Bob said:
Hi all,
I want to know what is the right thing to measure leakage inductance, A
or B?
Check this out:
http://my.dreamwiz.com/jyeonsuk/qna/q_leakage_inductance.pdf
Method A - method B only measures the inter-coil capacitance.
The thinking underlying method A is that the voltages across coils 1
and 2 are given by
V1 = L1. dI1/dt + M. dI2/dt
V2 = L2. dII2/dt + M. dI1/dt
where M is the mutual inductance of the two coils. If the coils are
100% coupled, then
M = (L1. L2 )^0.5
Method A forces V1 to be zero
L1.d1/dt + M. dI2/dt = 0
This can be re-arranged to gives us an expression for d I1/dt
dI1/dt = - (M/L1) /dI2/dt
which can be substituted into the second equation to give us
V2 = L2. dI2/dt - M^2/L1. dI2/dt
The method is imperfect, because slightly more real coils have
resistance, which means that
V1 = L1. dI1/dt + M. dI2/dt + R1.I1
V2 = L2. dI2/dt + M. dI1/dt + R2.I2
An even more realistic mathematical model would take the parallel
capacitace of each coil into account, and a serious model would include
a third single turn "coil" to represent the current induced in the
transformer core ...
Hope this helps.
