise one ckt.
Control high voltages during restoration to
avoid damage of Las/CVTs et.
Survival Power
Ensuring availability of back up power supplies such
as batteries, battery chargers, D.G sets to avoid effect
on non operation of circuit breakers, communication
systems etc., which can cause delay in restoration.
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Awareness of Restoration Plans
Training and necessary documentation may be
provided to Load Despatchers by respective LDCs.
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Exchange of Information
Exchange of information among SLDCs and between
RLDC and SLDCs is essential for proper coordination.
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12
SYSTEM STUDIES FOR MAKING
RESTORATION PLANS
1
§
§
§
§
2
Power flow
Multiple islands
Study voltage problems
Generator excitation limits
Transformer taps
Dynamic stability
§
To study load generation co-ordination
§
While load pick up, generation response
could be studied
3
§
§
EMTP
To determine what lines to be charged
Transient over voltages in switching
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13.
RESTORATION PLAN
v
Identification of collapsed power
system components and equipment.
v
Restart and supply start up power first
to hydro and gas stations
v
Startup power to thermal stations,
auxiliary power to sub-stations
v
Co-ordination of power plant start up
with load pick up to bring generators to
their stable minimum generation levels
v
Restore in sub-systems if multiple
sources of startup power available
v
Energising transmission lines with
acceptable transient and sustained over
voltages
v
While load pick up, check frequency
decline
v
Reintegration of sub-systems
v
Ensure discipline and avoid over
drawals until proper stabilization
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14.
ROLE OF LOAD DESPATCH CENTRES
v
Determine severity of collapse
v
v
Identify and initiate black start facilities
Import start up power from
neighbouring states or regions
Import more power to meet essential
loads from neighbouring states or regions
Decision making and guidance
Determine priority loads
Check unbalanced loading due to traction
Getting start up power from captive
power plants, if possible
Ensure communication links, SCADA
facilities
Guidance to sub-station/generating
station operators from the results of EMS
Identify points of reintegration and
synchronization
Reporting
v
v
v
v
v
v
v
v
v
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15.
TRAINING AND ROUTINE EXERCISES
v
Short time appreciation courses
v
Review of targets for restoration as
soon as a black start facility or inter-state /
inter-regional connection is stabilized.
v
Review of restoration plants after every
occurrence
v
Updating of restoration manually and
other documentation
v
The strategies of restoration should have
alternatives to enable flexibility
v
Training by experts
v
Interactive training and case studies
v
All constituents should participate in
training programmes
v
Formation of a command group
v
Mock exercises
v
Preparation of manuals on important
telephone numbers etc.
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16.
OVER VOLTAGE CONTROL DURING
RESTORATION
(A)
Sustained power frequency over
voltages
v Due to lightly loaded lines
v May cause under excitation of
generators
v May lead to self excitation of
generators
v Over fluxing of transformers
(generate harmonic distortions and cause
transformer over heating)
(B)
Transient voltage or switching surges
v caused by energisation and deenergisation of lines
or
v switching of capacitive elements
v In conjunction with sustained o/v may
cause arrestor failures
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Harmonic Resonance Voltages
v
Oscillatory un damped or weakly
damped
v
Of long duration
v
Originate from equipment non
linearities and switching natural frequency of
series resonance circuit formed by source
inductance and line charging capacitance.
v
Magnetizing in rush due to transformer
energisation
v
Lightly damped due to light loading of
lines
v
Over fluxing of transformers (beyond 1.1
pu)
2.
Equipment limitations
Transformers and Arrestors
1.2 p.u for one minute
1.4 p.u for 10 seconds
Circuit breakers
v
Will have reduced interrupting
capability
v
Can interrupt line charging currents
upto 1.2 p.u
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3.
Control of sustained over voltages
v
Sufficient under excitation
capability on the generators
v
Connect lagging p.f loads and
shunt reactors
v
Remove all sources of reactive
power and switch off capacitor banks
v
Run generators at maximum
possible reactive power output to allow
margin to adjust for large charging
reactive power during line switching
v
Tap staggering of transformers
v
Avoid extra parallel lines
v
Maintain low voltage profile on
the lines to reduce line charging
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4.
Control of switching transients
v Switching o/v may cause flash over and
damage to equipment
v Switching transients on fast transient caused
by ill timed closure of breakers
v To be controlled to 2.5 p.u for 400kV and 1.9
p.u for 800kV and 2.3 p.u for others
v Usually of fast front, low energy or slow front,
high energy transients.
v Keep steady state voltage below 1.2 p.u. Keep
generator terminal voltage around 0.8 p.u
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5.
Harmonic Resonance
v Transformers may get over excited and
generate harmonics
v Combination of system inductance and line
capacitance forms a series resonance circuit which
is excited by harmonic distortions produced by
transformer saturation
v Harmonics generated by magnetic current in
rush can also lead to harmonic resonance
v Sufficient load to be connected to the
underlying system at both ends to damp
oscillations
v Lower order resonances produce higher over
voltages
(3rd, 4th, 5th, 6th harmonics)
v To control over voltage due to transformer over
excitation, user lower taps (system studies)
v Harmonic resonance can be damped by
connecting loads at both ends
v Connect dead load on the transformer to be
energized
v Reduce number of highly loaded lines (in
parallel paths)
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