Application of computational fluid dynamics to predict the temperature-rise of gas insulated switchgears
Accurate temperature-rise prediction in gas insulated switchgears (GIS) is necessary to reduce the number of heat-run tests during the product development process. An electromagnetic-thermal-fluid coupled model using computational fluid dynamics (CFD) is developed to predict the temperature-rise of a 110-kV three phase GIS in common tank type. The GIS includes the three-position isolation/ground switch and the circuit breaker insulated with SF6 gas at 5 bar. In this model, the contact resistance, eddy current, skin effect, thermal flow, and thermal radiation are considered. The ohmic losses generated in the conducting components are calculated through the harmonic electromagnetic analysis with MAXWELL 3D software. Then, the predicted losses are imported to the commercial CFD software ANSYS Fluent to fulfill the thermal simulation. Based on this model, the distributions of heat generation, gas velocity, and temperature-rise are obtained. The results show that the maximum power density and temperature-rise both occur at the contact zones of the three-position isolation/ground switch. To verify the developed model, the temperature-rise tests of the GIS are carried out at 2200 A. The simulation and measurement results are close with a maximum error of 3.99 K.
Temperature Rise Calculation and Overheating Fault Analysis of Gas Insulated Switchgear Bus Connector Based on Coupled Field Theory
To understand the formation mechanism of overheating fault in bus connector of gas insulated switchgear(GIS), we developed a 3-D finite element model based on the coupled field theory to calculate the temperature rise in the bus connector. In the model, electrical contact resistance(ECR) and thermal contact resistance(TCR) are calculated based on structural field, and power loss, calculated based on current conduction analysis, is taken as the heat source in connector's temperature field for calculating the temperature rise. The model is validated by steady-current temperature-rise tests, and it is adopted for analyzing the influences of conductor insertion depth and short-circuit load current on connector temperature rise. It is concluded that short-circuit current will not thermally damage bus contact due to its short duration, and the depth of the inserting conductor is the direct cause of overheating faults in GIS bus connectors.
A simulation-based methodology for high-current heat-run testing of distribution system components
In this document, a procedure is presented that supplements low-voltage switchgear type testing according to IE 60439. Starting from experimental testing setup, a numerical 3-d simulation model is created for the electric heating, the resulting airflow and hence the cooling of the switchgear under the test conditions. Thereafter, this model’s predictions are compared to the corresponding experimental measurements. Introduction Heat-run testing of distribution system components is an essential task for both development processes and for type testing. In the case of low-voltage switchgears the procedure for type tests is covered by IEC 60439 and therefore fixed in procedure. However, during the development tests, significant amounts of time and costs can be saved with an intelligent combination of computer simulations and heat-run tests for verification purposes. Figure 1: Picture of the low voltage switchgear. The short circuit connection is visible on the right top. In this case study a prototype of a low-voltage switchgear unit has been modelled and simulated taking into account the non-uniform current distribution in the high-current copper-bars as well as the conduction, convection and heat radiation of the switchgear assembly. Figure 2: Calculation geometry overview of the simulated switchgear unit. The conducting copper bars are short-circuited at the left top each of the three phases has 6 bars. The air ventilation inlets are situated on both bottom sides. On the top, there are restricted air outlets. Air is actively blown into the system using six fan units at the bottom (see Figure 1 and Figure 2). The air outflow is only possible through slots in the perforated top region of the device. Experiment The test specimen consisted of three functional units with main busbars (cross section 100x10mm bare Cu, six per phase) without feeder brunches. Instead, the test was carried out with the aid of heating resistors of an equivalent power loss. The verification of temperature-rise limits was performed according to clause 8.2.1 of IEC and EN 60429-1. The test was carried out with the nominal current load of the main busbars (6700A, 50Hz) and with the aid of heating resistors of an equivalent power loss of the branch circuits. The assembly was arranged as in normal use. The temporary connections of the test sample to the testing transformer were realized with conductors of ≥ 3m length, cross section 100mm x 10mm bare Cu, four per phase, with each 10mm distance from surface to surface of the partial conductors. On the other side of the test sample’s busbars, a short circuit connection with 100mm x 10mm bare Cu, four C I R E D 20th International Conference on Electricity Distribution Prague, 8-11 June 2009