OVERVIEW
Natural phenomena as
lightning and power
irregularities
delivered from power
utilities are
responsible for
power failures and
possible damage to
sensitive electronic
equipment. Surge
arresters should
withstand an instant
high surge energy
and multiple
lightning and power
surge events.
Automated Arrestor
Test System; is an
automated system
deployed to test
surge arrestors.
Arrester testing is required
to insure that
arrestors will
operate as proposed
under critical
conditions.
Impulse test is
performed on three
capacitor bank
levels: 8/20µs, 2ms
and 10/350µs. For
example, consider
unit under test to
be a Strikesorb-80.
This includes a
single MOV disk of
80 mm diameter and
provides protection
from surges up to
200KA (8/20µs). This
is the maximum surge
current (8/20µs
waveform), as
specified in IEEE
C62.41-1 and NEMA
LS-1, that the surge
suppression module
can withstand
without damage or
deterioration of its
performance. So,
when the rated
voltage is applied
to unit under test,
the output voltage
and current detected
between the MOV’s
terminals should
draw the 8/20µs
waveform. Otherwise,
the MOV proves
improper operation
and expected
defects.
On contrary to
impulse test, Low
current AC and DC
tests the reference
voltage at operating
conditions. The
layout is divided to
two parts, a supply
input before UUT and
measurement part
after it. |
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HARDWARE
FUNCTIONALITY
Impulse Test
The main hardware
structure involved
is high voltage DC
Power Supply,
Capacitor Banks,
Switching panel,
Spark Gap, Turn
Table and Control
Cabinet.
- Production Level
Units under test are
placed on turn table
and charged to its
required testing
voltage through the
power supply,
8/20µs or 2ms
capacitor banks and
switching circuit.
As required voltage
is reached,
appropriate switches
open and close so
that charged power
is discharged in the
UUT between two
claming pistons
where output voltage
and current
measurements are
taken and waveform
is drawn. Note that
whole system is
controlled through
software,
controllers, control
cabinets, sensors,
PLCs, all working in
harmony to perform
the right job at
right time. Switches
are placed on
switching panel due
to a certain design
where each has a
safety margin
that shouldn't
intersect with
another closed
switch.
-
Research Level
This test at this
stage is done
occasionally for
research purposes.
The three capacitor
banks and the 200 KA
switch is involved
while turn table and
pistons aren't. The
8/20µs, 10/350µs
capacitor banks and
spark gap are
involved in
synchronous test.
The impulse test is
achieved as stated
before but via a
different supply,
switching circuit.
Synchronous test
required a different
hardware and
procedure.
This test is as if a
combination between
AC and impulse test.
When this type of
test is started by
software, the PC and
the controller can
do the job. The user
should choose the
phase at which the
trigger should occur
from the phase
selector knob on the
impulse console. The
phase selector knob
is connected to a
phase detector.
First the capacitor
bank is charged via
power supplies and
appropriate
switches. When done,
the Spark Gap switch
is enabled.
Simultaneously, a
variac
connected to a step
up transformer is
activated to give
the appropriate
voltage. Voltage is
ramped up manually
to the desired
level.
The low voltage
output is fed into
the phase detector
while the output of
the step up
transformer is fed
to the UUT, with
manual connection .
Simultaneously, the
ASD controller
connected to the
phase detector
enables it for
trigger. A high volt
signal produced at
the selected phase
ionizes the medium
around the Spark Gap
Switch to produce
the spark. Now
the circuit is fully
connected and the
charged voltage will
discharge in the UUT.
Measurements are
taken through
voltage probes
connected to UUT.
Low Current AC/DC
Test
This test is
initiated by
software after the
impulse test as UUT
are placed on turn
table. As the piston
clamps the UUT, PC
activates the AC or
DC power
supply and ramp up
the voltage to the
required level.
A voltage divider
and shunt connected
to the UUT, detect
the voltage and
current measurements
respectively. These
measurements are fed
to a signal
conditioner to
enhance the signal,
then to the PC via
DAQ card. The
software draws a
graph for the
detected voltage and
current for both AC
and DC tests. |
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