Benchmarking WECC Composite load model Parag Mitra Sr. Engineer Anish Gaikwad Sr. Project Manager

Load Model Benchmarking Versions of software used PSLF 19.02 PSS/E 33.9 PowerWorld 19 DSATools (TSAT) V16.1.27 (Release date Dec 14, 2016) Uniform implementation across all platforms Composite load model channels are now available in DSATools Channel names straightforward in Powerworld

Test system 3 bus test system proposed by Siemens PTI Generator and exciter use standard parameters GENROU IEEET1

Initialization of composite load model Possibly due to leakage reactance Xa Motor A Motor B Motor C Slip P Q PSSE 0.035 3.924 3.055 0.0195 3.347 1.962 1.673 PSLF 0.041 3.925 3.095 0.021 3.389 1.694 Powerworld  0.041 0.021   3.926  3.389  1.962  1.66 DSATools 3.045 0.02 3.246 1.623   Motor D Electronic ZIP P Q PSSE 4.906 2.37 1.96 0.95 2.94 1.43 PSLF 4.91 Powerworld  4.906  2.37 DSATools Swing Bus Mid Bus HV Bus/Substation bus Internal Load Bus V θ PSSE 1.01 1.00 -0.28 1.000 -0.84 0.999 - PSLF 1.007 Powerworld  1.01 DSATools  0 1.007   0.9986  - 

Performance of Motor A (Load torque=constant) Responses are almost identical across the 4 platforms Although similar in magnitude some fast oscillations can be seen in the TSAT output

Stalling of Motor A (WECC Recmd. Tripping/Reconnection)

Stalling of Motor A (No tripping)

Without trip and reconn. Stalling of Motor A With trip and reconn. Without trip and reconn. Had a discussion with Siemens. The difference is because the motor in PSSE starts up a little bit later. This is possibly due to difference in the value of Xa between the different vendors. PSS/E assumes a different value than PSLF and others TSAT recommends using a time step of 0.25 cycles or less for double cage IMs. Default time step is 0.5 cycles (This was causing TSAT to have numerical issues in our previous simulations)

Stalling/Restart of Motor A (Plots by Gary Thomann PTI) Xa= 0.8 times sub-transient reactance Xa= 0.6 times sub-transient reactance, Results match PSLF closely There is no standard documentation for this parameter

Reconnection of Motor B (Load torque α Speed2) Voltage at load bus Active power at load bus 100% motor tripping Reactive power at load bus Speed PSLF does not reconnect. TSAT does not let the motor to slow down as it did previously. TSAT suggested using trapezoidal integration for this simulation

Performance of Electronic Load The model response is identical across all the platforms in the current versions

Performance of ZIP Load The model response is identical across all the platforms in the current versions

Low voltage performance of ZIP Load a. Voltage at load bus b. Active power at load bus b. Reactive power at load bus 40% constant Z, 40% Constant I, 20% Constant P The differences need to be sorted out How is the low voltage behavior of the ZIP component modeled? Is this implementation uniform across all the software platforms?

Active power at load bus Reactive power at load bus Performance of Motor D Active power at load bus Reactive power at load bus PSLF output is different than the other tools. The hump is missing. Latest correspondence with Bill Price from PSLF indicates that this issue has been resolved and the updated model now matches with the other software tools

Motor D: Vstall and Vstallbrk PSS/E and Powerworld both handles a Vstall = 0, replaces it with Vstllbrk PSLF 19.0_02 has numerical issues if Vstall is small. However, if Vstall is set to 0, PSLF changes it to 0.6 TSAT generates the following message Source: Powerworld Documentation Problem is with Vstall and Tstall. Rstall and Xstall are ok

Some vendors may be doing this already (above figures from Powerworld) EPRI suggestion Some vendors may be doing this already (above figures from Powerworld) Proposed change If (Vstall<Vstallbrk) Vstall=Vstallbrk end Instructions: LMTF to supply recommended value of Vstall To prevent stalling set Vstall as recommended value and set Tstall as 9999 Motor D does not stall Motor moves on yellow marked path when voltage decreases Motor moves on yellow marked path back when voltage recovers Motor D stalls Motor moves on yellow marked path when voltage decreases Restartable part –yellow Non restartable part – green (till they trip)

  Current status PSS®E PSLF™ Powerworld TSAT Initialization Motor A, B, and C for a voltage dip Motor A, B, and C during stalled condition Tripping and reconnection capabilities of Motor A, B and C  Electronic load Static load Motor D (performance with voltage dip) Motor D (Vstall and Vstllbrk)