On Site Testing of Lightning Protection Devices

On Site Testing of Lightning Protection Devices
On Site Testing with Times Protect LP-SPT Surge Protection Tester (TechDoc)
On Site Testing of Lightning Protection Devices
After a severe thunderstorm with multiple tower strikes, how is a technician to know if the coaxial lightning
protectors are still operating properly? There are some obvious visual indications of damage such as
arcing / discoloration and melted / welded connectors, while the Return Loss / VSWR and Insertion Loss
in the transmission line system could provide some indication of impending failure. But until now, there
has been no simple field test to assure the protectors meet specifications.
The Times Protect LP-SPT Surge Protection
Tester is designed to test all coaxial cable RF
Lightning Protection products offered by Times
Microwave. Other LP products based on
transient protection devices such as GDT,
MOVS, TVS and SIDACs and mechanical
filter designs can be tested. Moreover the LPSPT is suitable for testing discrete transient
devices as well.
The LP-SPT consists of a battery operated
high voltage DC power supply providing an
output up to 1000 Volts at approximately 11.5mA. This output level provides enough
voltage to cause breakdown of the transient
device to occur without over-driving the device
with excessive current; providing a reliable and valid method for measuring peak breakdown voltages of
transient suppression devices. Although the test voltage is applied at a rise time rate of approximately
10kV/S, it is slow enough to facilitate valid testing of the device's rated “dc” breakdown voltage within the
tolerance specified by the device manufacturer while staying within the 1000 Volt operating range.
The LP-SPT is a rugged, simple to use handheld test instrument. The LP-SPT has a 3.5 digit LCD that
displays device under test peak breakdown voltage to a resolution of one Volt. Two type-N connectors
(male and female) at the top of the LP-SPT provide direct connection of an RF LP device to the tester. An
on-off switch and LED backlit “TEST” button facilitate operation and testing.
Coaxial protector product types and IS-SPT test readings
Gas Tube Type- Dc blocked, or non dc blocked "straight-through” permanent or replaceable gas tube.
A dc blocked protector uses a gas tube connected from the center pin
Surge
Protected
of the “surge” connector to the protector body and a discrete
component capacitor in series from the top of the gas tube to the
G
“protected” connector center pin. The capacitor blocks dc current flow
to a resistive component (rf coupling loop) long enough for the gas
tube to “turn on” and equalize the center conductor to local ground
potential. With center conductor and shield at the same potential, there is no current flow through
the protected equipment input, and the equipment is undamaged. Dc blocking allows a very low
energy pass-through to equipment. A dc blocked protector will have a specified frequency range
to maintain proper impedance match through the device. LP-SPT test - from surge side connector,
read 480 to 720 Volts with 600 Volt gas tube (e.g. LP-BTR/W series). Protected side connector, read
high (800-900 Volts) open.
© 2014 Times Microwave Systems All Rights Reserved
Page 1
On Site Testing with Times Protect LP-SPT Surge Protection Tester (TechDoc)
A non-dc blocked protector (“straight-through”) will share the incoming
Bi-directional
current with a resistive component (rf coupling loop). The gas tube will
turn on when the current through the resistive component in the
equipment input rises enough to create a voltage drop reflected back
G
to the protector’s gas tube. A longer coax jumper cable from the
protector to the equipment might produce a di/dt drop to forward bias
and facilitate the gas tube turn on, reducing the required current flow
through the protected equipment input. A non-dc blocked protector is bi-directional and can have
a very wide frequency range, as much as dc to 7 GHz (Times Protect product), but will pass
through more energy to the equipment than a dc blocked protector. Dc to tower top equipment
can be passed through a non dc blocked protector with gas tube turn on rated as close as
possible to the required dc voltage. LP-SPT test – from either connector, read installed gas tube
turn on voltage (as specified) +/- 20% Note: Readout could “jitter” when the test button is continuously activated while testing a gas tube.
The LP-SPT is designed to provide an activation voltage with just enough current (approximately 11.5mA) to keep the gas tube ionized for “turn on” measurement without damage. Since there is not
enough available current for a “hard turn on”, the gas tube could be in an unstable condition during
measurement. The range of “jitter” could be approximately the minimum and maximum acceptable
Voltage limit on the Test Reference guide supplied with the instrument.
Dc blocked mechanical filters (no gas tube) - Blocks dc and low frequency transient energy present during
lightning strike. Instantaneous protection, no activation time.
A dc blocked mechanical filter has a high current rated inductor
Surge
Protected
connected from the center pin of the “surge” connector to the protector
body. A conductor is continued from the top of the inductor to a
mechanical capacitor in series to the center pin of the “protected”
connector. This forms a high pass filter with a sharp low frequency cut
off and an extended high frequency band pass. As with any dc
blocked protector there is a specified frequency range to maintain proper impedance match
through the device. Dc blocking in a mechanical filter allows an extremely low energy passthrough to equipment. LP-SPT test - surge side connector and read very low approximately
(0 – 2 Volts) shorted. Test protected side and read very high (800-900 Volts) open.
Bi-Polar Diode Type - DC blocking in the RF path. RF decoupled / re-coupled solid state DC pass/protect
circuit for tower mounted preamp. Monitors peak voltage occurrence during lightning strike.
The solid state dc pass/protect protector, with a dc blocking capacitor in
Bi-directional
the rf path from connector to connector, is bi-directional, and includes
an rf isolated high current bi-polar diode. The diode is rf decoupled
with an inductor from each connector center pin. The two inductors
are connected together at the top of the diode, and the diode is
bonded back to the protector body. The diode turns on when the
voltage exceeds approximately 5 Volts (see Times Protect LP-GPX-05
specifications). All incoming differential voltages are limited to 5-7
Volts with a short 12 Volt residual pulse. LP-SPT test - will display the lowest turn on transient
device in a hybrid multi-component, dc pass/protect protector (read 5-7 Volts from either connector
with LP-GPX-05)
© 2014 Times Microwave Systems All Rights Reserved
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On Site Testing with Times Protect LP-SPT Surge Protection Tester (TechDoc)
On site testing of coaxial rf lightning protectors
Testing lightning protectors is most accurate and reliable when the protector is out of
circuit and attached directly to the LP-SPT. If a coax jumper is used for convenience,
“know thy jumper”. It must be tested and reliable!
A dc blocked protector must be tested with the surge side connector
attached to the LP-SPT. The protector can remain physically mounted
with the equipment jumper attached. Turn off equipment!
A non-dc blocked protector must be disconnected at both ends. The
protector can remain physically mounted. Test at either end.
A dc blocked mechanical filter must be must be tested with the surge
side connector attached to the LP-SPT. It can remain physically
mounted with the equipment jumper attached. Turn off equipment!
The solid state dc pass/protect protector, with dc blocking in the rf path
from connector to connector, must be disconnected at both ends. The
protector can remain physically mounted. Test at either end.
Note: When removing and replacing site coax feeders or equipment jumpers during LPSPT test procedure, make sure connectors are properly seated and equipment is
operating normally before leaving site.
On site testing of ac power lightning / surge protectors
Ac power protection must be disconnected from power source and load. For 240 Volt Bi-phase
devices, connect supplied alligator clip adapter to ac power input terminals
1. Connect alligator clips to neutral and ground, test and note results.
2. Connect alligator clips from each 120 Volt terminal to neutral, test and note results.
3. Connect alligator clips to both120 Volt terminals (240 Volts), test and note results.
Test results should agree with manufacturer’s turn-on specifications +/- 20%.
Testing telephone interfaces and individual surge protection components.
Telephone interface Disconnect line in and line out.
1. Connect alligator clips to line input tip terminal and ground, test and note results.
2. Connect alligator clips to line input ring terminal and ground, test and note results.
3. Connect alligator clips to tip and ring terminals, test and note results.
Test results should agree with manufacturer’s specifications +/- 20% for type of supplied service
(POTS, DSL, etc).
Individual components A simple alligator clip connection to individual surge components is all
that’s necessary for testing. Some components could be polarity sensitive. Reverse connection to
component if test reading is suspect.
Ken Rand – Times Microwave Systems, Senior Consultant – Protection Technologies
© 2014 Times Microwave Systems All Rights Reserved
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