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2 Functions

302

7SA522 Manual

C53000-G1176-C155-3

(Figure 2-125 left). This input initiates the breaker failure protection even if no current

flow is detected.

Common Phase

Initiation

Common phase initiation is used, for example, for lines without automatic reclosure,

for lines with only three-pole automatic reclosure, for transformer feeders, or if the bus-

bar protection trips. This is the only available initiation mode if the actual 7SA522

model is able to trip three-pole only.

If the breaker failure protection is intended to be initiated by further external protection

devices, it is recommended, for security reasons, to connect two binary inputs to the

device. Besides the trip command of the external relay to the binary input ´!%)

6WDUWSROHµ FNo.1415 it is recommended to connect also the general device

pickup to binary input ´!%)UHOHDVHµ FNo.1432. For Buchholz protection it is rec-

ommended that both inputs are connected to the device by two separate wire pairs.

Nevertheless, it is possible to initiate the breaker failure protection in single-channel

mode should a separate release criterion not be available. The signal ´!%)

UHOHDVHµ (FNo. 1432) must then not be assigned.

Figure 2-125 shows the operating principle. When the trip signal appears from any in-

ternal or external feeder protection and at least one current flow criterion (according

to Figure 2-122) is present, the breaker failure protection is initiated and the corre-

sponding delay time(s) is (are) started.

If the current criterion is not fulfilled for any of the phases, the position of the circuit

breaker auxiliary contact(s) is queried provided that this is available according to

Figure 2-124. If the circuit breaker poles have individual auxiliary contacts, the series

connection of the three normally closed (NC) auxiliary contacts is used. The circuit

breaker has operated correctly after a three-pole trip command only when none of the

phases carries current or when all three NC auxiliary contacts have closed.

Figure 2-124 illustrates how the internal signal “CB pole ≥L1 closed” is created (see

Figure 2-125 left) if at least one circuit breaker pole is closed.

Figure 2-124 Creation of signal "CB ≥ any pole closed"

If an internal protection function or an external protection device trips without current

flow, the internal input “Start internal w/o I” or the external input is used to initiate the

breaker failure protection via the binary input ´!%)6WDUWZR,µ. In this case, the

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