Department of Electrical and Energy Engineering LV FUSE Lecturer: Mr. SEAN Piseth Students: VORN Rithy (e20120795) YA Phalkun (e20140873) YAV Leakhena(e20140874) YORN Thort(e20120875)

Content Introduction History of fuse Function Characteristic of parameter Type of low voltage fuse Operation Application Advantages & diadvantages

Introduction Fuse is the cheapest form of protection against excessive currents. Low voltage fuses can be classified into: Cartridge fuse Rewireble fuse

What happened during 1774 until the final decade of 19th century? History of Fuse What happened during 1774 until the final decade of 19th century?

Function The following are general groups on which the protection systems are designed: Prevention of electric shock Prevention against Thermal effects Prevention against Over Current Prevention against Fault Current Prevention against Over Voltages

Characteristics Parameter of fuse Fuse element Melts when excessive current flows through it.

Characteristics Parameter of fuse (cont.) Current rating fuse The maximum current is carried by fuse without any overheating or melting. It depends on Temperature rise of fuse contacts of the fuse holder. Fusing element material Deterioration of fuse due to oxidation

Characteristics Parameter of fuse (cont.) Speed It refers to the speed at which a fuse is blown or destroyed. standard fuse may require twice its rated current to open in one second. fast-blow fuse may require twice its rated current to blow in 0.1 seconds. slow-blow fuse may require twice its rated current for tens of seconds to blow

Characteristics Parameter of fuse (cont.) Fusing current Minimum value of the current cause fuse element melts to interrupt the circuit. Fuse element material. Diameter of the element. More the diameter more is the current. The surroundings or place in which fuse is to be used. The type of enclosure used whether semi-closed or totally enclosed.

Characteristics Parameter of fuse (cont) Fusing factor fusing factor = Minimum fusing current / Rated current of fuse. Its value is always greater than one. The small the value of fusing factor, greater it is difficult to avoid the deterioration. Prospective current The r.m.s. value of the first loop of fault current. This fault current is asymmetrical and very large first loop. it generates sufficient energy to melt the fuse element.

Characteristics Parameter of fuse (cont.) Cut-off current The fault current value cause the fuse melts before achieving its peak value and depends value of prospective current, rated current of fuse, asymmetry of the fault current waveform

Characteristics Parameter of fuse (cont) Breaking Capacity Maximum current that fuse can safely interrupte. This should be higher than the prospective short-circuit current. Miniature fuses may have an interrupting rating only 10 times their rated current. Melting Time of Fuse or Pre-arching I2t The time taken by a fuse element to melt. It is counted from the instant, the over current starts to flow, to the instant when fuse element melt. It is the time integral of the square of the current through fuse during the pre-arching time.

Characteristics Parameter of fuse (cont.) Arcing Time of Fuse it is the time integral of the square of the current through the fuse during arcing time. The time accounted from the instant of arc initiated to the instant of arc being extinguished. Operating Time of Fuse The operating time of fuse is the time gap between the instant of flowing overcurrent and the instant of arc is finally extinguished Operating time of fuse = melting time + arcing time of fuse

Characteristics Parameter of fuse (cont.) Rated voltage The rated voltage of the fuse is specified the manufacturer. Voltage rating of the fuse must be equal to, or greater than Voltage of a single phase circuit Line voltage is case of three phase circuit Voltage between two outer wire in three wired DC circuit

Characteristics Parameter of fuse (cont.) Time Current Characteristics A curve detailing pre-arcing or operation time as a function of prospective current.

Characteristics Parameter of fuse (cont.) Cut-off Characteristics A curve detailing the cut-off current as a function of prospective current.

Characteristics Parameter of fuse (cont.) A curve or chart showing values of “pre-arcing” and “operating” let-through energy as a function of prospective current and voltage

Characteristics Parameter of fuse (cont.) Fuse law When the fuse achieve the steady state condition. Heat generated = watt.

Characteristics Parameter of fuse (cont) Fuse law The value of fuse constant k depends on the fuse element material Sir W.H. Preec has given the value of constant K for various fuse element material.

Type of low voltage fuse Low-voltage fuse may be divided into two group. Cartridge fuse. semi-enclosed fuses or rewireable fuse.

Cartridge fuse Fusible link or fuse-link Component which must designed to provide the necessary electrical operating characteristics Its construction required great studies.

Cartridge fuse The material used for fusible link have following material. Low specific heat. High thermal conductivity. Low melting and vaporization temperature. Low talent heats. Low density. Ease of connection to other conductor. Free from deterioration due to oxidation. Low cost

Cartridge fuse(cont.) Fusible link Body It must have good electrical insulating properties It should not the ingress of moisture. It should reasonably have good thermal conductivity It must mechanically be strong enough and capable of withstanding thermal shock.

Cartridge fuse(cont.) Filling material Conduct some heat energy away from fuse element to its body. Packing density is constant during production to get unchanged performance. High breaking capacity fuses are filled with granular quartz of high chemical purity.

Semi-enclosed fuse It has fuse carrier that fusible fuse. it is used in industrial application with neutral voltage not exceed 240 V and rated current 100A. fuse element are directly replaceable. Their breaking capacity is low, being limited to a maximum about 4000 A.

Type of Cartridge HRC fuse This is High Rupturing Capacity cartridge type of fuse or HRC fuse

Type of Cartridge Cut-off characteristics of HRC Time-current characteristics of HRC

Type of Cartridge I2t characteristics of HRC Fuse element of HRC

D-type cartridge fuse

Operation of fuse Fuse operate on the principle of heating effect of electric current. Normal or steady state operation. Abnormal or fault state operation.

Presented by Ms. YAV Leakhena Application of LV Fuse Presented by Ms. YAV Leakhena

Application of LV fuse fuse which is to protect a particular piece of equipment or circuit should ideally satisfy a number of criteria. points A and B, and in these circumstances the fuse would have to interrupt the circuit before the source and supply cables could suffer damage.

Circuit protection 1.Circuit voltage : operation of a fuse link under fault conditions 2. Fault level : assigned breaking capacities in excess of any fault current 3. Full load current : overloads such as motor starting surges can exceed this value 4.Ambient Temperature

5. Discrimination: Discrimination between fuse links can be checked by ensuring that the time/current characteristics do not overlap at any point. fault currents which produce pre-arcing times longer than 0.01 second in most cases.

B. Equipment Protection 1. Cable protection : Ib ≤ Iz 2. Protection of motors 3. Protection of power transformers 4. Protection of capacitors 5. Protection of semi-conductor device

LV Fuse Selection & Specification LV Fuse Selection & Specification Presented By Mr. YORN Thort Presented By Mr. YORN Thort

LV Fuse Selection How can we select the right LV fuse? Voltage Rating Ampere Rating Interrupting Rating Time-Delay vs. Non-Time-Delay Fuses Time Current Characteristics Code and Standards

LV Fuse Selection Voltage Rating LV fuse voltage rating: lower than 1000V Mostly voltage rating fuse are 125, 250, 300, 480 and 600V. It determine the ability of fuse to suppress the internal arcing.

LV Fuse Selection Ampere Rating General rule: But in some specific circumstance, it cab be greater: Motor circuit: (time-delay fuse) (non-time-delay fuse) Fuse Ampere Rating Fuse and Switch combination: (for continuous operation at 100% of its rating) Ampere rating range: from milli-amperes up to 6000A

Interrupting Rating (IR) LV Fuse Selection Interrupting Rating (IR) IR of LV fuse may be: 10kA, 40kA, 50kA, 80kA, 100kA and 200kA or 300kA . Current-limiting power fuses, UL Class L, J, RK1, RK5, T or CC have interrupting ratings of 200 kA, suitable for 99.9% of today’s applications. UL Class H and K fuses, which have low interrupting ratings of 10 kA and 50 kA respectively. The standardized IR values are 80kA for 415Vac and above, and 40kA for DC applications. The 240Vac designs have an IR of 50kA.

LV Fuse Selection Interrupting Rating (IR) (cont.) Figure: Some recommend rated breaking capacity of LV fuses.

Time-Delay vs. Non-time-delay Fuses LV Fuse Selection Time-Delay vs. Non-time-delay Fuses Time-Delay Fuses provide high performance short circuit and reliable overload protection in circuits subject to temporary overloads and surge currents. are designed to coincide with motor. are recommended for transformer and motor branch circuit applications. Can be sized much closer to motor loads with many advantages.

LV Fuse Selection Time-Delay Fuses (cont.) Example:

Time-Delay vs. Non-time-delay Fuses (cont.) LV Fuse Selection Time-Delay vs. Non-time-delay Fuses (cont.) Non-time-Delay Fuses Are used for non-inductive loads: lighting panels and metering centers. provide excellent short-circuit component protection. they are particularly suited for the protection of circuit breakers with low interrupting ratings.

Time-Current Characteristics LV Fuse Selection Time-Current Characteristics are used to evaluate or verify fuse performance and define a fuse. represents average data for the design. The more current the fuse sees, the faster it opens.

Applicable Code & Standard LV Fuse Selection Code and Standards Agency approval: Underwriters Laboratories (UL) and the Canadian Standards Association (CSA). Standards UL 248 and CSA C22.2 for LV Fuses. Applicable Code & Standard For industrial applications, use listed current-limiting Class L, J, RK1, RK5, T or CC fuses.

LV Fuse Selection Code and Standards (cont.)

Code and Standards (cont.) LV Fuse Selection Code and Standards (cont.) Figure: Code and Standards of Underwriters Laboratories, UL 248 for LV fuses.

Code and Standards (cont.) LV Fuse Selection Code and Standards (cont.) Figure: Code and Standards of the Canadian Standards Association (CSA), CSA C22.2 for LV fuses.

LV Fuse Specification KTK-R Class CC

Advantages and disadvantages Presented by Ms. YAV Leakhena

Advantages Safety : the protection level is not degraded by previous faults. High breaking capacity and energy limitation: Proven reliability : do not need replacing , highest quality. Accurate discrimination : well designed electrical installation Reliable short circuit and back-up protection Long life

B. Disadvantage required for renewing or replacing On heavy short circuit faults Electrical fuse cannot be used for very high voltage system For the system in which the over current faults likely to be occurred frequently,.

Conclusion A fuse is a type of over-current protective device that is designed to be a sacrificial element in an electrical power system. Fuses are designed to open circuits when excessive over-currents are present and are designed to prevent further damage to the system that might result if the fuse were not present.

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