Electrical Engineering: Key Concepts and Applications
Resistivity of Materials
Order the following materials from highest to lowest resistivity:
- Granite and sand (1500-10000 Ωm)
- Limestone (1000-5000 Ωm)
- Modified Granite and sand (100-600 Ωm)
- Peat (5-100 Ωm)
- Clay (50 Ωm)
Premade Busbars Advantages
Premade busbars are flexible and easy to install in large open areas, allowing for future modifications. They are ideal for installations in industrial and commercial areas, offices, laboratories, and all modular facilities subject to frequent changes.
Neutral Systems in Fire Risk Installations
The recommended system is the IT system, where the neutral is isolated or impedance-grounded.
IT System: First Insulation Fault Behavior
In an IT system, the first insulation fault does not trigger protection due to the high resistance in the fault loop. This results in a decreased fault current.
Auxiliary Power Supply Runtime
Auxiliary power supplies are crucial in situations where power loss could have significant consequences. The auxiliary power supply activates when the normal supply fails and continues until it is restored.
Land Resistivity: 1000 Ωm
A resistivity of 1000 Ωm indicates a limestone land type.
UPS: Uninterrupted Power Supply
UPS stands for Uninterrupted Power Supply.
AD8 and AQ1 Classifications
- AD8: The conductor is totally and permanently submerged in water.
- AQ1: The conductor is under insignificant lightning influence.
Prohibited Colors for Phase Conductors
The colors green and yellow, green, yellow, and light blue cannot be used for phase conductors.
Buried Ring Installation Procedure
The electrode should be buried around the perimeter of the foundation’s excavation. Ensure the bare conductor is in close contact with the ground (avoiding gravel or coarse aggregates). At least four conductors, well-separated, should be arranged vertically from the electrode for facility connections. Whenever possible, reinforcing bars within the concrete should be connected to the electrode.
Factors Affecting Ground Resistance
Factors that cause changes in resistance between the electrode and the ground include:
- Soil moisture
- Frost
- Aging
- Oxidation
Earth Resistance Calculation Formulas
For homogeneous land, the total resistance (R) is approximately equal to the resistance of a single bar divided by the number of bars (n), provided the bars are spaced at a distance > 4L:
R = ρ / (nL)
Where:
- L = Length of the bar (meters)
- ρ = Soil resistivity (ohm-meters)
- n = Number of bars
IP Code Voltage Applicability
The IP code applies to electrical equipment with voltages up to 72.5 kV.
IK Code: Mechanical Strength
IK code represents mechanical strength, indicating an equipment’s ability to withstand mechanical shock on all sides.
External Influences Classification
- A: Environment
- B: Utilization
- C: Building Construction
Main Objective of Equipotential Bonding
The primary goal is to prevent potential differences between conductive parts of an installation, especially in cases where an extraneous conductive part (e.g., a gas pipe) develops a potential due to an external fault. Equipotential bonding ensures that any stray current is safely directed to earth.
Conductor Marked with “1”
There are two possible interpretations:
- If a circuit includes a neutral conductor, it should be colored blue or marked with “1” for cables with more than five conductors.
- The number “1” may refer to external influences (referring to a specific classification within a standard).