ABB RELION REX640 Technical Manual page 1257

Protection and control

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1MRS759142 F

Figure 715: Simplified functional diagram of the blocking scheme, external fault

The unblocking function used with the blocking function provides a possibility to

supervise the communication channel. In this case, the CRL output signal is used as

a local blocking signal.

Directional comparison unblocking scheme DCUB

The unblocking function is a complementary logic which can be used together

with the permissive communication schemes. In the unblocking scheme, the

dependability of the permissive schemes is improved by using the loss of guard

signal from the communication equipment to create a CRL output signal locally. This

enables the permissive scheme to operate even if the communication channel is

interrupted or lost.

The unblocking function uses a carrier guard signal which must always be present.

The absence of the CRG signal for a time longer than the value of the

time setting generates a logical CRL signal. A communication failure shorter than

the value of the

The unblocking function is configured with the

Unblock mode = "Off": The unblocking function is disabled.

Unblock mode = "Permanent": If the CRG signal disappears for a longer time

than defined in the

generated. The CRL output signal remains active until the CRG signal reappears.

The communication failure is not signaled by the LCG output.

Technical Manual

The operation mode

recommended as the blocking is activated only for 150 ms after the

guard signal disappears. This results in an unwanted operation of the

Loss of carrier time setting is always ignored.

Loss of carrier time setting, the logical CRL signal is

Unblock mode = "Time window" is not

Unblock mode setting.

Protection related functions

Loss of carrier