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Electrical and electronic devices
must be suitably designed and protected to survive in the electrical as well as
the physical environment for which they are designed. To ensure that compatibility, we offer a range of EMC and
physical tests which simulate the worst-case stresses according to widely
accepted standards, including ANSI C37.90, IEC 1000-4-4, IEEE C62.41 and UL
1449. Following is a summary of those
tests:
Operational
Verification Test: Confirm the functional integrity of a device. The test
method employed to perform this test is a function of the type of device being
tested. It usually requires the configuration or programming of the device,
application of a control voltage, appropriate input signals such as voltage and
current, and monitoring one or more output conditions or quantities. The test
setup is usually configured to reflect in service conditions if necessary for
proper evaluation of the device. In other cases, a bench test is performed.
Measured parameters of possible interest may be accuracy, repeatability,
validation of manufacturer specifications and overall reliability. A favorable
outcome of this test is paramount in qualifying the device for use in any
application.
Physical Inspection:
The first and last step in performing a typical device test, the test specimen
initially is examined for deficiencies, followed by complete disassembly after
the test is completed. The inspection focuses first on physical construction
and workmanship and ends with close examination of printed circuit board design
and component selection. The outcome: a subjective assessment of the product’s
quality supported by results from other portions of the test.
Determine if a device is
affected by radiated electromagnetic, continuous waves. This test is performed,
in part, with reference to guidelines established by the ANSI/IEEE C37.90.2
Standard, or Trial-Use Standard Withstand Capability of Relay Systems to
Radiated Electromagnetic Interference From Transceivers. A RFI field strength
level of 10 V/m, at each test frequency, is most commonly used to determine
qualification. The test is applied using hand-held radios, and is conducted in
a manner that imposes both horizontal and vertically polarized continuous wave
modes. Currently, RFI testing is performed at a limited number of frequencies in
the VHF and UHF band, 150, 450 and 800 MHz. These frequencies were chosen
because they are representative of common communications channels used by field
personnel.
Electrostatic Discharge
poses a potential EMC threat to the increasing number of static and
microcomputer based equipment that are used in substation and plant
applications. To identify devices that may not be sufficiently hardened to
withstand this type of transient phenomenon, an electrostatic discharge test is
available. The test is performed at voltage levels of 8 and 15 kV in
non-contact (air discharge) mode. Both positive and negative polarities are
used for this test.
This test is excellent for devices employed in
power system applications. Two waveforms are specified in this test standard:
oscillatory (damped sinusoid) and fast transient waveforms. Together, these
high frequency disturbance waveforms simulate switching transients that may be
coupled onto the signal, control and power circuits of devices installed in a
substation environment. AEP performs these tests in accordance with the ANSI
specifications listed below:
The electrical fast transient/burst (EFT) is an EMC
test that is sued to evaluate the immunity of devices to a particular type of
switching transient. This type of event is characteristic of the transients
produced when switching inductive loads.
Combination Wave Test: The IEEE C62.41
combination wave surge test is used to simulate lightning surge events that
typically occur on low voltage ac power circuits. This test is available for
location categories B1 through C1, as defined by the C62.41 standard. Devices
that fall into these test categories include those that are connected to
feeders and short branch circuits and also those connected in low exposure
zones outside the service entrance. The combination wave test characteristics
consist of an adjustable open circuit test voltage ranging from 2 to 6 kV, with
1.2/50 us (rise time/fall time) impulse waveform followed by a maximum short
circuit current of 3 kA having an 8/20 us wave shape.
Ring Wave Surge Test: This test is for devices
that fall into location categories A1 through B3, which includes areas on long
branch circuits and short branch circuits. The test voltage is a 100 kHz
sinusoidal wave with an amplitude between 2 and 6 kV and current capabilities
of 200 and 500 amperes. This test simulates surges resulting from switching
events.
AEP performs environmental
tests over a wide temperature range on test specimens of varying dimensional
size. This test is conducted to observe the temperature stability of the device
under test and also to validate manufacturer specifications. An environmental
chamber having interior dimensions of 20 ¼
by 22 inches by 19 ½ inches is available to test relatively small objects.
Temperature is controllable over a range of –73 to +200 degrees Celsius. This
chamber can also provide humidity control in the range of 20 to 98 percent RH,
over a temperature range of +20 to 85 degrees Celsius. In addition, the small
chamber can be computer-controlled, providing a flexibility to perform
operations such as automatic temperature cycling, ramping and other test
sequences. For larger objects, a very large chamber with interior dimensions of
95 ¾ inches by 120 inches by 185 ½ inches is available, which permits testing
from 40 to +150 degrees Celsius. In this large chamber, humidity can be varied
from 10 to 98 percent RH, over a temperature rage of 10 to 70 degrees Celsius.
AEP can assess the level of safety that has been
designed into a product. Both ac and dc dielectric tests are available to
evaluate insulation integrity and electrical isolation. Virtually all devices
employed within the AEP System are subjected to either an ac or dc dielectric
test. In most cases, the ANSI/IEEE C37.90 standard is used as a guide to
conduct this test. Common test voltages are 1500 Vac (2121 Vdc) and 2500 Vac
(3535 Vdc) depending on the device being evaluated. AEP’s capability limit for
this particular test is virtually open-ended, but for devices being considered,
5 kV ac and 4 kV dc levels are easily performed.
The showering arc test is
essentially an electrical noise susceptibility test. The NEMA ICS-1983 test
standard is sued as a guide in performing this test. A NEMA standard noise
generator is used to perform the test. The test set generates broadband
electrical noise via an arcing spark gap, and couples the noise onto individual
conductors within a multiconductor cable. Conductors are then used as
input/output paths for the device under test. The test is designed to test
logic input and output circuits, excluding low-level logic such as TTL, and is
appropriate for devices with solid-state control input and output circuits such
as PLCs.
The current surge test is an AEP test standard that
is generally applied to protective relay and measuring devices. The test is
intended to simulate worst case fault conditions for devices that are installed
in relaying or metering current circuits. The test is performed using the
following test sequence, which simulates an automatic recessing sequence with
typical recessing and clearing times
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Electromagnetic
Compatibility & Qualification Testing
