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SIEMENS
FUNDAMENTOS DE LOS SISTEMAS DE
PROTECCION NUMERICOS
Protección de Motor
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Content of presentation
§ Technical data from the motor manufacturer§ Setting examples of thermal functions§ Overload protection stator (running motor)§ Restart inhibit function§
Motor starting time supervision§ Unbalanced load (negative sequence) protection
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Technical Data
MVA1,60S
154A6000V3S
IU3S
N
N
NNN
=
∗∗=
=
KW1379P
0.9580.9MVA1,60P
cosS P
N
N
NN
=∗∗=
∗∗= ηϕ
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Motor starting curve (acceleration)
Technicaldata (2)
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Technicaldata (3)
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9s13s
for Statoroverloadprotection
1,15
Technicaldata (3)
Locked rotorlimits with thegiven startingcurrent
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Stator overload protection(running motor under load)
This should be set to equal the k-factor.1,15 IN,MCurrent alarm stage
The value 2,5 IN,M
can be used for a short starting time. If a
longer starting time is possible (>20s), the limit should be
reduced to 2 I/IN,M.
2,5 I/IN,MCurrent limiting
During operation under rated condition the thermal memory is
always below 90%. With the default setting of 1,1, this is 83%
and in the case of k = 1,15, only 76%.
90%Thermal alarm stage
Take this from the thermal characteristic (technical data (4)); if
this is not available a k-factor of 1,1 can be used, because the
thermal class F/B is specified (see technical data (1))
1,15k-factor
Take this from the motor data sheet (technical data (4)) or set
an experienced-based value, e.g. 7 times the heating time
constant.
175 minCooling down time constant
Take this from the motor data sheet
(technical data (4)).
25 minHeating time constant
CommentValueSetting parameters
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Current limiting
Freezing the thermal memory during starting§ This is intended to avoid overfunction of the overload protection during
starting.§ Realization: 7SJ6
Internal limiting of the starting current§ The current fed to the thermal model is limited during starting. This
“slows down” the heating development. Current limiting should lie atapproximately 2,5 I/IN,M. Further reduction of limiting is recommended ifstarting times are long and successive warm starts are possible. Forexample, a value of 2 I/IN,M makes sense for a starting time of 52 s (at
0,8 UN).§ Realization: 7UM6
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Restart inhibit function
A time between 15 min and 30 min is recommended if no data is available. The
longer time must be chosen for longer starts.
20 minMinimum restart inhibit
time
A value of 10 is recommended at short starting times. A value of 5 can be
selected at clearly longer starting times. At a starting time of 50s and a setting of
5 the release command for a possible restart is given after approximately 30 min.
10Extension of time constant
at stop
This time is considered practicable and also takes running down to stand still into
consideration.
Note: Restarting of the motor is not possible during this time. The time must be
set to zero if only a blocking is to take place when the thermal limit is reached.
1 minRotor temperature
equalization time,
Take this from the motor data sheet (technical data (3)); if values are missing
assume the value 2.
2Warm starts
Take this from the motor data sheet (technical data (3)); if values are missing
assume the value 3.3Cold starts
Choose the time to the current (technical data (3)).
If the motor starts clearly faster, e.g. in 2,6 s, you can be a little bit generous with
the setting. Here we choose the lowest setting value of 3 s.
3 sStarting time
Take this from motor data sheet – current at rated voltage (technical data (1) and
(3)).
5,65 I/ IN,MStarting currentCommentValueSetting parameters
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Starting time supervision
With reduced voltage the starting current amounts to 3,9 I/
IN,M
.
Due to the lower starting current a value of 2 I/I N,M was
selected.
The typical value of 2,5 I/IN,M
used for standard motors.
2 I/ IN,MStart selection
To this end, the specified starting time must be compared
with the characteristic curve times (technical data 3). Go
below the thermal charac-teristic if there is an adequate safety
clearance. According to the figure in technical data (2) a value
of 9s is permissible in the case of a starting current of 5,65 I/
IN,M
in the warm start state. For this current the motor starting
time is specified as 3 s.
Chosen permissible starting time: 6 s
6 sMaximum permissible
starting time
Take this from the motor data sheet
(technical data (1)).
5,65 I/ IN,MStarting current
CommentValueSetting parameters
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Restart inhibit function
Play with the starting time and starting current to find a compromise for the
setting values.
Use the values at rated voltage and reduced voltage.
Proceeding:
Select the variant with the lowest calculated time constant for safety reasons
2StwcStRotor I)n-(nt≈τ
Data:nc = 3; nw= 2
100% UN
Iat = 5,65tSt = 3 s
70% UN
ISt = 3,9tSt = 10 s
)n-(n
n k wc
cRotor ≈
1,73k Rotor ≈
s95,85,651s3 2Rotor =∗∗≈τ
s1523,91s102
Rotor =∗∗≈τ
Take the values at100 % UN for safetyreasons.
Compromise:Starting can be set to 4s,because a voltage dip is thenormal case during motorstarting (than the rotor time
constant is τ ≈ 128 s)
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Thermal characteristics
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 71
10
100
1 .103
1 .104
Overload coldOverload warmStarting time supervisionLocked rotor warm
rated motor current
t i m e i n s e c o n d
s
5.89 103×
1
t i( )
t v i( )
t A j( )
t Aw j( )
71 i i, j,
Stator overloadcold
warm
Characteristic ofstarting timesupervision
Locked rotor limit(warm)
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Restart inhibit functionStart at 100% voltage
Settings:
nc = 3nw = 2ISt = 5,65 I/In,M
tSt = 3 s
Internalcalculated:Tau = 94,3 skRotor = 1,7
Simulation:
ISt = 5,65tSt = 3 s0 50 100 150 200 250 300 350 400 450
0
0.2
0.4
0.6
0.8
1
Threshold
Rotor temperaturestarting current
Time in second s
R o t o r t e m p e r a t u r e a n d c
u r r e n t i n p . u .
1.2
0
WE ex
Tempi
Ii
4390 i delT⋅
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Restart inhibit functionStart at 70% voltage, blocking is more sensitive
Settings:nc = 3nw = 2ISt = 5,65 I/In,M
tSt = 3 s
Internalcalculated:Tau = 94,3 skRotor = 1,7
Simulation:ISt
= 3,9tSt = 10 s
0 50 100 150 200 250 300 350 400 450 5000
0.5
1
1.5
Threshold
Rotor temperaturestarting current
Time in seconds
R o t o r t e m p e r a t u r e a n d c
u r r e n t i n p . u .
1.5
0
WEex
Tempi
Ii
4600 i delT⋅
After the 2. reclosing theinhibit function will be active.
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Unbalanced load protection
s2000,1
s2
I
I
K t
22
MN,
zul.2,
downCooling ==
=
Use the following relationship:200 sCooling down time of the
thermal model
The conservative setting of 2 s is chosen if the motor manufacturer
does not specify any details. The time really ought to be longer
comparable to synchronous machines is presupposed.
2 sThermal unbalanced load time
((I2 / I
N,M)2 t = K)
(internal designation:
FACTOR K )
Two phase operation under rated condition leads to a negative
sequence current of about 66 %. Due to the power be produced, it
will rise and will certainly reach values of 100%.
A tripping delay of about 3 s is recommended to allow for transient
phenomena.
0,4 I2 / IN,MTripping stage
Unless otherwise is specified this value should be set.
If this stage should also trip, it must be delayed appropriately
(approx. 15 - 30 s);
Suggestion: 20 s.
0,1 I2 / IN,MContinuously permissible
unbalanced load
CommentValueSetting parameters
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Unbalanced load protectionDifferences in the devices
2 definite time negative sequence stages§ Negative sequence current and time delay can be set per stage§ Realization: 7SJ6
Thermal unbalanced load protection§ Reduced thermal model considers the heating and cooling down
(I22 t = K)
§ Model starts with a integration if the negative sequence current is overthe pick-up threshold
§ Realization: 7UM62§
Additional available: 1 alarm stage and 1 definite time stage
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Characteristics unbalanced load protection(negative sequence protection)
0.1 0.2 0.3 0.4 0.51
10
100
1 .103
Negative sequence th ermal K=2s
negative sequence current
t i m e i n s e c o n d s
200
1
3
20
t neg j( )
0.6.01
0.1 0.4
j
Definitetimestages
Thermalcharacteristic