13-motor starter principles & techniques-rev1.0
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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
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