2.3 KiB
Special Transformers
Instrumentation transformers
6900V line. Its hard to make a meter for that. So, we make special transformers so we can measure it.
Potential Transformer
book calls em “Voltage transformers”
denoted as PTs, POTs, or VTs
Used for monitoring voltage and power.
This is what your power meter is on the side of your house
Made to have a high impedance. This means that you don’t have much power on the low voltage side, so its more accurate.
Current Transformers
used for monitoring current.
denoted as CTs
Usually 1 turn around the incoming cable.
Used in contactless current measurement
Used for exceedingly high currents (>400A)
If you ever deal with a current transformer, don’t touch it. The voltage on the meter is GIANT. And WHATEVER YOU DO. ==DON’T BREAK THE CIRCUIT.==
Always ground the secondary.
Large Design Problem
Given voltage and short-circuit/widthstand current
V_{util}=U
You may be given X\over R
Awesome. Now we know what the utility looks like.
This is all what we’ve done in class so far.
Now, we’re gonna add a transformer.
Z_{base}=\frac{E_p^2}{S}=\frac{4160V^2}{500kVA}\
Z_{base}=34.6\Omega\
Z_f=Z_{base}\times5%\
Z_f=1.73\Omega
Now we’re gonna add a load.
Alright. Given this, use the calculations above, and the following:
Z_{util}={4160V\over10kA}=0.416\Omega
You can now convert to a simple circuit like this:
[^1]
This can help you find I_p. You can then calculate I_s, calculate power, etc. etc. etc.
Or, you can find V_p for the transformer. This can also be represented at V_{FL}
Now we can find regulation:
regulation={V_{NL}-V_{FL}\over V_{FL}}
We can also find efficiency:
Efficiency ={P_{out}\over P_{in}}={V_{load}\times I_{load}\over V_{util}\times I_p}
Simple Circuit Review
Given a simple circuit, with just Z_{in} and V_{in}
All given numbers are in RMS
If you are asked to graph the waveform, tack a \sqrt2 on the end.
Inductors lag, capacitors lead
V_L=\frac{V_\phi}{\sqrt3}
Review delta vs wye
[1]:a2 actually means a^2, but qucs doesn’t understand powers in component names