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Revision 8.6
SECTION 2 : SYSTEM DESIGN
25
2.13.1.
Contactor Switching Times
The THYROMAT is designed to be able to switch contactors at zero current, parameters are provided
to enable the user to set the correct switching times so that, during contactors change over arcing is
avoided.
It is imperative that the users make themselves familiar with the contactors switching times relevant to
the installation.
2.13.2.
Contactors Drop Out Times
During directional contactors change over the THYROMAT provides a delay between the time that the
thyristors are turned off until the time that the contactor is de-energised. This will ensure that there is
no current flowing in the circuit at the instant that the contactor is required to drop out. This process
increases the electrical life of the contactor and allows the use of contactors with AC1 ratings as
opposed to contactors with AC3. Refer to Phase Shifter ON and OFF time parameters for further
details.
2.14. SELECTION OF CURRENT TRANSFORMERS
When selecting the current transformer (C.T.) ratio the following formula gives the minimum ratio that
should be considered:
C.T. rating > 60% of motor full load current
Example:
Motor full load current = 125A
Therefore the C.T ratio > 125/0.6
= 208,3A
The closest C.T. ratio available in the Thyromat BD is 300:1 A.
The available C.T. ratios are:
050:1
800:1
100:1
1000:1
200:1
1200:1
300:1
1500:1
400:1
2000:1
500:1
2500:1
600:1
3000:1
Note
CT’s are required for all hoist applications and
optional for travels.
All CT’s should have a VA
rating of at least 5 VA
