Organization of a reliable system of protectionElectrical Safety - one of the main conditions to prevent harm to users of electrical installations. It will provide protection not only man, but also devices. Properly calculated and mounted protective earth will prevent the negative impact of a broad spectrum of unpredictable emerging circulating currents eliminate their closure on the case. The result will be excluded the likelihood of traumatic lesions, as well as the failure of complex technical devices.
- Action system protective earth
- How are settled
- Classification of grounding devices
- Method of calculation parameters
- Driving and assembly circuit
- The grounding system without deep earthing
- Group system with artificial grounding
The purpose of protective earthing is to createelectrical connection to the ground of not live elements of metal, under threat of a voltage. The reason for occurrence of unwanted tension may be lightning strikes, short to ground, take-away capacity induction, appearing under the influence of adjacent current-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 system protective earth
The system is the protective earth is to reduce the step voltage and touch, in bringing them to safe values. As a result, the competent unit grounding system:
- reduced potential for grounded electrical equipment;
- aligned parameters of the potential grounds on which the users are, and the ground potential technical installation.
Important. In the absence of the electrical grounding to touch her body is just as dangerous as touching the electrical phase conductor.
Based on the reduction of value orpotential equalization grounding electrical equipment protective grounding principle of action helps to reduce body stress with respect to the object used for grounding, as is often the soil is used. What makes the current flowing through the body of the user, and contact voltage (step) will reach absolutely safe for human values and technology.
Ground will be executed fully,If the fault current indicators on the ground will not be increased by reducing the grounding resistance. This condition is fully compliant with network with isolated neutral - with the device a generator or transformer is not connected to the grounding system or connected to it through the large resistance of various measuring, signaling, protecting devices.
How are settled
In principle, the calculation of the protective ground isin the precise definition of the basic parameters. They are required to create a circuit that forms the safest step and touch voltage that appears at the time of phase-to-body. On the basis of the calculated values within the permissible limits, is calculated the number and size of earth, planned order of placement of single elements.
Classification of grounding devices
The origin of grounding divided into two categories, the production of calculations must take into account their specific differences and characteristics:
- Natural properties submitted by third partiesconductive parts directly in contact with the ground. The category of natural earth electrodes are also assigned the objects which electrical contact is made with the ground through the intermediate conductive medium.
The natural ground earthing set (clogged sink in the drill hole) vertical elements, connected by a horizontal
Also soil and water into the category of naturalearth electrodes include metal pipes of water and other communications laid trench method. As the grounding of natural origin can not be applied to pipelines with flammable and explosive substances, highway, constructed with partial use of PVC pipes and parts. It is designed to provide trouble-free electrical functional in emergency and normal operational and protective earth, eliminating the chance of injuries, mostly set in the ground.
- Artificial grounding represented mostly vertical or horizontal electrodes.
Method of calculation parameters
The following data is required to perform the calculations:
- the specific characteristics of electrical equipment,such as the type of installation and its main devices, operating voltages, possible ways to implement grounded neutral transforming and generating equipment;
- the size and configuration of the electrodes, making it possible to take into account the estimated depth of immersion into the soil;
- information about measurements of resistivitya primer on the territory equips earthing system, the characteristics of a particular climate zone (you can get them at a local weather service);
Presented in the context of circuit protective earthing
Important. When placing a protective earth ground system in two layers of data are needed on the resistivity of each of them, will need accurate data on the capacity of the upper layer.
- information about the availability of suitable naturalof earth, on which objects may be used for grounding, you will also need the actual current spreading resistance performance of these objects, obtained by the measurement;
- accurate values for calculated ground fault current calculated in a standard way;
- design characteristics of acceptable norms andrules PES stresses action grounding protection period, which is necessary if the calculations were made on the values of touch voltage and step voltage values.
Advantageously, the protective grounding and vanishingElectrical calculated for the cases to the installation of the grounding system in uniform soil. Now, however, developed and calculation methods are applied to the location of earth in a heterogeneous composition on the ground.
- Calculation of earth, which is located in a uniformenvironment, requires consideration of the freezing layer seasonally resistance values during periods of freezing and drying ground. special rates are used to obtain exact values used in calculations for earthing systems any complexity.
- Calculation of earth electrodes installed in two ormore 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 electrodes are installed, included in the complex structure of the group of earth.
Regardless of the method of calculations is common to all option schemes - required resistance, as determined in accordance with statutory regulations of the PES.
For electrical equipment with voltage up to 1 kVResistance calculation of the grounding element contained in the protective earth with isolated neutral (such as IT), carried out in accordance with the condition:
This inequality is a variable rgvalue resistance grounding device (expressed in ohms), a constant Upr.dop. - Parameter contact voltage (50), Ig - the total value of the earth fault, expressed in A.
According to regulatory requirements rg value variesranging from 4 ohms to 10 ohms (to the value of the lower limit does not impose specific requirements, the upper - the maximum permissible option), provided that the power supply network and connected in parallel transformers and generators are not greater than 100 kVA.
For the organization of protective earthing systems with higher voltage is used in the calculation of certain quantities:
- 0.5 ohms in electric effectively earthed with their characteristic high currents to the ground;
- not higher than 10 ohms at 250V contact voltage in isolated neutral systems (condition valid at low currents in the ground facility for equipment with voltage more than 1000 V).
Note. Preferred minimum parameters of resistance of grounding loops. The smaller the value, the more effective will be the current flow through the object with the least resistance.
Calculated for ground mounting system resistance to current spreading, calculated for earthing, during operation may increase. The value must be constantly monitored.
Driving and assembly circuit
In apartment buildings to protect occupants from injury installed circuit breakers, producing vanishing (blackout) the mains in case of breakdown or fault isolation.
In stand-alone housing and country houses due to lack oftechnical possibility of installing automatic breaking required protective earthing device that can be carried out, consult an electrician, or make their own hands.
The grounding system without deep earthing
circuit elements, which structure is not includeddeep earthing, can be installed in series or arranged in the form of a geometric figure. Form the contour depends on the features of the site. This method is applicable when the grounding line length of up to 3 meters.
- Deepens vertical grounding. The distance between installed vertically into 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 positioned, the greater the shielding effect.
- Running incremental measurement unit real values of earth resistance. They should be installed in an amount to provide the formation of a minimum of resistance.
Note. Often, a different number of ground elements is used for grounding of equal land area, as the resistance value affects soil resistivity.
- Connects single grounding. Earthing with corrosion-resistant coating are joined using special connectors. grounding devices of black metal are joined exclusively by welding seams are covered with mastic asphalt.
Group system with artificial grounding
It's simple, affordable selfexecution circuit protective grounding 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 m.
- At the apex of the triangle is desirable drilled out hole three meters deep. If it was decided to hammer vertical grounding sledgehammer, wells will be sufficient for 1,5 m.
Note. Scoring is much easier to subjects with pointed ends. Sharpen grinder material that is going to score.
As a material for verticalsuitable grounding a metal pipe with a diameter of 50 mm, 10 mm steel bars, angles with a side of 50 mm. It takes three segments of length of three meters. Horizontal grounding element can be made of nine meters of steel strip 4mm thick, 40 mm wide.
- Then mounted ground loops connected by welding with the conductor. It is made from a round bar or flat steel. He connects with a natural grounding.
Mounted circuit successfully execute appointmentprotective 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.
Having an idea of what is calledprotective earth to learn about the ways of electric device system can safely begin to self-assembly. Do not forget about measuring the resistance value after the installation. If there is no appropriate tools and skills required to call electricians.