BECKWITH ELECTRIC M?3311A, Instruction Book, Page: 228 / 450

4–101
System Setup and Setpoints – 4
4.6 Transformer Connections
Transformer Winding Selection
The M-3311A can be applied in either a two, three
or four winding transformer differential application.
For applications where a two or three winding differ -
ential is required, the user can set the relay system
configuration for
Two Winding
and designate the
winding current that will be disabled in the 87 Phase
Differential Current function.
Only the current input to the 87 function of the
disabled winding is not functional. All other func -
tions associated with the disabled winding may
be enabled if desired. If the application requires a
separate overcurrent function, the user may enable
the desired overcurrent functions.
Transformer and CT Configuration
The M-3311A includes Standard and Custom
methods of defining the transformer winding and
CT configurations. The Standard and Custom Con-
figuration options are made available by selecting
either
Disable
or
Enable
for the
Custom Mode for
Transformer and CT Connection .
Standard Transformer and CT Configuration
The standard transformer and CT configuration
selections consist of six connections for each trans -
former winding and CT configuration. The selectable
configurations are:
• Wye
• Delta-ab
• Delta-ac
• Inverse Wye
• Inverse Delta-ab
• Inverse Delta-ac
When the user selects from these connection
combinations, the relay automatically computes
the phase and magnitude compensation required
for the differential currents. The general expression
for the compensation is given below.
I
A
CompW
n
I
A
W
n
I
B
CompW
n
= Connect Type (WN)
I
B
W
n
I
C
CompW
n
I
C
W
n
( ( ) )
Where:
•
I
A
W
n
,
I
B
W
n
, and
I
C
W
n
are the uncompen-
sated currents entering/exiting winding “n”
of the transformer.
•
I
A
CompW
n
, etc. are the compensated
phase currents after being multiplied by
the 3x3 matrix ConnectType(N).
• The ConnectType(N) is a discrete number
representing the number of 30 degree
increments a balanced set of currents
with abc phase rotation will be rotated in
a counterclockwise rotation.
Types 0–11 correspond to phase shifts
of; 0°, 30°, 60°, …, 330° with a magnitude
gain of 1.
Types 13–23 correspond to phase shifts
of; 0°, 30°, 60°, …, 330° with a magnitude
gain of 1/
S
3.
The compensation calculation uses a counter
clockwise rotation from zero. Therefore a Delta-ab
transformer (defined as 30 degree leading) has a
compensation phase angle shift of 330°, (11x30°).
The Delta-ac transformer (defined as 30° lagging)
has a compensation phase angle shift of 30°,
(1x30°). For a system with acb phase rotation, the
compensation calculation uses a counterclockwise
rotation. For users more familiar with the IEC trans -
former configuration nomenclature, a comparison
between the IEC definitions and the Beckwith con -
nections is provided in Table 4-4. An example of
a ConnectType(1) or 30° compensation matrix is
illustrated below.
I
A
CompW
n
1 -1 0
I
A
W
n
I
B
CompW
n
= 0 1 -1
I
B
W
n
I
C
CompW
n
-1 0 1
I
C
W
n
Phase Angle Shift - Standard Connections
All inputs are compensated against a Reference Vec -
tor of zero degrees. The six standard connections
referenced previously result in 6 compensation types
for each transformer winding and 12 compensation
types for each CT. The transformer compensation
types are; 0, 1, 5, 6, 7, and 11, which correspond
to 30 degree phase shift multiples of; 0°, 30°, 150°,
180°, 210°, and 330°, all with a gain of one.
The CT compensation types consist of those com-
pensation types listed above and types 13, 17, 19,
and 23. Type 13, 17, 19 and 23 correspond to 30
degree phase shift multiples of; 30°, 150°, 210°,
and 330°, but with a magnitude gain of 1/
S
3.
( ( ) ) ( )