I'm trying to find something that would work as a voltage-controllable resistive load. I thought something simple might be available--where a DC control voltage could be used to yield a range of resistance values. Here are the basics:
Resistance: span ~ 200-20,000 ohms.
Sink capability: DC...
I understand how to translate positive sequence resistance values if they show up at a non-standard temperature on the test report.
But what if this happens with the provided zero sequence T-model test data? Section 9.5.3 of IEEE Std C57.12.90-2006 references Z1, Z2, and Z3 as "Constants" in...
We have formulas that estimate the zero-sequence impedance for CORE transformers based on the positive sequence values as follows:
2-winding: Z0 = Z1 x 0.90
3-winding: ZHL0 = 0.85 x ZHL1
ZHT0 = 0.75 x ZHT1
ZLT0 = 0.90 x ZLT1
Should it be the impedance that is...
Can anyone tell me why the above-mentioned standard goes through the trouble of defining the Protective Level "classification current" types in section 4.3.1, and then changes the terminology in section 5.4 to "coordinating current?"
thx,
john
Can someone familiar with electric utility practices tell me whether surge arresters are typically used for Capacitor Bank switching applications--for 69kV ungrounded double "Y" banks?
thx,
- john
Do any of you regularly include shunt capacitor banks in your overall system models when performing short-circuit calculations/Breaker rating studies, or do you consider this a dynamic situation that is distinct from this process?
- john
Hi...
Can someone provide a technical distinction between a surge arrester and a surge suppressor? I believe they are both given under the umbrella term, "surge protective device"?
thx,
john
Hi...
We initially specified a 69/13.8 kV transformer with an impedance of .1942 p.u. (56 MVA, 69 kV).
Then it was decided to specify the transformer with a high-side voltage of 67.275 kV instead.
The goal was to come up with an equivalent impedance at the new highside voltage... so that we...
In order to limit the Capacitor Outrush current for two 14.4 MVAR and one 18 MVAR 36 kV Capacitor Banks, it was determined that an 800 uH reactor will be required--for a General Purpose Breaker.
What would be the corresponding reactor size when using a Definite Purpose Breaker instead?
If a transformer test report, etc. references an "impedance voltage" in "%", then are they really giving you the impedance? [My understanding is that the impedance voltage is the voltage used during the short circuit test which causes the full load current to circulate; and...
Hi...
Is the procedure for calculating resistance the same for zig zag transformers as for other transformers; i.e. are there any subtleties to performing the load loss/kva load calculations?
thx,
john
Hi...
Given that one uses the series (winding) resistance values from the transformer test reports to estimate* the resistive part of transformer impedance...
...And for a 3-phase transformer, one uses the sum of the resistance values for the 3 phases... what does one do if the given...
Hi...
If a transformer test report specifies an impedance at a temperature other than expected, is there a required correction? I know that there are temperature adjustments for copper loss and resistance.... This would imply some affect on impedance as well.
In some cases the impedance is...
Because of a discrepancy in some data, I attempted to verify some charging current/charging power calculations, and I am at a loss. I have obtained the following formulas from an underground transmission systems reference book:
a. X1 = X0 = [1/(2*pi*f*C)] * 10E+6 Ohms/1000 feet
b. Ic =...
