I am having trouble with the negative sign used with Q=-v^2 B. I know you can\'t
ID: 3349327 • Letter: I
Question
I am having trouble with the negative sign used with Q=-v^2 B. I know you can't have negative component values. can someone please explain my mistake?
thank you
EE 104 LABORATORY EXERCISE 8 POWER FACTOR CORRECTION Answer Sheet B. CALCULATIONS ON UNCORRECTED SYSTEM 2. L Attach your calculations for the real and imaginary power drawn by each load; summarize results in the table below. Load P (watts) Q(VARs) Electric heat 30 hp ind. motor Incandesc. lamps 7 ti.T total 3. Power factor ofcomposite load: 2927 C. SIMULATION OF UNCORRECTED SYSTEM 1.-2. [Attach your calculations for the simulation component values; summarize results in the table below.] Simulation Components G (siemens) B (siemens) Inductance (mH) or Load Resistance (2) capacitance (HF) Electric heat 52123 motor Synchronous motor Lamps 5. LAttach a screen capture of your simulation diagram showing the meter readings) 6. Wattmeter reading from simulation 7. Simulated power factor (magnitude only) computed from P/VD: 90622 Power factor shown on wattmeter: 100rExplanation / Answer
I think,you have confusion in between load 2 & load 3.
Let me clear your confusion.
The load 2 is an induction motor which is always an inductive load. so for this, as a load, its Q will be always positive as it abosorbed the reavtive power from source. Thats why you have got its value +ve in your calculation i.e.21.930KVAR. Therfore for calulation of B for load 2, you should use Q=V2*B where B=1/XL.
Where as, the load 3 a synchronous motor, which can be act as inductive or capacitive load depends on its excitation:
If, Over excited : then capacitive load (Means it is supplying the reactive power to source)
under excited : then inductive load (Means it is absorbing the reactive power from source)
As you are getting its value -ve, i.e. -1.442 KVAR. Therefore for calculation of B for load 3 you should use Q= -V2*B,
where B=1/XC.(-ve sign here indicates that the load is supplying the KVAR to the system instead of absorbing)
IF you will do like this then the -ve sign will not troule you.
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