Software-Monitoring; Monitoring Of The External Instrument Transformer Circuits - Siemens SIPROTEC 7SA6 Manual

Distance protection relay for all voltage levels

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Table of Contents

6.21.1.2 Software–Monitoring

Current Symmetry

The voltage sum monitoring is only effective if the measuring input U

a displacement voltage which was generated externally.

For the continuous monitoring of the program execution, a time monitoring is incorpo-

rated in the hardware (hardware watchdog). The watchdog expires and resets the

processor system causing a complete reboot if the processor fails or when a program

loses synchronism.

A further software–watchdog ensures that errors in the program execution are detect-

ed. This watchdog also initiates a reset of the processor.

If a fault is not removed by the restart of the processor system, a new restart is at-

tempted. Following three failed restarts within 30 s the protection takes itself out of

service and the red LED "ERROR" is illuminated. The device ready relay resets and

alarms the device failure state with its normally closed contact.

Interruptions or short circuits in the secondary circuits of the current and voltage trans-

formers, as well as incorrect terminations (important during commissioning) are large-

ly recognized by the device and alarmed. To this end, the measured values are cycli-

cally checked in the background as long as no fault detection is present.

During normal system operation, a certain degree of current symmetry can be as-

sumed. This symmetry is checked in the device by means of a magnitude monitoring.

The smallest phase current is compared with the largest. Non-symmetry is detected

| < BAL. FACTOR I

is the largest and I

factor BAL. FACTOR I is a measure of the phase conductor non-symmetry, the

threshold value BALANCE I LIMIT represents the lower limit of the operating range

of this monitoring function (refer to Figure 6-140). Both parameters can be set. The

reset ratio is approx. 97 %.

This failure is alarmed by " Fail I balance ".

> BALANCE I LIMIT / I

is the smallest of the three phase currents. The symmetry

is connected to

C53000-G1176-C156-2