- Combination loads
Combination loads can be modeled by assigning a percent-
age of the total load to each of the above three load models.
The total line current entering the load is the sum of the
three components.
21.1.6.2 Delta Connected Loads
Figure 21.26 shows the model of a delta connected load.
The notation for the specified complex powers and volt-
ages is as follows:
Phase ab:jjffSab uab¼PabþjQab andjjffVab dab (21:176)
Phase bc:jjffSbc ubc¼PbcþjQbc andjjffVbc dbc (21:177)
Phase ca:jjffSca uca¼PcaþjQca andjjffVca dca (21:178)
- Constant real and reactive power loads
ILab¼
Sab
Vab
*
¼
jjSab
jjVab
ffdabuab¼jjffILab aab
ILbc¼
Sbc
Vbc
*
¼
jjSbc
jjVbc
ffdbcubc¼jjffILbc abc
ILca¼
Sca
Vca
*
¼
jjSca
jjVca
ffdcauca¼jjffILca aac (21:179)
In this model the line-to-line voltages will change during each iteration until convergence is achieved.
- Constant impedance loads
The constant load impedance is first determined from the specified complex power and line-to-neutral
voltages according to the following equation:
Zab¼
jjVab^2
Sab*
¼
jjVab^2
jjSab
ffuab¼jjffZab uab
Zbc¼
jjVLbc^2
S*bc
¼
jjVbc^2
jjSbc
ffubc¼jjffZbc ubc
Zca¼
jjVca^2
Sca*
¼
jjVca^2
jjSca
ffuca¼jjffZca uca (21:180)
The load currents as a function of the constant load impedances are given by the following equation:
ILab¼
Vab
Zab
¼
jjVanb
jjZab
ffdabuab¼jjffILab aab
ILbc¼
Vbc
Zbc
¼
jjVbc
jjZbc
ffdbcubc¼jjffILbc abc
ILca¼
Vca
Zca
¼
jjVca
jjZca
ffdcauca¼jjffILca aca (21:181)
ILb
ILa
ILc
ILca
ILab
ILbc
Sab
Sca Sbc
FIGURE 21.26 Delta connected load.
