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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 - 1/11
Features
Compact, economic design
Simple panel mounting for
retrofit applications
Two or three arc sensor inputs
Two high speed tripping duty
arc sense output contacts
Push button reset
Continuous arc sensor
supervision
Integrated self supervision
Fail alarm contact
20-60 & 36-150V DC auxiliary
versions
Introduction
Medium voltage switchgear is a key
element in the power supply chain.
Existing protection systems operate
effectively under most circumstances, but
they are too slow to handle arcing short
circuits.
Arcing faults can occur as a result of
insulation breakdown due to equipment
age & / or poor maintenance.
The degree of damage caused by arcing
depends principally on the duration of the
arc. If an arc lasts only 100ms, the
switchgear needs to be checked & the
insulation resistance measured before
power can be re-established. With a
200ms arc, the power supply will be
interrupted; the switchgear must be
checked; power is re-established only
after minor repairs. In the event of a
500ms arc the supply is interrupted, metal
parts of the switchgear are destroyed &
poisonous gases are emitted. A 1s arc
destroys most of the switchgear & may
cause a fire, injury to personnel & damage
to property.
The over-current caused by an arc is, due
to its resistance, lower than the over-
current caused by a “metallic” short circuit.
The over-current caused by the arc may
also be lower than the protection start
current when energising circuits or starting
large motors. The consequence of these
conditions is that a protection system
based solely on over-current detection
cannot effectively discriminate between
normal system currents & an arc fault
condition:
•
For moderate arc fault currents the trip
time of the over-current IDMT stage will
be too slow;
•
For very low arc fault currents the
instantaneous trip stage of a standard
over-current relay cannot be set low
enough.
Technical Bulletin
1S20
Arc Fault Monitor Relay
1S30 Sensors - front & back
1S20 depicted in panel mount case configuration
ARC Fault Protection
Made in Australia
Arc fault protection is a relatively new technique employed for the fast clearance of arcing
faults on BUS bars & within metal clad switchgear & associated cable boxes. The arc is
detected using an optical sensor & the signal input to a protection device which also
monitors the load current on the system. A trip signal can be achieved in less than 10ms
using arc detection only or within 15ms when using overcurrent check. This is considerably
faster than a traditional IDMT overcurrent relay & provides additional protection from the
onset of arcing faults with relatively low fault currents.
Arguably the greatest risk of arc fault damage exists at the CB cable termination & in the
CB chamber itself due to the slow clearance times of the IDMT feeder protection. The CB
cable termination is particularly at risk to ingress of moisture & rodent damage.
The problem of arc faults is most prevalent in older metal clad switchgear which already
has operational protection systems. The 1S20 Arc Fault Monitor has therefore been
designed for the following applications:
EXISTING SWITCHGEAR
Where a requirement exists to retrofit arc fault protection to metal clad switchgear utilizing
the existing overcurrent protection relay;
NEW SWITCHGEAR
Where a requirement exists to install arc fault protection to new switchgear for integration
with the customer preferred overcurrent feeder protection relay
.
