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What does this mean...anything?

What does this mean...anything?

What does this mean...anything?

(OP)
I'm somewhat unfamiliar with the process below and am not sure what it really means or if it is even correct.

3Hp motor; 3Ph; 415V; 84%Eff; 0.8pf

The problem started by:

(3Hp * 0.7457 * 0.8pf)/(415V * sqrt(3) * 0.84) = 3.0A [Active]

(3Hp * 0.7457 * sqrt(1-0.8^2))/(415V * sqrt(3) * 0.84) = 2.2A [Reactive]

(3Hp * 0.7457)/(415V * sqrt(3) * 0.84) = sqrt(Active^2 + Reactive^2) = 3.7A [Apparent]

Is there any validity to the above?

My understanding would be: (3Hp * 0.7457)/(415V * 0.8pf * sqrt(3) * 0.84) = 4.6A

RE: What does this mean...anything?

Your first two equations are wrong. Do not multiply by power factor 0.8. (Equation is also missing a 1000).

O.8 = power factor = KW/KVA, and KW = HP x 0.746. Multiplying HP by power factor gives units of (KW^2)/KVA. You already had KW since HP = k x KW.

Your last equation is correct.

Note that most motors have power factors in the 0.8-0.9 range and efficiency around 0.85 - 0.9. Assume 0.86 for both, 0.86^2 = 0.747, which cancels with 0.747 KW/HP in the numerator. That is why for most motors we can simplify and say 1 HP = 1 KVA and skip the power factor and efficiency except when very accurate detail is needed.
This assumption is close except for large and very small motors.

Amps = HP *1000/ (V x 1.732)

RE: What does this mean...anything?

Thank you for showing us that simplification.

The 1 HP / 1KW means 1 HP (output) or "useable developed motor load", and the 1 kW is "input" or "actual required power" right?

RE: What does this mean...anything?

When the motor power is given in HP I assume that kW is input power.
When the motor power is given in kW then I assume that kW is useable developed motor load.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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