HIGH VOLTAGE DEPARTMENT - HV SERVICES

1. Research Work

The research work of the High-Voltage Department is run on each of its fields of activity listed above. In past, there has been a series of minor research made to provide answers to various particular issues in parallel with in-depth and complex system research. The department researchers have participated in all the phases of construction and operation of the overall Slovenian electric power system. The quality of their work is assured by their:

knowledge of development and operation of the entire electric power system, expertise in construction, operation and technology of the high-voltage equipment, contacts with manufacturers of the high-voltage and other equipment, intensive use of computer methods in their research work experiences in the use of modern measuring and testing techniques, data archiving system set up with the so far made analyses and measurements, active participation in domestic and foreign professional bodies, continuous participation in international conferences, contacts with domestic and foreign research institutions.

The department research work is often connected with the activity of the high-voltage laboratory and mobile laboratory operating within the High-Voltage Department

2. High-Voltage Laboratory

There are various measurements and tests made on high-voltage equipment in the Department High-Voltage Laboratory. The emphasis is on high-voltage testing and checking of insulation.

Typical tests:

a. c. voltage tests at the power frequency of up to 50 Hz, atmospheric (1.2/50 µs) or switching (250/2500 µs) impulse voltage tests, and d. c. voltage tests

Testing takes place either in dry or wet rain conditions. Particular test conditions can be provided (for instance chopped impulse). There are also tests made involving considerably high currents, heating up, artificial ageing and similar.

Testing and measurement equipment:

The High-Voltage Laboratory is equipped with appropriate equipment as needed for generation of high d. c., a. c. and impulse voltages and currents, respectively. These facilities are:

2 x 200 kV a. c. generator of the maximal current on the high-voltage side of 50 mA, 2 x 350 kV a. c. generator of the maximal current on the high-voltage side of 1 A, 600 kV d. c. voltage generator with the highest rectifier current of 50 mA, generator producing 1.2/50 impulse voltage, 800 kV voltage and 4 kJ energy, generator producing 1.2/50 and 250/2500 impulse voltage, 1.5 MV voltage at the 1.2/50 and 1 MV at the 250/2500 wave and 40 kJ of energy, 8/20 current impulse generator for charging voltages of up to 30 kV at the impulse current of up to 20 kA

There is a series of methods used for measuring voltages, currents, temperature, time and any other parameter significant for later analysis. Various values (either instantaneous, effective or mean) are recorded and time variations of different magnitudes are registered and saved for the needs of later analysis.

Tested equipment:

Tests are made on high-voltage and other equipment. The ones most frequently tested ar:

insulator string and other insulation elements, surge arresters, voltage and current instrument transformers, high-voltage cables, equipment used to assure occupational safety

Any other equipment used in the electric power system can be tested and measured, too.

Special measurements:

Special measurements made by the High-Voltage Department are:

insulation resistance and loss angle measurements, resistance, capacitance and inductance measurements, temperature measurements taken at various points during heating, measurements of partial discharges taking place in the insulation, measurements of harmonic and other magnitudes, and measurements of the accuracy class of the voltage instrument transformers

Testing is made in compliance with standardised (SIST, EN IEC, DIN) and special methods. Any of the site measurements made with the mobile laboratory can also be in the stationary laboratory. Measurements are made with regularly calibrated analogue and digital measuring instruments. Most of the used instruments and procedures are computer-controlled. In the data intake, processing and graphic presentations, modern software and appropriate computer methods are employed.

3. Mobile Laboratory

Measurements to be on large and already installed equipment that cannot be transported in a simple way to the High-Voltage Laboratory are made with the Mobile Laboratory. These are mostly measurements of insulation as well as measurements and tests on the following equipment:

Power transformers:

measurements made with voltages of up to 5000 V of insulation resistance of the insulation between windings, measurements of the dielectric loss factor and of capacitance of the insulation between individual windings and on conductor isolators (bushings) of up to 10 kV, measurements of stray inductances of individual windings with the current of up to 1 A, measurements of magnetising currents, measurements of recovery voltages;

Instrument (voltage and current) transformers:

measurement of insulation resistance of high-voltage insulation with d. c. voltage of up to 5000 V, measurement of dielectric loss factor and capacitance of the high-voltage insulation of windings of inductive transformers and on capacitive dividers of capacitive transformers, various functional tests, measurement of recovery voltages;

Circuit breakers and disconnectors:

checking of the contact resistance by measuring the contact resistance on circuit breakers and disconnectors, recording of connection and disconnection times and simultaneity of pole operation on circuit breakers, measurement of the dielectric loss factor and capacitance on capacitors in/on circuit-breaker breaking chambers;

Generators:

measurement of insulation resistance, time constants and polarisation factor on insulation of individual phase windings with d. c. voltage of up to 5000 V, measurement of the dielectric loss factor and capacitance on insulation of individual phase windings up to the rated voltage, measurement of the partial discharge level, measurement of the capacitance current, measurement of insulation resistance of the excitation winding insulation (rotor).

Besides the above tests, the voltage test (2 Un + 1 kV) or the test with an increased voltage is still made in special cases.

High-voltage electric motors:

measurements of insulation resistance, time constants and polarisation factor on insulation of individual phase windings with the d. c. voltage of up to 5000 V, measurement of the dielectric loss factor and capacitance on the stator insulation up to the rated voltage, measurement of the partial discharge level, measurement of the capacitive current.

Besides the above tests, the voltage test (2 Un + 1 kV) or the test with an increased voltage is still made in special cases.

With the measuring systems of the mobile laboratory that can be transported to the measuring site there are frequently also other measurements and tests on various kinds of equipment made. These are:

a. c. voltage tests of busbars, a. c. and d. c. voltage test of cables, checking of the accuracy class of voltage and current transformers, and current and voltage recording during transient states and similar.
Department - HV
ADDRESS:
EIMV - department HV
Hajdrihova 2
1000 Ljubljana
SI-Slovenia

TELEPHONE:
00386 (0)1 474-3651