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Revision 8.6
SECTION 2 : SYSTEM DESIGN
21
Table 2-7 : Resistor Values
Motion
Ohms
% of K
R1
TOT
R2
TOT
R3
TOT
R4
TOT
Hoists, all motions with adequate torque margins
0.36 K
100
9
18
36
Hoists, large motors and motors with low torque margins
0.65 K
100
9
18
36
65
Travels
0.3 K
100
30
-
-
-
It is a requirement that a crane has the ability to lift 125% of the nominal load. This factor must be taken
into account during commissioning process only.
When selecting the current carrying capacities of the resistor grids and sections, the following factors
need to be considered:
Ambient temperature
Duty cycle
Slow speed operations
2.9.
SELECTION OF MAINS CIRCUIT BREAKERS
It is critical that the selection of the mains circuit breaker for the THYROMAT must be able to protect the
THYROMAT unit against most current surges.
It is
strongly recommended
that a circuit breaker type such as manufactured by Merlin Gerin (part
number NS
---
N-STR2
-
E or similar) is used. The suggested circuit breaker (STR electronic trip unit), is one
of the most flexible circuit breaker types with regards to protection settings in both the low and high short-
circuit protection ranges. The circuit breaker also has reflex tripping which is triggered by the energy
dissipated within the device when a short-circuit condition is experienced.
The correct selection of the circuit breaker will depend on the thyristor stack current rating and the slip-ring
motors nominal current rating. Table 2-8 lists the circuit breaker selection details for the various thyristor
stacks. It is possible to downsize the selected circuit breaker by matching it with current rating of the
individual slip-ring motor.
