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1.
INTRODUCTION
1.1
MULTILIN RELAY FEATURES
The Multilin relay is designed to fully protectthree phase
AC
motorsagainstcon-
ditions which can cause damage.
In
addition to motor protection, the relay has
features thatcan protectassociated mechanical equipment, givean alarm before
damage results from a process malfunction, diagnose problems after a fault and
allow verification of correct relay operation during routine maintenance.
One relay is required per motor. Since phase current is monitored through cur-
rent transformers, motors of any line voltage can be protected. The relay is used
as
a pilot device to cause a contactor or breaker to open under fault conditions;
that
is,
it does
not
carry the primary
motor
current.
TABLE
1-1
MULTILIN RELAY PROTECTION FEATURES
PROTECTION FEATURES
Overload (Selectable Curves) Trip/Alarm Outputs
Locked Rotor Status Indication
Stall-Mechanical
Jam Fault Diagnosis I
Repeated Starts Memory Lockout
Single Phase/Unbalance Simple
Adjustment-No
Tools
Ground Fault Easy to Retrofit
Over
Temperature Field Testable
Undercurrent CSA Approval
1.2 TYPICAL APPLICATIONS.
Versatile features and controls allow the relay to protect associated mechanical
equipment
as
well
as
the motor. In addition to the basic electrical protection for
motors listed in table 1-1, the relay can protect against common faults due to
process problems such as:
1)
Personal safety and mechanical
protection
of
pumps using the undercur·
rent feature
to
detect
loss
of
suction
or
a closed discharge valve.
2)
Personnel
safety
and mechanical
protection
of
tans against loss of air flow
in
mines or flow in steam generating boilers using the undercurrent feature.
3)
Electrical protection ofcompressormotorsfrom excessive run-uptimecaused
by
an
open outlet using the start timer.
4)
Mechanical protection
of
gears, pumps, fans, saw mill cutters and com-
pressors against mechanical jam using the rapid trip feature.
5) Safetyto personnel from shock hazard using the ground fault feature to detect
winding shorts
or
leakage currents from moisture
in
mines.
6) Protection of motors and equipment from operator abuse using the thermal
memory lockout feature.
1
Courtesy of NationalSwitchgear.com
