SERVICES AND LABS
ON SITE HIGH VOLTAGE TESTS
LCOE owns different mobile generation and measurement systems to perform off-line tests, standing out among them four resonant generators installed in mobile laboratories for testing the insulation and performing PD measurements, with rated voltages from 36 kV to 680 kV, and output currents up to 83 A, allowing testing up to 400 kV insulated cables more than 12 km long, as well as Gas Insulated Switchgear (GIS) with rated voltages up to 420 kV.
On site tests on cables and GIS switchgear after its installation are performed according to international Standards such is IEC 62067, IEC 60840, or IEC 62271-203, being LCOE accredited according to ISO 17025 to perform them.
LCOE has been performing on site HV tests since 2005.
COMMISSIONING TESTS ON INSULATED CABLE SYSTEMS
On site testing of cables after its installation is the suitable way to determine if the assembly of the accessories of the cable system after the lying of the cable have been performed correctly, allowing to fix any deviation found during the tests before putting the cable system on service with the full power of the network, thus avoiding the derived risk and significant damages to the cable system.
Dielectric test of the main insulation, together with the partial discharges measurement assures that the terminations and joints of the cable system are properly installed, assuring a safe energizing of the cable.
Other commissioning tests performed on site are the dielectric DC test of the sheath of cables, the measurement of the electrical resistance of the conductor and screen of the cable to verify its continuity, the capacitance of the cables, and the measurement of line impedances. The phase order and earthing system are also verified during and after the commissioning tests. These tests are usually additional required by the utilities or national regulations in order to assure the correct execution of the project, or to get the necessary parameters to adjust the different protections involved in the operation of the system.
ON LINE INSULATION DIAGNOSIS WITH PARTIAL DISCHARGES MEASUREMENT
Ageing of a high voltage insulation increase the probability of a failure of the affected system. Partial discharge measurement is currently considered the most effective way to asses the condition of a high voltage insulation in power cables.
On line PD measurement allows to perform this assessment without interrupting or interfering in the normal operation of the power grid, since partial discharges are measured using the system own voltage as the test voltage, and PD sensors are installed in the accessories of the cable system without the need to interrupt any earthing link.
Measurement of PD by domain expertise in all the accessible accessories of the cable allows to periodically evaluate the condition of the insulation and efficiently plan the maintenance program of the system.
LCOE uses state-of-the art technologies to perform on-line PD measurements. Depending on the particular characteristics of the circuit, different type of PD sensors (HF, VHF and UHF) as well as different filtering technologies (measuring frequency band selection, wavelet filter, etc.) are used to differentiate the electrical noise from the PD signals, different PD location techniques (reflectometry, GPS, etc.), and different ways for identifying the detected PD sources with the type of fault or cause that origins the PD signals. LCOE offers either periodical or continuous insulation monitoring services, by means of PD measurements on electrical grids, which allows analyzing the time evolution of PD patterns and evaluate its critical nature.
