Complex Imaginary Test 2 Problem 51

[Wildsoldier PE]

In this problem the voltage of the generator was not given. The way the problem was made makes it a very lonnngg problem... In the solutions they didn't count the Voltage drop in the line to get the output voltage of the generator which i think that to get the accurate generator voltage the voltage drop in the line needs to be counted. Attached is the way I worked this problem which took me like 12 minutes or more to solve. The solution using my way is not in the answers.

Let me know what you think!

 

[DK PE]

I just glanced quickly and just my $0.02 worth but I think you're making the problem too difficult. Determine the voltage at the generator just by using the turns ratio and ignoring losses (3125V). This establishes the base voltage/kVA/base Z AT THE GENERATOR. Then determine the bases at the point the line is (i.e. between the transformers, not the same base impedance as at the generator). Then convert the absolute impedances given to p.u.

I assume no connection Delta/Wye were given in the problem statement.

 

[Flyer_PE]

I just glanced quickly and just my $0.02 worth but I think you're making the problem too difficult. Determine the voltage at the generator just by using the turns ratio and ignoring losses (3125V). This establishes the base voltage/kVA/base Z AT THE GENERATOR. Then determine the bases at the point the line is (i.e. between the transformers, not the same base impedance as at the generator). Then convert the absolute impedances given to p.u.
I assume no connection Delta/Wye were given in the problem statement.

I would add that you don't need to know the generator output voltage to determine the PU value of the line. Simply determine the base impedance using the line voltage (6250 V) and the rated generator output of 20 kVA.

 

[Wildsoldier PE]

I just glanced quickly and just my $0.02 worth but I think you're making the problem too difficult. Determine the voltage at the generator just by using the turns ratio and ignoring losses (3125V). This establishes the base voltage/kVA/base Z AT THE GENERATOR. Then determine the bases at the point the line is (i.e. between the transformers, not the same base impedance as at the generator). Then convert the absolute impedances given to p.u.
I assume no connection Delta/Wye were given in the problem statement.

I would add that you don't need to know the generator output voltage to determine the PU value of the line. Simply determine the base impedance using the line voltage (6250 V) and the rated generator output of 20 kVA.

So for this type of problems shall i assume no voltage drop on the line to get the generator voltage?

 

[knight1fox3]

So for this type of problems shall i assume no voltage drop on the line to get the generator voltage?

I doubt that would be factored into the problem. NCEES tries to keep the problems simple and conceptual. Furthermore, if you don't know the length of the line or ohms to neutral, you won't be expected to account for voltage drop.

 

[DK PE]

So for this type of problems shall i assume no voltage drop on the line to get the generator voltage?

I would say this is a very typical problem where you are being tested on whether you know how to determine the bases at various parts of the system. In the example calcualations you showed, it appears you made a big assumption that the motor was running at ratings when in fact it could be disconnected. The voltage drop on the line is dependent on the load and in this case it isn't given.

You really need to know how to quickly look at a one-line like this, choose bases or use those given and determine the bases at various points in the system.