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Due to RMS continuous product improvement policy this information is subject to change without notice. 1S20/Issue R/28/02/2010 - 2/11
SWITCHGEAR ARC PROTECTION
Risk of arc fault damage exists at the CB cable termination & in
the CB chamber itself. The CB cable termination is particularly at
risk to ingress of moisture & rodent damage.
One, two or three arc sensors may be connected to the 1S20 Arc
Fault Monitors as depicted in the single line application diagrams
at right.
Figures 1 & 2 show the trip signals being used to trip the feeder
circuit breaker in the event of an arc fault occurring at any sensor
provided the overcurrent relay starter contact is picked up. In
these applications the overcurrent check stage is optional as the
consequence of a single feeder outage is less than the loss of an
entire BUS.
Figure 3 shows an application where a single 1S20 is applied for
the protection of the Cable box, CT chamber & CB chamber using
three sensors. In this configuration one arc trip output is used to
trip the feeder circuit breaker in the event of an arc fault in the
cable box / CT chamber. The second trip output is set for
independent operation to trip the BUS breaker (BUS overcurrent
check not shown), in the event of an arc fault in the CB chamber.
EXISTING SWITCHGEAR APPLICATIONS
The existing overcurrent relay protecting the feeder will normally
provide an independent output contact associated with the start
current setting of the relay. That is an output contact that will
close when a phase or earth fault current is detected above the
threshold which starts the internal relay timers. This starter
element should be set for instantaneous operation so that it will
pick up in the order of 15ms.
An Arc Fault Monitor relay 1S20 is installed on the switchgear
panel adjacent to the protection relay. The 1S20 is specifically
designed for simple retrofit to existing panels & requires only a
single 31mm mounting hole to be drilled. The 1S20 fits through
this hole, the designation label supplied with the unit positioned &
the retention shroud fitted. Refer Figure 12 & 13.
1S30 optical arc sensors are fitted in the cable termination box &
CT chamber as depicted in figure 2.
The overcurrent relay starter contact may optionally be wired in
series with the arc fault detection trip output contact as depicted
in figure 6. The resulting “AND” function trip output is wired to trip
the breaker in ~15ms in the event that an arc fault is detected
while the overcurrent start element is picked up.
The second arc trip & fail alarm contacts may be employed for
interface to a SCADA system for fault reporting.
NEW SWITCHGEAR APPLICATIONS
For new switchgear installations a modern numeric feeder
protection relay is likely to be employed which will have numerous
programming & configuration options.
The basic concept is the same as for the existing switchgear
application described above except that the additional features &
flexibility of modern feeder protection relay allows improved
system integration.
This may be achieved by using the second arc trip output contact
to interface to a programmable status input on the feeder
protection relay. Depending on the model of protection relay
being used this input may be programmed to provide an alarm
message on the HMI, time stamped event record available via its
communications link.
Where this level of system integration is employed the 1S20 does
not need to be mounted on the front panel as the alarm
indications are available on the feeder relay. Remote reset of the
1S20 LED is achieved by momentary interruption of the power
supply using a SCADA controlled series contact. The DIN rail
mounting option is a convenient alternative in this situation.
Switchgear Applications
Figure 1:
Single arc sensor - Cable box only
(Optional overcurrent check stage depicted)
1S30
1S20
50/51
Figure 2:
Two arc sensors - Cable box & CT chamber
(Optional overcurrent check stage depicted)
1S30
1S30
1S20
50/51
Figure 3:
Two arc sensors - Cable box & CT chamber
Independent trip to CB
(Optional overcurrent check stage depicted)
1S20
1S30
1S30
1S30
50/51
Trip BUS CB(s)
1S20
1S30
1S30
1S30
50/51
Trip BUS CB(s)
One arc sensor - CB chamber
Independent trip to BUS breaker
(BUS overcurrent check stage not shown)
