Electricity and Control September 2023

DRIVES, MOTORS + SWITCHGEAR : PRODUCTS + SERVICES

No unnecessary downtime with ZSI

When a fault occurs in a power distribution system, time is of the essence. Circuit breakers must react quickly and accurately if they are to limit service interruption, prevent equipment damage, and safeguard people. Zone Selectivity Interlocking (ZSI) goes beyond time selectivity and current selectivity to ensure faults are iso lated instantaneously, where they occur. So, the rest of the system – and the business – keeps running. ZSI is a key feature of Eaton’s NZM line of digital circuit breakers. Zone Selectivity Interlocking serves to speed up trip ping for some faults without sacrificing the coordination of the system or interjecting nuisance trips. Zone interlock ing devices can communicate across distribution zones to determine whether or not a device sees a fault condition. The ZSI function is optional on PXR 25 electronic trip units and can be enabled or disabled through the menu system or Eaton’s Power Xpert Protection Manager software. When ZSI is enabled, a fault within the zone of protec tion will immediately trip the breaker and send a signal to upstream trip units to restrain them from tripping immedi ately. The restraining signal causes the upstream circuit breakers to follow their expected set coordination time de lays, so the service is interrupted to the isolated fault area only and the fault is cleared in the shortest time possible.

The advantage of the zone selectivity feature, com pared to standard time-delayed selectivity, is the signifi cantly reduced delay time before tripping. This reduces the thermal and dynamic load, also protecting the sys tem. For additional safety of maintenance staff, Eaton recommends combining ZSI with maintenance mode ARMS™ (Arcflash reduction maintenance system™) to further reduce the amount of energy released. In cases of a signal wire damage the standard time-delayed selectivity function ensures the selectivity of the system. The drawing shows the principle of zone selective interlocking with three zones.

For more information contact Eaton SA. Visit: www.eaton.com/za/en-gb

SEPTEMBER 2023 Electricity + Control

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