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Saturday, January 2, 2010


January 1, 2010 Paramesh Malakar.
B. Sc. (Engineering), BHU

Indian Electricity Rules are very broad and wide guidelines for design, manufacture, construction, operation and maintenance of all electrical installations and Industrial Safety rules are inbuilt into it. These rules, being the body to cover all aspects of Electricity seems to be, at many a point, ambiguous and extraneous. However, an in-depth interpretation of these rules indicates the elements that need compliance to have a proven system to strong, reliable and safe.
It is felt to be utmost importance to discuss the safety aspects of electricity as electricity in various forms has become indispensable to the modern industry for maintaining propriety of generation, drive, control, communication, , announcement, safety and managing disasters.
Generation and handlings of power is given primary emphasis in this article as these are considered injurious to apparatuses and life.
An approach here is made to proceed from basic needs in simple language so that the contents are accessible to nonprofessionals also along with engineers since many such persons are being engaged in electrical work.

Safety at the dawn of civilization was included in the three basic needs. Food, Shelter and Clothing gave man the safety he needed. Inventions and the development the inventions brought about in mechanizing man’s ways demanded more safety. Safety took birth as a concept and to-day it has become a branch of engineering studies. Speaking commonly about safety is to imply use of safety appliances like welding goggles or radiation shields while doing welding or operating X-ray machines. However, if hazards of discharges, explosions, accidental contacts, possibility of lightning etc. are considered it will become apparent that safety considerations are to begin with design of machines and systems and are to be systematically inbuilt through manufacturing, installation and operation of plants and equipments.
The hazards faced are unpredictable and inestimable. But, while dealing with industrial hazards it is seen that these hazards are contained in definite and demarcated systems. In case the deficiencies of a system are known these can be eliminated by suitable design and working procedures.
Electrical safety aspects of industrial installations are related mainly to healthy operation during running, abnormal shutting down, switching in and out and maintenance working. Such electrical safety is not difficult to ensure if proper approach is adopted from blue-print-stage.
An industry is a unit, which processes inputs to obtain final product ? output. The nature of environment at different locations inside the industrial area is continuously changed due to abnormal operation and generation of wastes and pollutants. These locations may become HAZARDOUS from the point of view of electrical engineering depending on their degree of flammability. It is very essential that only proper electrical appliances and apparatuses are chosen for such areas which are turned hazardous by plant processes. Again rain, humidity, dust are also harmful for electrical installations.
Area, which does not have any risk of fire in their environment, is safe. In such safe area apparatuses designed and manufactured to meet the rated duty can be installed. However, where risk prevails the areas are hazardous. Hazardous areas of industrial installations are grouped into Divisions (Ref. IS5572) depending upon the presence occurrence of flammable gas or gas mixtures in ion it.
These are:
DIV 0: Where risk of fire is constantly present.
DIV I: Where risk of fire is present during normal operating condions.
DIV II: Where risk of fire is present during abnormal operating conditions.
These areas demand different safe features to be built into in electrical apparatuses as integrated features to make these suitable for such locations. In Div 0 areas electrical apparatuses, as far as practical should be avoided. However, if at all necessary flammability in the area is to be precisely defined and intrinsically safe units are to be installed. In Div I and II areas where explosive gas concentration is present but is within limit FLAMEPROOF APPARATUSES ( Ref IS 2148) or INCREASED SAFETY APPARATUSES (Ref. IS 6318) are to be used. Areas where rainfall, foreign matter and humidity become matter of concern enclosures of electrical apparatuses are to be WEATHER PROOF ? e.g., as per IS 4691 for induction motors, IS 2147 for LV switchboards and suitably protected against entry of foreign matter as contained in these standards. Electrical apparatuses are also available in pressurized, non-sparking, weatherproof etc type for installation and use in specific areas. MAJOR COMPONENTS OF INDUSTRIAL INSTALLATIONS
Industrial electrical installations mainly comprises of : a) Outdoor indoor sub stations, b) HV MV switchboards, c) LV PCCs & MCCs, d) Transformers, e) Motors, f) cable network, g) Overhead lines, h) switching stations, i) heaters, j) refrigerators, k) lighting systems etc. For safety of these, certain rules in the IE Rules are laid down. These are to be meticulously adhered to.
The important clauses are:-
IE Rule 29: Rule 29 make provision for ample power handling capacity, size, and strength. This rule says that any electrical apparatus, network or system must have sufficient capacity to handle the power energy required to do the specific job, its size must be adequate to handle the power requirement and must be convenient for use and it must have sufficient mechanical strength to avoid danger to human life or items in immediate vicinity. IE Rule 50: Rule 50 makes provision for application of suitable switches, breakers on primary, secondary sides of transformers, controllers of motors and use of suitable insulating materials. IE Rule 66: Rule 66 provides for metal-sheathed conductor system or for cable network the level of fault currents available to the rating of feed isolating switchgear or fuse gear on occurrence of fault. These IE Rules include electrical apparatuses for handling and use of electrical power and consider the aspect of amply designing and manufacturing these items. Such is also gets envisaged that suitability of use application of these is taken taken care of during blue print stage. These rules taken together with relevant Indian Standards grants details, which need consideration regarding safety of apparatuses in use. In addition to setting broad guidelines for manufacturing, I E Rules also provides for installation and testing of electrical apparatuses and systems; and various safety measures to be adopted while erection and commissioning is hand. IE Rule 51 : Rule 51 provides for sufficient inbuilt mechanical strength of electrical apparatuses, enclosing electrical live parts in earthed metal enclosures and installation guidelines as to permissiveness of space near switchboards for movement of working personnel. Rule 60,61 : Rule 60, 61 make it necessary to earth properly the electrical systems and testing it to ensure tat installations do not have hidden defects. Rule 64, 66, 67 : these rules make it necessary to have safety incorporated into the installations by means of protections, safety drains and soak pits, for transformer oil, preventing oil accumulation in trenches, arranging layouts such that faulty electrical component can be isolated immediately. These also provide for various tests regarding voltage withstand ability and insulation condition to ensure system capability to withstand over voltages and handling safely the fault currents. These also take care regarding safe earthing of electrical systems at different locations to avoid danger. GENERAL SAFETY ASPECTS
The general safety aspects of industrial installations are to take care of the followings at different stages:-
During selection :
Classification of areas. Selection f apparatuses suitable for the particular area. Taking proper care against possible misinterpretation of short descriptions like ? fire proof, flame proof, weather proof, submersible, relative humidity etc. and to properly establish their relation to actual working environment. Taking proper note to the short time and continuous duty ratings and relating the various operating parameters to the limiting values for safe working.

During Installation :
Name plate and Rating plate details to be related to the apparatuses and their proper installation referring to relevant IS Standard wherever applicable. The working safety of the location and proximity to other equipments for safe working and maintenance. Cable terminations and all connections should be of suitable type and size done by approved methods. Details designed for earthing and lightning arresters systems shold be strictly followed and any deficiency in execution should be compensated by addition alteration as necessary. Due care is to be taken to neutral apparatus earthings. Location of control gear to any electrical apparatus must be so positioned that it remains accessible during abnormality of apparatus or any other plat abnormality. Care is to be taken to prevent rain water accumulation and flowing in of surface water into cable trenches.

These broad guidelines and rules thus direct to wards establishing proper relation between the final use and capacity evaluation during design, manufacturing, selecting proper typr for use in different environment, steps to be taken during erection installation to make these safe. However, one point is of great importance here as to see how long the apparatus in operation remains intact and manufacturer maintains good margin and some critical properties of electrical apparatuses are lost durin ng operation. Some of these are :-
Di-electrical and physical properties of insulation. Spring tension of various contacts and resulting contact pressure. Ohmic resistance of electrical joints and terminations connections. Calibration of protective and measuring instruments and apparatuses.
In this instance while attention is on suitable capacity and suitable selection the author remembers two instances :-
On a motor – control – centre (MCC) a control fuse was blown in a motor switchgear compartment. Immediately no fault was detected, so the fuse , due to non availability of HRC fuse was rewired and put back. The neutral link was in position. The fault was lurking in the power contactor coil because of inter – turn short. Immediately on insertion of the fuse it blew with heavy sound and caused flash – over on the sleeved bus bars with naked joints running right behind the fuse base. Result was a burn injury to operator’s hand and plant tripping. This is a clear indication of risk involved in over sizing fuses. In another instance, there was a short circuit on LT switchgear. There the ACB compartment bakelite shutters were riveted to metal strips. While withdrawing the ACB one strip came out, touched bus bars, caused short circuit with heavy arc and fire. Such was the result of wrong selection and application during design and manufacturing. Later on, these strips were replaced with insulated bars.


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