Calculation of TRU input KVA 1

[patayloruk]

Could someone help me work out the KVA input to a TRU using the following information?

O/P DC amps=270 @ 28VDC
Efficiency 78%
Input is 115VAC 3 phase
power factor is = or better than .97

I have done some calculations and come up with Iput Amps per phase of 17.092 and a KVA rating of 5.72, is this correct?

Thanks in advance

Paul

 

[DanDel]

Assuming that 'O/P DC amps' is your load, then:
270A x 28V = 7560W
Efficiency of 78% would cause the DC input to the load to increase:
7560W/0.78 = 9692W
This value at 115V 3-phase(are you sure this is correct? not 120/208V or 115/200V 3-phase? What is the actual phase-to-phase voltage?):
kVA rating is:
9692W/0.97 = 9992VA
9992VA/115V(or whatever the phase-to-phase voltage is)/1.73 = 50.2A per phase

 

[jbartos]

Suggestion to the original posting: Additional information will be helpful, namely, there is a conversion AC-DC involved that has some efficiency, which is not stated. Also, the input needs to be clarified, whether it is 115V, 3phase, 4-wire implying the 208V input voltage phase to phase, namely, 208V/120V 3phase, 4-wire input. 115V 3phase 3-wire power supply is somewhat rare.

 

[patayloruk]

The input is 4 wire 115/200 Y connection
The efficiency of the TRU is 78%

 

[busbar]

TRU? {...for the Great Unwashed.}

 

[rbulsara]

The convention is to mention Line to Line voltage for a 3 phase suppply. For a 200Y/115V system, the 3-phase power should be called a 200V, 3-phase not 115, 3-phase as you mentioned. 115V is the per phase voltage for L-N neutral loads.

Your kVA rating is 9.992 or 9992 VA as stated earlier by dandale.

The line current will be 9992VA/(1.732*200V)=29A amps.

This assumes a 3 phase rectifier!

 

[patayloruk]

Thanks all

 

[busbar]

patayloruk, pardon me, but what is a TRU?

 

[stevenal]

From Gurunet:

TRU
TRU stands for:


Technical Resources Unit
Teenage Research Unlimited
Test Replaceable Unit
The Real Untouchables (rap group)
Thermal Receiving Unit (M1 tank thermal sight)
Thrust Reverser Unit
Total Return Unitrust
Toys R Us
Transformer Rectifier Unit
Transitional Rehabilitation Unit
Transmit Receive Unit
Transuranic (Nuclear Waste)
Transuranic Waste
Trujillo, Peru - Trujillo (Airport Code)
Turbidity Reducing Unit

 

[jbartos]

Comment on patayloruk (Electrical) Mar 11, 2004 marked ///\\Could someone help me work out the KVA input to a TRU using the following information?
O/P DC amps=270 @ 28VDC
Efficiency 78%
Input is 115VAC 3 phase
power factor is = or better than .97

I have done some calculations and come up with Iput Amps per phase of 17.092 and a KVA rating of 5.72, is this correct?
///No, it is not since the calculated 5.72kVA are smaller than the output kVA=kW=270ADC x 28VDC = 7560W. Where would the 7560W - 5720kW= 1840kW disappear?