Power system protection

Power system protection
Lecture 1
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Definition of the Power system protection
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
Branch of electrical power engineering deals with the
protection of electrical power systems from faults through
the isolation of faulted parts from the rest of the electrical
network.
The protective relays act only after an abnormal or
intolerable condition has occurred, with sufficient indication
to permit their operation.
Protection does not mean prevention, but rather, minimizing
the duration of the trouble and limiting the damage, outage
time, and related problems that may result otherwise.
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Components of Protection System
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
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Current and voltage transformers to step down the high
voltages and currents of the electrical power system to
convenient levels for the relays to deal with
Protective relays to sense the fault and initiate a trip, or
disconnection, order;
Circuit breakers to open/close the system based on relay
and autorecloser commands;
Batteries to provide power in case of power
disconnection in the system.
Communication channels to allow analysis of current and
voltage at remote terminals of a line and to allow remote
tripping of equipment.
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Function of Protection Relay
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
1. Reliability: assurance that the protection will perform
correctly.
2. Selectivity: maximum continuity of service with
minimum system disconnection.
3. Speed of operation: minimum fault duration and
consequent equipment damage and system instability.
4. Simplicity: minimum protective equipment and
associated circuitry to achieve the protection objectives.
5. Economics: maximum protection at minimal total cost.
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RELIABILITY
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
Reliability has two aspects, dependability and security.
Dependability is defined as the degree of certainty that a
relay or relay system will operate correctly.
Security relates to the degree of certainty that a relay or
relay system will not operate incorrectly.
In other words, dependability indicates the ability of the
protection system to perform correctly when required,
whereas
security is its ability to avoid unnecessary operation during
normal day-after-day operation, and faults and problems
outside the designated zone of operation.
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SELECTIVITY
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
Selectivity is the ability that a relay has to only open those
breakers that isolate the faulted element.
Selectivity discrimination can be achieved by time grading or
by unit protection.
Selectivity by time grading means that different zones of
operation are graded by time and that in the occurrence of a
fault, although a number of protections equipment respond,
only those relevant to the faulty zone complete the tripping
function.
Selectivity by unit protection means that the relay will only
operate under certain fault conditions occurring within a
clearly defined zone.
6 / 15
SPEED
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
The protection must isolates a trouble zone as rapidly as
possible.
■ In applications where selectivity is involved, faster
operation can be accomplished by more complex and a
higher-cost protection. Note: The faster the operation,
the higher the probability of incorrect operation.
■ Time, remains as one of the best means of distinguishing
between tolerable and intolerable transients.
A high-speed relay is that operates in less than
50ms = 3cycles (IEEE 100).
■
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Speed
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
Modern high-speed circuit breakers operate in the range of
17 − 50ms, 1 − 3cysles; others operate at less than
83ms = 5cycles. Thus, the total clearing time (relays plus
breaker) typically ranges from approximately
35 − 130ms = 2 − 8cycles
In the lower-voltage systems, in which time-coordination is
required between protective relays, relay-operating times
generally will be slower; typically on the order of 0.2-1.5 sec
for the primary zone. Primary-zone relay time longer than
1.5-2.0 sec are unusual for faults in this zone, but they are
possible and do exist.
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ECONOMICS
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
It is fundamental to obtain the maximum protection for the
minimum cost, and cost is always a major factor. The
lowest-priced, initial-cost-protective system may not be the
most reliable one; furthermore, it may involve greater
difficulties in installation and operation, as well as higher
maintenance costs. Protection costs are considered high
when considered alone, but they should be evaluated in the
light of the higher cost of the equipment they are protecting,
and the cost of an outage or loss of the protected equipment
through improper protection.
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PRINCIPLES OF RELAY APPLICATION
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
The power system is divided into protection zones defined by
the equipment and the available circuit breakers. Six
categories of protection zones are possible in each power
system:
1.
2.
3.
4.
5.
6.
generators and generator-transformer units,
transformers,
buses,
lines (transmission, subtransmission, and distribution)
utilization equipment (motors, static loads, or other),
capacitor or reactor banks (when separately protected).
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Protection Zones
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
Ideally, zones of protection should overlap, so that no part of
the power system is left unprotected.
graphics[scale=1.35]fig/zones01.png
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Observation
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
1. To disconnect only a faulty element, C.B’s are located in
the connections to each power element.
2. A separate zone of protection is around each system
element. The significance of this is that any failure
occurring within a given zone will cause the tripping
only those breakers.
3. Failures within the region where two adjacent protective
zones overlap, more B tripped than the minimum
necessary to disconnect faulty.
4. But, if there were no overlap, no breakers would be
tripped. (overlap is the lesser of the two evils)
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PROTECTIO ZONES
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
A S.C at X, the breakers of zone B, including breaker C,
will be tripped;
■ A S.C outside zone A, the relaying equipment of zone B
must also trip certain breakers in zone A if is necessary
to interrupt the flow of short circuit current from zone A
to the fault.
■ A fault at X, the same breakers in zone A will be tripped
unnecessarily for other faults in zone B to the right of
breaker C.
■
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PROTECTION ZONES
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
a typical arrangement of overlapping zones.
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EXAMPLE,
Definition of the
Power system
protection
Components of
Protection System
Function of
Protection Relay
RELIABILITY
SELECTIVITY
SPEED
Speed
ECONOMICS
PRINCIPLES OF
RELAY
APPLICATION
Protection Zones
Observation
PROTECTIO
ZONES
PROTECTION
ZONES
EXAMPLE,
What breakers should operate for a fault at,
F 1 , F 2 , F 3 , F 4 , F 5 , F 6 , F 7 F8 ,
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