Interruption Relay Wiring; Table 1 Relay Types Pros/Cons - Cortalk RMU5 Generic Installation And Configuration Manual

4.2.5 Interruption Relay Wiring

Wiring of the interruption relay requires some consideration for the type and size of rectifier being interrupted.
Consideration for lightning immunity is another issue that will affect relay type and installation point. Table 1 lists the
most common relay types along with their associated pros and cons.
Relay Type
Mechanical
Normally closed contact type
Mercury Displacement
Normally closed contact type
Solid State Triac (AC-only)
Installed on transformer primary
or
Installed on transformer sec. tap
Solid State MOSFET (DC-only)
Installed after rectifier diodes

Table 1 Relay Types Pros/Cons

The following figures show the most common connection methods for each of the relay types when installed on an AC
rectifier. The selected relay must be sized according to specifications from the relay manufacturer.
When using an alternate DC power source, such as thermo-electric generation or solar, only DC capable relays such as
mechanical, mercury displacement, or DC solid state MOSFET can be used on the output to the protected structure.
MOBILTEX® DATA LTD.
Calgary, Alberta
Pros
Inexpensive
Moderate cost
High current capacity
Low power loss (<10W w/100A load)
No heatsink required
Long contact life (millions of cycles)
Good lightning damage-immunity
Moderate cost
Good lightning damage-immunity
Fast switching
Low control current
High voltage switching(<=690VAC)
High current switching (<=125A)
Does not require external clamp diodes
No contact degradation over time
Least impact on pipeline waveforms
Fast switching
Lower switching surge
Low control current consumption
No contact degradation over time
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Cons
Short contact life (thousands of cycles)
Low current capacity (<25A)
Contact migration with DC loads
On/off activation times
High control current consumption
Environmental concerns
Transportation regulations
Disposal regulations
On/off activation times
High control current consumption
Requires heatsink
Large current surge (primary side)
Expensive
Poor lightning damage-immunity
Requires large heatsink
Requires external clamp diodes
Limited installation points
Maximum voltage/current tradeoff
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