Zone selective interlocking with AQ-200 devices

Zone selective interlocking with AQ-200 devices

GENERAL INFORMATION ABOUT ZONE SELECTIVE INTERLOCKING

WHAT IS ZONE SELECTIVE INTERLOCKING?

Zone Selective Interlocking (ZSI) is a communication scheme used with electronic trip units and protection relays for circuit breakers 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 distribution system. The zones are classified by their location downstream of the main circuit protective device which is generally defined as zone 1. Interlocking may be applied to faults between phases and/or faults to earth. This document will review Arcteq protective devices that utilize zone interlocking protection, connections and common practices.

WHAT IS THE PURPOSE OF ZONE SELECTIVE INTERLOCKING?

The purpose of ZSI is to speed up tripping for overcurrent faults without sacrificing the selectivity of the system. Zone selective interlocked devices can communicate across zones to determine which devices sees the fault condition. The device that is closest to the fault will trip without an intentional time delay and therefore reducing the fault clearing time and reducing the damage to the equipment. The advantages of ZSI increase with a higher number of grading levels, since time-based selectivity can result in unacceptably long delays at the supply end of the system.

Schematic diagram of an installation designed for multiple supplies with zone selective interlocking:


Example A – Short-circuit at position F3:
Circuit breakers Q1, Q2, Q3, Q5 and Q7 register a short-circuit. Q7 blocks Q5 by
means of the ZSI signal and, in consequence, Q1, Q2, and Q3 too, so that they do not trip
for I> with 50ms. Since Q7 does not receive a blocking signal from a subordinate circuit breaker, Q7 itself is responsible for interrupting the short-circuit as quickly as possible.
As an additional feature in the event of a problem with breaker Q7 (e.g. because Q7 is no
longer operational) then Q5, as a back-up, trips after its short time delay setting, I>> with 150ms.

Example B – Short-circuit at position F2:
Circuit-breakers Q1, Q2, Q3, and Q5 register a short-circuit; Q7 does not. For this reason,
Q5 does not receive a blocking signal from Q7, but provides a blocking signal to Q1, Q2,
and Q3. This information tells Q5, that it is the closest breaker upstream of the short-circuit and Q5 trips, with a delay of I> with 50ms instead of a delay of I>> 150ms. Clearance time is reduced by 100ms.

Example C – Short-circuit at position F1:
Only circuit-breakers Q1, Q2, and Q3 register a short-circuit and they do not receive a
blocking signal from any circuit-breaker at a subordinate grading level. For this reason, Q1, Q2 and Q3 trip after I> with 50ms. Time saved: 250ms.

ZONE SELECTIVE INTERLOCKING METHODS

There is two ways to implement the communication between downstream and upstream relays: First one is hardwired signaling from relays physical output contact to another relays digital input, second method of implementation is goose messaging when relays are connected to the same ethernet network with IEC61850 Goose capable relays.

ZONE SELECTIVE INTERLOCKING IN PRACTICE

HARDWIRED SIGNALING

This solution requires hardwiring between the relays involved in ZSI application. Downstream relay I> start signal contact is connected to the upstream relay digital input. Same thing is done to Io> start signal but different signal contact and digital inputs are used to tell the difference between the fault type.

Example of hardwired signalling:

Downstream relay Q1 I> operation time settings:


Downstream relay Q1 I> output settings:


Upstream relay Q0 I> operation time settings:


Upstream relay Q0 I> blocking input control:


Downstream relay Q1 Io> operation time settings:


Downstream relay Q1 Io> output settings:


Upstream relay Q0 Io> operation time settings:


Upstream relay Q0 Io> blocking input control:


GOOSE SIGNALING

This solution requires that relays involved in ZSI application are connected to the same ethernet network to allow goose messaging between relays. Downstream relay I> start signal is sent via goose message to upstream relays. Same thing is done to Io> start signal but different goose message is used to tell the difference between the fault type.

Example of GOOSE signaling:


Downstream relay Q1 I> operation time settings:


Upstream relay Q0 I> operation time settings:


Downstream relay Q1 Io> operation time settings:


Upstream relay Q0 Io> operation time settings:


Downstream relay Q1 I> output settings:


Downstream relay Q1 Io> output settings:


Downstream relay Q1 application ID setting for GOOSE publisher 1:


Downstream relay Q1 I> start and Io> start goose sending:


Upstream relay Q0 I> blocking input control:


Upstream relay Q0 Io> blocking input control:


Upstream relay Q0 goose subscriber:

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