- #1
ridemx
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Homework Statement
3 loads are connected to a source (1000Vrms, 60hz, 1 phase) in parallel
load 1:Inductive, 125kva, .28pf lagging
load 2:capacitive, 10kw, 40 kvar
load 3:resistive, 15kw
Find total S, P, Q, PF
Homework Equations
S=apparent (VA)
P=real (W)
Q=reactive (VAR)
S^2=P^2+Q^2
PF=P/S
The Attempt at a Solution
Using the above equations, I found the S,P,Q for all 3 loads as follows,
Load 1:
S=given=125kva
P=(125kva)(.28)=35kw
Q=sqrt[(125kva^2)-(35kw^2)]=120kvar
Load 2:
S=sqrt[(10kw^2)+(40kvar^2)]=41.23kva
P=given=10kw
Q=given=40kvar
load 3:
S=sqrt[(0^2)+(15kva^2)]=15kva
P=given=15kva
Q=0 since resistive
I added up all the P's Q's and S's to get
S=181.23kva
P=60kw
Q=160kvar
but then I checked myself using S^2=P^2+Q^2 and it doesn't work out
sqrt[(60kw^2)+(160kvar^2)]=170.9kva not 181.23kva
where did I screw up, can you not just add the loads?