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Section 7. Protection
Section 7. Protection
current sensors are required; Entellisys uses the
current sensors are required; Entellisys uses the
same current sensors that are provided in each
same current sensors that are provided in each
breaker cubicle for overcurrent protection and
breaker cubicle for overcurrent protection and
metering functions. The current sensors used in
metering functions. The current sensors used in
Entellisys will permit accurate identification of the
Entellisys will permit accurate identification of the
faulted circuit with as little as 1 ampere difference
faulted circuit with as little as 1 ampere difference
between the pulsed current and the ground current
between the pulsed current and the ground current
on an 800A frame feeder breaker. The pulsing sys-
on an 800A frame feeder breaker. The pulsing sys-
tem can also be operated manually from the HMI
tem can also be operated manually from the HMI
to faclitate location of a ground fault in equipment
to faclitate location of a ground fault in equipment
downstream of the Entellisys switchgear
downstream of the
Entellisys switchgear. .
Zone Selective Interlocking (ZSI) - short time and
Zone Selective Interlocking (ZSI) - short time and
ground fault
ground fault
The Entellisys system provides a zone-selective
The Entellisys system provides a zone-selective
interlocking function similar to that offered in many
interlocking function similar to that offered in many
electronic trip systems. However
electronic trip systems.
based ZSI system offers significant improvements
based ZSI system offers significant improvements
over the traditional
over
the traditional method. Its
method. Its capabilities i
the following:
the following:
• • Zone-s
Zone-select
elective
ive inter
interlocki
locking for up t
or levels.
or levels.
• • Contr
Control of trippi
ol of tripping with time band
ng with time bands as fast as
1.5 cycles.
1.5 cycles.
• • Full functionality
Full functionality with no
with no extra wiring o
• • Operati
Operation at any programme
on at any programmed delay for faults
within a zone of protection.
within a zone of protection.
• • Changing ZSI circuit
Changing ZSI circuit breaker relations
breaker relationships (tiers)
depending on which mains and ties are closed.
depending on which mains and ties are closed.
• • Delay increments of
Delay increments of 100 ms per level
100 ms per level to achieve
selectivity and maintain good backup protection.
selectivity and maintain good backup protection.
The zones for ground-fault protection are the same
The zones for ground-fault protection are the same
as as those for
those for multi-source
multi-source grounding pr
Within each zone and for each different topology,
Within each zone and for each different topology,
the circuit breakers are divided into tiers. Each tier
the circuit breakers are divided into tiers. Each tier
represents the time-delay hierarchy required to
represents the time-delay hierarchy required to
achieve
achieve optimum protec
optimum protection and
circuit breaker may be assigned to one of four tiers
circuit breaker may be assigned to one of four tiers
within a zone. The top tier is always labeled tier 0.
within a zone. The top tier is always labeled tier 0.
Next is tier 1, then tier 2, with the last and lowest
Next is tier 1, then tier 2, with the last and lowest
defined as tier 3. Hence, in a simple radial two-tier
defined as tier 3. Hence, in a simple radial two-tier
system, the feeders are labeled tier 1 and the main
system, the feeders are labeled tier 1 and the main
is tier 0.
is tier 0.
For substations that are operated with the tie
For substations that are operated with the tie
normally-open, the tie and the mains could be set
normally-open, the tie and the mains could be set
at at tier 0. This wi
tier 0. This will allow the
ll allow the tie and the mains
operate at minimum (or set) delay for a fault in their
operate at minimum (or set) delay for a fault in their
zone of protection or feeder set delay plus 100ms
zone of protection or feeder set delay plus 100ms
if the fault is below a feeder. If the substation is run
if the fault is below a feeder. If the substation is run
from one transformer with the tie closed it may be
from one transformer with the tie closed it may be
However, the
, the Entellisys-
Entellisys-
capabilities include
nclude
ng for up to four zo
o four zones
nes
s as fast as
extra wiring or devices.
r devices.
d delay for faults
hips (tiers)
to achieve
grounding protection.
otection.
tion and selectivity. Eac
selectivity. Each h
tie and the mains to to
preferable to set the tie at tier 1 and the mains at
preferable to set the tie at tier 1 and the mains at
tier 0 to achieve tie to main selectivity.
tier 0 to achieve tie to main selectivity.
How short-time ZSI works
How short-time ZSI works
In the Entellisys ZSI model, the highest-level main
In the Entellisys ZSI model, the highest-level main
circuit breaker is labeled tier 0. So in a simple double-
circuit breaker is labeled tier 0. So in a simple double-
ended substation, the mains are each tier 0, the tie
ended substation, the mains are each tier 0, the tie
is tier 1, and the feeders are all tier 2. In the following
is tier 1, and the feeders are all tier 2. In the following
explanation, the terms lower- or higher-numbered
explanation, the terms lower- or higher-numbered
tier indicate in which direction the action is intended.
tier indicate in which direction the action is intended.
Whenever the CPU detects that a breaker in one
Whenever the CPU detects that a breaker in one
or more of the defined ZSI zones has gone into ST
or more of the defined ZSI zones has gone into ST
pickup, it performs the following actions:
pickup, it performs the following actions:
1. Based on the tier to which the circuit breaker
1. Based on the tier to which the circuit breaker
belongs, it sets the short-time delays for all
belongs, it sets the short-time delays for all
breakers with the next-lower tier number to the
breakers with the next-lower tier number to the
short-time delay time of the circuit breaker in
short-time delay time of the circuit breaker in
pickup plus 100ms. Thus a breaker with a tier
pickup plus 100ms. Thus a breaker with a tier
number of 2 sets the short-time delays of the
number of 2 sets the short-time delays of the
breakers with tier number 1. Note that a breaker,
breakers with tier number 1. Note that a breaker,
for example a tie, can reside in multiple zones.
for example a tie, can reside in multiple zones.
However unless a circuit breaker is detecting fault
However unless a circuit breaker is detecting fault
current, it will not trip regardless of tier setting.
current, it will not trip regardless of tier setting.
2. Each circuit breaker whose short-time delay
2. Each circuit breaker whose short-time delay
setting was changed in step 1, sets the short-time
setting was changed in step 1, sets the short-time
delays for all
delays for all the breakers
the breakers with the next
tier number to the new delay, plus 100ms. For
tier number to the new delay, plus 100ms. For
example; each tier 1 breaker whose short-time
example; each tier 1 breaker whose short-time
delay was changed will, in turn, change the
delay was changed will, in turn, change the
short-time delay for tier 0 breakers in the same
short-time delay for tier 0 breakers in the same
zone (or zones) by adding 100ms to its own
zone (or zones) by adding 100ms to its own
delay and making that the new tier 0 delay.
delay and making that the new tier 0 delay.
3. Continue this process of changing the short-time
3. Continue this process of changing the short-time
delay of bre
delay of breakers
akers in the zone wit
in the zone with the next
lower-tier number until tier 0 is reached. (Tier 0
lower-tier number until tier 0 is reached. (Tier 0
breakers are typically mains.)
breakers are typically mains.)
4. All modifi
4. All modified short-time delays
ed short-time delays of the breakers
the zone are set to their original values, after all
the zone are set to their original values, after all
short-time elements cool off completely.
short-time elements cool off completely.
It should be noted that the ZSI system never lowers
It should be noted that the ZSI system never lowers
the time delay of a circuit breaker, but only increases
the time delay of a circuit breaker, but only increases
the delays of circuit breakers with lower tier numbers
the delays of circuit breakers with lower tier numbers
than the breaker for which the short-time fault
than the breaker for which the short-time fault
current was identified by the CPU within the same
current was identified by the CPU within the same
zone. The time delay of a circuit breaker is never
zone. The time delay of a circuit breaker is never
increased past a maximum time delay of 400ms.
increased past a maximum time delay of 400ms.
How ground-fault ZSI works
How ground-fault ZSI works
The algorithm for ground-fault protection is the
The algorithm for ground-fault protection is the
same as short-time ZSI, except for multi-source
same as short-time ZSI, except for multi-source
with the next-lower
-lower
h the next
of the breakers in in
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