Download WECC_Composite_Load_Model_Specifications

WECC Composite Load Model (CMPLDW)
Phase 1 Specifications
October 2, 2014
 Overall Specifications

The overall structure of the CMPLDW model is shown in Figure 1.
Load Bus
System Bus
Low-side
(230, 115, 69kV)
Feeder
Bus
Equiv.
1:T
Rfdr +j Xfdr
jXxf
Fb Bfdr
Bss
(1-Fb) Bfdr
M
Motor A
M
Motor B
M
Motor C
M
Motor D
UVLS
Electronic
UFLS
PV
Static
Figure 1 CMPLDW Model Structure
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
Any load can be represented in dynamic simulations by a CMPLDW model.
All of the P and Q of the load will be included in the CMPLDW model.
Fractions of the load can be tripped by relay action via the load shed
signal. Such tripping will simulate tripping an equivalent amount of
aggregate feeder and of each load element, but not the substation
transformer or capacitor (Bss).
Shunt capacitance – The feeder capacitors (FbBfdr and (1-Fb)Bfdr) will
be computed during initialization of the dynamic simulation to produce
the total Q at the system bus.
Static Load Model equations:
P = Po * (P1c * V P1e + P2c * V P2e + P3 ) * (1 + Pf * f )
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
Q = Qo * (Q1c * V Q1e + Q2c * V Q2e + Q3 ) * (1 + Qf * f )
Po = Pload ( 1. – Fma – Fmb – Fmc - Fmd)
Qo = Po * tan ( acos(PFs) )
P3 = 1. – P1c – P2c
Q3 = 1. – Q1c – Q2c
Type 3 motor model – standard 3-phase induction motor model, e.g.
PSLF MOTORW model with undervoltage tripping and exponential
mechanical torque:
Tm = Tmo * Etrq
 Type 1 motor model – single-phase performance-based air conditioner
compressor model developed by WECC LMTF, including tripping by
contactor, U/V relay, and thermal protection. See appendix A for
details.
 For each composite load model, input data will be:
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
Location – bus number, (name, kV), load ID
MVA=xxx – feeder & xfmr MVA base
- if xxx < 0, abs. value = loading factor = load MW / MVA base
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- if xxx = 0., loading factor = default value (0.8)
Bss - Substation shunt B (pu of MVA base)

Feeder
- Rfdr - Feeder R (pu of MVA base)
- Xfdr - Feeder X (pu of MVA base)
- Fb –fraction of feeder reactive compensation applied at the
substation end of the feeder
If Xfdr = 0., feeder is omitted, but feeder capacitor is included.

Substation transformer
- Xxf – transformer reactance – p.u. of xfmr MVA base
If Xxf = 0., transformer is omitted.
- Tfixls - Fixed xfmr tap ratio on low-voltage side
- LTC – LTC flag – (1=active; 0=inactive)
- Tmin - LTC min tap (pu)
- Tmax - LTC max tap (pu)
- Step - LTC step size (pu)
- Vmin - LTC Vmin (low side pu)
- Vmax - LTC Vmax (low side pu)
- Tdel - LTC time delay to initiate tap adjustment(sec.)
- Ttap - LTC time delay between tap steps(sec.)
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Rcmp - LTC Rcomp (pu)
Xcmp - LTC Xcomp (pu)

Load composition
- Fma - Motor A fraction
- Fmb - Motor B fraction
- Fmc - Motor C fraction
- Fmd - Motor D fraction
- Fel – Electronic load fraction

Electronic load parameters
- PFel – Electronic load power factor
- Vd1 - Voltage below which electronic load decreases (pu)
- Vd2 - Voltage below which electronic load is zero (pu)
- frcel - Fraction of electronic load that recovers from low voltage
trip

Static load parameters
- PFs - Power factor
- P1e - P1 exponent
- P1c - P1 coefficient
- P2e - P2 exponent
- P2c - P2 coefficient
- Pfrq – frequency sensitivity
- Q1e - Q1 exponent
- Q1c - Q1 coefficient
- Q2e - Q2 exponent
- Q2c - Q2 coefficient
- Qfrq – frequency sensitivity

Motor types (3=3-phase; 1=1-phase A/C performance model)
- Mtypa - Motor type
- Mtypb - Motor type
- Mtypc - Motor type
- Mtypd - Motor type
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For each motor with Fm > 0, include the following parameters:
For each Type 3 motor (x):
- LFmx - Loading factor (MW / MVA rating)
- Rsx – Stator resistance (pu)
- Lsx – Synchronous reactance (pu)
- Lpx – Transient reactance (pu)
- Lppx – Subtransient reactance (pu)
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Tpox – Transient open circuit time constant (sec.)
Tppox – Subtransient open circuit time constant (sec.)
Hx – Inertia constant (sec.)
Etrqx – Mechanical torque exponent
Vtr1x – First U/V Trip V (pu)
Ttr1x – First U/V Trip delay time (sec)
Ftr1x – First U/V Trip fraction
Vrc1x – First U/V reconnection V (pu)
Trc1x – First U/V reconnection delay time (sec)
Vtr2x – Second U/V Trip V (pu)
Ttr2x – Second U/V Trip delay time (sec)
Ftr2x – Second U/V Trip fraction
Vrc2x – Second U/V reconnection V (pu)
Trc2x – Second U/V reconnection delay time (sec)
For each Type 1 motor (x):
- LFmx - Loading factor (MW / MVA rating)
- CompPFx – Power factor
- Vstallx – Stall voltage (pu)
- Rstallx – Stall resistance (pu)
- Xstallx – Stall reactance (pu)
- Tstallx – Stall time delay (sec.)
- Frstx – Fraction of load that can restart after stalling
- Vrstx – Voltage at which restart can occur (pu)
- Trstx – Restart time delay (sec.)
- Fuvrx – Fraction of load with undervoltage relay protection
- Vtr1x – First U/V Trip V (pu)
- Ttr1x – First U/V Trip delay time (sec)
- Vtr2x – Second U/V Trip V (pu)
- Ttr2x – Second U/V Trip delay time (sec)
- Vc1offx – Contactor voltage at which tripping starts (pu)
- Vc2offx – Contactor voltage at which tripping is complete (pu)
- Vc1onx – Contactor voltage at which reconnection is complete (pu)
- Vc2onx – Contactor voltage at which reconnection starts (pu)
- Tthx – Thermal time constant (sec)
- Th1tx – Thermal protection trip start level (pu temperature)
- Th1tx – Thermal protection trip completion level (pu temperature)
- Tvx – Voltage measurement lag (sec.)
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 Output variables will be:
 Level 1
-
Pld – Total MW at system bus
Qld – Total MVAr at system bus
 Level 2
-
Pshd – load[].pshed value for this load MW
Vls – pu voltage at substation low-side bus
Vld – pu voltage at load end of feeder
 Level 3
- Pst – Static load component MW
- Qst – Static load component MVAr
- Pel – Electronic load MW
- Pel – Electronic load MVAr
For each motor in use:
- Pmx – Motor P, MW
- Qmx – Motor Q, MVAr
 Level 4
For each Type 3 motor in use:
- spdx – motor speed, pu
- Tmx – Motor mechanical torque, pu
- Tex – Motor electrical torque, pu
- fuvx – Fraction of motor not tripped by UV relay
For each Type 1 motor in use:
- fuvx – Fraction of motor not tripped by UV relay
- fcnx – Fraction of motor not tripped by contactor
- crAx – current in non-restarting part of load, pu
- crBx – current in restarting part of load, pu
 Level 5
-
Fmx – Fraction of motor not tripped by load shedding relay
 Level 9 - for type 1 motors
-
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tmpA – temperature in non-restarting part of load, pu
fthA – Fraction of in non-restarting part of load not tripped by
thermal protection
tmpB – temperature in restarting part of load, pu
fthB – Fraction of in restarting part of load not tripped by
thermal protection
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 Initialization process:
1.
2.
3.
4.
5.
6.
Get total load P & Q, system bus V from power flow
Add low-side bus and load bus to Ymatrix
Add xfmr and feeder to Y matrix
Compute low-side bus voltage with tap = 1.
Adjust LTC tap to put compensated voltage at midpoint of Vmin, Vmax
Compute low-side and load bus voltages. (If load bus voltage is < 0.95,
reduce Rfdr and Xfdr to bring it above 0.95.)
7. Initialize motor models and static load models – obtain total load
component Q
8. Set Bf1 [= Fb*Bf] and Bf2 [=(1-Fb)*Bf] to match total load Q
9. If Bf < 0. (inductive), reduce Bss to make Bf = 0.
10. If (Fb > 0. or Bss changed) iterate steps 6,7,8,9 to convergence on load
bus voltage.
 Calculations during normal running:
 sorc mode: (before network solution)
 Use low-side voltage, load voltage, and frequency from previous
network solution
 Compute current injection at load bus from motor and static load
models.
 If LTC tap has changed, compute current injections at system and
low-side buses to reflect tap change.
 netw mode: (iteration with network solution)
 Update current injection at load bus from motor and static load
models based on change in load bus voltage.
 alge mode: (after network solution)
-
Check for tripping conditions and modify models as required
 rate mode: (diff. equation update)
-
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Update derivatives of state variables in motor models
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Appendix A –Performance-based Single-phase A/C Model
The model represents a composite of many individual single-phase A/C
compressors and their protective devices as shown below.
VC , F
Motor A
Motor B
P A +jQ A
P B +jQ B
UV
R elay
S hunt
K THA
jQ S
P +jQ
K UV

K UV
K C ON
K C ON
1 – F rst
K THB
T hermal R elay
C ontactors
T hermal R elay
V,F
F rst

The compressor motor model is divided into two parts:
Motor A – Those compressors that can’t restart soon after stalling
Motor B – Those compressors that can restart soon after stalling
The motors are represented by algebraic equations, as follows:
If V > 0.86:
P = Po * (1 + f )
Q = [Q’o + 6 * (V – 0.86) 2 ] * (1 - 3.3 * f )
If V < 0.86 and V > V’stall:
P = [Po + 12 * (0.86 – V) 3.2 ] * (1 + f )
Q = [Q’o + 11 * (0.86 – V) 2.5 ] * (1 - 3.3 * f )
If V < V’stall:
P = Gstall * V * V
Q = - Bstall * V * V
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If V < Vstall for t > Tstall, motor stays in stalled state.
For “B” motor, if V > Vrst for t > Trst, the motor restarts.
Initialization calculations:
Q’o = tan ( acos(CompPF) ) - 6 * (1. – 0.86) 2
V’stall is calculated to determine the voltage level at which there is an
intersection between the stall power characteristic and the transition
characteristic used below V = 0.86:
for ( V = 0.4; V < Vstall; V += 0.01 )
{
pst = Gstall * V2
p_comp = Po + 12 * (0.86 – V) 3.2
if ( p_comp < pst )
{
V’stall = V
break
}
}
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