GE P743 - Circuit Breaker Fail and Undercurrent Function

Settings
P74x/EN ST/N
a7
MiCOM P74
1, P742, P743
(ST) 4-
21
ST
Menu Text Default Setting
Setting Range
Step Size
Min. Max.
Ι
N
>1 Current Set 0.30*Ι
n
0.10*Ι
n
32.00*Ι
n
0.01*Ι
n
Pick-up setting for the first stage earth fault element.
Ι
N
>1 Time Delay
1.00s 0.00s 100.00s 0.01s
Time-delay setting for the first stage definite time element.
Ι
N
>1 TMS
1.000 0.025 1.200 0.025
Setting for the time multiplier setting to adjust the operating time of the IEC IDMT
characteristic.
Ι
N
>1 Time Dial
7.0 0.5 15.0 0.1
Setting for the time multiplier setting to adjust the operating time of the IEEE/US IDMT
curves.
Ι
N
>1 Reset Char
DT DT/Inverse
Setting to determine the type of reset/release characteristic of the IEEE/US curves.
Ι
N
>1tReset
0.0 0.0 100.0 0.1
Setting to determine the reset/release time for definite time reset characteristic.
Ι
N
>2 Function
Disabled
Disabled / 87BBP&N blocking / High Set I>2 / I>2 &
87BBP&N / 87BB/P blocking / 87BB/N blocking /
I>2 & 87BB/P / I>2 & 87BB/N
Setting to en
able or disable the second stage definite time element. If the function is
disabled, then all associated settings with the exception of this setting, are hidden.
The overcurrent can be used as high set overcurrent, to block the 87BB protection for
phase an
d earth fault element (87BBO&N blocking) , only the 87BB phase element
(87BB/P blocking), only the 87BB SEF element (87BB/N blocking), or a combination of the
different functions
Ι
N
>2 Current Set 20.00* Ι
n
0.10*Ι
n
32.00* Ι
n
0.01* Ι
n
Pick-up setting for the second stage earth fault element.
Ι
N
>2 Time Delay
1.00s 0.00s 10.00s 0.01s
Setting for the operating time delay for the second stage earth fault element.
Block Drop-Off 0.3s 0.2s 6s 0.1s
Adjust the differential busbar protection (87BB) blocking function during drop-off time from
200ms to 6s.
1.2.7 Circuit breaker fail and undercurrent function (“CB Fail” column – P742/P743)
This function consists of two-stage circuit breaker fail functions that can be initiated by:
• Internal protection element initiation.
• External protection element initiation.
For current-based protection, the reset condition is based on undercurrent operation to
determine that the CB has opened. For the non-current based protection, the reset criteria
may be selected by means of a setting for determining a CB Failure condition.
It is common practice to use low set undercurrent elements in protection relays to indicate
that circuit breaker poles have interrupted the fault or load current, as required.