5. Technical description
5.1. Functional description
5.1.4. Protection
5.1.4.9. Inverse definite minimum time
The low-set overcurrent and ground-fault elements can be given an inverse definite minimum time (IDMT) characteristic. At IDMT characteristic, the operate time of the element is dependent on the current value: the higher the current value, the shorter the operate time.
The relay provides nine IDMT characteristics, of which four comply with the IEC 60255-3 and three with the IEEE C37.112 standard. Two are special characteristics according to ABB praxis and are referred to as RI and RD.
The time/current characteristics can be selected either via the HMI or the SPA bus as follows:
Table 5.1.4.9.-1 Time/current characteristic settings Value Time/current characteristic
0 Definite time
1 IEC Extremely inverse 2 IEC Very inverse 3 IEC Normal inverse 4 IEC Long-time inverse
5 RI-type
6 IEEE Extremely inverse 7 IEEE Very inverse 8 IEEE inverse 9 RD-type (RXIDG)
IDMT characteristics according to IEC 60255-3
The relay provides four time/current curve groups which comply with the IEC 60255-3 standard: normal inverse, very inverse, extremely inverse and long-time inverse. The relationship between long-time and current is expressed as follows:
t s
[ ]
=⎛⎝⎜Mαβ−1⎞⎠⎟×TD (4)t = operate time
M = multiplies of pickup current TD = time dial
The actual operate time of the relay (see Fig. 1...Fig. 5.1.4.9.-4) includes an additional filter and detection time and the operate time of the trip output contact. When the operate time of the relay is calculated as above, approximately 30 ms should be added to the result t.
Table 5.1.4.9.-2 Values of constantsα and β
Time/current curve group α β
Normal inverse 0.02 0.14
Very inverse 1.0 13.5
Extremely inverse 2.0 80.0
Long-time inverse 1.0 120
According to the standard, the normal current range is 2...20 times the set pickup value at normal inverse, very inverse or extremely inverse characteristic. The relay is to start before the current exceeds the set pickup value by 1.3 times. At long-time
inverse characteristic, the normal current range is specified to be 2...7 times the set pickup value, and the relay is to start before the current exceeds the set pickup value by 1.1 times
Table 5.1.4.9.-3 Operate time tolerances specified by the standard
Ma) Normalb) Veryb) Extremelyb) Long timeb)
2 2.22E 2.34E 2.44E 2.34E
5 1.13E 1.26E 1.48E 1.26E
7 - - - 1.00E
10 1.01E 1.01E 1.02E
-20 1.00E 1.00E 1.00E
-a)Multiples or pickup current (a phase and ground)
b)E = accuracy in percent; - = not specified
Within the normal current range the inverse-time element fulfills the tolerance requirements of class 5 or ±25 ms at all degrees of inversity.
The time/current curve groups based on the IEC standard are illustrated in Fig. 5.1.4.9.-1...Fig. 5.1.4.9.-4.
If the ratio between the current and the set pickup value is higher than 20, the operate time is the same as when the ratio is 20.
TD
0.2 0.3 0.4 0.5 0.6 0.70.8 0.91 2 3 4 5 67 89 10 20 30 40 70 60 50 t/s
1 2 3 4 5 6 7 8 910 20
0.02 0.03 0.04 0.05 0.06 0.070.08 0.090.1
0.05 0.1 0.2 0.3 0.4 0.6 0.8 1.0
0.5 0.7 0.9
CURRENT IN MULTIPLES OF SETTING
A070033
Fig. 5.1.4.9.-1 Normal inverse-time characteristic
TD
0.2 0.3 0.4 0.5 0.6 0.70.8 0.91 2 3 4 5 67 89 10 20 30 40 70 60 50 t/s
1 2 3 4 5 6 7 8 910 20
0.02 0.03 0.04 0.05 0.06 0.070.08 0.090.1
0.05 0.1 0.2 0.3 0.4 0.6 0.8 1.0
0.7 0.5 0.9
CURRENT IN MULTIPLES OF SETTING
A070034
Fig. 5.1.4.9.-2 Very inverse-time characteristic
TD 0.2
0.3 0.4 0.5 0.6 0.70.8 0.91 2 3 4 5 67 89 10 20 30 40 70 60 50 t/s
1 2 3 4 5 6 7 8 910 20
0.02 0.03 0.04 0.05 0.06 0.070.08 0.090.1
0.05 0.1 0.2 0.3 0.4 0.6 0.8 1.0
CURRENT IN MULTIPLES OF SETTING
A070035
Fig. 5.1.4.9.-3 Extremely inverse-time characteristic
2 3 4 5 6 78 109 20 30 40 50 6070 8090 100 200 300 400 700 600 500 t/s
TD
1 2 3 4 5 6 7 8 910 20
0.2 0.3 0.4 0.5 0.60.7 0.80.91
0.05 0.1 0.2 0.3 0.4 0.7 1.0
0.5 0.6 0.80.9
CURRENT IN MULTIPLES OF SETTING
A070036
Fig. 5.1.4.9.-4 Long-time inverse-time characteristic
IDMT characteristics according to the IEEE C37.112
REF610 provides three time/current curve groups which comply with the IEEE C37.112 standard: extremely inverse, very inverse and inverse. The relationship between time and current is expressed as follows:
t s A
Mp B TD
[ ]
=( )
− +⎛
⎝
⎜⎜
⎞
⎠
⎟⎟×
1 (5)
t = operate time
M = multiplies of pickup current
TD = time dial
The actual operate time of the relay (see Fig. 5...Fig. 5.1.4.9.-7) includes an additional filter and detection time and the operate time of the trip output contact. When the operate time of the relay is calculated as above, approximately 30 ms should be added to the result t.
Table 5.1.4.9.-4 Values of constants A, B and P
Time/current curve group A B P
Extremely inverse 6.407 0.025 2.0
Very inverse 2.855 0.0712 2.0
Inverse 0.0086 0.0185 0.02
The time/current curve groups based on the IEEE standard are illustrated in Fig. 5.1.4.9.-5...Fig. 5.1.4.9.-7.
0.2 0.3 0.4 0.5 0.6 0.70.8 0.91 2 3 4 5 6 78 109 20 30 40 70 60 50 t/s
TD
1 2 3 4 5 6 7 8 910 20
0.02 0.03 0.04 0.05 0.06 0.070.08 0.090.1
1 2 3 4 5 6 8 15 10 12
CURRENT IN MULTIPLES OF SETTING
A070050
Fig. 5.1.4.9.-5 Extremely inverse-time characteristic
0.2 0.3 0.4 0.5 0.60.7 0.80.91 2 3 4 5 6 78 109 20 30 40 70 60 50 t/s
TD
1 2 3 4 5 6 7 8 910 20
0.02 0.03 0.04 0.05 0.06 0.070.08
0.090.1 1
2 3 4 5 6 8 15 10 12
CURRENT IN MULTIPLES OF SETTING
A070051
Fig. 5.1.4.9.-6 Very inverse-time characteristic
TD
0.2 0.3 0.4 0.5 0.6 0.70.8 0.91 2 3 4 5 6 78 109 20 30 40 70 60 50 t/s
1 2 3 4 5 6 7 8 910 20
0.02 0.03 0.04 0.05 0.06 0.070.08 0.090.1
1 2 3 4 5 6 8 15 10 12
CURRENT IN MULTIPLES OF SETTING
A070052
Fig. 5.1.4.9.-7 Inverse-time characteristic
RI-type characteristic
The RI-type characteristic is a special characteristic which is principally used for obtaining time grading with mechanical relays. The relationship between time and current is expressed as follows:
t s TD
M
[ ]
=− ×
0 339 0 236 1
. . (6)
t = operate time
M = multiplies of pickup current
TD = time dial
The actual operate time of the relay (see Fig. 5.1.4.9.-8) includes an additional filter and detection time and the operate time of the trip output contact. When the operate time of the relay is calculated as above, approximately 30 ms should be added to the result t.
The RI-type characteristic is illustrated in Fig. 5.1.4.9.-8.
TD
0.2 0.3 0.4 0.5 0.60.7 0.80.91 2 3 4 5 67 89 10 20 30 40 70 60 50 t/s
1 2 3 4 5 6 7 8 910 20
0.02 0.03 0.04 0.05 0.06 0.070.080.090.1
0.05 0.2 0.3 0.4 0.5 0.6 0.7 1.0 0.80.9
0.1
CURRENT IN MULTIPLES OF SETTING
A070038
Fig. 5.1.4.9.-8 RI-type characteristic
RD-type characteristic (RXIDG)
The RD-type characteristic is a special characteristic, which is principally used in ground-fault protection and which requires a high degree of selectivity even at high resistance faults. The protection can operate in a selective way even if it is not directional. Mathematically, the time/current characteristic can be expressed as follows:
t s M
e TD
[ ]
=5 8 1 35. − . ×log ⎛⎝⎜ ⎞⎠⎟ (7)t = operate time
M = multiplies of pickup current
TD = time dial
The actual operate time of the relay includes an additional filter and detection time and the operate time of the trip output contact. When the operate time of the relay is calculated as above, approximately 30 ms should be added to the result t.
If the ratio between the current and the set start value is higher than 40, the operate time will be the same as when the ratio is 40.
The RD-type characteristic is illustrated in Fig. 5.1.4.9.-9.
0.2
CURRENT IN MULTIPLES OF SETTING TD
A070037
Fig. 5.1.4.9.-9 RD-type inverse-time characteristic