EMR-5000
IM02602012E
ZI - Zone Interlocking
Elements
ZI
Principle – General Use
The purpose of zone interlocking is to speed up tripping for some faults without sacrificing the coordination of the
system and interjecting nuisance trips into the system. Zone interlocking devices can communicate across distribution
zones to determine whether or not a device sees a fault condition.
Zone interlocking is a communication scheme used with breakers and protective relays to improve the level of
protection in a power distribution system. This is achieved through communication between the downstream and
upstream devices in a power system. The zones are classified by their location downstream of the main circuit
protective device which is generally defined as Zone 1.
By definition, a selectively coordinated system is one where by adjusting the trip unit pickup and time delay settings, the
breaker closest to the fault trips first. The upstream breaker serves two functions: (1) back-up protection to the
downstream breaker and (2) protection of the conductors between the upstream and downstream breakers.
For faults which occur on the conductors between the upstream and downstream breakers, it is ideal for the upstream
breaker to trip with no time delay. This is the feature provided by Zone Selective Interlocking.
The zone interlocking information can be transferred to or received from other compatible zone interlocking devices by
means of suitable communication cables. The single zone interlock terminal block, with its 3-wire scheme, can be used
for either phase zone interlocking, ground zone interlocking, or a combination of the two. If phase and ground zone
interlocking are combined, the potential consequences must be understood before implementation.
Systems containing multiple sources, or where the direction of power flow varies, require
special considerations, or may not be suitable for this feature.
The breaker failure pickup signal »BF.P
ICKUP
« is implicitly connected to zone interlocking,
so that NO zone interlock output signal can be sent to the upstream device if a breaker
failure on a downstream device is detected.
Description of the Functions and Features
Configurable protection functions to initiate the zone interlocking OUTPUT signal (start functions).
Remove zone interlocking OUTPUT signal immediately after detection of a breaker failure.
Reset time (about ten cycles - settable) to interrupt OUTPUT signal for durable trip signal.
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