Section 4
1MAC050144-MB C
Protection functions
308
615 series ANSI
Technical Manual
However, in case of unbalanced phase currents, the negative sequence current also causes
additional heating. By deploying a protection based on both current components, abnormal
heating of the motor is avoided.
The thermal load is calculated based on different situations or operations and it also
depends on phase current level. The equations used for the heating up calculations are:
(Equation 20)
(Equation 21)
I
TRMS value of the measured max of phase currents
Ir
set Rated current, FLC or internal FLC
I2
measured negative sequence current
k
set value of
Overload factor
K2
set value of
Negative Seq
factor
p
set value of
Weighting factor
τ
time constant
The equation
Θ
B
is used when the values of all the phase currents are below the overload
limit, that is, k x I
r
. The equation
Θ
A
is used when the value of any one of the phase
currents exceeds the overload limit.
During overload condition, the thermal level calculator calculates the value of
Θ
B
in
background, and when the overload ends the thermal level is brought linearly from
Θ
A
to
Θ
B
with a speed of 1.66 percent per second. For the motor at standstill, that is, when the
current is below the value of 0.12 x I
r
, the cooling is expressed as:
(Equation 22)
Θ
02
initial thermal level when cooling begins
B
r
r
t
I
k I
K
I
k I
e
p
=
×
⎛
⎝
⎜
⎞
⎠
⎟ +
×
×
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
× −
(
)
×
−
2
2
2
2
1
/
%
A
r
r
t
I
k I
K
I
k I
e
=
×
⎛
⎝
⎜
⎞
⎠
⎟ +
×
×
⎛
⎝
⎜
⎞
⎠
⎟
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
× −
(
)
×
−
2
2
2
2
1
100
/
%
=
×
−
02
e
t
Содержание 615 Series ANSI
Страница 1: ...Relion Protection and Control 615 series ANSI Technical Manual ...
Страница 2: ......
Страница 29: ...1MAC050144 MB C Section 615 series ANSI 22 Technical Manual ...
Страница 389: ...Section 4 1MAC050144 MB C Protection functions 382 615 series ANSI Technical Manual ...
Страница 485: ...Section 6 1MAC050144 MB C Supervision functions 478 615 series ANSI Technical Manual ...
Страница 635: ...Section 10 1MAC050144 MB C Other functions 628 615 series ANSI Technical Manual ...
Страница 707: ...Section 15 1MAC050144 MB C Applicable standards and regulations 700 615 series ANSI Technical Manual ...
Страница 711: ...Section 16 1MAC050144 MB C Glossary 704 615 series ANSI Technical Manual ...
Страница 712: ......