Category: electrical Safety

Classification of Temperature We will now learn about the classification of temperature. In addition, we will also understand the importance of temperature. Importance of Temperature Temperature is one of the most essential factors in process engineering to detect a hazardous condition in plant and in equipment. The Safety Integral Level (SIL) measures the safety instrument function. SIL specifies a target level of risk reduction. The International Electro-technical Commission (IEC) 615081 standard assigns SIL to the devices, which are able to eliminate device fault and detect the fault. Classification of Temperature for Electrical Equipment There are some insulation classes, which allow a maximum permissible temperature for the safety of devices. Electric instruments can be downsized by insulation technique of higher thermal endurance. The following table shows maximum allowable temperature and the materials used for various types of insulation − Insulation Classes Maximum Permissible Temperature (ᵒC) Material Used Y 90 Cotton, silk or paper A 105 Reinforced Class-Y materials with impregnated varnish or insulation oil E 120 Combination of different materials B 130 Inorganic material with adhesives F 155 Class-B materials that are upgraded with adhesives, silicon and alkyd-resin varnish of higher thermal endurance H 180 Inorganic material glued with silicon resin or adhesives of equivalent performance C >180 100% inorganic material Classification of Temperature for Hazardous Areas The temperature classification describes the threshold temperature for the hazardous area. The value of minimum ignition temperature is classified from T1 to T6. This classification of temperature identifies a temperature that an instrument will produce at ambient environment temperature (40ᵒ C). The identified temperature is called maximum surface temperature. T1 − The minimum ignition temperature > 450ᵒ C and the maximum surface temperature generated by the instrument is 450ᵒ C. T6 − The minimum ignition temperature > 85ᵒ C and the maximum surface temperature generated by the instrument is 85ᵒ C. Temperature Classification Minimum Ignition Temperature Temperature Maximum Surface Temperature T1 >450ᵒC [842ᵒF] 450ᵒC [842ᵒF] T2 >300ᵒC [572ᵒF] 300ᵒC [572ᵒF] T3 >200ᵒC [392ᵒF] 200ᵒC [392ᵒF] T4 >135ᵒC [275ᵒF] 135ᵒC [275ᵒF] T5 >100ᵒC [212ᵒF] 100ᵒC [212ᵒF] T6 >85ᵒC [185ᵒF] 85ᵒC [185ᵒF] If there is any measure issue that occurs with the hazardous area instrument, it can be repaired. The repair section is of three basic categories. Factory Repair Only The device must go through some safety test procedures and returned to the factory. Field Repair It is difficult to instruct the end user technician practically. If there is any difficulty to solve the issue, an authorized factory personnel should be employed. Field Repair by End-user − This involves direct replacement in terms of form, fit and function. Temperature Measurement Temperature measuring instrument is designed in accordance with the safety standards. In industrial environment temperature measurement is required for a wide variety of needs and applications. A large number of sensors and devices fulfill such demand. The measuring instruments are as follows − Thermometer Thermostat Thermistor Thermopile RTD (Resistance Temperature Detector) Thermocouple Questions 1. In which insulation class the inorganic material with adhesive is used? a) Class E b) Class Y c) Class B d) Class A Ans: c Explanation − According to table 1, the inorganic material with adhesive can permit only 130ᵒC insulation which refers to Class B type. 2. What is the maximum surface temperature (in ᵒC) in the T4 type of temperature? a) 100 b) 135 c) 200 d) 235 Ans: b Explanation − According to table 2, the lower hazardous is a classification of temperature is T4 which allows 135ᵒC of maximum surface temperature to cause a hazard. 3. Which of the following is not a temperature measuring instrument? a) Thermocouple b) RTD c) Thermistor d) Barometer Ans: d Explanation − Thermocouple, RTD and thermistor are the temperatures measuring instrument but barometer measures air pressure. Learning working make money

Protection Against Weather Complexities It has now become common that with bad weather like storm or heavy rains, there will be loss of power or electricity. This affects the masses at large. And, people at the coastal regions are the most affected when there is failure of electricity due to flooding. 67% of the electrical outage instances have been a result of natural calamities such as lightening, snowfall and wind. To minimize the cost and mitigate issues of outage, protecting electrical assets is necessary. Protecting Electrical Network In this section, we will see how to protect electrical networks from natural calamities. Maintenance For critical systems, UPS and the backup generator should be installed and maintained properly. If the power is cut off from the grid, the backups are utilized. Regular maintenance service ensures the reliability of equipment and safer work environment. Electrical Network Design Correct electrical design minimizes the voltage transients generated when there is lightening. An electrical model should be tested through all possible scenario; the faults and weaknesses of various areas are to be predicted. A proper design should provide − redundancy alternative paths automatic transferring loads Testing of System The backup supplies and alternative paths should be tested periodically. Consider testing the following − the condition of backup equipment the system logic in case of failure or for new installations the response of site personnel in emergency situation when the utility supply fails Management Data management and analytics help in predicting the problems, finding solution to prevent the problems or solve an already occurred problem. The management system focuses on the following two areas − Outage Management System The OMS provides data and information from a variety of sources, faults, allowing maintenance and engaging electrical workers to repair and restore. Asset Management System A track record of facility’s assets, predicted lifecycle and technical specifications must be maintained to ensure a reliable and resilient network. Protection against extreme weather condition The extreme weather condition refers to the lightning that could be catastrophic for the electric devices. Consider the following points to keep your devices safe. An electrical surge can fry a circuit board of electronic equipment like TV, laptop and sound system, etc. A top-notch surge protector can be used to prevent the damages. There are three characteristic that need to be considered while buying a high-quality surge protector (SP) − Low clamp level − It takes a voltage to trigger the SP and to divert the electricity to the ground Low response time − It takes nanoseconds of time to respond the surge High surge capability − It takes some amount of voltage that an SP can take and function properly It is not required to depend upon the warranty of SP. Attach a status check light with it which shows the last surge. Avoid overloading a power strip surge protector, which may increase the risk of damaging the electronic equipment. Standards against Dirt and Water According to the International Electro-technical Commission (IEC) standards 60529, the International Protection Marking classifies the degree of protection which is provided against intrusion, dust, accidental contact and water by the mechanical casing and electrical enclosure. The Ingress Protection (IP) defines from which the equipment is protected in normal condition. The first digit indicates the protection of equipment against solids. The second digit indicates the protection of equipment against harmful entry of various forms of moisture. The following table lists down the IP Codes and their meanings − 1st digit Protection from Solid 2nd digit Protection from Moisture 1 Hand Protected: protection from solid objects greater than 50mm in diameter 1 Drip proof against vertical water drops 2 Finger protected: protection against the object > 12.5mm 2 Drip proof when tilted at angles up to 15ᵒ 3 Tool protected: protection from the object with a diameter or thickness > 2.5mm 3 Rain/Spray proof when water falling at an angle up to 60ᵒ 4 Wire protected: protection against the objects with a diameter or thickness > 1.0mm 4 Splash-proof when water splashed from any direction 5 Dust accumulation protected: protection from the dust interfering with the operation 5 Jet proof when water projected through a nozzle(dia 6.3 mm) at a pressure from any direction 6 Dust penetration protected: protection against penetration of dust 6 Jet proof when water projected through a nozzle(dia 12.5 mm) at a pressure from any direction 7 Watertight proof when temporary immersion in water 8 Pressure watertight when continuous submersion in water The following table lists down the letters that define hazardous parts. Some other letters provide additional information related to the protection of the equipment. Level Hazardous parts A Back of hand B Finger C Tool D Wire The following table lists down a few letters in IP codes − Letter Meaning F Oil resistant H High voltage device M Device moving during water test S Device standing still during water test W Weather conditions Questions 1. Which device requires nanoseconds of time to respond the surge? a) Low clamp level device b) Low response time device c) High surge capability device d) None of these Ans: b Explanation Justifying the name, the low response time device requires only nanoseconds of time to respond to the surge, recognize the fault and commands the protective device to trip. 2. IP codes follow the standard of __________. a) IEC b) BIS c) NFPA d) NEMA Ans: a Explanation The International Electro-technical Commission of Europe describes the Ingress Protection of mechanical and electrical enclosures of equipment. 3. What is the meaning of enclosure IP56? a) Protection against insertion of the finger and vertically dripping in water b) Dust resistant and can be immersed in water c) Protection against dust and high-pressure water jets from any direction d) None of these Ans: c Explanation In IP56, the first digit 5 refers to protection against dust and the second digit 6 refers to the protection from high-pressure water jets from any direction. By combining both digits, the outcome refers to option C.

Electrical Safety – Short Circuit Protection A short-circuit condition means a circuit allows the current to flow through an unintended path with very low electrical impedance. It is a direct contact between two points of different electric potential. The short circuit protection system is broken down into the following systems − Alternating Current System Phase to Ground contact Phase to Neutral contact Phase to Phase contact Contact between windings of an electrical machine in a phase Direct Current System Pole to Ground contact Contact between two poles There can be numerous causes resulting in the above type of contacts including damage to the insulation of conductors, loose, broken or stripped wires and cables, and deposition of conducting materials such as dust, moisture, etc. Major Causes of Short Circuit A sudden surge of current equals to hundred times of working current flows through the circuit. This leads to the damage of electrical equipment. The following two phenomena are responsible for the devastating effects of short circuits − Thermal Phenomenon This phenomenon refers to the energy released into the electrical circuit when short-circuiting current flows through the circuit. This thermal effect results in the causes of a short circuit − Melting of the conductor contacts Damage to insulation Generation of electrical arcs Destruction of the thermal elements in the bimetallic relay Electro-dynamic Phenomenon This phenomenon refers to the production of intensive mechanical stress when the current crosses and results in the following conditions − Breakage of the conductors Repulsion of contacts inside the contactors Distortion of conductors in windings Short Circuit Protection Devices To protect the devices and people from short circuit hazards, protecting devices are used in electrical circuits. These devices can detect the faults and trip the circuit immediately before the surge current reaches to the maximum. There are two popular protecting devices used frequently in every electrical circuit. Fuse Fuse is operated once in the circuit and then must be replaced after the trip occurs. It is helpful for phase by phase (single pole) protection. It offers a high breaking capacity at low volume, which limits electro-dynamic stress. Following images show different types of fuse − Circuit Breaker Circuit breakers can be reset either manually or automatically. It automathy breaks the circuit within a short cutoff time and separates the load from the power supply that protects the circuit from any damage. The magnetic triggers of CB open the poles. CBs limit both the thermal and thermodynamic effects. It works faster than a fuse. For example, Molded Case Circuit Breaker (MCCB), Molded Case Switch (MCS), Air/Oil/SF6/Vacuum Circuit Breaker (ACB/OCB/SCB/VCB). The following images show different types of circuit breakers: Characteristics of Short Circuit Protection Devices We will now learn the different characteristics of short circuit protection devices. The characteristics are shown below − Breaking Capacity The maximum value of the estimated short circuit current that can enable the device to break the circuit at a given voltage is called the breaking capacity. Closing Capacity The maximum short circuit current that can enable the device to reach its rated voltage at specific condition is called the closing capacity. It is the rational multiple of breaking capacity. Learning working make money

Low Voltage Overload Protection We will now learn the different concepts related to low voltage overload protection. Low Voltage Release If the line voltage decreases to an abnormally low value, then the electrical machinery is damaged or unable to start the service. Because of the low voltage, the shunt coil on final contact holding solenoid of the starter disconnects the motor from the line. After the line voltage recovery the motor resumes its service. Low voltage release is unexpected and dangerous. To protect the machines, low voltage protection should be provided. Low Voltage Over-current Fault In low voltage condition, the protection against temperature is known as over-current protection. There are three major causes of over-current. The causes are listed below − By equipment overload The overload condition occurs when equipment is subjected to more than its rated value. This results in excessive heat production. By short circuits If there is any connection between the line to line or line to neutral conductors, it leads to short circuit. This generates temperature above the designated ratings. By ground faults If the electrical current flows from a conductor to uninsulated metal, then ground fault occurs. Overload Protection The current flows in the circuit based on the demand of loads. If the amount of current increases and exceeds the rating of the electrical equipment, then the system is overloaded. The wires or cables may not with withstand the higher current. The wires get hot and even melt the insulation. This leads to fire hazards. Therefore, overload protection is necessary to avoid such accidents. Causes of Overload Condition Following are the different causes of overload condition − Overuse of extension cords and multiple plug adapters on the same circuit. Running too many appliances at a time. When more electricity is used like electric decoration. The following image shows the overuse of extension cord − The following image shows how a fire hazard is triggered due to overloading − Signs of Low Voltage Overloading Let us now see the different signs of low voltage overloading. Following are the different signs − Flickering of lights Sparks from appliances or wall sockets Warm switch plates Dimming of lights, television sets Speed reduction of motors To avoid such problems, fuse and miniature circuit breakers are used as protecting devices. In fault condition, the fuse should blow and circuit breaker should open the circuit. It is also important to protect the conductors as well as equipment from the higher current. Conductor Protection Every cable has a current rating, which is the maximum safe current capacity of the cable. This current carrying capacity depends on the following factors − Material − Aluminum or Copper A structure − Individual conductor or grouped conductors Path medium − Open air, grounded, or near the hot furnace or inside well-ventilated room, etc. The fuse or breaker should be chosen based on the size of the cable. When the fault current reaches the fuse, it will blow. This gives a temporary overload condition to the cable. The cable must carry momentary overloads for a very short time period. A small amount of overheating cannot build a dangerous level. This is called slow blow protector. Equipment Protection The fuse and circuit breaker can protect the cable. However, these are not sensitive to protect a small use device plugged into the circuit. Therefore, these protection devices are built into the appliances to protect from overload. The external fuses are used in the main service panels or sub-panels but the equipment fuse or breakers protect every part of the electrical equipment that secures the system. The following image shows the thermal fuse inside a motor − Learning working make money