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System design & power flow, Skriv slide 12-17 för hand - Coggle Diagram
System design & power flow
Building Lines
Transfer power from one point to another
Limited prerequisites
Power
Voltage
Distance
One line at the time
Which technology
Power
Voltage
Distance
Optimizing grid
Do we ever ge the opportunities to build ultimate grid?
In areas where no distribution grid exist today
In very old grids
Collection grids
Wind power
Wave power
Tidal power
Make the best out of what we got
Optimal power flow
Power flow
Intoduction
Most important tool in power system operation and planning
See how the system work
On-line analyses
State estimation
Security analysis
Economic analysis
Optimal operation
Loss coefficients
Optimal pricing
Off-line analyses
Operation analyses
Planning analyses
Network expansion planning
Power exchange planning
Security and adequacy analyses
Faults
Stability
Problem description
A snapshot of the system
Knowing the demand and/or generation of power in each bus, find out:
bus voltages
load flow in lines and transformers
A single phase representation is usually adequate since power systems are usually balanced
The problem is described through a nonlinear system of equations
Need of iterative solution techniques
Solution technique: accuracy vs. computing time
Most used tool in steady state power system analysis
Problem
Associated with each bus are 4 quantities:
Real power
Reactive power
Voltage magnitude
Phase angle between voltages
Three types of buses are represented in the load flow calculations:
Slack bus provides the additional real and reactive power to meet the losses
Voltage magnitude and angle are specified
Voltage controlled buses
Voltage magnitude and real power are specified
Load buses
Real and reactive power are specified
How to solve equations
We have a set of non-linear equations --> a network can only be solved iteratively (no direct solution)!
A load flow calculation is therefore done in a given pattern:
Check that sufficient variables are known (2n)
Give initial values to those voltages and angles that are unkown
Calculate the active and reactive power injections
Compare with known values of active and reactive power
Repeat the calculations until the accuracy between calculated and known powers is sufficient
OPF
Optimal power flow
The goal of an OPF is to determine the ''best'' way to instantaneously operate a power system
Usually ''best'' = minimizing operating cost
OPF considers the impact of transmission system
OPF is used as basis for real-time pricing in many electricity markets
From PF to OPF
The power flow equations are introduced in OPF as demand-supply balances
The demand-supply balance is effected at each bus individually, not for the aggregated system
The optimum solution yields a set of generation variables that minimize cost while satisfying the physical laws of flow of electricity
Security constraints
OPF can include security constraints which represent operation of the system after contingency outages
allow the system operator to dispatch the system in a defensive manner --> security constrained OPF
if the contingency actually happened, the no limits are violated
Optimal power flow
Inequality contraints
transmission line/transformer/interface flow limits
generator MW limits
generator reactive MVAr limits or capability curves
bus voltage magnitudes
Available controls (i.e. control/optimization variables):
Generator MW outputs
OLTS transformer taps, phase-shift taps
Reactive power compensation devices (switched capacitor settings, SVCs, etc)
Load shedding
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