REPORTSPECIAL SUBJECT SUPPLY ELECRICAL

Topic: Protection against electric shocks

SVTH: Dương Văn Trí

GVGD: TS_ Võ Viết Cường

HCM, Ngày 09 tháng 03 năm 2010

UNIVERSITY OF EDUCATION AND TECHNICAL HO CHI MINH CITY

Objective:

Protection against electric shocks effect.

Content:

1 - General

2 - Protection against direct contact

3 - Protection against indirect contact

4 - Protection of goods in case of insulation fault

5 - CONCLUSION

1- General

1.1-Electric shock a current > 30mA

human body

danger

(if not interrupted in a very short time)

Consequence:

Affects essentially the muscular,

circulatory and respiratory functions,

serious burns, injury or death

Zones time/current of effects of AC current on human body when passing from left hand to feet

1.2 - Direct and indirect contact Direct contact Indirect contact

A direct contact refers to a person coming into contact with a conductor which is livein normal circumstances

Contact with an exposedconductive-part which is not normally alive, but has become alive accidentally (due to insulation failure or some other cause).

2 - Protection against direct contact

Protection by the insulation of live parts

Protection by means of barriers or enclosures

Particular measures of protection

(Safety Extra-Low Voltage)

Partial measures of protection

Protection by means of obstacles, or by placing out of arm’s reach

Additional measure of protection against direct contact

Lack of proper maintenance

Imprudence, carelessness

Normal (or abnormal) wear and tear of insulation

Accidental contact

Immersion in water, etc

Use of residual current operating device

Reasons:

3 - Protection against indirect contact3.1 - Automatic disconnection of the supply

The earthing of all exposed-conductive-parts of electrical equipment in the installation and the constitution of an equipotential bonding network

Automatic disconnection of the supply of the section of the installation concerned

Disconnecting-time limits

Depends:

Illustration of the dangerous touch voltage Uc

TT systemHigh sensitivity RCD

3.2 - Automatic disconnection for TT system

Maximum operating time of RCD’s (in seconds)

RA is the resistance of the earth electrode for the installation

IΔn is the rated residual operating current of the RCD

3.3 - Automatic disconnection for TN systems

>= Ia

Id = the fault current

Ia = current equal to the value required to operate the protective device in the timespecified

Uo = nominal phase to neutral voltage

Zs = earth-fault current loop impedance

Zc = the faulty-circuit loop impedance

The automatic disconnection for TN system is achieved by overcurrent protective devices or RCD’s

Protection by means of CB Protection by means of fuses

Disconnection by CB for a TN system Disconnection by fuses for a TN system

Im < Uo/Zs or 0,8Uo/Zc Ia < Uo/Zs or 0,8Uo/Zc

3.4 - Automatic disconnection on a second fault in an ITsystem

First fault situation

Second Fault situation

Application of RCDs when exposed-conductive-parts are earthed individually or by grroup on IT system

Case 2Case 1

Correspondence between the earth leakage capacitance and the first fault current

3.5 - Protection against direct or indirectcontact without automatic disconnection of supply

The use of SELV

The use of PELV(Protection by Extra Low Voltage)

FELV system(Functional Extra-Low Voltage)

The electrical separation of circuits

Class II equipment

Out-of-arm’s reach or interposition of obstacles

Earth-free equipotential chambers

4.2 Ground Fault Protection (GFP)

“Residual Sensing” “Source Ground Return” “Zero Sequence”

4 - Protection of goods in case of insulation fault 4.1 Measures of protection against fire risk with RCDs

CONCLUSION

Protection against electric shocks help us to avoid mishaps by cause electric current. Without measure protective is called absolute, however, protection still is necessary.

The report help us to understand method against electric shocks and practical to achieve effect.