10-06-2017, 07:10 AM
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INTELIGENT LOAD SHEDDING(ILS)
AN EFFECTIVE APPROACH TO LOAD SHEDDING
INTRODUCTION
Load shedding is a process in which a suitable amount load is thrown off
in order to maintain system stability during over loaded condition
Generation- load unbalance problems
Load shedding in industrial units
Problems of frequency decay
Frequency is propotional to speed
Gas turbines are sensitive to frequency
Low frequency problem with thermal power plants
Frequency decay affects quality of industrial products
Frequency below 49.5Hz make s/m unstable
Is load shedding necessary
Conventional load shedding schems
1.Breaker interlock load shedding
2.Under frequecy relay load shedding
3.PLC based load shedding
Breaker interlock load shedding
Load shedding based on hard-wire signal &circuit-breakers
Fast load shedding
Load shedding based on worst case scenario
Only one stage load shedding
Excessive load shedding
Modification costlier
Under frequency relay load shedding
Used to drop load automatically in accordance with the pre determined
schedule
Fixed load reduction at fixed frequency level
Upon reaching the set point &pre-specified time delay the relay trips load
breakers
Cycle repeats until s/m frequency recovered
Slow response time
Incorrect or excessive load shedding
Analysis knowledge is lost
PLC based load shedding
Load shedding based on Load vs num of generator online or under
frequency detection
Shed a preset sequence of load
Use of distributed n/w via power management s/m
Automatic load relief
Monitoring of power s/m is limited to portion of n/w
s/m wide operating condition is missing from decision making process result
in incorrect load shedding
Priority load list doesn t
take into account the dynamic behaviour of the s/m
INTELLIGENT LOAD SHEDDING
Requirements of ILS s/m
1.Pre-disturbance operating conditions
2.post-disturbance operating conditions
3.Nature and duration of disturbance
4.s/m transient response to a disturbance
Functions of blocks
Knowledgebase-possess s/m dynamic behavior
Advanced Monitoring
Network Models
Trigger List
Load Shed Optimizer- computes optimal load shedding
tables corresponding to system changes.
Distributed Controls -utilize PLCs to rapidly execute the load shedding
actions
With the architecture described above, an ILS
scheme provides the following benefits:
Time-variant load shedding tables, which reflect
true status, and loading conditions for the
sheddable loads.
Optimal combination of sheddable loads to
maximize load preservation.
Fast response to disturbance triggers (less than
100 ms in most cases).
Environment to accelerate operator training with
the ability to simulate and validate load shed decicion
The internal electrical network supplies a total load
of about 45 MW, and is constituted by the following:
Substation interconnecting the internal electrical
system to the power grid by two, three-winding
transformers 34.5/13.8 kV rated at 20 MVA,
supplying three main switchboards.
Internal distribution system operating at 60 hertz
organized into main distribution switchboards,
rated at 13.8 kV and 4.16 kV, which supplies
large MV motors and/or distribution feeders as
well as several low voltage distribution
switchboards.
Total generation of 15 MW obtained from one
generator (Genset C).
The plant is normally importing 23 MW from the
utility, is supplemented by an onsite generator.
Frequency relays are located throughout the
system including the terminal bus of an onsite generator
conclusion
ILS is better than any of the conventional load shedding scheme
ILS is essential for indusrial application
