Overheating (electricity)

Overheating is a phenomenon of rising of temperature in an electric circuit (or portion of a circuit). Overheating causes potential damage to the circuit components, and can cause fire, explosion, or injury. Damage caused by overheating is commonly irreversible; i.e. the only way to repair is to replace some components.

Failed IC in a laptop. Wrong input voltage has caused massive overheating of the chip and melted the plastic casing.

Causes

When overheating, the temperature of the part rises above the operating temperature. Overheating can take place:

  1. if heat is produced in more than expected amount (such as in cases of short-circuits, or applying more voltage than rated), or
  2. if heat dissipation is poor, so that normally produced waste heat does not drain away properly.

Overheating may be caused from any accidental fault of the circuit (such as short-circuit or spark-gap), or may be caused from a wrong design or manufacture (such as the lack of a proper heat dissipation system).

Due to accumulation of heat, the system reaches an equilibrium of heat accumulation vs. dissipation at a much higher temperature than expected.

Gallery: some causes, effects, and cause-effect loops for overheating
  • A short circuit caused by overvoltage destroys an integrated circuit.
  • Joule heating or resistive heating is sometimes helpful such as in a heating coil. But Joule heating occurs, to some extent, in all the conductive parts of a circuit.
  • infrared-thermal image of a motor
  • An electric arc created between two nails
  • Electric arc (spark) between two wires. This can cause overheating and ignition.
  • On un-insulated wires, trees facilitated short-circuit in storms.
  • An insulator can handle only certain voltage, above which a breakdown of the insulator takes place. This chart shows voltage-current relation before breakdown.
  • Electricity applied to deliberately start up a fire (ignite) wastes in an incinerator. The same could happen in a circuit or building.

Preventive measures
Main article: Thermal management (electronics)

Use of circuit breaker or fuse

Circuit-breakers can be placed at different portions of a circuit (in series to the path of current it will affect). If more current than expected goes through the circuit-breaker, the circuit breaker "opens" the circuit and stops all current. A fuse is a kind of widely used circuit breaker that involves direct effect of Joule-overheating. A fuse is always placed in series with the path of current it will affect. Depending on the build, there is usually a narrow (often a hairline) wire of definite-material in the fuse. When more-than expected current flows through the fuse, the fuse-wire overheats (melts) and "opens" the circuit. In some devices, more than one

Gallery: Circuit breakers and fuses used to stop current.
  • Miniature time-delay fuse to interrupt 0.3 A current at 250 V after 100 s, and 15 A current at 250 V in 0.1 s
  • MEM rewirable fuse holders (30 A and 15 A)
  • A 115 kV high-voltage fuse near a hydroelectric power plant
  • A two-pole miniature circuit breaker
  • Inside of a circuit breaker
  • Oil circuit breakers

Use of heat-dissipating systems

Many systems will use ventilator holes or slits kept on the box of equipment to dissipate heat. Heat sinks are often attached to portions of the circuit that produce more heat or are more vulnerable to heat. Fans are also often used. Some high-voltage instruments are kept immersed in oil. In some cases, to remove unwanted heat, some cooling system like air conditioning or refrigerating Fheat-pumps may be required.

Gallery: Methods of improving heat dissipation from equipment
  • A pin-, straight- and flared fin heat sink types.
  • pin fin heat sink with thermal profile and air flow movement
  • straight finned heat sink with thermal profile and air flow
  • Active heat sink with a fan and heat pipes.
  • A fan-cooled heat sink on the processor of a personal computer.
  • Passive heatsink on a chipset.
  • Oil transformer with air convection cooled heat exchangers
  • Small resistor with low power (watt)-dissipation capacity. Useful only at low currents.
  • An aluminium-housed power resistor rated for 50 W when heat-sinked
  • VZR power resistor 1.5 kΩ 12 W
  • A power-resistor
  • A power resistor

Control within circuit-design

Sometimes special circuits are built for the purpose of sensing and controlling the temperature or voltage status. In these circuits, devices such as thermistors (Temperature dependent resistors), VDRs (voltage-dependent resistors), thermostats (that switch off the circuit at higher-temperature) and sensors (such as infrared-thermometers) are used to modify the current upon different conditions such as circuit-temperature and input voltage.

Gallery: Control of temperature with special mechanisms in circuits
  • Bimetallic thermostat for buildings
  • Millivolt thermostat interior mechanism
  • Bimetallic strip-thermostat working principle schematic
  • working principle of bimetallic strip.
  • Bimetal coil reacts to lighter
  • Digital thermostat
  • Thermistors. They can be NTC or PTC according response to warming.
  • Metal-oxide varistor (voltage-dependent resistor)
  • High voltage varistor
  • An infrared thermometer

Proper manufacture
Main article: Building code

For certain definite purpose in a definite electrical equipment or a portion of it, definite type and size of materials (for boards,wires, insulators) with proper rating for voltage, current and temperature,are used. The circuit-resistance never kept too-low. Sometimes some parts placed inside the board and box, maintaining a proper distance from each other, to avoid heat-damage and short-circuit-damage. To prevent short-circuit, on the wire-joints, appropriate types of electrical connectors and mechanical fasteners used.

Gallery: material-requirement for circuit build-up
  • A device for measuring standard wire gauge.
  • Stranded copper lamp cord, 16 gauge
  • Cross-section of copper high-voltage cable rated at 400 kV.
  • 3-core copper wire power cable, each core with individual colour-coded insulating sheaths all contained within an outer protective sheath
  • 10 kV ceramic insulator, showing sheds

See also

References

    Sources
    1. http://www.ufba.org.nz/images/documents/hazardsandsafeguards.pdf
    2. "Classification of Electrical Overheating Modes - Electro-Mechanical Recertifiers, Inc". Retrieved 27 August 2016.
    3. ElectroTechnik. "What are the reasons for transformer overheating?". Retrieved 27 August 2016.
    4. "The Basics of Electrical Overheating". Retrieved 27 August 2016.
    5. http://www.testequipmentdepot.com/application-notes/pdf/power-quality/case-study-the-overheating-transformer_an.pdf
    6. http://protectowire.com/documents/ds-8899.pdf
    7. http://www.mirusinternational.com/downloads/hmt_faq10.pdf
    8. http://www.learnabout-electronics.org/Downloads/ac_theory_module11.pdf
    9. "Power Transformers". Retrieved 27 August 2016.
    10. http://sound.whsites.net/xfmr.htm
    11. http://sound.whsites.net/xfmr-6.jpg
    12. "Top 14 Reasons Electrical Service Installations Get Red Tagged". Retrieved 27 August 2016.
    13. http://ecmweb.com/site-files/ecmweb.com/files/uploads/2016/03/Electrical-Service-Meltdown-6.jpg
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