Medium Voltage Application Guide

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13684.A Maximum cut-off current (kA) peak 13682.A SWITCHGEAR Circuit Design (Motor circuit with fuses) A contactor always needs some form of back-up short circuit protection. Although circuit breakers can be used for this purpose, it is more common to use MV HRC fuses. Fuses have higher fault breaking capacity, are very fast acting and are a good current limiting device. Consider the following direct-on-line motor circuit, which includes a line contactor, short circuit protection fuses and a motor protection relay, providing overload protection. Assume an operating supply of 6.6 kV/50 Hz and a motor FLC of 120 A. Typical DOL circuit with contactor, fuses and relay 6.6 kV / 50 Hz F1 K1 CT1 PR 3 M1 M 3 (FLC = 120 A) Step 1: Select the contactor Rated voltage U r ≥ operating voltage U and AC3 rating I e ≥ motor FLC A 7.2 kV/50 Hz contactor with an AC3 rating of 200 A will be adequate Step 2: Select the fuse The manufacturer will specify the maximum allowable fuse size. As a general rule, the nominal rating of the fuse should be 1.5 times the motor FLC. In this case I (fuse) = 1.5 x 120 = 180 A Use a 200 A fuse. On a time-current curve, check that the contactor thermal withstand curve lies outside the total clearing curve of the fuse. From the fuse cut-off curve, the "limited" prospective short circuit current of the fuse must be less than the short-time withstand current rating of the contactor. I sc' (fuse) ≤ I k (contactor) Assume the 7.2 kV/50 Hz, 200 A contactor has a short-time withstand current rating I k of 8 kA and the prospective rms fault current level I sc at the point of installation is 10 kA. 100 50 20 10 315 250 200 160 100 5 63 2 1.0 2 5 10 20 50 100 Prospective current (kA) rms From the fuse cut-off curve, we can see that a prospective rms fault current of 10 kA (I sc ) will be limited to 4 kA (I sc' ) by the 200 A fuse. Check that I sc' (fuse) ≤ I k (contactor). 4 kA ≤ 8 kA The fuse is suitable for use with the contactor. Page 98 Medium Voltage Application Guide 710-12280-00A
13525.A Time (s) SWITCHGEAR Step 3: Select an overload curve The nominal current setting of the curve is set for the motor FLC. In this case, set overload protection so that I n = 120 A The overload curve (hot curve) needs to lie outside the motor start curve and intersect with the fuse curve at a point before the maximum breaking current I c of the contactor. 1 3 4 5 Motor FLC Motor start current Overload curve - nominal setting (In) Overload curve - hot Fuse total clearing curve Contactor maximum break current (Ic) Contactor thermal withstand curve 2 7 6 Current (A) 710-12280-00A Medium Voltage Application Guide Page 99
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Medium Voltage Application Guide
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CONTENTS 4 Switchgear .............
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INTRODUCTION 1 Introduction This re
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03340.B Current Torque MOTORS magne
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Torque Current MOTORS Typical start
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03340.B Current Torque MOTORS 2.2 M
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13190.A Current Torque 13193.A Curr
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MOTORS How does soft start compare
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MOTORS Soft starters Electronic sof
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MOTORS Bypassed VFD installation 1
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13473.A SOFT STARTERS Open loop sof
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SOFT STARTERS 3.2 Benefits Electric
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13490.A 13489.A SOFT STARTERS Snubb
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SOFT STARTERS Enclosed soft starter
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12996.A SOFT STARTERS Local control
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SOFT STARTERS Key Features MVS soft
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SOFT STARTERS Vibration ...........
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SOFT STARTERS MVX Soft Starter Over
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SOFT STARTERS General Technical Dat
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11083.B 11082.B SOFT STARTERS Power
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13015.A 13013.A SOFT STARTERS Soft
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SOFT STARTERS Predictive Maintenanc
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SOFT STARTERS Medium voltage starte
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STAR T STO P RESET INPU TA INPU T B
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Page 84 and 85: SWITCHGEAR Resonant frequency The b
Page 86 and 87: SWITCHGEAR Interlock scheme 1: Two
Page 88 and 89: SWITCHGEAR Causes of internal arc T
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Page 104 and 105: SWITCHGEAR IEC Ratings Disconnector
Page 106 and 107: Pre-arcing time (seconds or minutes
Page 108 and 109: SWITCHGEAR Nominal current, In (A)
Page 110 and 111: 13745.A Fuse rating (A) 13697.A Fus
Page 112 and 113: SWITCHGEAR Current Transformers A c
Page 114 and 115: Flux () SWITCHGEAR Exercises 1. A C
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Page 118 and 119: SWITCHGEAR Exercise 2: Protection C
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SWITCHGEAR Exercise For a motor run
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SWITCHGEAR The total coefficient fa
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SWITCHGEAR Short-time withstand cur
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14009.A SWITCHGEAR Mechanical stren
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SWITCHGEAR Resonant frequency The b
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Current 13850.A SWITCHGEAR Synchron
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13854.A 13852.A 13853.A SWITCHGEAR
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SWITCHGEAR 4.6 Switchgear Inspectio
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SWITCHGEAR Commissioning Tools and
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SWITCHGEAR 62271-302 High voltage s
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13856.A 13855.A SWITCHGEAR 4.9 IEC
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SWITCHGEAR 4.10 Protection index IP
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SCHEMATIC DIAGRAMS 5 Schematic Diag
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14043.A 14042.A SCHEMATIC DIAGRAMS
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14046.A 14045.A SCHEMATIC DIAGRAMS
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14049.A SCHEMATIC DIAGRAMS 5.5 MVS
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14051.A SCHEMATIC DIAGRAMS 5.6 MVX
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RESOURCES 6 Resources 6.1 Equipment
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CONTENTS Contents Introduction ....
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2. ENVIRONMENTAL SPECIFICATIONS Env
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LOGIC CONTROL CONFIGURATION 3.2 Ope
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LOGIC CONTROL CONFIGURATION 3.6 Met
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SPECIFICATION: MVX Solid State Redu
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1. 1. INTRODUCTION Introduction 1.1
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ENVIRONMENTAL SPECIFICATIONS The eq
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LOGIC CONTROL CONFIGURATION 3.2 Ope
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LOGIC CONTROL CONFIGURATION 3.6 Met
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SPECIFICATION: Power factor Correct
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1 INTRODUCTION Introduction 1.1 Sco
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3 SUPPORT AND SERVICES Support and
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CONTENTS Contents Introduction ....
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2. DOCUMENTATION Documentation 2.1
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3.2.2 MV Equipment a) Circuit break
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ELECTRICAL SUPPLY 9. Circuit breake
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RESOURCES 6.2 Metric/Imperial Conve
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RESOURCES 6.4 Incoterms Internation
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RESOURCES kW Active power unit LRC
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