Fuji Electric BW1000RAE, Technical Information

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87
3
Selection and application
3-16 Ground fault protection in system applications
Continued
Comparison
item Wiring system
TT IT
Circuit
diagram
L
1
L
2
L
3
N
L
1
L
2
L
3
Features s!LLEXPOSEDCONDUCTIVEPARTSOFTHEEQUIPMENTARECONNECTED
to a ground electrode that is completely separate from the
power supply ground.
s4HISSYSTEMISTHEMOSTCOMMONLYUSEDIN*APAN
s!LLEXPOSEDCONDUCTIVEPARTSOFTHEEQUIPMENTARECONNECTED
to a ground electrode that is completely separate from the
power supply ground.
s4HEPOWERSUPPLYISCONNECTEDTOGROUNDTHROUGHINSERTED
ground impedance or is completely disconnected from
ground.
s4HISWIRINGSYSTEMISWIDELYUSEDIN.ORWAY)N*APAN
however, greater emphasis is placed on circuits that supply
power without interruption rather than on those that shut down
the power supply.
Indirect
contact
protection
standards 50V
t
Ia × R
A
R
A
: Sum of the ground resistance and the protective conductor
resistance connected to exposed conductive parts.
Ia: Current that trips the MCCB automatically. (With an ELCB,
Ia is the rated sensitivity current I
'
n.)
The MCCB is as follows.
s7ITHINVERSETIMEDELAYCHARACTERISTICS)AISTHECURRENTTHAT
can trip the MCCB automatically within 5 s.
s7ITHINSTANTANEOUSTRIPPINGCHARACTERISTICS)AISTHESMALLEST
current that can trip the MCCB automatically.
50V
t
Id × R
A
R
A
: Same as that on the left.
Id: Ground fault current at the first occurrence of a ground
fault where impedance between the phase conductor and
exposed conductor parts can be ignored. It is derived
from the leak current and total ground impedance of the
electrical equipment.
s)NSTALLANINSULATIONMONITORINGDEVICETHATINDICATESTHE
first occurrence of a ground fault in order to maintain an
uninterrupted power supply.
s0OWERSUPPLYSHUTDOWNCONDITIONSFOLLOWINGTHElRST
occurrence of a ground fault or with the second occurrence of
a ground fault should be provided separately.
Applicable
protective
device
s-##"ONLYIF2
A
is very low however)
s%,#"
s)NSULATIONMONITORINGDEVICE
s-##"
s%,#"
Application
(design)
precautions 1. Select a suitable ground fault protection device for the
protection system.
2. Overcurrent breaking precautions:
s4HEADDITIONALCONDITIONSOUTLINEDABOVEMUSTBEPROVIDED
separately.
s/THERPRECAUTIONSARETHESAMEAS4.#ITEMSAND
11. Select a suitable ground fault protection device for the
protection system.
2. The power supply can shut down automatically when a
second ground fault occurs with overcurrent breaking.
3. Id
t
I
'
n when leak current breaking is used. Here, the power
supply can shut down automatically when the first ground
fault occurs.