Emergency operation mode of electrical network

Task 4. In an emergency (short-circuiting the phase conductor to the ground through the current spreading ground resistance R_g) make a comparative analysis of the dangers of human touch to a working phase conductor in isolated and earthed neutral. To investigate the nature of ground resistance R_g effect on the value I_h of the current flowing through the human body.

The experiment results should be written in the report (table 8.6) of laboratory work and build graphs I_h = I (R_g) for both types of networks.

Table 8.6.

The dependence of the current I_h, mA, on voltage U_A, V
and resistance of ground R_g

Task 5. In an emergency (short-circuiting phase wire to the ground through the resistor current spreading ground resistance R_g) perform a study of the nature of resistance to the influence of the human body circuit by touching to a working phase conductor in isolated and earthed neutral on the value I_h of the current flowing through the human.

The experiment results should be written in the report (table 8.7) of laboratory work and build graphs I_h = I (R_h) for both types of networks.

Table 8.7.

The dependence of the current I_h, mA, on voltage U_A, V
and resistance of human body R_h

Control questions for self-examination:

1. Tell about the effects of an electric current to the human body.

2. The nature of the current impact on the human body.

3. Categories of premises at the risk of electric injuries.

4. What is the protective earth? What is its purpose?

5. What is protective neutral earthing and shutdown? What are their principles of operation?

6. What determines the resistance value of the grounding devices?

7. What are the regulatory requirements for the magnitude of resistance of grounding devices?

8. What determines the volume resistivity of the soil?

9. What factors influence the degree of electric shock to persons?

10. What parameters determine the current passing through the human body at the touch of a two-phase?

11. What is called the earthed neutral?

12. What is called the isolated neutral?

13. What are the parameters that affect to the current passing through person who touched the phase in the three-phase network with an isolated neutral?

6. What parameters determine the current flowing through the person touching a phase in a three-phase network with earthed neutral?

7. What parameters determine the current flowing through the person touching the phase in three-phase systems with earthed and isolated neutral in an emergency?