3-Phase Monitor Relays Overview by Macromatic
3-Phase Monitor Relays protect motors and equipment from expensive
damage due to voltage faults on three-phase systems. Refer to the table
below for more information on the level of protection offered by each
product, then click one of the Series to see details about a specific
product type.
All products work on 50/60 Hz 
Depending on the unit selected, it will protect three-phase equipment against:
Phase Loss: - total loss of one or more of
the three phases. Also known as "single phasing." Typically caused by a
blown fuse, broken wire, or worn contact. This condition would result
in a motor drawing locked rotor current during start-up. In addition, a
three phase motor will continue to run after losing a phase, resulting
in possible motor burn-out.
Phase Reversal: - reversing any two of the
three phases will cause a three phase motor to run in the opposite
direction. This may cause damage to driven machinery or injury to
personnel. The condition usually occurs as a result of mistakes made
during routine maintenance or when modifications are made to the
circuit.
Phase Unbalance: unbalance of a three phase
system occurs when single phase loads are connected such that one or two
of the lines (phases) carry more or less of the load. This could cause
motors to run at temperatures above published ratings.
Undervoltage: when voltage in all three lines
of a three phase system drop simultaneously. This could result in an
increase in current & motor heating and a reduction in motor
performance.
Overvoltage: - when voltage in all three
lines of a three phase system increase simultaneously. Could cause a
decrease in load current & poor power factor.
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