Transcript Motor - Schneider Electric

Which MV motor starter
to choose?
E&S - Tony Narusevicius - 20-09-2005 - English
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Network
starter
Motor
Load
The MV starter and motor are the links between the
electrical network and the mechanical load
E&S - Tony Narusevicius - 20-09-2005 - English
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Network
The motor starter must be designed to limit the
constraints to the network, the motor and the load
Protection
Motor
Load
Overcurrent
Thermal (I²t) rotor
Thermal (Pt100) stator
The type of motor starter will influence
the perturbations on the network
the mechanical strength to the mechanical load
the starting torque on the shaft
The protection will protect the motor
E&S - Tony Narusevicius - 20-09-2005 - English
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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
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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
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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
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The most common motor: asynchronous motor
phase 2
phase 3
phase 1
 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
120°
E&S - Tony Narusevicius - 20-09-2005 - English
 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)
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Influence of the service voltage on the motor torque
Torque
V"s > V's
V's >Vs
starting torque
Vs
acceleration torque
Ns
N (speed)
The lower the voltage; the lower the motor torque
If the motor torque is lower than the resistant torque the motor does not start
E&S - Tony Narusevicius - 20-09-2005 - English
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Asynchronous motor
single cage rotor
double cage
deep slot rotor motor
starting torque
low
from 0.6 to 1 Tr
slightly higher
from 0.8 to 1.2 Tr
maximum torque
around 2 to 2.2 Tr
around 2 to 2.2 Tr
(slightly higher for deep slots)
from 4.5 to 5.5 Ir
from 5 to 6.5 Ir
starting current
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
these motors are ideal for intensive use and hazardous environments
E&S - Tony Narusevicius - 20-09-2005 - English
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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
Rr ’'
>
Rr ’
>
R= rotor resistance
T max
Ts
T load
N
E&S - Tony Narusevicius - 20-09-2005 - English
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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
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1
Load torque curves of machines
compressor
E&S - Tony Narusevicius - 20-09-2005 - English
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2
Starting conditions:
motor torque must always be greater than the load torque
the motor does not start
the motor starts
running point
E&S - Tony Narusevicius - 20-09-2005 - English
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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
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Network
Direct stator starting on full voltage (FVNR)
Protection
Motor
Load
 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)
E&S - Tony Narusevicius - 20-09-2005 - English
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Network
Reduced voltage by reactance
L1
Protection
Motor
Load
 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
Id/In
I
Tmax
I L1shunted
4
T with L1
2
I with L1
2
Tr
1
If(Tr)
In
resistant torque
N
N1 Nn
E&S - Tony Narusevicius - 20-09-2005 - English
N
N1 Nn
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Reduced voltage by auto-transformer
Ct1
Network
Motor
Load
Ct2
Protection
Ct3
 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.
Id/In
T/Tn
I
Tmax
4
2
2
Tr
1
If(Tr)
In
resistant torque
N
N
N1
N1 Nn
E&S - Tony Narusevicius - 20-09-2005 - English
N1 Nn
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Auto Transformer starting Sequence
First stage:
CT1 must be closed before CT2.
CT1 and CT2 are closed
CT3 is open
Second stage:
First stage :
the motor is starting with reduced voltage.
CT1 is opened
CT2
CT2 remains closed
Third stage:
Second stage:
the motor is running in series with part of the
autotransformer winding.
CT3 remains open
CT3 is closed
CT3
CT2
CT2 remains closed
CT1 remains open
CT1
CT3
The motor is always supplied during the
second stage, when CT1 is open.
Third stage:
the motor runs at full voltage.
CT2
M
CT1
CT3
CT1 is opened
CT2 are
andclosed
CT3 are closed
CT2
M
CT1
M
E&S - Tony Narusevicius - 20-09-2005 - English
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Network
Reduced voltage by Soft Starter
Protection
Soft starter
Motor
Load
 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
E&S - Tony Narusevicius - 20-09-2005 - English
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Soft starter setting: different possibilities




current limitation setting
torque control setting
mix of both
........
 deceleration possibilities
E&S - Tony Narusevicius - 20-09-2005 - English
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Network
Soft starter setting: current limitation
Soft starter
Protection
Motor
Load
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
fix frequency
T/Tn
T=function
Tmax
2
( )
U
Un
Is/In
I and Torque
limited T= Tn * (In / Il)2
4
2
Il
2
Tr
1
Limit of the starting current
Tsn
In
If(Tr)
Tlimited
resistant torque
N
N1 Nn
E&S - Tony Narusevicius - 20-09-2005 - English
N
N1 Nn
2
1
Network
Soft starter setting: torque control
Soft starter
Protection
Motor
Load
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
I and T
N and
CT
torque control
speed ramp
fonction of
torque ramp
x In
I starter
U starter=> F
I1
Un
In
Tn
U1
T1
Nn
Tn
resistant torque
T1 = k.I1
F1
E&S - Tony Narusevicius - 20-09-2005 - English
t
t1
resistant torque
t
t1
2
2
Network
Soft starter: normal setting
Protection
Soft starter
Motor
Load
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 speed
the ramp time expires
a 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 torque
The 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.
E&S - Tony Narusevicius - 20-09-2005 - English
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Network
Soft starter setting: deceleration
Protection
Soft starter
Motor
Load
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.
E&S - Tony Narusevicius - 20-09-2005 - English
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Starting mode selection table
application
Permanent or
quasi
permanent
process<1/day
Frequent
starts>1/day
Starting
mode
Machines requiring
high start torque
Motor with low
current inrush or
low power
Pumps fans,
Machines starting
compressors, with low torque
frequent starts
1 Circuit
breaker or
1 contactor
Direct On Line /
Full voltage
1 contactor
Simplicity,
less investment
On starting:
High torque
High current inrush
High mechanical stress
Reduction of current in rush
on starting
Poor power factor
Stator by
reactance
Optimisation
When starting
Stator by
of starting
current must be
autotransformer
characteristics reduced, but the
necessary starting or soft starter
torque maintained
Optimisation
of high torque The most difficult
rotor
starting
starts
characteristics
E&S - Tony Narusevicius - 20-09-2005 - English
Controlled Advantages
by
disadvantages
3 contactors
Optimisation of torque and
current inrush on starting
2 contactors
expensive
generally
3 contactors
Small current inrush and
high starting torque
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Starting mode selection table
yes
- deceleration control ?
- the drive between motor and load
is able to withstand the mechanical
stress of a direct on line start
no
no
yes
- constant torque with high starting
torque as crushers, grinders, mixers ......
yes
no
Network requirement
- accepts full starting current?
- accepts starting voltage drop?
-accepts the starting reactive
consumption power?
no
Investment Increase
yes
no
yes
no
yes
- accepts the current oscillation
during an open transition?
yes
VSD
specific
no
yes
- accepts the harmonics during
the starting period
no
yes
FVNR
E&S - Tony Narusevicius - 20-09-2005 - English
no
RVAT
RVSS
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main protection
 overload
 overcurrent, thermal image, and thermal sensors
 short circuits
 To protect the motor and the network
 fuses and instantaneous over-current relay
 bearing overload temperature
 simulated by relay
 thermocople
 RTD
 faults give rise to:
 increased current in the stator
 earth leakage protection
(differential protection)
 vital to comply with the worker protection
protection windings and magnetic circuit
 zero sequence current relay
 under-voltage: common protection, prevents the motor on
working on overload
 over-voltage: fluctuations on the network
 prevents long motor starting and over temperature
 speed or current
 thermal protection
 Incomplete phase, phase
reversal and unbalance
 insulation fault in the
winding
 stator/ frame
 under and over voltage
 incomplete starting or
frequent starts
 locked rotor
 under power or
undercurrent
 other protection
E&S - Tony Narusevicius - 20-09-2005 - English
 protection of the motor against thermal damage
 mainly for pumps
 specified by motor manufacturers
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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 cosj *h)
 where
 Pm: power of the motor
 Us service voltage
 cosj power factor
 h efficiency of the motor

Ir contactor > Is * k (k derating factor)
 if the altitude <1000m k=1
E&S - Tony Narusevicius - 20-09-2005 - English
Altitude (ft)
Voltage
Current
3300 (1000 m) and below
5000 (1500 m)
10,000 (3000 m)
1.00
0.95
0.80
1.00
0.99
0.96
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What do you think?
For an asynchronous motor,
true
false
the highest starting torque is supplied by the Full Voltage Motor starter
the higher the voltage, the higher the starting torque
with a full voltage motor starter the network capability to accept the inrush current needs to be verified
the inrush current may generate a voltage drop at the terminals of the motor
the distance between the motor starter and the motor has no influence on motor starting
motor starting through an auto-transformer is always a cycle of three steps
it is possible to continuously operate an auto transformer motor starter on an intermediate step
the auto transformer motor starter may be used for every application
the auto transformer is generally designed in accordance with the motor use for each project
different starting configurations are available in the soft starters
Soft starters use an electronic device to reduce the voltage
Soft starters maybe used to adapt the running speed
Soft starter maybe used to control the deceleration
soft starter needs 2 contactors
with a soft starter it is possible to adjust the starting torque to the resistant torque
E&S - Tony Narusevicius - 20-09-2005 - English
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Do you agree?
For an asynchronous motor,
true
false
the highest starting torque is supplied by the Full Voltage Motor starter
the higher the voltage, the higher the starting torque
with a full voltage motor starter the network capability to accept the inrush current needs to be verified
the inrush current may generate a voltage drop at the terminals of the motor
the distance between the motor starter and the motor has no influence on motor starting
motor starting through an auto-transformer is always a cycle of three steps
it is possible to continuously operate an auto transformer motor starter on an intermediate step
the auto transformer motor starter may be used for every application
the auto transformer is generally designed in accordance with the motor use for each project
different starting configurations are available in the soft starters
Soft starters use an electronic device to reduce the voltage
Soft starters maybe used to adapt the running speed
Soft starter maybe used to control the deceleration
soft starter needs 2 contactors
with a soft starter it is possible to adjust the starting torque to the resistant torque
for some application the soft starter may create inrush current similar to the full voltage motor starter
E&S - Tony Narusevicius - 20-09-2005 - English
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