High voltage cable systems and their connection to Gas Insulated Substations (GIS) substations have created numerous over-voltages problems and insulation failures.
LCOE performs specific studies of transients in the high voltage electrical grids, especially on the insulated high voltage cables and their connection to GIS and high voltage overhead lines.
The studies are made using the EMTP-ATP software and own tools, developed for determining the over-voltages in the sheath of the high voltage cables that are connected in different configurations (cross-bonding, single-point, etc.).
Situations, such as the transition between overhead lines to cable systems are practical cases commonly simulated in order to choose the best solution.
EMTP-ATP studies and on site measurements have allowed to model and evaluate the expected over-voltages that may appear, in order to control its effect by means of an appropriate selection of sheath voltage limiters (SVL) and the appropriate sheath bonding.
These studies contain mainly:
Temporary and transient over-voltages due to short-circuits, switching and lightning.
Selection of sheath voltage limiters (SVL).
Insulation coordination criteria.
EMTP-ATP Software and SPACS Software (developed by LCOE) for analysis.
HIGH VOLTAGE SUBSTATION STUDIES
During switching operations or earth faults in SF6 gas insulated switchgear, very fast transient over-voltages (VFTO) occur. These over-voltages can stress the insulation of the high voltage equipment, adjacent equipment and secondary circuits connected to voltage and current transformers.
Very fast transient over-voltages are a major concern for equipment connected to high voltage Gas Insulated Substations (GIS) because of the risk of damage to instruments and control systems connected to the low voltage side. Efforts to determine the effects of VFTO on high and low voltage equipment require sufficiently accurate measurements of the peak and time parameters of the transient pulses
LCOE has specific models which represents the behaviour of Gas Insulated Substations (GIS) and their lines connected.
These models have been developed according to previous studies and measurements in real installations.
LCOE carries out studies and on-site measurements for insulation coordination analysis to evaluate very fast transient over-voltages caused by switching operations and faults.
These studies contain mainly:
On-site measurements to determine very fast transient over-voltages measurements and calibration.
Insulation Coordination analysis.
EMTP-ATP software modelling according to specific design implemented in the GIS substations.
CABLE FAILURE ANALYSIS
Analysis of premature cable failures and its accessories (cable terminations, joints, etc.) are carried out by means of dissection of remaining rests. Additionally, EMTP-ATP and SPACS software are also used to determine the operations conditions and possible causes of the failure.
Furthermore, a maintenance analysis is carried out in order to prevent these failures.
LCOE develops software packages for specific applications:
High Voltage and High current Impulses measurements according to IEC standards.
Modelling of operation of High Voltage Cable Systems “SPACS” (Software for Power Analysis of Cable System). This tool allows simulate any king of cable system configuration (Solid bonding, Single point, Solid Bonding, etc.), even if they are bonded to overhead lines and GIS, in order to evaluate different conditions of fault. Induced voltages and currents in cable sheaths are calculated by SPACS. This tool is used for new insulated lines as well as for the already existing ones for selecting sheath voltage limiters.
SERVICES FOR HIGH VOLTAGE LABORATORIES
LCOE offers consulting services to High Voltage laboratories:
High Voltage generation systems. Impulse generators.
High Voltage measuring systems. Dividers, attenuators and digital recorders equipped with specific software developed by LCOE.
Testing and measurement techniques implementation.
Courses related to High Voltage testing techniques and metrology.
NEW FACILITIES AND TESTING TECHNIQUES
LCOE participates in several European projects funded by EURAMET (European Association of National Metrology Institutes) collaborating with other National Metrology Institutes (NMI).
These projects are focused on developing pre-normative testing, new prototypes for measuring systems, calibration procedures, etc.
The main research lines in which LCOE participates are:
Very Fast Transients (VFT).
These developments provide us new and more effectiveness methods for industry applications
LCOE offers new facilities developed and procedures for testing and calibration purposes.
Active and reactive energy measurements in high voltage grids up to 24 kV with harmonics content up to 5 KHz AC.
Phantom power source to generate voltage and current waveforms with a frequency content from the fundamental frequency (16.7 Hz or 50 Hz) up to 5 kHz (for harmonic contents) for voltage level up to 25 kV and up to 500 A for current for laboratory and on site calibrations.
Very Fast Transient (VFT) calibration setup composed by a step voltage generator up to 100 kV with a rise time less than 10 ns and a reference measuring system. GIS installation.
Procedure for the calibration of Energy Measurement Systems (EMS) used in AC railway systems.
Procedure for the qualification of PD analysers working in the High Frequency range (0.1 - 30 MHz) used to analyse the insulation condition of High Voltage DC and AC cable systems.
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