SPDM CONTROL BOX 2 – COMPOSITION
NIDEC ASI S.P.A. – SPDM CONTROL BOX USER MANUAL
IMSPDCB2EN 23
C - D closed
A - C open
B - D open
jumper JP1 closed
X52 - X53 resistor R176 22k
X54 - X55 resistor R177 22k
2.7.2 CT load resistors (burden resistors)
The burden resistors, normally mounted on card P at terminals X56, X57 - X58, X59 (that are internally connected in parallel), set the
maximum delivered current la
M
.
The voltage between positive terminal X57 (or X59) and negative terminal X56 (or X58) is proportional to the current: 2·V (average)
corresponds to the maximum converter current.
For the burden resistors calculation it is necessary to introduce the following definitions:
Ia
M
= maximum converter output current : maximum current value to be delivered in permanent conditions by the converter
(parameter [06.53]).
Ia
N
= rated current of the motor : max current to be drawn in permanent conditions by the motor (parameter
[05.03]).
NOTE: The Ia
M
current can be higher than the Ia
N
, provided that is in accordance with the motor load cycles.
The following relationship is valid
R = 2
N
Ia
p
S
M
•
Where N
S
is the equivalent Current Tranformers turns ratio connected to terminals X10A-1… X10A-4.
Rp is the equivalent burden resistance (in Ohm). Such resistance can be obtained by soldering two resistors on the turrets x56 – 57 and x58 –
59 placed inside the control-box on the P-board (the turrets x56-57 are internally connected with the turrets x58 – 59).
As alternative, the burden resistors can be placed outside the control box connecting them to the terminals X10A-7 and X10A-8.
The connection to the external burden resistors should be made using a 1m maximum length of unshielded twisted-pair with section of 2.5 mm
2
(AWG14).
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