Phil -
You can't be serious. Generally, your responses show an excellent technical knowledge. I'm certain you already understand this. You really need to read your responses again - and do the math again.
Addressing your reply # 15: Paraphrasing the original question, “Is the performance of a single-phase motor affected if its RUN or START Cap is replaced with one having different parameters? My answer was, and still is, Yes! ...
And my answer is, 'It depends on which parameters are changed. If the only difference is the new cap has higher working voltage, then the motor performance is not affected.
...
1) Co’s rated-impedance Xo is 40.8Ω, and Cn’s rated-impedance, Xn is 40.8Ω
Okay X = 1/(jwC) = -j/(377 x 65 x 10^-6) = -j40.8. So both caps have the same impedance. And that impedance is independent of the working voltage. Good
...
2) Co’s rated-current Io is 5.9A, and Cn’s rated-current, In is 10.3A.
The current through a 65uf at 240V => 240/40.8 = 5.9A
The current through a 65uf at 420V => 420/40.8 = 10.3A
Alright those numbers are good
...
3) Co’s rated VAr(o) is (Vo)x(Io) or 1,410, while Cn’s rated VAr
is 2,850.
This is the first error in your calc/reasoning:
For Co rated vars, you used Co rated voltage, 240V, and Co rated current, 5.9A which gave you Co rated vars = 240 x 5.9 = 1416 Vars.
For Cn, you used 240V, and 10.3A to get Cn rated vars. That would be in error. Using your reasoning, Cn rated vars = 420 x 10.3 = 4326Vars. If you want the rated vars, you must use the rated voltage. You account for the circuit voltage later.
...
4) Putting Cn in the circuit having a ‘working’ voltage of 240 Volts, produces a VAr
’ of 886, or about 31% of its capacity.
You appear to have reduced Cn rated vars by the ratio of the squares of the circuit voltage to Cn rated voltage. (240^2)/(420^2) = .326 I get ~33%, but that is close enough to your answer of 31%. So that gives me (Cn vars in a 240V circuit) = 4326 x .33 = 1427 Vars.
Isn't that just amazingly close to the value for a 240V rated cap in a 240V circuit. Why I'll bet it is within the roundoff error.
...
5) This corresponds to an adjusted Cn’ = 0.31 x 65 or 21uF.
And that is just wrong.
Capacitance does not change with the circuit voltage.
Capacitive Impedance does not change with circuit voltage.
Reactive VARS change with circuit voltage.
But in this case the circuit voltage was 240v and remained 240V. Changing the capacitor did not change the circuit voltage. In the 240V circuit, Cn vars are the same as Co vars.
ice
