GA Tech - 3 phase sequence question

[bethy]

On P-47b & P-47c Sample problem.

V(ab) = -V(ba) = 200 angle -30 degree

V(bc) = -V(cb) = 200 angle 90 degree

V(ca) = -V(ac) = 200 angle 210 degree

I used calculator to get the answer from V1, V2, V3 by convert -200 angle 150 degree to rectangler and then convert it back to polar to get 200 angle -30 degree (same with the other).

Is that the only way to find the correct angle? Does anyone has different method?

Thanks,

 

[Wildsoldier PE]

On P-47b & P-47c Sample problem.
V(ab) = -V(ba) = 200 angle -30 degree

V(bc) = -V(cb) = 200 angle 90 degree

V(ca) = -V(ac) = 200 angle 210 degree

I used calculator to get the answer from V1, V2, V3 by convert -200 angle 150 degree to rectangler and then convert it back to polar to get 200 angle -30 degree (same with the other).

Is that the only way to find the correct angle? Does anyone has different method?

Thanks,

I dont have my GA Tech binder with me right now but you only need to get one voltage with one angle, the other voltages can be calculated really easy with the phase sequence.

for positive sequence

Vab<0

Vbc<-120

Vca<+120

for negative sequence

Vab<0

Vbc<+120

Vca<-120

Magnitudes stays the same if balance so what he did and using negative sequence

Vab = 200<-30 this is the calculated voltage then to get the other voltages using negative sequence

Vbc = 200<(-30+120) = 200<90

Vca = 200<(-30-120) = 200<-150 = 200<210 = 200<(360-150)

I don't know if i answer the question or if this helps.

 

[bethy]

Let me give you more infor.

The problem given:

Vac = 200<30

Vba = 200<150

Vcb = 200<270

Find the sequence? How do you convert 200<150 to become Vab = 200<-30 (without using calculator)?

 

[Wildsoldier PE]

Let me give you more infor.
The problem given:

Vac = 200<30

Vba = 200<150

Vcb = 200<270

Find the sequence? How do you convert 200<150 to become Vab = 200<-30 (without using calculator)?

Lets take a reference voltage Vba<150 this looks to be - sequence since Voltage angle for cb is 270.....150+120=270

so

Vba=200<150

Vcb=200<150+120=200<270

Vac=200<150-120=200<30

Now where to get that minus (-) 30 i don't know...could be an error.

 

[bethy]

Let me give you more infor.
The problem given:

Vac = 200<30

Vba = 200<150

Vcb = 200<270

Find the sequence? How do you convert 200<150 to become Vab = 200<-30 (without using calculator)?

Lets take a reference voltage Vba<150 this looks to be - sequence since Voltage angle for cb is 270.....150+120=270

so

Vba=200<150

Vcb=200<150+120=200<270

Vac=200<150-120=200<30

Now where to get that minus (-) 30 i don't know...could be an error.

He (Dr Callen) converted:

Vab = -Vba = 200<-30 (That is what I don't get! How to get <-30? I used calculator convert -Vba = -200<150 to get <-30).

Vbc = -Vcb = 200<90

Vca = -Vac = 200<210

 

[EEVA PE]

Let me give you more infor.
The problem given:

Vac = 200<30

Vba = 200<150

Vcb = 200<270

Find the sequence? How do you convert 200<150 to become Vab = 200<-30 (without using calculator)?

Lets take a reference voltage Vba<150 this looks to be - sequence since Voltage angle for cb is 270.....150+120=270

so

Vba=200<150

Vcb=200<150+120=200<270

Vac=200<150-120=200<30

Now where to get that minus (-) 30 i don't know...could be an error.

He (Dr Callen) converted:

Vab = -Vba = 200<-30 (That is what I don't get! How to get <-30? I used calculator convert -Vba = -200<150 to get <-30).

Vbc = -Vcb = 200<90

Vca = -Vac = 200<210

(200<150)X(-1<-180)=-200<-30

+/- 180 degree is half a circle which is like multiplying by -1