Motor StarterPrinciples

& Techniques

Presenter :

What’s a Motor Starter ? Starting and stopping of a motor Protection of devices against effects of electrical faults Ensure safety of personnel

Maximize continuity of service

On load breaking

Protect against damages caused by high fault current

Protection against effects of overload current

Making & breaking of current drawn by the load

Isolation

Short circuit

protection

O/L Protection

Switching

Power Control

Disconnection from LV source

Type of Motor Starters

CONVENTIONAL Methods Direct-On-Line (DOL)

Star / Delta

Auto-transformer

Primary resistance

ELECTRONIC MethodsSoft Starters

Variable Speed Drives

The choice of starting method depends on the application(starting time, type of motor, torque, fixed / variable speed...)

Common Motor Starters

DDirect-OOn-LLine Starterso Motor is connected directly to line with a contactor and a thermal overload relay

o Easy to install, usually for motor < 30kW

o High starting torque & the motor draws very high peak current

I I I

M

Q1

K

L1 L2 L3

TORI start = (5 to 8) x I

full-load

Power Circuit Control Circuit

Torque/Speed Curve Current/Speed Curve

DDirect-OOn-LLine Starters

I I I

M

Q1

K

L1

L2

L3

I I I

M

Q1

K

L1

L2

L3

TOR

2 Components DOL StarterIsolation + Protection : Surion GP..B Switching : Contactor Series M/CL

3 Components DOL StarterShort-circuit Protection : RecordPlus MCCB Switching : Contactor Series CL/CKThermal Overload Protection : RT

DDirect-OOn-LLine Starters

Star-Delta starters

Pre-requisites for Star-Delta Starters: o Motor stator windings must terminate in 6 terminals

o Motor windings must be rated at Line voltage when connected in delta

U1 V1 W1

U2 V2W2

A1 B1 C1

A2 B2C2

U V W

X YZ

Star-Delta starters

U1 V1 W1

U2 V2W2

AsynchronousAsynchronousSquirrel cageSquirrel cage

motormotorU1

U2

V1

V2

W1

W2

Star Circuit

U1

V1

W1U2

V2

W2

L1L1

L2L2L3L3

Delta Circuit

L2L2L3L3

L1L1

START RUN

Star-Delta startersTorque/Speed Curve Current/Speed Curve

o Starting current is reduced to 1/3o Starting torque is reduced to 1/3o Reduce mechanical stress on the machine and on the load

Star-Delta startersPower Circuit Control Circuit

Auto Transformer starterso Motor is started at a reduced voltage and has 3 stages

o Commonly used for high power motors (>100kW)

o Expensive solution because of the auto-transformer

M

L1 L2 L3L1 L2 L3

22ndnd Stage Stage

M

L1 L2 L3L1 L2 L3

11stst Stage Stage11stst Stage Stage 33rdrd Stage Stage

M

L1 L2 L3L1 L2 L3

I start = n2 x I DOL

Solid State Soft Starters

o Step-less smooth acceleration from “START” to “RUN”

o Possibility to have deceleration control too

o Adjustable starting current and starting torque

o Reduced mechanical stress to the entire system by eliminating the sudden changes in currents

Solid State Soft Starters

Solid state soft starters ASTATplus

Comparison of motor starters

Conventional Starters Solid State Starters

Comparison of motor starters

Utilization Categories

Utilisation Categories

They define the making and breaking conditions at Rated Operational Current (Ie) and at the Rated Operational Voltage (Ue). They depend on:

The nature of the load to be switched (resistive, squirrel cage motor, etc) The conditions under which making and breaking occurs (motor started or stalled, reversing direction of operation, etc)

Utilisation Categories

Classes of TOR

Tripping classes for TOR

Coordination of Motor Starters

What’s the purpose of Coordination ?The Objectives:When short-circuits are encountered, the motor starter must :

Interrupt swiftly Eliminate danger to personnel and equipment Minimize down-time

- cut repair cost

- cut equipment replacement costs

Optimum Combination of : Short circuit protective device Contactor Thermal Overload Relay

What’s a Coordinated Starter?

Level of Coordination :For a load, the coordination

depends on : The electrical environment The selection of the motor starter

componentsM

I> I>I>

U1

V1

W1

1/L

1

3/L

2

5/L

3

- F1

- KM1

2 4 6

2 4 6

1 3 5

1 3 5

2 4 6

Thermal Overload

Relay

Contactor

short circuit

Protection

device

Priority for Protection for PERSONNEL & PROPERTY: Successful interruption of fault No fire hazard

Equipment : Limit the extent of damage to the starter No damages to conductors, terminals, mounting base,

etc

Reduce Downtime : Continuity-of-service to increase productivity

Coordination of the Protection devices (Coordination Standard IEC 60947-4-1)

IEC60947 defines 2 levels of Coordination

IEC 60947-4-1• Type 1 Coordination• Type 2 Coordination

NO danger to persons or installation

Contactor and/or Thermal Overload Relay may be damaged

Before restarting, the starter may need to be checked/repaired

Type 1 Coordination (IEC60947-4-1)

By definition:“Under short-circuit conditions, the contactor or starter shall cause no danger to persons or installation and may not be suitable for further service”

Type 2 Coordination (IEC60947-4-1) By definition :

“Under short-circuit conditions, the contactor or starter shall cause no danger to persons or installation and shall be suitable for further use. The risk of contact welding is recognized, in which case the manufacturer shall indicate the measures to be taken as regards the maintenance of the equipment”

In the event of short-circuits………

HIGH RISK to operators

HIGH RISK to the installation; and

All motor starter components will have to be replaced before restarting

No Coordination means Highly

DANGEROUS

Warning!!….. Worst Case…..

NO Coordination

TYPE 1 Coordination

TYPE 2 Coordination

What do we recommend?

Depending on the operating conditions encountered

The Goal : to strike a balance between the user’s needs and the cost of components

When to use what?

Type 2 coordinationThermal/Magnetic Trip unit with Class 10 TOR

Type 2 coordinationElectronic Trip unit (SMR2) with Class 10 TOR

Type 2 coordinationMagBreak Trip unit with Class 20 TOR

COMPARISIONIEC 60947-4-1

No Coordination Type 1 Type 2

DANGER -> persons / installation HIGH RISK NO NO

DAMAGE -> Contactor/ TOR May be NO

Suitable for further use NO YES

Before restarting-> STARTER must be replaced checked/repaired simple check

readjust setting -> STARTER NO

COMPARISON Highly DANGEROUS Low cost Reliable

Worst OK Best

Summary• Overview of conventional motor starters

– DOL starters– Star-Delta starters– Auto-trans starters– Solid-State starters

• Utilization categories of contactors and classes of TOR

– AC1 to AC4– Class10, 10A, 20 & 30

• Co-ordination of motor starters– Type1 & Type 2