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Introduction to Power Electronicsand

Protection Methods

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Semiconductor Fuses

Extremely fast acting protective devices

Provides protection for scr, diodes, triacs, thyristors and other solid state devices

Intended primarily for short circuit protection but most will provide overload protection against currents of 2 times fuse rating or greater

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Standard fuse: AJT100

Semiconductor fuse:A70QS100-4

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Standard fuse: AJT100

Semiconductor fuse: A70QS100-4

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The Fuse: A Thermal Device: Conduction

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When the thermal equilibrium is reached, dissipated heat = heat generated;

the temperature is stabilized

The rated current (In) of the fuse is a value assigned by the manufacturer and is the RMS current which the fuse is designed to carry continuously under specified test conditions.

Main Current

Heat generated

Fuse Current Rating - I n

The Fuse: A Thermal Device

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How a Fuse Operates

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How the Fuse Operates-Time Current Characteristic

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UR vs gR (Short Circuit only vs Full Range)

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The Fuse: A Thermal DeviceHigh Fault Current

Reduced Sections (n)

Melting temperature of the fuse element

Fault current

Heat generated

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How the Fuse Operates: High fault Current

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Current Limiting Fuse

A Fuse reduces the short-circuit current.

Minimizes the energy through the path under fault

Minimizes magnetic forces function of Ipeak 2

Minimizes thermal stress function of IRMS 2 x clearing time

Current limitation = Reduction in system damage

As a result, it also:

Prospective fault current

Current limited by the fuse

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How the Fuse Operates – High Fault CurrentPeak let-thru Data

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How the Fuse Operates – High Fault CurrentFuse I2t Data - Table

Ampere

Rating (A)

Melting I2t

(kA2s)

Total

Clearing I2t at

Vn (kA2s)

Watts Loss

at In (W)

125 2.1 6.9 22150 3.3 11 29175 4.2 14 35200 5.9 19 41225 9 30 37250 12.6 42 42300 16.7 55 53350 21.5 72 54400 29.7 99 75450 36.7 125 78500 47.1 160 92600 65.2 222 116700 103.6 332 125800 135.3 433 143

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How the Fuse Operates – High Fault CurrentClearing I 2t vs. Applied Voltage

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Semiconductor Fuse Standards

IEC 269.4 was the only standard until July 1998 when UL 248-13 went into effect.

Designed with characteristics necessary to protect device. Most are Component Recognized.

Low clearing I2tLimited peak arc voltageCycling capabilityMeasured watts lossSpecial mounting stylesDC capability

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Fuse current rating

The Fuse: Withstand and Protect

Low High

To Withstand Steady State

Current

To Clear Quickly for Protection Purposes

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Power Electronic Applications

Protection Objectives

clearing I2t of fuse < I2t withstand of devicepeak arc voltage of fuse < PIV devicefuse voltage rating > max circuit voltagefor DC applications the fuse voltage capability equal to or greater than the maximum applied voltage at the time constant of the application

Considerations

fuse must be capable of carrying the load at the ambient temperature and air flow conditionsfuse must be capable of surviving occasional overload conditionsfuse must have a sufficient life under cyclic load conditions

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Power Semiconductor Protection – The Devices

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Power Semiconductor Protection – The Devices

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Power Semiconductor Protection – The Devices

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1. What type of circuit do you have? Please describe and provide sketch (if possible), include fuse placement.

2. Application voltage – What is the highest voltage the fuse must interrupt?

Vac rms Frequency

Vdc L/R time constant

SEMICONDUCTOR FUSE APPLICATIONS QUESTIONAIRE

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3. Current Rating/ Load Characteristics - Describe the load

– Full load amps thru fuse– Describe any overloads where the fuse must not operate

during normal operation. Provide current and time profile (how much, for how long, how often). Sketch out current profile if possible.

– Describe any momentary inrush currents where the fuse must not operate (how much, for how long, how often).

4. Are there any other protective devices used in the circuit?– What type?– Location?– Purpose?– Is coordination required between this device and the fuse?– If yes, please describe?

SEMICONDUCTOR FUSE APPLICATIONS QUESTIONAIRE

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5. What is the maximum available fault current (Amps. rmssymmetrical)?- What is the minimum current the fuse must open on? - Is there a time requirement for this?

6. Semiconductor Characteristics and required protection.- What type of device (SCR, diode, power transistor, IGBT, other) are we protecting?- What is the I2t withstand of device?- What is the PIV (peak inverse voltage) of device?- Is I2t protection required or are we only trying to isolate a faulted component?- If only isolation is required, what is the maximum permissible fuse let-thru I2t (explosion I2t limit of device)

SEMICONDUCTOR FUSE APPLICATIONS QUESTIONAIRE

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7. Fuse environment.- What is the ambient temperature surrounding the fuse?- Is cooling provided? - If cooling is provided, please give characteristics (forced air cooled – air flow speed, water cooled – provide specifics)

8. How is the fuse connected to in system?- What type of connection is preferred (Blade, end-contact, ferrule, special – specify)- What is bus cross-section?- What size cable?

SEMICONDUCTOR FUSE APPLICATIONS QUESTIONAIRE

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Mersen Semiconductor Fuse Product Line

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Type 128: END CONTACT(Tapped style, hockey puck)

Type 4: BLADEType 1: FERRULE

Type 2: FERRULE 13/32 X 1.5”(10X38mm)

Round Semiconductor Fuse Mounting Options

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Semiconductor Fuse Indication OptionsRound Body Semiconductor Fuses…

-4IL; -128IL

-4TI; -128TI

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Semiconductor Fuse product offering(Square Body N.A. & European Style)

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Square body semiconductor fuses indication Option

Indicator

Micro-switch MS3V1-5 (PSC3*)MS7V1-5 (PSC7*)

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Round or Square

Round

– Body sizes increase with amp rating

– Ferrule, blade or hockey puck mounting

– None indicating standard

– Visual or remote indicator opt.– Small amp ferrules widely used

world wide

Square

4 body sizes + 2 doubles

– 7 mounting styles in each size (Blade and tapped)

– Multiple amp rating each size

– All with indication– Widely used world wide

– ~600A and higher – cost effective and compact

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Round/Square – Special Purpose

440 to 3800V

0.8A to 1000A

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Square – Specials

600 to 4200V

6A to 400