Previous in Forum: Power factor Tariff   Next in Forum: relay setting
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
5 comments
Rate Comments: Nested
Butterfly2
Active Contributor

Join Date: Sep 2009
Location: Pakistan
Posts: 11

Transformer vs load

09/05/2009 1:07 AM

1. The customers connected to a transformer are operating electrical loads with name-plate rating totaling 250 kW

2. The 220-volt wiring between the load and transformer is properly sized and there is virtually no voltage drop on the circuit.

Case 2:

1. Same load.

2. The 220-volt wiring is substantially undersized and there is significant voltage drop on the circuit.

Question: Is the electric load seen by the transformer the same in both cases, or is the electric load on the transformer higher in the second case?
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
2
sb
Guru

Join Date: Mar 2007
Posts: 2550
Good Answers: 103
#1

Re: Transformer vs load

09/05/2009 1:45 AM

It depends on the type of load, and for that the 250KW rating is insufficient information.

Try to make an equivalent circuit on the load side. The circuit will be

1) Cable Resistance+ reactance (Inductive/capacitive as the case may be) both will be available from the cable data.

2) In series with load. The Load impedance will be dependant on the voltage available at its input.

- For certain loads, the power will be almost maintained constant, ie the drop in voltage will cause the current to go up, further dropping the voltage available, till it stabilises at some value- eg motors.

- For certain loads, resistive, the power is dependant on voltage - eg resistive loads.

- For some loads it may be a bit more complicated- the voltage drop in quite a few motors will cause speed drop, and that will result in power drop (especially if connected to pump) in cubic relation.

These are a few of the examples, just to show there is no straight answer to the question.

And remember there is a shooting up current in an already undersized cable.

__________________
 Fantastic ideas for a Fantastic World, I make the illogical logical.They put me in cars,they put me in yer tv.They put me in stereos and those little radios you stick in your ears.They even put me in watches, they have teeny gremlins for your watches
Register to Reply Good Answer (Score 2)
No more Good Answers. Go to first "Almost" Good Answer
harry potter
Power-User

Join Date: Nov 2008
Location: India
Posts: 333
Good Answers: 6
#2

Re: Transformer vs load

09/05/2009 11:38 AM

hi!

very interesting q.

it depends upon the customers using the electric load.

case 1 : if customers do not have faciclities like voltage stabilizers / boosters, then electric load in both the cases will be different, but to what extent is depending upon the nature of load. and losses or volt drops in the distributing net work. ( this is what the case with many supply authorities in India, where volt drops in the distribution net work provide low voltages to the users, leading to lower electricity billing collections, but unbilled distribution losses are to be born by the supply authorities )

case 2 : if customers have constant power or fix speed loads ( say by voltage boosters / compressors, induction motors ), then power consumption in actual load by customers plus significant energy losses in the distribution net work = load on transformer, which is definitely higher then your case 1.

__________________
 Exploring the Science of Electricity
Register to Reply
dkwarner
Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 6215
Good Answers: 248
#3

Re: Transformer vs load

09/05/2009 11:57 PM

Measure it and find out!

__________________
 Teaching is a great experience, but there is no better teacher than experience.
Register to Reply
soebfatehi
Power-User

Join Date: Jun 2009
Posts: 223
Good Answers: 15
#4

Re: Transformer vs load

09/06/2009 2:10 AM

to analyze this one requires to know the power factor of the load and the resistance and capacitance of the cable . . . in any case the load seen by the transformer will be the vector sum of the cable as a load and the applied load . . . hence bigger as a "load" . . . the connected load will suffer an undervoltage and it remains to be seen if it can be driven effectively.
Register to Reply Score 1 for Good Answer
No more "Almost" Good Answers.
jraubsr
Power-User

Join Date: Sep 2009
Location: Houston, TX
Posts: 118
#5

Re: Transformer vs load

09/13/2009 6:32 PM

The transformer is oversized!

__________________
 Thank you for your help - By far the best info site!
Register to Reply
Register to Reply
Have a Different Question?
5 comments

Good Answers:

These comments received enough positive votes to make them "good answers".

"Almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, vote them!
Copy to Clipboard

Users who posted comments:

dkwarner (1); harry potter (1); jraubsr (1); sb (1); soebfatehi (1)

Previous in Forum: Power factor Tariff   Next in Forum: relay setting

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General Discussion
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (61 right now)
Show Members
Advertisement