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Thermography & Electrical Temperatures Limits Temperature Rise Reference & Fault Category Table:Fault CategoryTemperature RiseRecommendations1 >50°CMust be repaired immediately2 25-50°CRepair at the earliest opportunity3 8-25°CInvestigate during next scheduled maintenance4 0.5?C – 8?CAdvisory Thumb rule: 1. Refer the adjacent same elements .Corrective action should be taken, if the temperature higher.2. BS EN 60439?states a maximum indoor ambient temperature of?40?C.3. Temperature rise consider starting with 40?C temperatures.4. As a general guidance rule, the temperature within the?low voltage switchgear?should not exceed 50/55?C. If Switch room/Plant room ambient are typically considered to be?up to 25°C?this relates to a 25/30K rise above ambient. In the maximum ambient condition of 40?C, this relates to a 10/15K rise above ambient.General Electrical Connections Inspection & maintenance : 1. Terminate power supply to the respected Electrical element and make sure there is no supply after power termination.2. Visual Inspect the Contacts or terminations for burns, scaling and loose contact etc.3. Verify the element; it is as per the standard use like under rated, not as per the design or not as per the manufacturer guidelines etc.4. Remove the connection and clean with the Electrical contact cleaner and tighten well.5. Verify the Current quality and Thermal signature after corrections made.Causes of Temperature Rise:1. Loose or rusted contact.2. Defective Materials, such as slag Cracks, excess porosity etc presented in materials.3. Defective elements (while in manufacturing).4. Dust, moisture and lack of proper ventilation.5. Under rated wiring or material.6. Excess operating Conditions than recommendations by manufacturer. etc..7. Improper Design and Changes made in original design with out proper knowledge .Recommended Practice :1. Install and operate the Electrical equipments and its auxiliaries as per manufacturer guidelines.2. Maintain proper ventilation, Heat sinks and House keeping.3. Verify the product quality machine required while installation or change of elements.4. Identify and monitor the electrical element life span and replace.5. Make sure and Monitor Power Quality .Equipment type Max. Time between inspectionsTransformers12 months 440V motor control centers ?Air-conditioned 6-12 months ????Non-air conditioned or older 4-6 monthsElectrical distribution equipment 4-6 monthsLarge motors* 12 monthsSmaller motors 4-6 monthsClassification of the insulationAEBFH?max. temperature °Cabsolutely short-circuit proof windings150165175190210Windings with protection device:-? during the length of T, see table 33)-? after the first hour, peak value-? after the first hour, arithmetic average200175150215190165225200175240215190260235210Outer housings (which can be touched with norm probe)Rubber insulation of the conductorsPVC-insulation of the conductorsSurface (e.g. every area of the surface of a plywood board, which is covered by the transformer)105?8585105ComponentsTemperatureWindings (coils and metal sheets in connection to them), if the insulation system is made of:- Material with thermal class A- Material with thermal class E- Material with thermal class B- Material with thermal class F- Material with thermal class H100115120140165The classification of materials is conforming to IEC 60058 and IEC 60216. The values are adapted given the fact, that during these tests, the temperatures are average values, not hotspots.*Warming at short-circuit and overload conform generally?to?BS EN61558Class AClass A?insulation consists of materials such as cotton, silk and paper when suitably impregnated or coated or when immersed in a dielectric liquid such as oil. Other materials or combinations of materials may be included in this class if by experience or tests they can be shown to be capable of operation at the Class A temperature.?Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 105C, 221F.Class BClass B?insulation consists of materials or combinations of materials such as mica, glass fibre, asbestos, etc., with suitable bonding, impregnating or coating substances (beware a few older applications used asbestos). Other materials or combination of materials, not necessarily inorganic, may be included in this class, if by experience or tests they can be shown to be capable of operation at the class B temperature.Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 130C, 266F.Class CClass C?insulation consists of materials or combinations of materials such as mica, porcelain, glass, quartz with or without an inorganic binder (beware a few older applications used asbestos). Other materials or combinations of materials may be included in this class, if by experience or tests they can be shown to be capable of operation at temperatures above the Class H limit. Specific materials or combinations of materials in this class will have a temperature limit, which is dependent upon their physical, chemical and electrical properties.Maximum allowed temperature: (IEC60034-1 only): >180C, 356F.Class EClass E?insulation consists of materials or combinations of materials, which by experience or tests can be shown to be capable of operation at Class E temperature (materials possessing a degree of thermal stability allowing them to be operated at a temperature 15 Centigrade degrees higher than Class A materials).Maximum allowed temperature: (IEC60034-1 only): 120C, 248F.Class FClass F?insulation consists of materials or combinations of materials such as mica, glass fibre, asbestos, etc., with suitable bonding, impregnating or coating substances, as well as other materials or combinations of materials, not necessarily inorganic, which by experience or tests can be shown to be capable of operation at the Class F temperature (materials possessing a degree of thermal stability allowing them to be operated at a temperature 25 Centigrade degrees higher than Class B materials).Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 155C, 311F.Class HClass H?insulation consists of materials such as silicone elastomer and combinations of materials such as mica, glass fibre, asbestos etc., with suitable bonding, impregnating or coating substances such as appropriate silicone resins. Other materials or combinations of materials may be included in this class if by experience or tests they can be shown to be capable of operation at the Class H temperature.Maximum allowed temperature: (IEC60034-1 & NEMA MG1-12.43): 180C, 356F.Wire Conductor Ampacity to Temperature Rating:Maximum Operating Temperature.Insulation TypesInsulation TypesInsulation Types60°C (140°F)75°C (167°F)90°C (194°F)?TW, UF?FEPW, RH, RHW, TBS, SA, SIS, FEP, THHW, THW, THWN, FEPB, MI, RHH, XHHW, USE, ZW RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2 Conductor insulation temperature °CPVC ≤ 300 mm2PVC > 300 mm2EPR XLPERubber 60 °CInitial temperature °C70709060Final temperature °C160140250200Material of conductor:115 103 143 141 CopperAluminium76 68 94 93 Temperature rise limit valuesThe relevant standards such as IEC 60947-1 (low voltage switchgear) and IEC 60439-1 (Low voltage switchgear assemblies) define upper limits for the temperatures of the relevant constructive parts. IEC 60204 (Safety of machinery – Electrical equipment of machines) refers to IEC 60439-1.Temperature-rise limit values in accordance with IEC 60947 and IEC 60439PartReference (ambient) temperatureTemperature limit (absolute) *1Metallic manual operating means40 °C55 … 65 °CNon-metallic manual operating means40 °C65 … 75 °CMetallic parts intended to be touched but not handheld40 °C70 … 80 °CNon-metallic parts intended to be touched but not hand-held40 °C80 … 90 °CMetallic surfaces not intended to be touched40 °C80 … 90 °CNon-metallic surfaces not intended to be touched40 °C90 … 100 °CTerminals for external connections?(Cu silver- or nickel plated)40 °C110 … 120 °CThe melting point and specific resistance of different metals used for fuse wireMetalMelting point Specific ResistanceAluminium 240oF2.86 μ Ω - cmCopper 2000oF1.72 μ Ω - cmLead 624oF21.0 μ Ω - cmSilver 1830oF1.64 μ Ω - cmTin 463oF11.3 μ Ω - cmZinc 787oF6.1 μ Ω - cmConverting Formulae :From To Fahrenheit To Celsius To Kelvin Fahrenheit (F)F (F - 32) * 5/9 (F - 32) * 5/9 + 273.15 Celsius (C or o)(C * 9/5) + 32 C C + 273.15 Kelvin (K)(K - 273.15) * 9/5 + 32 K - 273.15 K ReferenceASTM E-1934, ISO/AWI 10881 Standard of Thermography Analysis .ISO/CD 10880 Non-destructive testing -- Infrared thermographic testing -- General principlesISO/DIS 18251-1 Non-destructive testing -- Infrared thermography? -- System and equipment -- Part 1: Description of characteristics(IEC60034-1 & NEMA MG1-12.43)BS EN 60439?. BS EN61558IEC 60947-1, . IEC 60204, IEC 60439-1 etc.. ................
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