Protective earth - calculation circuit and system design, eliminating the threat of defeat

By Admin | Garden And Buildings / Communication
09 May 2016

Organisation reliable system protecting electrical safety - one of the main conditions to prevent injury to users of electrical installations.It will provide protection not only man, but also devices.Properly calculated and installed protective earth to prevent negative effects of a broad spectrum of unpredictable emerging circulating currents eliminate their closure on the case.This will exclude the possibility of traumatic injuries and the failure of complex technical devices.

Content

purpose of protective earthing is to create an electrical connection to the ground of not live metallic elements endangered tensions.The cause unwanted tensions may be lightning strikes, short to ground, take-away capacity induction, appearing under the influence of adjacent cu

rrent-carrying devices or their parts, and a number of other situations.The connection can be made with the ground or its equivalent, such as sea or river water, which lies in the career of coal and other natural or man-made objects with similar properties.

action of protective grounding ↑

Work protective earthing system is to reduce the stress parameters step and touch, in bringing them to a safe value.As a result of the grounding system of the competent unit:

  • reduced potential grounded electrical equipment;
  • aligned parameters of the potential grounds on which the users are, and the earth potential of technical installations.

important.In the absence of grounding electrical touch her body is just as dangerous as touching the electrical phase conductor.

Driving protective earth
Driving protective ground:
r - resistance grounding devices
u - contact voltage

Based on the reduction of value or on the lining of the potential grounding of electrical engineering principle of the protective grounding reduces the stress of the housing relative used to earth the object, aswhich is often used in soil.What makes the current passing through the user's body and the contact voltage (step) will reach absolutely safe for human values ​​and technology.

grounding function will be carried out fully if the performance of the earth current will not be increased by reducing the resistance of the earth.This condition is fully consistent with the isolated neutral network - the device generator or transformer is not connected to the grounding system or connected to it through a lot of resistance of various measuring, signaling, protecting devices.

As settlements ↑

principle calculation protective ground is the precise definition of the basic parameters.They are required to create the schema forming safe maximum voltage step and touches that occur at the time of the phase circuit to the housing.On the basis of the calculated values ​​included in the limits calculated the number and size of earth, planned order of placement of single elements.

Classification grounding devices ↑

By origin grounding divided into two categories, the production of calculations must take into account their specific differences and characteristics:

  • natural objects represented extraneous conductive parts in direct contact with the ground.The category of natural earth electrodes are also referred objects that electrical contact with the ground is done through an intermediate conductive medium.
Natural earth electrode - soil
in natural soil earthing set (clogged, lowered into drilled wells) vertical elements connected by a horizontal

addition of soil and water to the category of natural grounding metal pipes carry water and other communications laid trench method.As the earthing of natural origin can not be applied to pipelines with flammable and explosive substances, highway construction with partial use of PVC pipes and parts.It is designed to provide trouble-free functionality of electrical equipment in emergency and normal operational and protective earth, eliminating the likelihood of injuries, mostly set in the ground.

  • Artificial grounding presented mostly vertical or horizontal electrodes.

method of calculating parameters ↑

to perform the calculations required the following information:

  • specific electrical characteristics, such as the type of installation and its major device operating voltages, the possible ways to implement the grounded neutral transforming and generating equipment;
  • size and configuration of the electrodes, making it possible to take into account the anticipated depth of immersion into the soil;
  • information on the resistivity measurements of soil layer on the territory equips earthing system, the characteristics of a particular climatic zone (you can get them at a local weather service);
presented in the context of circuit protective earthing

important.When placing the system protective earth ground in the two layers need data on the resistivity of each of them, will need accurate data on the capacity of the upper layer.

  • information about the availability of suitable natural grounding, what objects can be used to ground the real figures will also require current spreading resistance of these objects obtained by the measurement;
  • accurate values ​​for calculated ground fault current, calculated in a standard way;
  • design characteristics of acceptable standards and regulations PES stresses the period of the grounding protection is necessary if the calculations were made on the values ​​of contact voltage and the values ​​of the voltage step.

Mostly protective earth and vanishing electric calculated for cases the installation of the grounding system in a homogeneous soil.Now, however, they developed and applied methods of calculation with the location of earth in a heterogeneous composition of the earth.

  • Calculation of earth, located in a homogeneous environment, it requires taking into account the values ​​of the resistance layer in the freezing seasonal periods of freezing and drying ground.For exact values ​​are special factors used in the calculation of earthing systems of any complexity.
  • calculation earthing installed in two or more layers of soil, requires consideration of the resistance values ​​of all layers.The calculation is based on consideration of all the potential induced on the mounted electrodes included in the complex structure of the group of earth.

Regardless of the method of calculations is common to all option schemes - required resistance, determined in accordance with statutory regulations of the PES.

for electrical equipment with voltage up to 1 kV calculation of the resistance of the grounding element, part of the protective ground with isolated neutral (such as IT), carried out in accordance with the condition:

This inequality variable R s is a resistance value of the groundingdevice (expressed in ohms), a constant U pr.dop.- Setting voltage contact (50), I s - the total value of the earth fault, expressed in A.

As regulatory compliance significance R z ranges from 4 ohms to 10 ohms (to the value of the lower limit does not imposespecial requirements, the top - the maximum permissible parameter), provided that the power supply network and connected in parallel transformers and generators are not greater than 100 kVA.

To organize protective earthing systems with higher voltage is applied in the calculation of other quantities:

  • 0,5 Ohm in electric effectively earthed with their characteristic large currents in the ground;
  • no higher than 10 ohms at 250V voltage ground in systems with insulated neutral (the condition is really at low currents in the ground facility for equipment with voltage more than 1000 V).

Notice.Preferred minimum parameters resistance ground loops.The smaller the value, the more effective will be the current through the motion objects with the least resistance.

calculated for the installation of the grounding system impedance current spreading evaluated for earthing during operation may increase.The value must be constantly monitored.

scheme and installation of circuit ↑

In apartment buildings to protect occupants from injury installed breakers producing vanishing (blackout) the electrical network in case of breakdown or fault isolation.

In standalone homes and country houses because of the lack of technical possibility of installing automatic breaking device is required protective earth that can be done, consult an electrician, or make your own hands.

Driving the installation of the system protective earth
linear arrangement of earth, buried up to the rock

grounding system without deep earthing ↑

circuit elements, which are not part of a deep earth electrode, can be mounted in series or arranged in the form of a geometric figure.Form the contour depends on the characteristics of the site.This method is applicable when the grounding line length up to 3 meters.

  • deepens vertical grounding.The distance between the vertical to the ground earthing is calculated from the length of the data part of the system grounding.This is to minimize the shielding, since the closer the elements are located, the greater the shielding effect.
  • carried out in stages measured actual values ​​of resistance of single earth electrodes.They must be set in an amount to the formation of a minimum of resistance.

Notice.Often grounding equal area of ​​land used different number of ground elements, as the resistance value affects the resistivity of the soil.

  • Connects single grounding.Earthing with corrosion-resistant coating are joined using special connectors.Devices ground black metal are joined exclusively by welding seams are covered with mastic asphalt.
Special Connectors
Connection with bolts is permissible only in the case of the installation of a corrosion-resistant coating;
earth connection to the contour of black metal by welding is performed, followed by fastening with a bolt

group system with artificial grounding ↑

It is simple, accessible to the independent exercise circuit protective earthing circuit in the form of an isosceles triangle.This electrical safety system have a meter from the bottom of the cap or walls.

  • In accordance with the selected configuration dug a trench depth of 0.8 meters.The length of each side of the triangle 3 meters.
  • the vertices of the triangle is desirable wells drilled out the three-meter depth.If you decide to score a sledgehammer vertical grounding, it will be enough wells 1.5 m.
Driving group ground loop
Driving group circuit protective earthing

Notice.Scoring is much easier to subjects with pointed ends.Sharpen grinder material that is going to score.

The material is suitable for vertical grounding a metal pipe with a diameter of 50 mm, 10 mm steel bars, angles with a side of 50 mm.It will take three segments of length of three meters.Horizontal grounding element can be made of nine meters of steel strip of thickness 4mm, width of 40 mm.

  • then mount a ground loop is connected by welding with the conductor.It is made from a round bar or flat steel.He connects with a natural grounding.
Location earthing
plan layout of the triangular contour protective earth

Mounted circuit successfully fulfill the protective purpose of the resistance, if it is connected to a steel laid in the ground water supply, the metal casings of water wells, to the other w / w, and metal structures.After installation, all protective earth trenches and development is necessary to fill a uniform soil without inclusions of rubble and debris.

View the video will help to visualize the principle of operation of the device and method of the simplest ground for a country house:

get an idea of ​​what is called the protective earth to learn about the ways of electric devices of the system can safely begin to self-assembly.Do not forget about measuring the resistance value after installation.If there is no appropriate tools and skills needed to call electricians.