Progress Report 7
7/12/05-7/19/05
There were issues with the inductance measurements I took last week that were to
be ironed out this week. Based on last week’s measurements, the magnetizing inductance
I extracted was very close to the desired value of 6.4mH. After reviewing the equipment
and procedure with Dr. Ngo, I went to SABER to run some theoretical simulations that
would tell me what to expect when using the measurement equipment. The simulation
schematics can be found here. These schematics show two configurations of the
transformer: one with the secondary side “opened” (the 1GΩ resistor) and one with the
secondary side “shorted” (the 0.00001Ω resistor). The input impedance seen from these
two schematics can be seen here. From these values at 60Hz, the input inductance can be
calculated and equations can be extracted.
3.6191
 9.6mH
2 (60)
2.0118

 5.34mH
2 (60)
Lin open 
Lin  short
A quick examination of the schematic tells that the open circuit inductance is merely the
sum of the magnetizing inductance and the primary leakage inductance. Thus,
Lin open  LM  LLP
Only slightly more complicated is the short circuit inductance. A quick examination of
the circuit shows that the leakage and magnetizing inductance become paralleled once the
load is shorted. Thus, the input inductance seen by the measurement device will be the
parallel combination of the secondary leakage and the magnetizing inductance summed
with the primary leakage:
Linshort  LLP  LM LLS
These new results warranted a new round of measurements be conducted to
ascertain the truth values for the transformer. Using the Wayne Kerr impedance analyzer
set for 100mV at 60Hz, the transformer was tested again. This time the inductance
measurements were taken solely from the inductance model, not the transformer model.
First, the inductance was measured from the primary side with the secondary
opened. Then, the secondary was shorted and the inductance was again measured. Finally,
the secondary was measured with the primary opened. This was done to ensure the
secondary leakage value was accurate, also. The table below gives all the data:
Input L
Primary (secondary
Primary (secondary
Secondary (Primary
open)
shorted)
open)
6.61mH
3.41mH
6.63mH
6.61mH  LM  LLP
6.63mH  LM  LLS
3.41mH  LLP 
LM  LLS
LM  LLS
3.41mH  (6.61mH  LM ) 
LM *(6.63mH  LM )
6.63mH
 LM  4.61mH
 LLP  2mH , LLS  2.02mH
The values for the current transformer are a 4.61mH magnetizing inductance and
approximately 2mH of leakage inductance per side. While this is short of the expected
6.4mH of magnetizing inductance, it does show that the original assumption that the
leakage would be half the magnetizing was fairly accurate.
The next step is to integrate these values into the simulation to determine the
value of the input capacitor that will still ensure the output of the rectifier will have 20V
and 15W. Recall the schematic here. The inductors were replaced with their new values
and the input capacitor was found to be 112uF.
There are still issues that I will take up with Dr. Ngo tomorrow concerning the
testing of the transformer. Chief among these concerns are the coupling of the data
transmission primary to the power secondary, input current levels, and input resistance.
Dan
7/12/05