ABB RELION REX640 Technical Manual page 1042

Protection and control

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Protection functions

The directional negative sequence impedance function is normally used on

incoming line or feeder connected to the busbar, which is made to operate in the

specified direction for secured operation. The fault direction can be either referred

as forward or reverse of the relay.

There are different directional elements used to determine the direction of

faults, one such element is negative sequence impedance. The calculated negative

sequence impedance is sensitive enough to identify fault in power system networks

with strong source where less negative-sequence voltage and current will be present

during faults.

By using suitable restraint factor, it is also possible to avoid false tripping with

systems having un-transposed lines where some default negative sequence current

will be present during normal operation.

Application example

Relay setting calculation for the DNZPDIS function is shown with below application

example of parallel lines with two end sources of power system network.

Figure 580: Power system network with parallel line and two sources

Setting value calculation

Line parameters:

Total impedance (Z

tot = (0.126 + j0.60 ohm/km) * 100 km

Magnitude of positive sequence impedance (Z

settings are obtained to set the relay located at circuit breaker 1(CB1).

Resistance = 0.126 ohm/km

Reactance = 0.600 ohm/km

Line length = 100 km

tot) of line1 or line2 is calculated below

= 12.6 + j60.1 in ohm

Forward fault

Reverse fault

tot) = 60.4 ohm. The following

1MRS759142 F

(Equation 279)

Technical Manual