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(23-02-2010, 06:39 AM)om sai Wrote: send me details of above topic

please send me complete report ofthe topic is "surge protection of modren devices"

OVERVOLTAGE PROTECTION DEVICES

Technologies involved:
In the voltage switching category comes the Spark Gaps(SG) and Gas Discharge Tube(GDT) technology. In the Voltage limiting category comes the metal oxide varistor technology(MOV) and the siicon avalanche diode(SAD) technologies.
1)AIR TERMINATIONS
To protect the volume from direct lightning strikes
and to avoid uncontrolled strikes air termination are
used . Air termination is comprised by
air-termination rods and air-termination wires.
The location of air terminations is usually defined
by the ˜rolling sphere˜ method

2) BUILDING AND ROOM SHIELDS
Extended metal components, like
metal roofs and facades etc form an effective
effective electromagnetic shield by their meshed
interconnection are especially important for
shielding magnetic fields. They are also important
for creation of lightning protection zones.
In principle, a steel reinforcement and the metal
window and door frames can form an
electromagnetic cage.

3)SHIELDS FOR CABLES IN BUILDINGS
Cables shall be run near the equipotential bonding
lines. These are parts of the steel construction,
reinforced walls, cable supporting structures, cable
trays or other electrically conductive parts which
are connected to the equipotential bonding system
at least at both ends. Pair-twisted signal cables are to be preferred.

4)EQUIPOTENTIAL BONDING
Lightning protection equipotential bonding of a
protected volume includes all incoming metal
installations. In the case of extended
telecommunication systems, a duly shaped
lightning protection equipotential bonding bar
installed at ground level inside the building also
functions as an earth bus and is usually installed as
an earth ring bus inside the building. The earth ring
bus, a ring equipotential bonding bar, is a copper
bar having a minimum cross section of 50mm2 for
surface mounting.

5)ARRESTERS
surge protection devices are classified as: lightning current arresters and surge
arresters.Lightning current arresters must be able to
discharge lightning currents or considerable
parts of them non-destructively.
Surge arresters only serve limiting overvoltages
at relatively low-energy surge currents.

6)Instrument Solutions
Remote instruments and analyzers: The most susceptible instruments in a typical process facility tend to fall into one of three general
categories “ analyzers, remote mounted instrumentation, and load/weight cells which employ highly sensitive microprocessors, ICs, or strain gage sensors and
are often mounted on tall/isolated structures or the upper decks of process plants.

DCS or PLC control system::
This is where the control element, the brains of the system,
resides. The DCS/PLC manufacturers offer only minimal surge protection devices. The common element to both ends of the system is the signal and power wiring. These are the
metallic power and information highways previously discussed. Once the surge couples onto this
highway, at typically up to 7,500 Volts/15 Amperes for switching transients and up to 100 Million
Volts/300,000 Amperes for a near lightning, it travels at 2/3 the speed of light in both directions on
the conductor seeking low resistance pathways to ground.the most effective defense is a combination of Automatic Isolation systems, normal mode Surge Protection Devices installed at both ends of the loop and
on every metallic conductor associated with the system, and a true low-impedance grounding
system.

MODERN SPARK GAP TECHNOLOGY FOR
LIGHTNING AND SURGE PROTECTION
The suge protection is normally based on Metal Oxide Varistor (MOV) tech-
nology; sometimes combined with Gas Discharge Tubes (GDT)
and/or Silicon Avalanche Diodes (SAD).
SPARK GAPS IN RADAX-FLOW
TECHNOLOGY AND WITH ENERGY FLOW
CONTROL
after the spark
gap has been fired and the lightning cur-
rent has been discharged to ground, the
power supply is feeding the arc. Now, to
interrupt the arc far before the zero cross-
ing, itâ„¢s necessary to increase the arc
voltage (counter voltage) to the level of
the power supply. The internal insulation material used in the
spark gap heats up after the arc is gener-
ated, providing an internal gas flow
which lengthens the arc and reduces the
arcâ„¢s diameter which consequently
increases the impedance and the voltage drop

report:
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check out this pdf too:
eeel.nist.gov/817/pubs/spd.../files/Protect%20techniques.pdf
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http://studentbank.in/report-surge-curre...ull-report

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