GE P444 User Manual

Application Notes
P44x/EN AP/Hb
6
MiCOM P40 Agile P442, P444
(AP) 5-
117
CBF operation can be used to backtrip upstream circuit breakers to ensure that the fault is
isolated correctly. CBF operation can also reset all start output contacts, ensuring that any
blocks asserted on upstream protection are removed.
The ‘CBF Blocks I>‘ and ‘CBF Blocks IN>‘ settings are used to remove starts issued from the
overcurrent and earth elements respectively following a breaker fail time out. The start is
removed when the cell is set to Enabled.
4.14.1 Typical settings
4.14.1.1 Breaker Fail Timer Settings
Typical time-delay settings to use are as follows:
CB Fail Reset Mechanism tBF time delay
Typical delay for 2½ cycle
circuit breaker
Initiating element reset
CB interrupti
ng time + element reset
time (max.) + error in tBF timer +
safety margin
50 + 50 + 10 + 50
= 160 ms
CB open
CB auxiliary contacts
opening/closing time (max.) + error
in tBF timer + safety margin
50 + 10 + 50
= 110 ms
Undercurrent elements
CB interrupting time + undercurrent
element operating time (max.) +
safety margin
50 + 25 + 50
= 125 ms
Note that all CB Fail resetting involves the operation of the undercurrent elements. Where
element reset or CB open resetting is used the undercurrent time setting should still be used
if this proves to be the worst case.
The examples above consider direct tripping of a 2½ cycle circuit breaker. Note that where
auxiliary tripping relays are used, an additional 10-15 ms must be added to allow for trip
relay operation.
4.14.1.2 Breaker Fail Undercurrent Settings
The phase undercurrent settings (I<) must be set less than load current, to ensure that I<
operation indicates that the circuit breaker pole is open. A typical setting for overhead line or
cable circuits is 20% In, with 5% In common for generator circuit breaker CBF.
4.14.2 Breaker Failure Protection Configurations
Resetting of the CBF is possible from a breaker open indication (from the relay’s pole dead
logic) or from a protection reset. In these cases resetting is only allowed provided the
undercurrent elements have also been reset. The resetting options are summarised in the
following table.
Initiation
(Menu selectable)
CB fail timer reset mechanism
Current based protection -
(eg. 50/51/46/21/87..)
The resetting mechanism is fixed.
[IA< operates] AND
[IB< operates] AND
[IC< operates] AND
[IN< operates]
Non-current based protection
(eg. 27/59/81/32L..)
Three options are available. The user can select from the
following options.
[All I< and IN< elements operate]
[Protection element reset]
AND [All I< and IN< elements operate]
CB open (all 3 poles)
AND [All I< and IN< elements operate]

GE P444 Specifications

General

Brand	GE
Model	P444
Category	Protection Device
Language	English