ABB RELION REX640 Technical Manual page 645

Protection and control

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1MRS759142 F

Operation principle

The function can be enabled and disabled with the

corresponding parameter values are "On" and "Off".

The function can also be set into test mode by setting the

"test/blocked".

The operation of the line differential protection and related measurements,

stabilized and instantaneous stages can be described using a module diagram.

I3P (remote)

Figure 361: Functional module diagram. I_LOC_x stands for current of the local end and I_REM_x for

phase currents of the remote ends.

Stabilized low stage

In the stabilized low stage, the higher the load current is, the higher the differential

current required for tripping is. This happens on normal operation or during

external faults. When an internal fault occurs, the currents on both sides of the

protected object flow towards the fault and cause the stabilizing current to be

considerably lower. This makes the operation more sensitive during internal faults.

The low stage includes a timer delay functionality.

The characteristic of the low stage taking the apparent differential current into

account is influenced by various factors:

• Small tapped loads within the protection zone

• Current transformer errors

• Current transformer saturation

• Small asymmetry of the communication channel go and return paths

• Small steady state line charging current

• In-zone transformer no load current

• Impact of tap changer positions

Technical Manual

Differential

Transformer vector

group matching

Zero-sequence

component elimination

Operation setting. The

Operation setting to

Protection functions