Load Characteristic Model: MOTOR_CMP

 

Following checks and corrections are applied during Validation and AutoCorrection.

  • If 0 < Tpo < Mult*TimeStep then Tpo = Mult*TimeStep
  • If 0.0 < Tppo < 0.5*Mult*TimeStep then Tppo = 0, ElseIf 0.5*Mult*TimeStep < Tppo < Mult*TimeStep then Tppo = Mult*TimeStep
  • If H < 0.01 then H = 0.01.
  • Pul: This is a normalized value, thus check if greater than 1, or less than 0; this catches a user ending a percentage value but do not autocorrect the value.
  • If Lp > 0.4*Ls then Lp = 0.4*Ls
  • If Lpp > Lp then Lpp = Lp

Mult represents the user-specified value Minimum time constant size as multiple of time step option on the Validation page of the Transient Stability Dialog

TimeStep represents the integration time step being used as described on TimeStep

Model Equations and/or Block Diagrams

-MOTOR_CMP is similar to MOTORW, with the following exceptions

-The MVABase for this model is equal to MVABase = (Pinitial/Lfm)

-Etrq is the exponent for the torque equation. Thus if Etrq = 0 that represents constant torque, but would be equivalent equivalent to a MOTORW D parameter of 1.

-Reminder: MOTOR_CMP again does not include the parameter Ll (leakage reactance), so again its behavior is determined by the global option regarding how to handle MOTORW models

-There are 2 stages of under-voltage load tripping and restarting defined with this model. The motor will be reduced by a fraction of Ftr1 if the terminal voltage falls below Vtr1 for Ttr1 seconds. This portion of the load will reconnect however if the voltage subsequently got above Vrc1 for Ttrc1 seconds.

-Similar process is done for the Vtr2, Ttr2, Ftr2, Vrc2, and Trc2 parameters.

-Note however that this tripping and reconnected is not modeling the dynamics of different portions of the loads slowing down and restarting. There is only one rotor speed state for this entire load model which is an approximation of 1000s of individual motors. The fractions of load that trip and then reconnect will not exhibit the restarting torques seen with an individual motor model.

-This model is used inside the CMPLDW and CMLD composite models

Parameters:

Lfm Lfm
Ra Stator resistance, p.u.
Ls Synchronous reactance
Lp Transient reactance
Lpp Sub-transient reactance, p.u.
Tpo Transient rotor time constant
Tppo Sub-transient rotor time constant, sec.
H Inertia constant, sec.
Etrq Exponent for the torque equation.
Vtr1 Fall Below Terminal Voltage 1
TTr1 Fall Below Time 1
Ftr1 Fraction of Motor Reduced 1
Vrc1 Reconnect Terminal Voltage 1
Trc1 Reconnect Time 1
Vtr2 Fall Below Terminal Voltage 2
TTr2 Fall Below Time 2
Ftr2 Fraction of Motor Reduced 2
Vrc2 Reconnect Terminal Voltage 1
Trc2 Reconnect Time 2