On-site testing of generator bus-type current transformers rated at 10...50kA according to the commonly applied test procedure hardly appears to be practicable or reasonable. The problem is connected with transportation of test equipment in view of its large size and weight.
The problem was solved by the specialists from D.I. Mendeleyev Scientific and Research Institute for Metrology (VNIIM) in cooperation with NIIVA research institute by developing the ingenious experimental-computational method (MI 3123-2008). The method implies that on-site CT tests are conducted indirectly. This technique makes it possible to determine ratio and angle errors of the CT just by comparison made in one test point. The errors in other test points are calculated from the voltage-current curve of the CT plotted while it is running idle (with primary winding opened).
Scope of supply
Basic steps of testing:
|1||Determining ratio and angle error of the instrument current transformer under test according to a standard test procedure, e.g. in a test point which is 20% of nominal current value.||Reference current transformers TTIP with adjustable source of current IT5000; comparator Energomonitor 3.3T1-C|
|2||Constructing a Voltage-Current curve for the CT-under-test secondary winding throughout the whole current operating range from 1% to 120%||Voltage-Current Curve Converter (CT VCC)|
|3||Determining the values of CT-under-test errors from the Voltage-Current curve considering the systematic error introduced into the CT ratio and angle errors by transformer core material||Special-purpose PC software for automatic CT error calculation "Delta-TT"|