Quiz 2 Flashcards
(50 cards)
Why do we build lines?
Transfer power from one point to another
What are the prerequisites when building new lines?
Power, Voltage, Distance
How are new lines built?
One line at a time
where do we get opportunities to build ultimate grids?
Areas without distribution grid.
In very old grids.
Collection grids.
otherwise: make best with what we got.
What are examples of collection grids?
Wind Power
Wave Power
tidal Power
What is power flow?
Most important tool in power system operation and planning.
What analysis can be made on-line from monotoring the power flow?
State estimation
Security analysis
Economic analysis
What does on-line economic analysis of power flow allow us to determain?
Optimal operation
Loss coefficients
Optimal pricing
What analysis can be made off-line from monotoring the power flow?
Operation analysis
planning analysis
What does off-line planning analysis of power flow allow us to determain?
Network expansion planning
Power exchange planning
Security and adequacy analyses (Faults, Stability)
What are some problems with analysing power flow?
It’s only a snapshot of the system.
modeled using simple methods to a complex mathematical problem
solved using iterative techniques
accuracy vs. computing time
what needs to be known to calculate demand and/or generation of power in each bus?
bus voltages
load flow in lines and transformers.
What 4 quantities are associated with each bus?
– The real power
– The reactive power
– The voltage magnitude
– The phase angle between voltages
Slack bus provides the additional real and reactive power to meet
the losses. What quantities are specified?
Voltage magnitude and angle are specified
Voltage controlled buses. What quantities are specified?
Voltage magnitude and real power are specified
Load buses. What quantities are specified?
Real and reactive power are specified
How do we solve power flow equations?
iteratively
what steps are taken when solving power flow equations?
– Check that sufficient variables are known (2n)
– Give initial values to those voltages and angles, which are
unknown.
– Calculate the active and reactive power injections.
– Compare with known values of active and reactive power.
– Repeat the calculation until the accuracy between calculated and
known powers is sufficient.
What is 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 the transmission system
- OPF is used as basis for real-time pricing in many electricity markets.
What are inequality constraints in optimal power flow?
– transmission line/transformer/interface flow limits
– generator MW limits
– generator reactive power MVAr limits or capability curves
– bus voltage magnitudes
What available controls exist when optimizing power flow?
– Generator MW outputs
– OLTC transformer taps, phase-shift taps
– Reactive power compensation devices (switched capacitor
settings, SVCs, etc.)
– Load shedding
– etc.
What are some common causes of faults in EPS?
- Faults in apparatus
- Branches and trees on OH-lines
- Damage cables
- Ice loaded OH-lines
- Vandalism
- Lightning
- etc.
what is a fault?
”An unwanted connection between phases or
between phases and ground”
What fault causes the maximum current?
3-phases
3-phases and ground
