Transformer models in EMTP/ATP

Core representation
• Attached to the fictitious N+1th winding
• Topologically “correct” core model, with
nonlinear inductances representing
each leg and limb
– Triplex
– 3- and 5-legged core
• Flux linkage-current relation by Frolich
equation and relative lengths and
areas.
• Fitting to Test Report
λ
i
λ =
a'
+ b'
⋅|
i |
i
R o
L l R l
L o
R y
L y
L l R l
R y
L y
L l R l
R o
L o
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11/6/2012
Transformer modeling at high
frequency
• Transformer models in EMTP are valid for
frequencies up to 2 kHz
• To study phenomena with characteristic frequency in
range of 2 - 30 kHz, capacitive coupling among
windings and to ground must be added
• Above 30 kHz a more detailed representation of
internal winding arrangement is required
– Interwinding and interturn/disks capacitances must be taken
into account
• Above 100 kHz the presence of ferromagnetic
material has just secondary importance.