Hi Mari and Ray, This technical report, http://arxiv.org/abs/1411.0359, proposes two methods for generating “reasonable” thermal limits.
The first method is based on a statistical approach and maps the values for r, x, kv_base to a thermal limit. The other computes a thermal limit using the bounds on the bus voltages and the phase angle difference across a line. Take care when using these approaches, as Ray indicated, there is no substitution for a calculation using the line's material specification and length. Cheers, -Carleton On May 6, 2015, at 3:59 AM, Ray Zimmerman <[email protected]<mailto:[email protected]>> wrote: Unfortunately, I’m not aware of any good method for creating reasonable thermal limits that does not depend on details of the transmission lines themselves (voltage level, conductor configuration, etc.). Ray On May 5, 2015, at 12:02 PM, Mari Hardersen Prydz <[email protected]<mailto:[email protected]>> wrote: Thank you for the clarifying answer. I have one more question I hope you can give me some thoughts on. I'm working with different test cases where some of them have very high thermal limits, like case118 and the GBnetwork (Great Britain, http://www.maths.ed.ac.uk/optenergy/NetworkData/). I would like to assign more realistic thermal limits to these, but I have understood that retrieving correct data is very difficult. Is it possible to say anything about what the "normal" thermal limit values can be? Or what is realistic considering the share of branches where congestion occurs in a network? Thanks for any help on the subject. Sincerely, Mari Prydz On 5 May 2015 at 15:48, Ray Zimmerman <[email protected]<mailto:[email protected]>> wrote: Hi Mari, It is only RATE_A that is used by the OPF. Since the flow at either end of the branch (for AC OPF) are in general not equal, there are actually two sets of branch flow constraints, those constraining flow at the “from bus” end and those constraining flow at the “to bus” end. Usually, if a flow constraint is binding, it is binding only at one end, but this is not always the case. In any case, adding the two multipliers together should give you the sensitivity of the objective function to changes in RATE_A. Ray On May 5, 2015, at 6:49 AM, Mari Hardersen Prydz <[email protected]<mailto:[email protected]>> wrote: Dear all, I'm running the ACOPF on different test cases, and would like to find the effect on the objective function value when changing the thermal limits (rate A, B and C). Firstly, is it only rate A that limits the power flow, or will rate B and C also affect this? So far I have looked at the multipliers MU_SF and MU_ST (bresults.branch(i,18) and bresults.branch(i,19)), but I'm not sure how to put these two values together to represent the branch (as the thermal limits are set for the branches and not each node). Is there another dual variable for the branch flow constraints that represents the branch and not the to and from node? Thanks for any help on the subject. Sincerely, Mari Prydz Norwegian University of Science and Technology -- Mvh Mari Hardersen Prydz, M.Sc. student, industrial economics and technology management, Norwegian University of Science and Technology, Tel: + 47 98077194 ________________________________ The information in this e-mail may be confidential and subject to legal professional privilege and/or copyright. National ICT Australia Limited accepts no liability for any damage caused by this email or its attachments.
