Bender RC48N-70-10 A, Operating Manual

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9 TGH1397en/11.2006
3. System description
3.1 Features
3.1.1 Areas of application
Installations featuring high-resistance neutral-earthing are used whenever power supply fail-
ure would incur significant costs due to production downtimes (e.g. the automotive industry,
chemicals industry). With this type of installation, an insulation fault between a phase and
the earth will not result in failure of the power supply. However, the insulation fault must
be located and rectified as quickly as possible to avoid tripping the overcurrent protective
device as a result of an additional insulation fault in a second phase.
3.1.2 Description of function
In the case of high-resistance earthed installations, the maximum earth-fault current between
the transformer neutral and earth is limited by means of a neutral earthing resistor (NER).
The RC48N-70... ground-fault and neutral-grounding monitoring system monitors the status
of the NER and the earth-fault current flowing through this resistor.
The safe operation of the system can only be ensured if the maximum earth-fault current is
smaller than the trip current for the overcurrent protective device. In the event of a malfunc-
tion, the earth-fault current is detected by a W0-S15 measuring current transformer. If the set
response values and delay are exceeded, the RC48N-70... will signal an alarm. Alarm messag-
es are indicated by means of the “ALARM Ground Fault” and “ALARM Resistor Fault” LEDs
on the RC48N as well as by the integrated H3 alarm lamp. There is also the option of con-
necting an external indicator (alarm annunciator panel). In this case, the H1 and H2 alarm
lamps signal the relevant alarm messages.
The alarm remains pending (i.e. is stored) until it is reset using the integrated RESET key.
The alarm relay can be used to trip a circuit-breaker. Depending on the type of circuit-break-
er’s tripping coil, the operating mode can be set either to N/O operation or N/C operation.