User Manual

3UG4 / 3RR2 monitoring relays
Manual, 02/2013, NEB927043002000/RS-AA/002
205
3UG458. insulation monitoring relay.
10
Overview
The 3UG458. insulation monitoring relays are used for monitoring the insulation resistance
(in accordance with IEC 61557-8) between ungrounded single-phase or three-phase AC
systems and a protective conductor.
The family comprises the following devices:
● Insulation monitoring relays for ungrounded AC systems with a rated system voltage of
up to U
n
= 400 V AC.
● Insulation monitoring relays for ungrounded AC systems, DC systems, and mixed AC/DC
systems with a rated system voltage of up to U
n
= 250 V AC and U
n
= 300 V DC.
● Insulation monitoring relays for ungrounded AC systems, DC systems, and mixed AC/DC
systems with a rated system voltage of up to U
n
= 400 V AC and U
n
= 600 V DC.
The measuring range can be extended up to U
n
= 690 V AC and U
n
= 1000 V DC by
using an upstream module.
Ungrounded, insulated systems (IT networks) are always used when high requirements are
placed on the reliability of the power supply, e.g. emergency lighting. IT systems are
supplied via an isolation transformer or voltage sources such as batteries or a generator. An
insulation fault that occurs between an external conductor and ground represents a
grounding of this conductor. This does not result in the closing of a circuit and operation can
continue without hazard (single fault security). Before a second insulation fault occurs, the
first fault must be corrected (e.g. in accordance with DIN VDE 0100-410). Insulation
monitoring relays are used to implement this requirement. The insulation monitoring relays
measure the resistance of the external conductor and the neutral conductor against ground,
and immediately report a fault if the set insulation resistance is undershot. This procedure
enables controlled shutdown, or correction of the fault without interrupting the power supply.
The insulation monitoring relays monitor the following fault types, depending on the version:
● Open circuit
● Incorrect settings
● Ungrounded, strictly AC systems for insulation faults
● Ungrounded, strictly DC systems for insulation faults
● Ungrounded, mixed DC systems and AC systems for insulation faults (e.g. AC systems
with rectifiers or switched-mode power supplies)