High Voltage Online (Live Wire) Testing Solution provides the ratio error of the CT/PT Kit, without going for a shut down of the industry. HV Live wire screening method is easy and time-efficient. Besides the waveform & harmonics analysis, CT saturation error or any other error can be identified easily.
Industries are reluctant & resistive to outages/shutdowns, as it affects their operations for the duration of the test.
In many cases HV Consumers’ CTPT is tested only once in their lifetime, at the time of installation, when its guaranteed to be healthy. Over the period of time either tampering/ageing may cause CTs to deteriorate which affects the revenue of Periodic annual testing of CT’s tend to be compromised due to the inconveniences that it involves.
Distribution Utility needs to put in a lot of background work- documentation, follow-ups & arrangements for such 11kV/33kV CTPT Testing, because the industry needs to give its concurrence for a shutdown.
Offline/with-outage CT/PT Testing may take 2 to 5 hours or more in certain cases, which results in loss of Revenue & man-hours of Distribution Utility as well as Industries.
HV Consumers CT/PT Testing is carried out Online/Live Wire without shutdown of the industry. It will certify healthiness and find out irregularities if any at the consumer end.
All high value consumers are provided utility supply at high voltage, typically 11kV, 33kV, 66kV or sometimes
even higher. The energy consumption of these consumers are measured at reduced voltages and reduced currents
using CT/PT kit or reduction instrument transformers. As these consumers account for substantial portion of
the utility’s revenue, any error in the metering system, which includes meters and the CT/PT kit, will have a
great impact in its revenue. Thus, as per various guidelines and regulatory orders, the utilities are required
to test the metering system periodically; in India, the periodicity being is one year.
As the CT/PT kits are connected to high voltages, the testing cannot be done by the conventional methods of
directly connecting a test equipment. In general, the utility takes a shutdown of the line, removes the CT/PT
kit from the structure and uses various methods such as primary injection kit or secondary injection kit to
measure the accuracy of the instrument transformers. The meters are tested for accuracy using portable
reference standards. On completion of the testing, if the errors are within the permissible limits, the CT/PT
kit is installed and line energized.
As evident, this process is cumbersome, and requires a shutdown of the industry / commercial premises,
resulting in loss of revenue for the utility for the duration of the testing. Besides, the industries are not
willing to take the shutdown as per schedule, as their production gets affected.
The off-line method of testing CT/PT kits requires shutdown and removal fo the kit for testing using either
primary or secondary injection method. As these kits are tested periodically, perhaps once every year, it has
been established that percentage of CT/PT kits going beyond permissible errors is as low as 3%. Therefore, the
question is – can we screen the CT/PT kits while in the high-voltage circuit and check their errors, and if
the errors are high, then opt for a complete testing as mandated in the off-line method?
The high voltage testing of CT/PT kit involves directly measuring the voltage and currents at the high voltage
lines (primary side) and simultaneously measure the voltages and currents on the low voltage line (secondary
side) to get the ratio of both PT and CT. Also, measurement of harmonics at both the primary and secondary
give an indication about the saturation levels of the CT; most often encountered error.
Yes. The high voltage testing can be effectively used for measuring the primary and secondary parameters
simultaneously, and thereby calculate the efficiency under actual load conditions while in circuit.
In many countries, including India, the power transformers of capacities from 100 kVA to 500 kVA are rewound
after a defect, and these are tested for basic parameters in the factory, which may not truly reflect its
efficiency under energized conditions. Thus high voltage testing helps the utilities to quickly check the
health of the power transformers very quickly.
