Electric parameters can be defined either in SI or in pu ('per unit') units. Meters allow this choice for output-signals.
Note that 'pu' only affects input-output and precalculation whereas the model equations always refer to SI.
The relation between values in SI- and pu-units is given by:
value_pu = value_SI/base_SI
Base values are defined by nominal values in case of pu-units.
As independent base-values (for electrical quantities) we use voltage and apparent power
V_base, S_base
from which other values are deduced according to the relation
I_base*V_base = S_base R_base*I_base = V_base
The relation between inductance L and impedance X or capacitance C and susceptance B involving a frequency according to
omega*L = X omega*C = B
is always based on the nominal angular frequency
omega = omega_nom
Norms, amplitudes and effective values, an example (voltage 400 | 230 V)
abc-representation:
v_abc = {v_a, v_b, v_c} voltage vector, phase to neutral
|v_abc| = sqrt(v_abc*v_abc) voltage three-phase norm
dqo-representation:
v_dqo = {v_d, v_q, v_o} voltage vector, phase to neutral
|v_dqo| = sqrt(v_dqo*v_dqo) voltage three-phase norm
relation abc to dqo:
v_dqo = P*v_abc P: orthogonal transform abc to dqo vpp_dq = P*(v_b - v_c), .. definition phase to phase voltage dq |v_abc| = |v_dqo| as P orthogonal
| pu | V | ||
|---|---|---|---|
| Three-phase norm | |v_abc| | 1 | 400 |
| Single-phase amplitude | ampl (v_a), .. | sqrt(2/3) | 326 |
| Single-phase effective | eff (v_a), .. | 1/sqrt(3) | 230 |
| Phase to phase amplitude | ampl (v_b - v_c), .. | sqrt(2) | 565 |
| Phase to phase effective | eff (v_b - v_c), .. | 1 | 400 |
| Three-phase norm | |v_dqo| | 1 | 400 |
| Phase to phase dq-norm | |vpp_dq| | sqrt(2) | 565 |