Ampcontrol IPC1, Руководство пользователя

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IPC1 USER MANUAL ISSUE 9
-15-
Ensure that the earth connections are reliably
installed, as this is the basis of protection, for all
barriers, including the CCMC.
(D) Overload & Earth Leakage Toroids
Current transformers are not ideal devices and if
correct procedures are not followed during
installation, nuisance tripping can result.
If, for example, we consider a single phase earth
leakage system where active and neutral pass through
a toroid, then at all times currents in the two wires are
equal and opposite so that the net current through the
toroid is zero. An ideal current transformer would
have all the flux from each wire contained in the core
and so would accurately add the opposing fluxes to
get a net result to zero. A real current transformer has
“leakage fluxes”. That is, a very small proportion of
the total flux from each cable is not contained in the
core, but in the space outside it and as result it may
link some turns but not others, depending on the
positioning of the cables.
The effect of this is that a small output may be
obtained from the CT where none would arise if the
device were ideal.
The size of the error will vary from CT to CT of the
same type because of slight differences in the core
and the symmetry of the winding.
Problems caused in this way become worse as CT
sizes increase, as currents increase and a decrease
occurs in the symmetry of the cables. Nuisance
tripping tends to occur when the total current rises,
such as when a large motor is started.
This is not normally a problem with the current levels
found in flameproof enclosure applications. To help
avoid problems in other applications, select the
smallest internal diameter CT, to suit the cable size.
(E) Toroid Installation Guide Lines
1.
Keep cables as close to the centre of the toroid
as possible. Do not tie them to one side of the
toroid. Remember to aim at symmetry.
2.
Do not bring the cables back past the toroid
within one diameter of the CT, trying to cram
cables into a small space reduces symmetry
and may lead to problems, which are difficult
to solve.
3.
Avoid placing the CT near any device, which
produces magnetic fields - whether it is a
transformer or other cables. Try to maintain
several CT diameters clearance.
4. Many small cables tend to be worse than say
three large ones. Try to position the CT in the
circuit with this in mind.
12.2 Wiring Installation
The connections to the IPC Relay consist of a mix of
intrinsically safe circuits through to “high” voltage
supplies and relay contact circuits. To ensure the
integrity of the intrinsic safety is maintained and to
reduce induction from high voltages, care needs to be
taken in the layout of the wiring and the installation.
For installations on high voltage systems (>3.3kV) it
is advisable to install a power supply filter, eg
Schaffner FN612-1106 (1A, 250VAC chassis
mounted filter) adjacent to the IPC Relay. The earth
should be connected to Pin 7 on the relay as directly
as possible.
The IPC Relay’s approval requires that the relay is
installed in accordance with the Australian Standard
for Intrinsic Safety Installation AS2381.7. Anyone
installing IPC Relays should therefore have a good
understanding of AS2381.7.
(A) Intrinsically Safe Circuits:
Duty Pin Signal Recommended Cable
Type
Pilot Core 6
7 Pilot
Earth Single core screened
Screen = 0V (See note
1, page 15)
Serial
Comms
Port 8
9
10
11
12 +Vsc
TXE
TXD
RDI
OV Four core screened
*Screen = OV
Remote
Display 13
14
12 Data
+Vdm
OV Two core screened
*Screen = OV
Note 1: That the 0V is internally connected to the
IPC Relay’s earth (pin 7). The screen therefore
should NOT be earthed at any other point.
It is recommended that these circuits be separately
loomed from all non-IS circuits.
(B) Low Voltage Signals
Although these signals are not IS signals themselves,
they connect to the low voltage side of the IPC
Relay’s internal “infallible” transformer. This
transformer is designed and certified to comply with
section 3.2.2 of AS2380.7. This means that it “is not
liable to become defective in such a manner as would
lower the intrinsic safety of the circuit”, (from
definitions section of AS2380.7). Care must therefore
be taken to ensure these circuits cannot come into
contact with higher voltages (eg via insulation
breakdown, or broken wires etc). It is recommended
that these circuits be run in a separate loom from both
the IS circuits and the “high” voltage circuits. To
ensure that interference is kept to a minimum, the
following cabling is recommended.