which mv motor starter to choose?
DESCRIPTION
Which MV motor starter to choose?. starter. Network. Load. Motor. The MV starter and motor are the links between the electrical network and the mechanical load. Motor. Load. Protection. Network. Overcurrent Thermal (I²t) rotor Thermal (Pt100) stator. - PowerPoint PPT PresentationTRANSCRIPT
E&S - Tony Narusevicius - 20-09-2005 - English 1
Which MV motor starter to choose?
E&S - Tony Narusevicius - 20-09-2005 - English 2
The MV starter and motor are the links between the electrical network and the mechanical load
LoadMotor
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starter
E&S - Tony Narusevicius - 20-09-2005 - English 3
The motor starter must be designed to limit the constraints to the network, the motor and the load
The type of motor starter will influencethe perturbations on the networkthe mechanical strength to the mechanical loadthe starting torque on the shaft
The protection will protect the motor
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OvercurrentThermal (I²t) rotorThermal (Pt100) stator
Protection LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 4
The network has constraints
Acceptable inrush current
Acceptable starting undervoltage
Acceptable power factor
short circuit withstand
Acceptable harmonics
E&S - Tony Narusevicius - 20-09-2005 - English 5
The load has constraints
Resistant torque curve
Starting inertia
Acceptable mechanical stress
operating conditions Starting time number of starts automatic starting operating cycle overload locked rotor current deceleration control
........
E&S - Tony Narusevicius - 20-09-2005 - English 6
The motor-starter must be designed to control, protect and supervise the motor for maintenance
Motor control: local or remote; automation....
Electrical motor protection short circuit under-voltage ........
Preventive protection temperature through thermal image or sensors bearing vibration sensors moisture derating for altitude .........
The design of the motor starter should decrease the number of spare parts....
.........
E&S - Tony Narusevicius - 20-09-2005 - English 7
The most common motor: asynchronous motor
the 3 windings of the stator are placed at 120° and are fed by the service voltage
these 3 coils create a rotating magnetic field around the axis of the stator
this magnetic field creates a current in the rotor the rotation of the rotor N is lightly slower as the
magnetic field one Ns
There are 2 types of asynchronous motors single or double cage motors (rotor is short
circuited) slip ring rotor motor (resistance of the rotor can
be modified by introducing external resistances)
phase 1
phase 2 phase 3
120°
E&S - Tony Narusevicius - 20-09-2005 - English 8
Influence of the service voltage on the motor torque
N (speed)Ns
starting torque
V"s > V's
Vs
V's >Vs
resistant torque
Torque
acceleration torque
The lower the voltage; the lower the motor torqueIf the motor torque is lower than the resistant torque the motor does not start
E&S - Tony Narusevicius - 20-09-2005 - English 9
Asynchronous motor
single cage rotordouble cage
deep slot rotor motor
starting torque lowfrom 0.6 to 1 Tr
slightly higherfrom 0.8 to 1.2 Tr
maximum torque around 2 to 2.2 Traround 2 to 2.2 Tr
(slightly higher for deep slots)
starting current from 4.5 to 5.5 Ir from 5 to 6.5 Ir
these motors are ideal for intensive use and hazardous environments
excellent mechanical and electrical robustness simplicity of design no brushes
relatively low power factor 0.8 to 0.9 on full load if asynchronous installed motor power is high reactive, power compensation may be required
E&S - Tony Narusevicius - 20-09-2005 - English 10
Asynchronous slip ring rotor motor
the impedance of the rotor winding can be modified by introducing external resistances.
by decreasing external resistance on starting (from Rr" to R), the characteristic of the torque is translated and the starting torque adapted to the torque of the machine.T
N
Ts
T max
T load
R= rotor resistanceRr ’ >Rr ’' >
E&S - Tony Narusevicius - 20-09-2005 - English 11
Synchronous motor
The main differences with asynchronous motors are: their constant speed (synchronous speed) the rotor circuit supplied with Dc the power factor which may be set by the exciting current
In a conventional synchronous motor controller the DC power is applied from an external source brushes and slip rings carry the current to the field winding
A brushless synchronous motor it generates its own DC power for its field the amount of DC power is controlled through induction low current DC power applied from the controller
E&S - Tony Narusevicius - 20-09-2005 - English 12
Load torque curves of machines
compressor
E&S - Tony Narusevicius - 20-09-2005 - English 13
Starting conditions:motor torque must always be greater than the load torque
the motor starts
the motor does not start
running point
E&S - Tony Narusevicius - 20-09-2005 - English 14
Some of the different types of MV motor starter
Full voltage on the stator or direct on line FVNR or DOL
Reduced Voltage through reactance
Reduced Voltage through auto-transformer RVAT
Reduced Voltage trough soft starter RVSS (SoftStart)
E&S - Tony Narusevicius - 20-09-2005 - English 15
Direct stator starting on full voltage (FVNR)
Locked rotor current on starting is around 4 to 7 In depending on motor characteristics
starting time of 1 to 10 seconds depending on the moment of total inertia (motor + machine), motor torque and load torque
the network must be able to withstand the starting current without disturbing other loads
the machine being driven must be able to withstand the mechanical impact due to the motor torque
This mode is very popular (simple, robust, not expensive)
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Protection LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 16
Reduced voltage by reactance
This starting mode reduces current inrush on the network in the simplest manner. Since the motor starting torque is low, the machines being driven must have a relatively low torque during star up: compressors; centrifugal pumps; converter sets....
T/Tn T L1shunted
T with L1
Tr
N
Nn
resistant torque
N1
1
2
Tmax
IId/In
N
NnN1
2
4
InIf(Tr)
I L1shunted
I with L1
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L1Protection LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 17
Reduced voltage by auto-transformer
This system is recommended for high power motors. It has the advantage of not dissipating energy.
It can be used to obtain, for the same decrease in current, less reduction in torque than with the reactor starter.
N1
Net
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rk
Ct3
Ct2
Ct1
Protection
T/Tn
Tr
N
Nn
resistant torque
N1
1
2
Tmax
Ct1 and Ct2 closedCt2 closedCt2 and Ct3 closed
IId/In
N
NnN1
2
4
InIf(Tr)
Ct2 and Ct3 closed
Ct2 closed
Ct1 and Ct2 closed
LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 18
Auto Transformer starting Sequence
Second stage: the motor is running in series with part of the autotransformer winding.
The motor is always supplied during the second stage, when CT1 is open.
First stage:
CT1 must be closed before CT2.
CT1 and CT2 are closed
CT3 is open
CT1
CT2
CT3
M
Second stage:
CT1 is opened
CT2 remains closed
CT3 remains open
CT1
CT2
CT3
M
CT1 and CT2 are closed
CT1 is openedCT2 are closedCT2 and CT3 are closed
Third stage: the motor runs at full voltage.
First stage :the motor is starting with reduced voltage.
Third stage:
CT3 is closed
CT2 remains closed
CT1 remains open
CT1
CT2
CT3
M
E&S - Tony Narusevicius - 20-09-2005 - English 19
Reduced voltage by Soft Starter
The soft starter is an solid state device which controls the starting period of the motor
depending on the application several settings are possible. When the motor is running a contactor shunts the electronic starting
module. Advantages
Reduction of starting current Reduction of starting torque and mechanical shock ( the torque may
be adjusted to the resistant torque) smooth acceleration and deceleration of the motor
It is a solution when auto-transformer motor starter is not possible.
But it is not a variable speed starter Only the price limits the use of the Soft Starter
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Soft starterProtection LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 20
Soft starter setting: different possibilities
current limitation setting torque control setting mix of both ........
deceleration possibilities
E&S - Tony Narusevicius - 20-09-2005 - English 21
Soft starter setting: current limitation
T/Tn
0,6 Un
0,85 Un
Un
Tr
N
Nn
resistant torque
N1
1
2
Tmax
fix frequency
T=function UUn( )
2I and Torque
Is/In
Il
Tsn
Tlimited
limited T= Tn * (In / Il)2
N
NnN1
2
4
InIf(Tr)
Limit of the starting current
The voltage is increased until the starting current reaches the limit, then voltage is maintained at this current, and then the voltage is increased again up to the service voltage
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Soft starterProtection LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 22
Soft starter setting: torque control
The voltage is set to have a motor torque just above the resistant torque.If the resistant torque is constant the starting voltage may be close the full voltage; the inrush current maybe close the direct on line inrush current
T1 = k.I1
N and TC
t
t1
Tn
Nn
resistant torque
I and T
tt1
I1
In
x In
Tn
T1U1
I starter
Un
resistant torque
torque control
U starter=>
speed ramp fonction oftorque ramp
LoadMotor
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Soft starterProtection
E&S - Tony Narusevicius - 20-09-2005 - English 23
Soft starter: normal setting
The initial torque setting applies sufficient voltage to the motor to cause the motor shaft to begin to turn.This voltage is gradually increased overtime (as per the ramp time setting) until either:
the motor accelerates to full speedthe ramp time expiresa current limit is reached.
If the motor has not reached the full speed at the end of the ramp setting, the current limit setting will proportionally control the maximum output torqueThe current remains limited for as long it takes the motor to accelerate to full speed.
When the motor reaches full speed and the current drops to running level, the by pass contactor shunts the soft starter module.The motor is now running at the full voltage.
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Soft starterProtection LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 24
Soft starter setting: deceleration
The starter may be used to control the deceleration by slowly reducing the voltage to the motor upon initiating a stop command
the most common application for the decel feature is pumping application, in which a controlled stop prevents water hammer and mechanical damage to the system.
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Soft starterProtection LoadMotor
E&S - Tony Narusevicius - 20-09-2005 - English 25
Starting mode selection table
application Startingmode
Controlledby
Advantagesdisadvantages
Permanent orquasipermanentprocess<1/day
Machines requiringhigh start torque
1 Circuitbreaker or1 contactor
Frequentstarts>1/day
Motor with lowcurrent inrush orlow power
Direct On Line /Full voltage 1 contactor
Simplicity,less investment
On starting:High torqueHigh current inrushHigh mechanical stress
Pumps fans,compressors,frequent starts
Machines startingwith low torque Stator by
reactance
Reduction of current in rushon startingPoor power factor
Optimisationof startingcharacteristics
When startingcurrent must bereduced, but thenecessary startingtorque maintained
Stator byautotransformer
or soft starter
3 contactors
2 contactors
Optimisation of torque andcurrent inrush on starting
expensive
Optimisationof high torquestartingcharacteristics
The most difficultstarts
rotor generally3 contactors
Small current inrush andhigh starting torque
E&S - Tony Narusevicius - 20-09-2005 - English 26
Network requirement
Starting mode selection table
- accepts the current oscillation during an open transition?
-accepts the starting reactive consumption power?
Investment Increase
- deceleration control ?
- constant torque with high starting torque as crushers, grinders, mixers ......
- the drive between motor and load is able to withstand the mechanical stress of a direct on line start
- accepts full starting current?- accepts starting voltage drop?
yes
yes
yes
yes
no
no
no
nono
no
yes
yes
no
no
- accepts the harmonics during the starting period
VSDspecific
no
FVNR RVAT RVSS
yes
yes
yes
E&S - Tony Narusevicius - 20-09-2005 - English 27
main protection
overload overcurrent, thermal image, and thermal sensors
short circuits To protect the motor and the network fuses and instantaneous over-current relay
thermal protection bearing overload temperature simulated by relay thermocople RTD
Incomplete phase, phasereversal and unbalance
faults give rise to: increased current in the stator
insulation fault in thewinding
earth leakage protection(differential protection)
stator/ frame vital to comply with the worker protectionprotection windings and magnetic circuit
zero sequence current relay under and over voltage under-voltage: common protection, prevents the motor on
working on overload over-voltage: fluctuations on the network
incomplete starting orfrequent starts
prevents long motor starting and over temperature speed or current
locked rotor protection of the motor against thermal damage under power or
undercurrent mainly for pumps
other protection specified by motor manufacturers
E&S - Tony Narusevicius - 20-09-2005 - English 28
Rating Current of the contactor
The power of a motor is the mechanical power.To determine the rating of the contactor we have to calculate the full load current of the motor.
The electrical power of the motor will be the mechanical one divided by the efficiency.
Is= Pm/(Us x V3 cos where
Pm: power of the motor Us service voltage cospower factor efficiency of the motor
Ir contactor > Is * k (k derating factor) if the altitude <1000m k=1
Altitude (ft) Voltage Current
3300 (1000 m) and below 1.00 1.005000 (1500 m) 0.95 0.9910,000 (3000 m) 0.80 0.96
E&S - Tony Narusevicius - 20-09-2005 - English 29
What do you think?
For an asynchronous motor,true false
the highest starting torque is supplied by the Full Voltage Motor starterthe higher the voltage, the higher the starting torquewith a full voltage motor starter the network capability to accept the inrush current needs to be verifiedthe inrush current may generate a voltage drop at the terminals of the motorthe distance between the motor starter and the motor has no influence on motor startingmotor starting through an auto-transformer is always a cycle of three stepsit is possible to continuously operate an auto transformer motor starter on an intermediate stepthe auto transformer motor starter may be used for every applicationthe auto transformer is generally designed in accordance with the motor use for each projectdifferent starting configurations are available in the soft startersSoft starters use an electronic device to reduce the voltageSoft starters maybe used to adapt the running speedSoft starter maybe used to control the decelerationsoft starter needs 2 contactorswith a soft starter it is possible to adjust the starting torque to the resistant torque
E&S - Tony Narusevicius - 20-09-2005 - English 30
Do you agree?
For an asynchronous motor,true false
the highest starting torque is supplied by the Full Voltage Motor starterthe higher the voltage, the higher the starting torquewith a full voltage motor starter the network capability to accept the inrush current needs to be verifiedthe inrush current may generate a voltage drop at the terminals of the motorthe distance between the motor starter and the motor has no influence on motor startingmotor starting through an auto-transformer is always a cycle of three stepsit is possible to continuously operate an auto transformer motor starter on an intermediate stepthe auto transformer motor starter may be used for every applicationthe auto transformer is generally designed in accordance with the motor use for each projectdifferent starting configurations are available in the soft startersSoft starters use an electronic device to reduce the voltageSoft starters maybe used to adapt the running speedSoft starter maybe used to control the decelerationsoft starter needs 2 contactorswith a soft starter it is possible to adjust the starting torque to the resistant torquefor some application the soft starter may create inrush current similar to the full voltage motor starter