Total power measurement in 3-phase unbalanced delta system
The 3 Power meter method uses the meter impedance to create a virtual Y neutral node with 3 V readings 
Thus 3 meter method can measure the P in each phase and total.
Using scalar VA products in each phase can get any result you need (VAR, PF)
the total apparent power (scalar product) can also be measured using true Vrms* true Irms
the reactive power can be computed by vector geometry.