This document provides an explanation of the principles behind a BiTT (Toroidal Transformer) system. It discusses how the BiTT uses saturation of a small primary core to control flux flow through secondary cores. Most secondary flux travels through the unsaturated secondary cores, while a small amount flows through the saturated primary core. This allows the BiTT to borrow reactive power from the source on the primary side, while delivering real power to loads on the secondary side.

1. A BiTTOF EXPLANATION
The principle in a nutshell

2. Rob Woudenberg
PrimCoil
Sec2
Coil
Sec1
coil
P-S1 P-S2
AC

no load no load
NO LOAD (1):
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Core

3. Rob Woudenberg
NO LOAD (2):
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Primary Core
Small volume
Near saturation
High flux reluctance
Uses large part of the B-H curve
HB
Used
B-H area
Iprim
Time
1
1
2
2

4. Rob Woudenberg
P-S1 P-S2
AC

On
load
On
load
S1-P
S1-S2
S2-S1
S2-P
PrimCoil
R
R
ON LOAD (1)
Sec1
coil
Sec2
Coil
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Core

5. Rob Woudenberg
ON LOAD (2)
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Secondary Cores
Big volume
No saturation:
Low flux reluctance
Uses only small part of the B-H curve
HB
Used
B-H area
Isec
Time
1
1
2
2

6. Rob Woudenberg
FLUX
 Initial primary flux P-S2 and P-S1 create near saturation,
making the primary core a high reluctance core part
 Counter flux P-xx caused by the load resistors at secondary
coils are created in non-saturated core parts and have low
reluctance
 The secondary fluxes can choose between a high reluctance path or
a low reluctance path.
 Most of the secondary flux will travel the low reluctance path, through the
secondary cores
 Remaining secondary flux will travel through the high reluctance path, through
the primary core
 Flux flow can be compared with current in a parallel resistor circuit:
 V represents the secondary flux source
 10 Ω represents the secondary cores as seen by the primary,
causes large flux flow
 10 kΩ represents the primary core as seen by the secondary,
causes small flux flow
10Ω
10kΩ
V
I1 I2
+
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7. Rob Woudenberg
COIL FLUX COUPLE COEFFICIENTS
The BiTT employs Mutual and Non-Mutual Coupling
Coefficients in symmetric and non symmetric ways
 Mutual coupling:
 Primary to Secondary 1* (≈0.5)
 Primary to Secondary 2* (≈0.5)
 Secondary 1 to secondary 2 (≈1)
 Secondary 2 to secondary 1 (≈1)
 Non-mutual coupling:
 Secondary 1 to Primary (≈0)
 Secondary 2 to Primary (≈0)
* Note : The Coupling Coefficient is actually 1 but each Secondary only gets
1/2 the Primary Flux which is akin to saying a CC of 0.5 when in fact it is actually a CC of 1.
PrimCoil
Sec2
Coil
Sec1
coil
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Core

8. Rob Woudenberg
Primary saturation area
Primary saturation area
FLUX TUNING
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In the BiTT, ideally,
secondary flux is 0 degrees
in phase with the primary flux.
This will block the flux in a
maximized way from the
secondary coils by
optimizing saturation of
the primary coil.
time
I
Prim
Sec
BiTT primary flux result
Secondary flux phase of a
common transformer
Common transformer
primary flux result
As a reference, the secondary
flux of a common transformer
will be ≈180 degrees out of
phase with the primary flux.
This leads to decrease of the
primary core saturation and
decreases the impedance as
seen by the power source at
the primary coil.

9. Rob Woudenberg
POWER FACTOR
 On no load
 BiTT ‘borrows’* mostly reactive power, PF0 ≈ 0
 On load
 The BiTT primary coil ‘borrows’* mostly reactive power,
PFL ≈ PF0- CL
 May slightly differ due to flux flow from secondary to primary coils,
causing a slight decrease of PF with an estimated correction
CL (0 <CL < 0.1)
* Borrows means power is returned to primary power source
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10. Rob Woudenberg
CONSUMED AND DELIVERED POWER
 Consumed and returned power
 Consumed power is equal to the real power consumed: Veff x Ieff x cos(*)
 Returned power is equal to the reactive power : Veff x Ieff x sin(*)
 Mainly determined by the impedance of the primary coil
 Bad couple factor (CC > 0) between secondary and primary coils may add extra
consumed real power
 Delivered power
 Driven by flux generated by primary coil
 In theory infinitive, but in practice limited by load value and internal coil
resistance of secondary coils
* Note:  is angle between voltage and current
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