If PIM 2 is at risk from disturbance from PIM1, it If the power supply upstream of the UPS is lost can be shut down by relay R1 if the transformer and if the neutral conductor remains connected, secondary voltage is zero.
this RCD will continue to provide protection, as Protection in the event of a second fault is then long as its power supply is connected to the
ensured:
UPS output.
v In a TN system if the frames are connected
If the neutral conductor is broken, operation will v In a TT system if the frames are not connected switch to an IT system.
This configuration does however present a
DC circuits not isolated from upstream and
problem as it totally disconnects the power
downstream equipment
supply to all loads.
In this case, the neutral systems
If continuity of service is essential and in
upstream and downstream of the UPS must be
particular in the case of redundant UPSs, use
identical.
the configurations in Figure 55 .
A
U3
B
E
Cb
D
(*)
F
U2
SS
G
U1
C
R
O
H
(*) Loads not needing to be put into operation
Fig. 54 : Protection of persons for DC circuits in a UPS link not isolated from the upstream and downstream equipment operating as a TT system -Basic implementation-A
U3
B
E
Cb
D
F
U2
SS
U1
Cn
Gn
Jn
C1
G1
J1
R
O
H
(*)
(*) Loads not needing to be put into operation
Fig. 55 : Protection of persons for DC circuits in a UPS link not isolated from the upstream and downstream equipment operating as a TT system -Implementation for optimizing continuity of service-Cahier Technique Schneider Electric no. 129 / p.38
The RCDs installed upstream of the rectifier and v PIM 1, if there is voltage upstream of the UPS
downstream of the inverter on each link will trip v PIM 2, if the UPS is providing an autonomous
circuit-breakers C and J on each of the links.
power supply to the loads (see Fig. 56 ).
Discrimination between these RCDs and the
PIM 2 is started up via relay R2 only in the
RCD upstream of the bypass channel must be
event of the loss of the upstream voltage.
checked in order to ensure the availability of this Despite the absence of the upstream voltage, it channel.
is possible, even very probable, that the neutral c Equipment operating as a TN system
conductor will remain connected. A circuit-
To protect persons, usually, as soon as an
breaker will trip either in the event of a fault or insulation fault occurs, circuit-breakers C and H
for maintenance purposes.
trip. If the conditions required for correct
If PIM 2 is at risk from disturbance from PIM 1, operation are not met, for example for the TNS
it will be shut down by relay R1 if the
system, the configurations described in the
transformer secondary voltage is zero.
previous section (for the TT system) must be
Protection in the event of a second fault is then used.
ensured:
c Downstream equipment operating as an IT
v In a TN system if the frames are connected
system
v In a TT system if the frames are not
The DC circuits are monitored by:
connected
A
U3
B
E
R1
Cb
D
F
U2
SS
PIM 1
U1
C
G
R
O
H
(*)
R2
PIM 2
(*) Loads not needing to be put into operation
Fig. 56 : Protection of persons for DC circuits in a UPS link not isolated from the upstream and downstream equipment operating as an IT system
Cahier Technique Schneider Electric no. 129 / p.39
7 Conclusion
This document demonstrates that setting up
equipment to protect persons against indirect
contact on line supplies with DC circuits is
actually more complex than it first seems.
Particular attention must therefore be paid to the various configurations that can be installed or may occur during operation, for example in the
event of a fault.
This is why it is often advisable to use equipment supported by thorough documentation and
assistance from specialists or professional
system builders to obtain a complete and reliable solution for a specific requirement in a given
configuration.
Cahier Technique Schneider Electric no. 129 / p.40
Bibliography
Standards
c IEC 60364, NF C 15-100: Low-voltage
electrical installations
c IEC and EN 60439-1: Low voltage switchgear
and controlgear assemblies Type-tested and
partially type-tested assemblies
c IEC 60529: Degrees of protection provided by
enclosures (IP code)
c IEC 60755: General requirements for residual
current protection devices
c IEC and EN 62040: Uninterruptible power
systems (UPS)
v Part 1-1: General and safety requirements for UPS used in operator access areas
v Part 1-2: General and safety requirements for UPS used in restricted access locations
v Part 3: Method of specifying the performance
and test requirements
Guide
c UTE C 15402: Guide pratique. Alimentations
sans interruption ( ASI ) de type statique. Règles d’installation.
Schneider Electric Cahiers Techniques
c Residual current devices in LV,
R. CALVAS, Cahier Technique no. 114
c Earthing systems in LV,
B. LACROIX, R. CALVAS,
Cahier Technique no. 172
c Earthing systems worldwide and evolutions,
B. LACROIX, R. CALVAS,
Cahier Technique no. 173
c The IT earthing system (unearthed neutral)
in LV, F. JULLIEN, I. HERITIER,
Cahier Technique no. 178
Cahier Technique Schneider Electric no. 129 / p.41
ic
Electr
Schneider Electric
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