Datasheet

INTERACTION
A sudden current change within a conductor generates Radio Frequency Interference (RFI). Thus,
unsuppressed Phase Angle thyristor or triac power systems inherently generate RFI, rising to
maximum at mid-phase angle. High impedance Phase Angle controlled thyristor trigger circuits can
be considered as sensitive receivers of any generated RFI.
These two characteristics of adjacent Phase Angle controlled systems can cause interaction (also
called Cross-talk or Tracking), unless the following procedures are used.
Zero Voltage Switching (ZVS) control removes this problem and should always be first choice in
multi-thyristor systems for resistive loads.
Both Phase Angle and Burst Firing control are detailed further on page 2.
INTERACTION
CAUSES AND REMEDIES
ITA
X10213
INTERACTION REMEDIES IN PHASE-ANGLE CONTROL SYSTEMS
In sensitive applications, interference must be suppressed to comply with Electromagnetic
Compatibility Regulations 1992 (SI 1992 No. 2372), this includes emissions and immunity
standards, to prevent and protect against interaction with other components. This may be achieved
by the addition of a series, parallel combination filter network.
The following guidelines are important aspects for correct circuit layout, to help eliminate interaction
problems in power application circuits:-
1
Run both leads of each power circuit as a twisted pair and when practical, avoid close proximity to
other RFI transmitting or receiving components. Earth leads should be rated higher than the
maximum power of the circuit and kept as short as possible.
2
Ideally, to achieve the above, keep the widest possible spacing between phase angle firing controlled
circuits and other large power carrying conductors.
3
Any high impedance signal/control wires should be kept as short as possible, preferably twisted,
shielded and separate from power cables.
4
Avoid wires encircling magnetic components (e.g. Transformers).
5
A series inductance fitted in the supply line will limit di/dt at thyristor switch-on and consequent
transmitted output, reducing the risk of interaction ( See RFI Data Sheet).
Interaction is a whole system phenomena resulting from the nature of phase-angle thyristor control
and will almost always be eliminated by some or all of the above steps.
RFI FILTERS
A ‘type’ filter would normally be required because of the function of Phase Angle control firing of
Power circuits, to reduce the RFI to an acceptable level of EMC emission standards. These standards
are identified on the appropriate Declaration of Conformity, to address the ‘CE’ marking of products.
Particular attention should be paid to ‘good earth bonding’ and current selection for the F1-series
‘type’ filters which incorporates a series choke, to achieve maximum choke efficiency.
see also RFI Datasheets for connections and available ‘type’ filters.