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Revision 8.6
SECTION 2 : SYSTEM DESIGN
24
2.12. SELECTION OF CABLES
The following paragraphs detail the selection of power supply and control power cables.
2.12.1.
Power Supply Cables
The specifications of the mains power supply cables must be calculated according to recognised
standards (e.g. BS 7671) a
nd the cable manufacturer’s recommendations.
Several factors need to be taken into consideration to ensure selection of the correct power supply
cables. The most important considerations are; the ambient operating temperatures, the cyclic duration
factor of the application, the cable length and the voltage drop across the cables caused by higher
motor currents during acceleration and reverse plugging conditions.
The selection of the main circuit breaker and the trip setting value should be taken into account when
selecting the mains power cables. It is advisable to select the cables conservatively to ensure that
efficient protection of the thyristor stack is not compromised.
Armoured PVC insulated cables are normally used along the bridge and crab, and flexible PVC or
rubber-insulated cables are used on festoon systems. The selection of cable selection also largely
depends on the environmental conditions that the crane will operate in.
2.12.2
Control Supply Cables
The THYROMAT uses interposing relays to allow the use of an external control voltage of 110 VAC or
220 VAC, which is not sensitive to external noise interference. Therefore the use of standard
armoured control power cables is sufficient, the cables should have a minimum diameter of 1.5 mm²,
preferably a cable diameter of 2,5 mm² should be used for improved mechanical strength.
2.13. SELECTION OF STATOR REVERSING CONTACTORS
It is only necessary to rate the contactors for thermal current (Ith) because the THYROMAT switches the
reversing contactors at zero current and voltage. The thermal current selection depends on the type of
application (i.e. Standard or Severe Crane Duties).
For Standard Duty applications, at least 1.1 x In (nominal current) at AC1 rating is recommended.
For severe duty applications, at least 1.4 x In (nominal current) at AC1 rating is recommended.
Example:
A slip-ring motor is to be used in a severe application, the motor has a mechanical rating of
100 A.
Therefore:
AC1 = 1.4 x In
= 1.4 x 100
= 140 Ampere
According to information provided by the manufacturer the selected contactors would be LC1-F115 which
has a rating of 200 A at AC1 or 115 A at AC3.
