cpp - Process technology for the chemical industry 02.2018

The ESS30-S provides physical
isolation, interrupting the
load circuit reliably with a
clearance distance
ensures electronic disconnection after
150 ms. The circuit is physically isolated
after 5 s.
Physical isolation
Standard electronic circuit protectors normally
do not offer physical isolation. They are
fitted with a power Mosfet to disconnect or
switch off the load circuit. If the Mosfet is
conductive, its low resistance allows current
to flow through the electronic circuit protector.
If the power Mosfet is blocked, it has
high impedance and thus prevents current
flow. High resistance of the Mosfet, however,
cannot prevent leakage currents from
flowing in the blocked state. In addition,
each semi-conductor switch has an integral
inverse diode. In the event of a linked failure
on the load level, the diode may allow a
direct return supply from this level to the
24 V(DC) level. Additional physical isolation
ensured by the electronic circuit protector
would prevent such a return supply.
This physically isolating switching element
is connected in series with the power Mosfet.
A short circuit causes the Mosfet to first
of all disconnect the circuit electronically
and protects the switch mode power supply
against overload. This happens within
150 ms. The electronic circuit breaker has
an additional mechanical switching element
which opens the load circuit within 5 s in
the event of a failure, creating a clearance so
that the circuit is physically isolated. Hazardous
system conditions are reliably prevented.
In addition, a faulty return supply
to the 24 V(DC) control level can be ruled
out.
Modules increase hazard potential
Modular system and plant designs will become
increasingly prevalent in the chemical
and pharmaceutical industries in the
coming years. The importance of power distribution
and wiring in the field will continue
to grow. In conduits or drag lines,
there are often a large number of cables laid
in parallel. Although separating the different
voltage levels is a requirement, it is very
often not implemented in practice. Particularly
with existing systems, space is limited
and so are the installation options. A return
supply of the 230/400 V(AC) load voltage
to the control voltage level can have catastrophic
consequences. The ESS30-S limits
the failure by means of physical isolation, so
that only one circuit is affected. Damage to
the entire system at once is excluded. The
ESS30-S provides extra safety and increased
system availability. This is the reason why
major German chemical companies request
not only electronic protection in their plants
but also physical isolation. In addition, as
described above, leakage currents may cause
the circuit protector’s visual status indication
to glow. Service technicians are frequently
unsure about what to do in such
cases, so that they eventually decide to replace
the installed devices. Today, the chemical
company in question relies exclusively
on electronic circuit breakers with physical
isolation.
Perfect power distribution
E-T-A’s ESS30-S is ideal for use in the
chemical and pharmaceutical industries because
it combines active current limitation
with physical isolation. It unites the advantages
of an electronic circuit protector with
the added value of physical isolation. It is
due to this function that the ESS30-S is approved
to DIN EN 60934 as a circuit breaker
for equipment protection. In combination
with the Module 18plus, it forms a modular
and flexible power distribution system
which offers a complete overview of the
24 V(DC) supply and allows a modular design,
tailor-made to the plant’s requirements.
Enhanced flexibility and reduced
wiring time are further advantages. The system
also includes a supply module for up to
80 A. A busbar system provides interconnection
of all modules. Owing to the plug-in
design, the individual circuit breakers can
be exchanged at any time and system adjustments
implemented easily. The integral
group signalling rounds off the system.
www.cpp-net.com
Online search: cpp0218eta
Hall 11.0, Booth C43
AUTHOR:
THOMAS KRAMER
Business Field Manager,
Division Automation &
Process Control,
E-T-A
cpp 02-2018 47