Comments On The Test Equipment - GE Multilin MIGII Instruction Manual

9.2 COMMENTS ON THE TEST EQUIPMENT

9 RELAY COMMISSIONING
9.2COMMENTS ON THE TEST EQUIPMENT
All devices that work with alternating current are influenced by frequency. Since a non-sinusoidal waveform results from a
fundamental frequency wave plus a series of harmonics of this fundamental wave, it can be concluded that devices working
with alternating current (relays) are influenced by the applied waveform.
In order to correctly test relays that operate under alternating current, it is fundamental to use a sinusoidal current and/or
voltage wave. The purity of the sinusoidal wave (the lack of harmonics) cannot be expressed in a specific form for a given
relay. Each relay that is provided with tuned circuits, R-L and R-C circuits or non-linear elements (such a inverse time
overcurrent relays) will be affected by non-sinusoidal waveforms.
These relays respond to the current waveform in a different way from most AC ampere-meters. If the power supply network
that is used for the test contains a considerable amount of harmonics, the ampere-meter and relay responses will be
different.
The relays are calibrated by the manufacturer using a 50 or 60 Hz power supply network with minimum harmonic contents.
When the reception or installation tests are carried out, a power supply network with a harmonic-free waveform must be
used.
Ampere-meters and stop-watches that are used for carrying out the test must be calibrated and their accuracy must be
better than that of the relay. The power supply network used for the tests must remain stable, mainly at levels close to the
test pick-up current, as well as for the time for which the relay operates according to the curve under test.
It is important to stress that the test accuracy depends on the power supply network conditions as well as on the
instruments used. Functional tests carried out under inappropriate power supply conditions or using inappropriate
instruments can be used for ensuring that the relay works roughly correctly and, therefore, for verifying its characteristics in
an approximate manner.
Here follows a list of tests that can be used to check that the unit is fully operational. For a more limited test for the
reception of units we recommend carrying out only the tests listed in sections: , 9.3. and from 9.6 to 9.20, both included.
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9-2 MIGII Digital Protection for Electrical Machines GEK-113188A