P= 1.732 X 230V X 42A X 0.85 = 10,731.06 W or 10.73 kW

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Discussion Overview

The discussion revolves around calculating the full load kVA and kW input for a 15 hp, 230V three-phase induction motor with a full load current of 42A. Participants explore the implications of the motor's connection type (Wye or Delta) and the interpretation of voltage and current specifications.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that the full load current of 42A refers to the line current, while the voltage of 230V could be interpreted as either line-to-line or phase voltage.
  • Calculations for kVA and kW are presented for both Wye and Delta configurations, with results suggesting kVA values of 16kVA (Wye) and 27kVA (Delta), and kW values of 13.5kW (Wye) and 23.4kW (Delta).
  • There is uncertainty regarding the interpretation of "per terminal" in relation to the voltage and current, with some participants expressing frustration over the ambiguity in terminology.
  • Participants discuss the rated power of the motor (15HP or 11kW) versus the calculated input power (13.5kW), questioning whether the latter represents actual input power.
  • A participant mentions finding an online three-phase calculator as a resource for verifying calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the 230V specification refers to line-to-line voltage or phase voltage, indicating ongoing uncertainty. There is also no agreement on the interpretation of "per terminal" in the context of the motor's specifications.

Contextual Notes

The discussion highlights ambiguities in terminology related to three-phase motors, particularly regarding voltage and current definitions, which may affect calculations. Participants express varying interpretations of the motor's specifications without resolving these ambiguities.

Who May Find This Useful

This discussion may be useful for students and professionals working with three-phase induction motors, particularly those interested in electrical engineering calculations and terminology clarification.

JGrecs
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3 PHASE INDUCTION MOTOR

A 15 hp/230V, three phase induction motor has a full load current of 42A per terminal.
15HP= 11kW

find:
a) Full load kVA input
b) If the full load power factor is lagging 0.85, what is the kW input.

My question: How do I know whether its connected Wye or Delta?a) kVA= 1.732 X ELine X ILine

ELine= 230V ILine=IPhase (Wye) and ILine=IPhase X 1.732 (Delta)

b) P= 1.732 X Eline X ILineX PF
 
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A)

Wye: kVA= 1.732 X 230V X 40A

kVA= 16kVA

Delta: kVA= 1.732 X 230V X 69A

kVA= 27kVA

B)

Wye: P= 1.732 X 230V X 40A X 0.85

P= 13.5kW

Delta: P= 1.732 X 230V X 69A X 0.85

P= 23.4kWHow do these look?
 
The problem stated the motor current as 42A per terminal. So that would be the line current. The motor is said to be 230V, so I think you can take that as the line-to-line voltage.
 
Ok, so "per terminal" refers to "Line-to-Line"?
so Id go with these:

kVA= 1.732 X 230V X 40A
kVA= 16kVA

P= 1.732 X 230V X 40A X 0.85
P= 13.5kW

Also, the 15HP (11kW) stated in the original question. Would that be the motors rated power, while the 13.5kW calculated would be its input power?
 
JGrecs said:
Ok, so "per terminal" refers to "Line-to-Line"?
Well, at the very least it refers to the line current since the motor's terminals are where the lines connect. I'm less certain about the interpretation of the wording for the "230V, three phase...". It could refer to the "three phase voltage", making the individual line voltages about 133V. Or it could be the line-to-line voltage. [I hate these ambiguities due to topic-specific "common-knowledge" jargon!]
so Id go with these:

kVA= 1.732 X 230V X 40A
kVA= 16kVA

P= 1.732 X 230V X 40A X 0.85
P= 13.5kW
Yeah, looks good as far as I can tell.
Also, the 15HP (11kW) stated in the original question. Would that be the motors rated power, while the 13.5kW calculated would be its input power?
That would be my interpretation.
 
gneill said:
Well, at the very least it refers to the line current since the motor's terminals are where the lines connect. I'm less certain about the interpretation of the wording for the "230V, three phase...". It could refer to the "three phase voltage", making the individual line voltages about 133V. Or it could be the line-to-line voltage. [I hate these ambiguities due to topic-specific "common-knowledge" jargon!]

Yeah, looks good as far as I can tell.

That would be my interpretation.

Yeah my prof likes to throw us off with his wording heh.
Thanks again for your help.
I have 3 more questions to go. Ill post them in this thread If I am stuck.
 
Nice! Good find :smile:
 

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