Specialized laboratory for testing insulation systems

History

The early stages of study, developing theoretical background and learning about the nature and behaviour of insulation materials were made in the late 1960s of the 20th century, which is when the laboratory's job of testing insulation systems began. The laboratory is fully equipped with specialized measuring tools, and theoretical knowledge was put into practice by conducting tests on actual objects, such as power and measurement transformers and rotating machines (hydrogenerators, turbogenerators, and HV motors) in the power system of the region's neighbouring nations, including the something called Community of power industry in former Yugoslavia (ZEP) and later Power industry of Serbia (EPS).

Analyses, condition assessments, and suggestions are based on an extensive database that has been methodically compiled over the past nearly 50 years of measurement findings. The close collaboration with the Specialized Laboratory for Testing Insulating Paper and Oil on a multidisciplinary strategy to diagnose the level of energy and measure transformers with oil-paper insulation is a specific benefit. To more accurately evaluate the state of EE equipment's insulation systems, the laboratory adopts global trends, participates in the work of international sister organizations, introduces new techniques, and creates and perfects non-standard techniques.

Primary activity

Testing of power transformers, at the installation site in a de-energized state:

Tests of oil-paper insulation parameters
insulation resistance measurement with absorption coefficient calculation (Risol, Ka)
measuring the capacity (C) and dielectric loss factor (tgδ ) of the winding insulation, particularly the transient (introductory) insulators (with measuring connection)
Inspection of the magnetic circuit and winding condition
measuring transformation ratio and coupling check (Ratio)
measuring magnetizing currents and idle loss power at low voltage ( I0 , P0 )
measurement of short-circuit impedance, i.e. dissipation inductance ( Lx )
determining the coil's electrical resistance (RCu) (at ET with load regulation switch in all switch positions)
using the SFRA technique to record the frequency responses of transformer coils
examination of oil-paper insulation using dielectric spectroscopy in the time domain (RVM) and frequency domain (FDS/PDC)
testing of the ground control switch using static and dynamic resistance measurements ( DRM )

On-site testing of power transformers in on-line mode (under operational voltage):

measuring the intensity of partial discharges ( PD )
detection of partial discharges using acoustic (ultrasound) method
UHF partial discharge detection

Testing of measuring transformers at the installation site:

Insulation tests

Insulation resistance measurement with polarization index calculation ( Risol, Ip )
calculating the dielectric loss factor (( tgδ ) and capacity ( C )
Tests of measuring transformers in on-line mode, under voltage
detection of partial discharges using acoustic (ultrasound) method
UHF partial discharge detection

Rotating machine testing:

Electrical testing of hydro (HG) and turbo (TG) generator insulation systems and windings, as well as high voltage motors (HVM):

measurement of stator and rotor winding electrical resistances (with HG distribution of one-way voltage drops by poles or inter-pole connections)
assessment of insulation resistance, polarization index, and specific discharge currents ( DD test)
insulation testing using a high DC test voltage and measurement of drain current ( Step Voltage test, Ramp test)
assessment of the dielectric loss factor - tgδ (with calculation of the growth in - tgδ ) and capacity
measuring the strength of partial discharges ( off-line and on-line )
using an increased alternating voltage to evaluate the insulation of the stator winding
rotor winding impedance measurement (for HG determination of impedance distribution by poles)
using a repetition pulse generator, examine the inter-turn insulation of the TG rotor - RSO test
Examination of high-voltage motor stators with an impulse generator (BAKER test) -
EDA-III test methodology

Testing of the magnetic circuit of rotating machines (HG and TG):

by using the suggested induction method (High Flux test), with thermal imaging of the stator surface and power loss estimation (in cooperation with the Specialized Laboratory for Thermographic Testing of the Institute)

Examination of the magnetic circuit using the low induction method ( ELCID test)
Testing the magnetic core's tightness - BUMP test
Flow measurement in water-cooled generator stator windings
Using FFT analysis to measure voltages and currents on large rotating machine shafts ( in cooperation with the Automation Center )