In addition to theoretical and practical basic knowledge, standards, regulations and computer-aided programs that are valid for each project are needed for planning, sizing, calculation and evaluation of grounding projects in electrical installations. Healthy installation and operation of electrical installations is very important for the safety of life and property.
Grounding in electrical installations is examined in two main parts.
Grounding in LV installations
Grounding in HV installations
What is Grounding? If we answer the question;
Grounding system; It can be defined as establishing a conductive connection between the designated touch points of panels, devices and machines and the earth electrode. This earth electrode (grounding stake, grounding plate, etc.) is buried in the ground as a conductive part and realizes an electrical connection with the earth.
Grounding is the connection of the device body to the earth by establishing a conductive connection between the devices and the earth, for reasons such as insulation failures that may occur in the devices. In this way, there is no problem for people because the fault current flows towards the earth. If there is no grounding, death may occur depending on the level of this current, as fault currents will flow through the person touching this device. Therefore, thanks to earthing, the leakage currents are safely directed to earth and if connected to an automatic tripping system (residual current relay, etc.), the electrical energy is safely cut off.
What are the Types of Grounding?
Protection Grounding
It is the direct connection of non-voltage conductive plant sections to grounders or grounded sections to ensure that the electrical circuit is opened with overcurrent protection devices in an insulation fault.
Examples of conservation earthing;
Body metallic parts of electric motors and generators, traverses,
Conductive and accessible parts of buildings,
Lead sheath and metal armor of low and high voltage cables,
Secondary windings of measuring transformers,
Protection wires of high voltage aerial lines,
Operational Grounding
Grounding of active sections and zero conductor is called operational grounding. Operational grounding is done in two ways. These are:
► Resistance-free operational earthing: It is the earthing made directly without putting resistance in the earthing circuit.
Resistive operational grounding: It is the earthing made through an ohmic, inductive or capacitive resistor and is generally applied in MV systems.
Grounding Against Lightning
In the event of a lightning strike, it is the grounding of conductive sections not related to the operating current circuit in order to prevent jumps to the conductors under voltage due to the operation to a large extent and to transmit the lightning current to the ground. However, at this point, the lightning impulse current cannot be completely transferred to the ground and some of the impulse is directed from the grounding line to our electrical installation. If there is no internal lightning (surge arrester) system in our installation, damage may occur in our main panel, secondary panel and devices.
Terms Related to Grounding
1) Soil: It is the expression of the earth as matter and place, where the electric potential is zero at every point. Example: humus soil, clay soil, sandy soil, mud, rocky land.
2) Reference soil (neutral soil): It is the part of the earth that is far enough from the grounding facility and outside the impact area of the grounding facility. Between any two points in this section, the voltage caused by the ground current is negligibly small.
3) Grounding conductor: It is a conductor laid outside the ground or insulated inside the ground that connects a device or facility part to be grounded to a grounding device. If an isolating connection, a disconnector, or a grounding coil or resistor is connected to the connection between the neutral conductor or the main conductor and the grounding device, then only the connection between the grounding conductor and the ground side terminal closest to the specified devices is the grounding conductor.
4) Grounding bar (grounding bonding conductor): It is a grounding bar (conductor) to which more than one grounding conductor is connected.
5) Grounding facility: It is the whole of grounding conductors and grounding conductors that are connected to each other as conductors and located within a limited area, or that perform the same function (such as unpainted pole legs, armor and metal cable sheaths).
Change of earth potential and voltages around the grounding device
6) Grounding: Connecting an electrically conductive part to the ground through a grounding facility.
7) Grounding: It is all the tools, devices and methods used for grounding. Groundings are distinguished according to their types, purposes and shapes:
7.1) Definitions according to grounding types:
i) Direct grounding: It is grounding that does not contain any resistance other than the grounding resistance.
ii) Indirect grounding: It is grounding made with ohmic, inductive or capacitive resistors additionally connected to the grounding conductor.
iii) Open grounding: It is the grounding to which a surge arrester or addulator is connected on the grounding conductor.
7.2) Definitions according to the purposes of grounding:
i) Protection grounding: It is the grounding of a conductive part that is not in the operating current circuit in order to protect people against dangerous touch voltages.
ii) Operational grounding: It is the grounding of a point of the operating current circuit for the normal operation of devices and facilities. This grounding can be done in two ways:
-Resistive (direct) operational grounding: In this case, there is no resistance other than the normal grounding impedance on the grounding path.
-Resistive operating grounding: In this case, there are additional ohmic, inductive or capacitive resistances.
iii) Function grounding: It is the grounding made for the purpose of fulfilling the desired function of a communication facility or an operating element. Functional grounding also carries the operating currents of communication devices that use ground as a return conductor.
iv) Function and protection grounding: It is grounding in which function grounding is used using the same grounding conductor and is also used as protection grounding.
v) Low-noise grounding: It is a grounding connection whose level of interference (with distorting magnitudes) transmitted from external sources does not produce unacceptable effects that cause information losses in the computing or similar hardware to which it is connected.
vi) Grounding against lightning: In case of a lightning strike, it is the grounding of conductive parts that are not related to the operating current circuit, in order to largely prevent jumps (back jumps) to the conductors that are under voltage due to operation and to transmit the lightning current to the ground.
vii) Rail system grounding: It is the direct, indirect or open connection between the conductive parts and the rail system ground. Rail system ground is the rails and the conductive parts connected to them, which serve as return conductors and are connected to the ground through sleepers or grounding facilities.
7.3) Definitions according to the type of grounding:
i) Individual (singular) grounding: It is the grounding in which the operating element or device is connected only to its own grounding.
ii) Star-shaped grounding: It is the collection of grounding conductors of many operating elements or devices in a star shape at a grounded point.
iii) Multiple grounding: Grounding in which an operating element or device is connected to several grounded conductors (e.g. potential equalization conductor, protection conductor (PE) or functional grounding conductor (FE)). These grounding conductors may be connected to the same grounding bonding conductor or to different grounders.
iv) Surface grounding: It is the grounding in which the conductive parts of the operating elements or devices and communication facilities to be grounded that do not carry operating current are connected to each other in the form of a network to protective grounding or to function and protection grounding.
8) Grounder (grounding electrode): These are conductive parts that are buried in the ground and have a conductive connection with the ground, or are embedded in concrete and have a large surface connection.
9) Grounder types:
9.1) Grounders according to location:
i) Surface grounder: Generally 0.5 - 1 m. It is a grounding device placed at a depth between . It can be made of galvanized strip or round or stranded conductor and can be a star, ring, eye grounder or a mixture of these.
ii) Deep grounder: It is a grounder that is generally placed vertically deeper than 1 m. It can be made of galvanized pipe, round bar or similar profile materials.
9.2) Grounders according to shape and profile:
i) Strip grounder: It is a grounder made with strip-shaped conductive material.
ii) Pipe and profile grounder: It is the grounder made with conductive material in the form of pipe and profile.
iii) Stranded conductor grounder: It is the grounder made with stranded conductive material. The wires forming the stranded conductor should not be thin.
iv) Natural grounding: Metal parts such as steel sections, pipe installations, foundation piles of structures that are in contact with soil or water directly or through concrete, whose main purpose is not grounding, but are effective as grounding.
v) Cable with grounding effect: It is the cable whose metal sheath, shield (screen) and armor have conductivity compared to the ground and have the characteristics of strip grounding.
vi) Bare grounding connection conductor: The part of the bare grounding conductor connected to a grounding conductor remaining in the ground is considered a part of the grounding conductor.
vii) Foundation grounder (grounder placed in the foundation): It is a conductor embedded in concrete and in contact with the soil (through the concrete) on a large surface.
10) Potential regulator grounder: It is the grounder that serves to regulate the potential distribution rather than providing a certain propagation resistance.
11) Soil resistivity (pE): It is the electrical resistivity of the soil. This resistance is usually given as ohm m2/m or ohm-m. This resistance is the resistance between two opposite surfaces of a clay cube with a side length of 1 m.
12) Propagation resistance (RE) of the grounding device or grounding facility: It is the resistance of the soil between a grounding device or grounding facility and the reference soil. The dissipation resistance is approximately acceptable as ohmic resistance.
13) Grounding resistance: It is the sum of the propagation resistance of the grounding device and the resistance of the grounding conductor.
14) Total grounding resistance: It is the total resistance of all groundings that can be measured in a place and are measured.
15) Grounding impedance (ZE): It is the alternating current resistance between a grounding facility and the reference ground (at operating frequency). The absolute value of this impedance is obtained by parallel connection of the propagation resistances of grounders and chain effect conductor impedances such as ground conductors and cables with grounding effect.
16) Impact grounding resistance: It is the resistance that is effective during the passage of lightning currents between any point of a grounding facility and the reference ground.
17) Grounding voltage (earth potential rise) (UE): It is the voltage occurring between a grounding facility and the reference ground.
18) Earth potential: It is the voltage between a point on the earth and the reference earth.
19) Touch voltage (UT): It is the part of the ground voltage that can be bridged by humans (see Figure-2). In this case, the current path on the human body is from hand to foot (horizontal distance to the touchable place is approximately 1 m) or from hand to hand.
20) Expected touch voltage (greatest possible touch voltage) (UST): It is the voltage that occurs during an earth fault between the conductive parts and the ground, while these parts are not yet touched (source voltage).
21) Step voltage (US): It is the part of the ground voltage that a person can bridge with a step distance of 1 m. In this case, the current path on the human body is from foot to foot.
22) Potential distribution: When a body short circuit occurs as a result of an error in a grounded electrical operating element, it is the distribution of the potential on the earth, starting from the reference ground and towards the electrical operating element in question to be measured.
Current, voltage and resistances in a transformer substation whose star point is grounded through a low-value resistor in the event of an earth fault
23) Regulation of potential distribution (potential regulation): Regulation of the potential distribution of a grounding facility is to affect the potential distribution by placing potential regulator grounders to reduce step and touch voltages (see Figure-2). It does not matter whether the regulating grounders are connected to the grounding facility or not.
24) Potential equalization: Elimination of potential differences. For example, they are arrangements made to eliminate potential differences between protection conductors, conductive pipes and conductive building parts, or between these pipes and building parts.
25) Function potential balancing: These are arrangements made to reduce the voltage between conductive parts to values low enough for an operating element, device or facility to operate smoothly.
26) Protection potential balancing: These are arrangements made to prevent the emergence of high voltages between conductive parts.
27) Function and protection potential balancing: It is the combination of function potential balancing and protection potential balancing and is sufficient to ensure the conditions foreseen for an operating element, device or facility in terms of both function and protection.
28) Potential equalization line (equipotential bonding): These are the connection conductors used to ensure potential balancing.
29) Insulation of the place you step on: It means increasing the resistance between the place you step on and the ground so that unacceptable touch voltages cannot occur.
30) Potential drift: It is the transfer of the rising potential of a grounding facility to the region with a lower potential or to the reference soil region by a conductor connected to this facility (for example, metal cable sheaths, PEN conductor, water pipe, railway). A potential difference occurs in this conductor compared to its surroundings.
31) Global grounding system: It is a grounding system obtained by connecting local grounding facilities to each other and ensures that no dangerous grounding voltage (earth potential increase) occurs in grounding facilities located in close proximity to each other. Such systems allow ground fault current to be divided, thus reducing the ground voltage in the local grounding system. Such a system forms an equipotential surface.