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Traditionally, selective coordination requires setting the pickup on the upstream breaker above the available fault current or slower than the clearing time of downstream devices. Figure 1. These settings will be in effect until a downstream feeder circuit breaker sends a restraint signal. This time for most low voltagepower circuit breaker is around 50ms. For a fault downstream of the feeder circuit breaker, the trip unit of this feeder circuit breaker willsend a restraint signal to the trip unit of the main circuit breaker and will then trip to clear thefault within the programmed time. The short time, the Page 3 of 7 ground fault and instantaneous protection of the trip unit on the main circuit breakers would staywhere they were programmed, at the minimum possible values and clear the fault.
A newer technology like GE‟s zone selective interlocking with Instantaneous protection (I-ZSI) enabled all the time has been developed to provide safety.
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Also referred as blocking signal or ZSI signal. A logic signal transmitted from one overcurrent device to another to alter the protective behavior of a circuit breaker. Last month, we discussed GE's EntelliGuard Trip Unit, which featured I-ZSI and WFR technologies. For a more in-depth look at how these.
The way ZSI works is downstream breakers that sense fault current signal the upstream breakers to let them know they are sensing and reacting to the fault current.
It adds the Secondstwo measured peak values and if the resultantvalue is double the threshold, it will pick-up and 1.
Zone selective interlocking on Instantaneousrequires that the trip units be connected by twisted pair copper cables and enables the arc flashenergy level to be reduced to a very low value in the switchgear and switchboard. For a fault within the equipment, between the main and feeder circuit breakers, there would beno restraint signal from any of the trip units on the feeder circuit breakers and the short timedelay and the ground fault delay of the trip unit on the main circuit breaker would automaticallyreduce from the set value to the minimum possible delay of ms.
Set the trip unit of the main circuit breaker to the ZSI restraint setting as shown in Figure 2 — Restraint.
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I-ZSI simultaneously provides arc fault protection and instantaneous selectivity, which GE claims is an industry first.
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In either case, thesum of the two peaks will be much less thandouble the threshold and therefore the trip unitwill not commit to trip.
They do not respond tothe signal in the instantaneous region of thefault Figure 3. Darrin Bock is senior product manager for low voltage power circuit breakers, and Bhavika Shah is commercial leadership program for low voltage power circuit breakers at GE Energy Services www.
Shota Rustaveli National Science Foundation (Georgia) // ZSI Centre for Social Innovation
Add to this the signal processing time, operation of Page 4 of 7. The way ZSI works is downstream breakers that sense fault current signal the upstream breakers to let them know they are sensing and reacting to the fault current. Although the trip unitcommits later than other trip units, it clears thefault in the same time as other circuit breakers.
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Connect the trip units of the downstream feeder circuit breakers to the upstream main circuit breaker using twisted pair copper conductors to provide the restraint signal.
For a fault within the equipment, between the main and feeder circuit breakers, there would beno restraint signal from any of the trip units on the feeder circuit breakers.  Safety organizations, local authorities, and owner-operators demand better personnel protection and state-of-the-art capabilities to minimize hazards while simultaneously preserving power flow to critical loads as reliably as possible. However, the performance that was acceptable in the past may no longer be good enough.  ZSI has existed in ground fault and short-time protection for many years allowing upstream breakers that would otherwise have been set to operate very slowly to have shorter delays for ground fault and short time. Creation Tutorial. No Text Content! |