Load transfer switches

by

Saman RajapaksaAssistant manager-technical training

ROTAX LTD

Classification of load transfer switches a) type of construction

b) type of transition

c) type of source

d) type of application

e) compliance with different international standard publications

Type of construction

a) knife blade type

b) magnetic contactor type (IEC 60947-4-1)

c) circuit breaker type (IEC 60947-2)

d) power contactor type (IEC 60947-3)

e) static type (IEC 62310)

Type of construction

Knife blade type

Non load breaking Manually operated Slow switching transfer process No arc chutes Limited life span Cheaper in cost

Magnetic contactor type

Electrically held contacts Drop out on loss of control voltage Mechanically interlocked Possibility to close both contactors together Not a true double throw device Padlocking not possible Manual operation not possible Low short circuit fault current rating

Circuit breaker type Protection/switching

combined changeover device

comprises multi components

Slow transfer speed due to motor operator

Designed for short circuit making/breaking capabilities

Side by side or superposed mounting

Not a true double throw device

Power contactor type

Extremely High short circuit making capabilities Compact unit with less auxiliaries Inherent mechanical interlock due to double throw

device One ordering code for the complete unit

Static type

Two live sources required Extremely fast switching transition in less than ¼

cycle Silicon controlled rectifier technology Used for critical loads with two reliable/ independent

power sources High cost discourages standby applications

Type of Transition

type of source

Type of Application

Manual load transfer switch

Semi automatic load transfer switch

Fully automatic load transfer switch

Manual load transfer switch

Independent manual operation

Front/side (left/right) operating positions

Standard /delayed transition options

Complies with IEC 60947-3 standard

Semi automatic load transfer switch

Remote transfer switch equipment (RTSE) receiving external commands for switching

Motor/solenoid operation

Manual operation possible

Complies with IEC 60947-3 standard

Fully automatic load transfer switch

Comprises of a motorized load transfer switch with inbuilt controller

Programmable control /operating sequence Sensing of supply voltage/frequency of

mains/generator Complies with IEC 60947-6-1 standard

Compliance with standards

IEC 60947 - low voltage switch gear and control gear

Part 2 - circuit breakers Part 3 - switches, disconnecters, Part 4-1 – electromechanical contactors Part 6-1 - automatic transfer switch

equipment IEC 62310 - static transfer switches

IEC 60947-6-1

Formulated for ATSE equipment Classifies ATSE as class PC and class

CB Class PC – capable of making /withstanding

but not intended for breaking short circuit currents

Class CB -capable of making/breaking short circuit currents with over current releases

Utilization categories (continued)

IEC 60947-3 utilization categories

AC-20A/AC-20B- connect/disconnect under no load conditions

AC-21A/AC-21B-switching resistive loads AC-22A/AC-22B-switching mixed

resistive/inductive loads AC23-A/AC-23B –switching motor/highly

inductive loads

Utilization categories (continued)

IEC 60947-6-1 utilization categories

AC -31A/AC-31B - non inductive loads AC- 33A/AC-33B -mixed motor/resistive

loads AC-35A/ AC-35B –electric discharge lamp

loads AC-36A/ AC-36B- incandescent lamp loads

Salient features of ATSE equipment

Customer assembled switching units (circuit breakers/contactors etc) will not comply with IEC60947-6-1

Factory assembled switching units tested as per the standard by independent testing authorities ( eg; KEMA) comply with IEC 60947-6-1

Salient features of ATSE equipment (continued)

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