ABB 41-101U, Instruction Leaflet

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41-101U Type CO Overcurrent Relay
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2.0 CONSTRUCTION AND OPERATION
The type CO relays consist of an overcurrent unit
(CO), an indicating contactor switch (ICS), and an in-
dicating instantaneous trip unit (IIT) when required.
The principal component parts of the relay and their
location are shown in Figures 1 through 5.
2.1 ELECTROMAGNET
The electromagnets for the types CO-5, CO-6,
CO-7, CO-8 and CO-9 relays have a main tapped
coil located on the center leg of an “E” type laminat-
ed structure that produces a flux which divides and
returns through the outer legs. A shading coil causes
the flux through the left leg to lag the main pole flux.
The out-of-phase fluxes thus produced in the air gap
cause a contact closing torque. A torque controlled
CO has the lag coil connections of the electromagnet
brought out to separate terminals. This permits con-
trol of the closing torque such that only when these
terminals are connected together will the unit oper-
ate.
The electromagnets for the types CO-2 and CO-11
relays have a main coil consisting of a tapped prima-
ry winding and a fixed secondary winding. Identical
coils are on the outer legs of the lamination structure
and are connected to the main coil fixed secondary
in a manner so that the combination of all the fluxes
produced by the electromagnet result in out-of-
phase fluxes in the air gap. The out-of-phase air gap
fluxes produced cause a contact closing torque.
2.2 INDICATING CONTACTOR SWITCH UNIT
(ICS)
The dc indicating contactor switch is a small clapper
type device. A magnetic armature, to which leaf-
spring mounted contacts are attached, is attracted to
the magnetic core upon energization of the switch.
When the switch closes the moving contacts bridge
two stationary contacts, completing the trip circuit.
Also during this operation two fingers on the arma-
ture deflect a spring located on the front of the
switch, which allows the operation indicator target to
drop.
The front spring, in addition to holding the target,
provides restraint for the armature and thus controls
the pickup value of the switch.
2.3 INDICATING INSTANTANEOUS TRIP UNIT
(IIT)
The instantaneous trip unit is a small ac operated
clapper type device. A magnetic armature, to which
leaf-spring mounted contacts are attached, is at-
tracted to the magnetic core upon energization of the
switch. When the switch closes, the moving contacts
bridge two stationary contacts completing the trip cir-
cuit. Also, during the operation, two fingers on the ar-
mature deflect a spring located on the front of the
switch which allows the operation indictor target to
drop.
Figure 6: External Schematic of the Circuit-Closing Type CO Relay for Phase and Ground Overcurrent
Protection on a Three-Phase System.
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