Demand and PF Calculation

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sdg.marinusvz
2013-03-01 05:36

[posted from an email]
Can you tell me how you calculate your PFactor, it has come to our attention that I'm not taking the factor into account, when calculating the MTD MVA.

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sdg.marinusvz
2013-03-01 05:37

I assume you're talking about calculating power factor from instantaneous values?

Here follows a code snippet to explain our algorithm (explanation of the variable names are given below the snippet):

double p1 = 0;
try{p1=(v1 * i1 * Math.cos( Math.toRadians(i1a-v1a))) / 1000.0;}catch(Exception e){}
double p2 = 0;
try{p2=(v2 * i2 * Math.cos( Math.toRadians(i2a-v2a))) / 1000.0;}catch(Exception e){}
double p3 = 0;
try{p3=(v3 * i3 * Math.cos( Math.toRadians(i3a-v3a))) / 1000.0;}catch(Exception e){}
double q1 = 0;
try{q1=(v1 * i1 * Math.sin( Math.toRadians(i1a-v1a))) / 1000.0;}catch(Exception e){}
double q2 = 0;
try{q2=(v2 * i2 * Math.sin( Math.toRadians(i2a-v2a))) / 1000.0;}catch(Exception e){}
double q3 = 0;
try{q3=(v3 * i3 * Math.sin( Math.toRadians(i3a-v3a))) / 1000.0;}catch(Exception e){}
double s1 = Math.sqrt(p1*p1+q1*q1);
double s2 = Math.sqrt(p2*p2+q2*q2);
double s3 = Math.sqrt(p3*p3+q3*q3);
double pT = p1 + p2 + p3;
double qT = q1 + q2 + q3;
double sT = Math.sqrt(pT*pT+qT*qT);

double pf1 = p1/s1;
double pf2 = p2/s2;
double pf3 = p3/s3;
double pfT = pT / sT;


where:
v1 = red voltage
v2 = white voltage
v3 = blue voltage
i1 = red current
i2 = white current
i3 = blue current
v1a = red voltage phasor angle
v2a = white voltage phasor angle
v3a = blue voltage phasor angle
i1a = red current phasor angle
i2a = white current phasor angle
i3a = blue current phasor angle
p1 = Red Active Energy
p2 = white Active Energy
p3 = blue Active Energy
q1 = Red Reactive Energy
q2 = white Reactive Energy
q3 = blue Reactive Energy
pT = total Active Energy
qT = total Reactive Energy
sT = Demand (kVA)
pf1 = red power factor
pf2 = white power factor
pf2 = blue power factor
pfT = total power factor


On the Profile Graph and for Billing values, we take the values from the meter's profile log, and therefore we don't use the instantaneous values to determine the power factor for billing. (it already gives me the total kWh and kVAh per half hour, so in that case I just divide the kWh by the kVAh - for a particular half hour).

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