The Power Flow Equations Iowa State University（爱荷华州立大学的功率流方程）.pdf

The DC Power Flow Equations 1.0 Introduction Contingency analysis occurs within the EMS by assessing each possible contingency (usually all N-1) one at a time. That is, we start from a solved power flow case representing current conditions (from the state estimator), then perform contingency assessment as follows: 1. If all contingencies assessed, go to 5. 2. Go to next contingency, remove the element and re-solve the power flow case, 3. Identify whether performance is acceptable or not by checking for overloads and voltage out of limits; o If unacceptable, identify preventive or corrective action 4. Go to (1) 5. End For a 50,000 bus system, with perhaps 2000 contingencies to be assessed (much lower than all N-1), if each powerflow re-solve requires 10 seconds, we require about 5.5 hours on a sequential computer. Of course, we may use parallelism on this problem very effectively (e.g., 10 computers, with each assigned to perform 200 contingencies, will get the job done in about 33 minutes). But what would be of most benefit is if we can reduce the time per contingency to 0.1 seconds instead of 10. Then the sequential computer requires only 3.3 minutes, and the 10 parallel computers require only 20 seconds! Therefore, in these notes we take a close look at the DC power flow, because it is this method which forms the basis for obtaining very fast answers in contingency assessment. Some typical numbers as of 2007 are given below: 1 Org Scan # of SE EMS model size # of CA rate msrments rate (# of buses) cont. rate BPA 2 sec 5 min 6000 5 min MISO 4 sec 120,000 90 s