Transcript Power Systems - WordPress.com

My Time in CURENT
Graham Treasure
Quick Recap
• First semester
– Electrical theory
– Introduction to programming
– I already gave this talk
• Second Semester
– Applications of knowledge from first semester
– I will focus on this
Power Systems
• Consists of generators, loads, buses, and lines
• 3 Types of Buses
– Swing Bus (Vθ)
– Generator Bus (PQ)
– Load Bus (PV)
• 4 Variables; but with a combination of buses,
we can still obtain all of them
4 Bus System from book ‘Power
System Analysis’, John J. Grainger
Power Flow Calculation
• First, I learned to do it in Matlab using Power
Systems Toolbox
– This involves intensive tabulation of data
• Next, I learned to draw it as a one line diagram
in PSAT
9 Bus System
Dynamic Simulation
• How a power system responds to a fault
• We used three types
– Line Fault
– Bus Fault
– Generator Trip
• This helps us find ways to improve power
system stability.
– Right now, we just simulated the response.
Line/Bus Fault
• These occur when a line or bus becomes
grounded
• No change in generation/load
• System returns to its original state after the
fault is cleared
• Faults generally do not last longer than five
cycles (<0.1s) due to protection relays
Generator Trip
• This occurs when a generator goes offline
– Overload, inspection, or just turned off
• Unlike bus/line faults, the system does not
return to its original state
• Frequency oscillates until its new state
• Generator Trip vs. Load Shedding
Electric Physics
• Power and Voltage relation
• Once the limit is reached, the line trips and
the whole system crashes
– Leading to blackouts like the Northeast Blackout
of 2003
• Thus, we need to know the maximum load
available at the load buses.
Main Project
• Given the 39 Bus New England Power System,
determine which bus (in the Connecticut area
is the most vulnerable.)
This area is a load center, so any system
crash will likely be on buses 4, 7, 8, 12,
31 (attached to 6)
How
•
•
•
•
Start with the loadflow file of this system
Alter the load for one bus
Run a powerflow calculation
^^ All this can be recorded in Python and redone
by simply altering and rerunning the program.
• Raise the load on the bus until the system
diverges.
– Then go back and forth until divergence is found
within a 10 MW range
Main Project
• Simulations on PSSE for Buses
Bus Number
Base Power
(MW)
Highest
Power
Tolerance
(MW)
Power
Change (MW)
4
500
2820
2320
7
233.8
2260
2026.2
8
522
2640
2118
12
8.5
2120
2111.5
31
9.2
1400
1390.8
WHY?
• When load in a system is increased, it
generally affects the loads in proportion to the
original voltage.
• SO to find the most vulnerable bus, we must
increase the loads on all the buses in the
system. The previous tests can give us a good
starting point.
New Simulations
• Increased load in increments
• Per unit voltage can be determined in a
loadflow calculation
Data
As you can guess, copy and paste came in real handy.
Data
Pop Quiz: Why didn’t all of the voltages drop?
Answer: Some are generator buses! In power
flow, the voltages of the generators are fixed.
Not always the case in dynamics
Conclusion
• When the power flow of the system increases,
we should watch bus 31, as it has the lowest
load limit.
– This does not mean other should be ignored
– Loads can vary independently, so another bus may
reach its limit first
– This is based on a constant PQ load model. Thus, it
is a preliminary test. The load may be modeled by
current, impedance, induction motor, or a
combination of them.