BASIC FUNCTIONALITIES
OF GRID OPERATION
Dr M. S. R. Murty
Power System Operation
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Efficiency
Reliability
Economy and
Security
Benefits of grid interconnection
• Improving reliability
• Reduced investment due to sharing of the
generating resources
• Improved load factor and increase in load
diversity
• Coordination of maintenance schedules
Power System
• Generation, Transmission and Distribution
of electrical energy
• Generation Sources:
• Thermal: Conventional Steam, Diesel
• Hydro, Nuclear, Gas Turbine , Renewable
Typical Energy Scenario
Hydro
15.96%
Wind
1.99%
Biomass
1.19%
Solar thermal
0.40%
Nuclear
5.06%
Diesel
0.48%
Gas
14.49%
Coal
60.44%
Power Plant Schemes
Thermal, Hydro, Nuclear,
Combined Cycle
Simple Boiler scheme
Governor
Controls
Guide vane
position
Hydro Turbine scheme
Hydro Power
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P = 9.8 η Q H where P = power
(kilowatts)
η = plant efficiency
Q = discharge flow rate (meter3 /s)
H = head (meter)
Nuclear : PWR
Combined Cycle (Brayton & Rankine
Cycles)
EXHAUST GAS
LOW PRESSURE STEAM
(For Deaeration)
AIR
INLET
FUEL
INTERMEDIATE PRESSURE STEAM
(To Intermediate Pressure Steam Turbine)
COMBUSTOR
HIGH PRESSURE STEAM
(To High Pressure Steam Turbine)
GENERATOR
HEAT RECOVERY
STEAM
GENERATOR
GENERATOR
ELECTRIC
POWER
COMPRESSOR
TURBINE
ELECTRIC
POWER
GAS TURBINE
STEAM TURBINE
HIGH
INTERMEDIATE
PRESSURE PRESSURE
STEAM
STEAM
CONDENSATE RETURN TO HRSG
STEAM
EXHAUST
Combined Cycle Captive Power Plant
AUX
BOILERS
NAPHTHA
GAS OIL
4 x 125 TPH
Refinery Fuel Oil
8 X 30 MW
GAS TURBINE
NAPHTHA
GAS OIL
11 KV
8 X 125 TPH
33 KV
HRSG
4 X 30 MW
STEAM
TURBINE
TO REFINERY
11 KV
TO GEB
132/220 kV
33 KV
HP steam 42 Kg/cm2
Power
Steam
MP steam 17 Kg/cm2
INSTALLED CAPACITY
PRESENT GENERATION
EXPORT TO GEB CAPABILITY
360 MW
269 MW
80 MW
1500 TPH
979 TPH
------------
To
Refinery
Sample load curve
Base Load and Peak Load Power plants
• Base load: The unvarying load, which occurs almost the
whole day on the power plant
• Base power plants: (i) low operating cost (ii) capability of
working continuously for the long periods (iii)
requirement of few operating personnel and their repair
should be economical and speedy.
• Peak loads: Various peak demands of the load over and
above the base load
• Peak power plants: Capability of quick start,
synchronization and taking up of system load and quick
response to load variation.
Base Load and Peak Load Power plants
(contd.,)
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Hydro : Well suited for both base load and peak load operations.
The hydro-power plants should be employed for base load operation
as far as possible because of their higher capital cost.
However during the periods of draught, hydro-plants may be used
as peak load plants.
A steam power plant gives minimum cost of generation per unit
when used as base load plant. However, in order to save fuel it may
be used as peak load plant.
Nuclear power plants are suitable only for base load operation at
high load factors
Gas turbine power plants are suitable for supplying peak loads
Diesel power plants play a very little role in bulk power generation
because of their uneconomical operation costs.
Power Plant Control
• Plant parameters are to be maintained by
closed loop control
• Boiler: Steam parameters like pressure,
temperature, other process parameters
like furnace pressure, drum level
• Turbine- Generator : Power (MW), speed
or frequency
Boiler and Turbine Controls
DESH
SH1
Spray
DRUM
Q
W
W
Fuel
. Flux
.
.
Air
BOILER
Master Pressure
Control
GOVERNOR
Q
Temperature
Control
3
FW
150 at a
540ºC
H
T
P
I
P
T
G
Gas
Drum Level
control
SH2
RH
COND
GENERATOR CONTROLS
Hydro Generator Capability
Curve
Power System : One line
diagram
25-bus power system
Distribution System : Typical
Load Despatch Centers:
Functions
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System operation and control
Interregional transfer of power, covering
contingency analysis and operational planning
on real time basis
Scheduling / re-scheduling of generation
System restoration following grid disturbances
Operation of regional pool account and
regional reactive energy account.
Load Dispatch centers OR System
Control centers
• Constantly monitor the power flows, frequency and
voltage at each system point and the load on each
network component.
• Keep an eye on all the circuit-breakers in the grid
• Receive all the necessary data in real time through
extensive telecommunications network.
• When a network component is switched off following a
network incident (e.g. a lightening strike or a severed
cable) or when maintenance work is being carried out,
dispatchers can activate or deactivate certain network
components remotely.
• Coordination of planning of maintenance of
generating machines of various generating
companies
• Planning for maintaining proper voltages through
review of reactive compensation requirement
through system studies and monitoring of
installed capacitors
Transmision criteria
• Transmission System shall be capable of
withstanding the following contingency
outages :
• Outage of a 132 kV / 220 kV /400 kV line
• Outage of single Interconnecting
transformer
• Outage of one pole of HVDC Bipole line
• Without necessitating load shedding or
rescheduling of generation during Steady
State Operation
• All the Generating Units may operate
within their reactive capability curves and
the network voltage profile shall also be
maintained within voltage limits specified.
• The transmission system shall be capable
of withstanding the loss of most severe
single system infeed without loss of
stability.
Abnormalities
• Loss of supply
• Prolonged operation of the system
frequency below and above specified
limits.
• Unacceptable high or low voltage
• System instability
• Unacceptable overloading of transmission
system elements.
Power System Controls
• Generation Controls
- Real Power-Frequency ( P-f) control
- Reactive Power- Voltage (Q-V) Control
• Network Controls
- Breaker, Transformer taps Controls, Series/Shunt
Compensators & FACTS Controllers
• Load Controls
• System Wide/Dispatching Controls
- Energy Management System (EMS)
- Distribution Automation System (DAS)
Time Scales: Power system operation
• Regulation -- seconds to a few minutes -similar to variations in customer demand
• Load-following -- tens of minutes to a few
hours -- usage follows predictable patterns
• Scheduling and commitment of generating
units -- one to several days
Time Scales: Power system operation
Real time control of Generation
• System voltage, frequency and stability
• System frequency is controlled through
adjustment of the mechanical power of the
generators using speed governor
feedback and area generation control
(AGC)
• Dynamic stability enhancement:
adjustment of the generator’s excitation
voltage via the power system stabilizer
(PSS) loop
• And transmission level FACTS devices
Power System Operation: Time
frame
• Load control: under severe stability
conditions such as under-frequency load
shedding
• Traditionally load is viewed as a variable
uncontrolled demand, and the generation
must constantly adjust to reliably meet the
demand.
System Security
• The ability of a power system in normal
operation to undergo a likely disturbance
without entering an emergency or a restorative
state.
• The objective of security control is to keep the
power system in the normal state.
Need for frequency regulation
• Wide variation in frequency causes damage to
electrical equipment in industries, agriculture
etc.,
• Power plant equipment like turbines, generators
and auxiliaries get damaged
• Turbine last stage blades are susceptible to
damage due to low frequency operation
• Product quality like in rolling mills is severely
affected by frequency fluctuation
• Power system security is severely affected at
low frequencies
Security Assessment /
Control
Normal
SECURE
Restorative Control
INSECURE
EMERGENCY
RESTORATIVE
Emergency Control
A Typical Architecture of an Energy Management System
Grid Code
Grid Code
• Grid code is a technical document
containing the rules governing the
operation, maintenance and development
of the transmission system
• The grid code is intended to establish the
reciprocal obligations of all participants
who are part of the transmission system
operator.
• The grid code specifies a minimum of
technical, design and operational plant
criteria
• Planning code: provides for the supply of
information for planning and development
studies.
• The connection conditions specifies a
minimum of technical, design and
operational plant criteria
• Operating code contains details for high
level operational procedures for example
demand control, operational planning and
data provision.
• Marketing Code: Energy trading,
Ancillary services
SUMMARY
• Maintaining system security, reliability, quality, stability and
ensuring economic operation are the major operating
concerns.
• On line monitoring, operation and control of the modern
day power systems is performed by computer aided
monitoring & dispatching systems (SCADA / EMS)
• Distribution systems are monitored by Distribution
Automation (DA) systems.