ABB RELION REF610, Техническое справочное руководство

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When the thermal capacity, influenced by the thermal history of the cable, exceeds
the set alarm level, 49 ALARM, the element will generate an alarm signal. The
thermal alarm can be used to avoid unnecessary tripping due to a beginning
overload. The thermal level at various constant currents are presented in the table
below:
Table 5.1.4.4.-1 Thermal level at constant currents
I/FLA Thermal level (%)
1.0 90.7
0.9 73.5
0.8 58
0.7 44.4
0.5 22.7
0.3 8.2
0 0
When the thermal capacity exceeds the trip level, the element will generate a trip
signal. The operate time, i.e. the time from when the element picks up until it trips,
is determined by the time constant,
τ
, and depends on the cable (cable cross section
area and cable rated voltage). The time constant is provided by the cable
manufacturer. For a 22 kV cable, the typical time constant is 20 minutes. For operate
times, see Fig. 5.1.4.4.-1...Fig. 5.1.4.4.-3. The operate time is calculated as follows:
t
I
FLA
I
FLA
I
FLA
p
= ×
⎛
⎝⎜ ⎞
⎠⎟
−
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝⎜ ⎞
⎠⎟
−
⎫
⎬
⎪
⎪
⎭
⎪
⎪
⎧
⎨
⎪
τ
ln
.
2
2
2
1 1025
⎪⎪
⎩
⎪
⎪
(2)
I = phase current value
FLA = set full load current
I
p
= prior load current
t = operate time (in minutes)
τ
= time constant (in minutes)
ln = natural logarithm
At power up, the thermal level will be set to 75 percent of the thermal capacity of
the cable. This will ensure that the element will trip within a safe time span in case
of an overload. The calculated thermal level will approach the thermal level of the
cable.
Element 49 can be set out of operation in SGF3. This state will be indicated by
dashes on the LCD and by
“
999
”
when the set full load current is read via serial
communication.
At an alarm level below 75 percent, connecting the auxiliary supply to
the relay will cause a thermal alarm due to the initialization of the
thermal level to 75 percent of the thermal capacity of the cable. The
thermal level can be reset via the HMI during power up.
Feeder Protection Relay
Technical Reference Manual - ANSI Version
REF610 REF610
1MRS755535