KNOWLEDGE PARTNER
http://www.utilities-me.com August 2019 / Utilities Middle East 31
SUITABLE EQUIPMENT FOR RELIABLE
TESTING
In principle, any test set that can output a cur-
rent and a voltage is suitable for the major-
ity of wiring tests. It should also have at least
two inputs for measuring current and/or volt-
age. However, a closer look at many of the test
sets already available on the market reveals
they have major disadvantages when used
for such tests because some errors - for exam-
ple, auto-reclosing of the testing switch - are
impossible to detect.
Polarity checking with traditional sources
and measuring inputs is of course possible,
but a cable always has to be run from the mea-
suring point in the installation to the source,
something that is expensive. If this is not
done, multiple errors will sometimes not be
detected.
OMICRON has launched the COMPANO
100 a new device that, among other things, is
optimised to test the wiring of transformer
circuits.
What makes the COMPANO 100 useful
for wiring testing is that at 10 kg, it is signifi -
cantly lighter than comparable devices, bat-
tery-powered, therefore highly portable and
allows special DC-free polarity check signal.
It has a special circuit for detecting breaks
in current transformer circuits, for example,
when checking test plugs or test switches,
allows regulated outputs for direct adjust-
ment of set points and it is equipped with an
emergency stop switch for the highest levels
of safety.
The sources and inputs also enable the
device to be employed for numerous other
tests, such as simple relay tests, micro-resis-
tance measurements, and the ground resis-
tance measurements of small grounding sys-
tems.
PROPOSAL FOR A RELIABLE TESTING
METHOD
Once the transformers have been energised
and grounded according to the fi ve safety
rules, a primary injection is used to verify the
grounding of the secondary circuits, followed
by the transformation ratios (if required)
and the polarities of the transformers. The
details will not be set out here, but this step
will detect the errors numbered 1, 3 and 4 in
the previous list.
The remaining tests can be carried out
more easily using a secondary injection. The
test set can remain next to the transformers
for all these tests.
Polarity checking of the secondary wiring
is performed using the CPOL method familiar
from other OMICRON devices. This involves
injecting a saw-tooth signal into the current
and voltage transformer circuits.
This signal has no DC component, so mag-
netization of the transformer is never a prob-
lem. The small, battery-powered CPOL polar-
ity checker can then be used to carry out mea-
surements anywhere in the installation - both
in the current and voltage circuits - without
requiring a connection to a source. It shows if
the measurement is being carried out in the
right circuit and whether the polarity of the
circuit is correct. This approach will detect
errors 6, 7 and 8 in the list.TEST SWITCH MALFUNCTIONS POSE
DANGER TO PERSONNEL
Another feature of the COMPANO 100 is its
ability to detect breaks in the current circuit.
It is well known that relay test switches must
short when the current transformer circuit
is activated before they disconnect the relay
from the circuit.This is an area where not all test switches
have proved reliable, a situation that can pose
a danger to personnel. Checking this function
by means of a primary injection is, however,
not advisable (in fact it can be extremely dan-
gerous), as doing so would, if the test switch
were to malfunction during the test, generate
precisely these excessively high voltages.
By detecting breaks in the secondary cir-
cuit, the COMPANO 100 performs this test in
a straightforward manner without exposing
the tester to danger.
If the test switch is some distance away
from the source, the device can be confi gured
to disconnect the output automatically if a
break is detected in the circuit. The tester can
then operate the relevant test switch a couple
of times in succession without having to be
anywhere near the test set, and, in doing so,
establish whether a break has occurred with-
out having to check the display on his or her
device. The duration of the break will be also
shown on the display.
The remaining sources can now be
checked for possible polarity errors by simul-
taneous injection in the current and voltage
transformers, and reading off the sign of the
active power indicator on the relay display.
This method can reveal the remaining possi-
ble polarity errors (numbers 2 and 9), espe-
cially in the case of primary injection in the
current transformer.
The sources and inputs present in the
COMPANO 100 enable the device to be
employed for a range of other tests, such as
simple relay tests, micro-resistance measure-
ments, and the ground resistance measure-
ments of small grounding systems.Polarity checking with
traditional sources and
measuring inputs is of
course possible, but a cable
always has to be run from
the measuring point in the
installation to the source.”