6. comparator
TRANSCRIPT
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Different types of relay and
characteristics
Overcurrent relay
Directional overcurrent relay Differential relay
Distance relay
Overvoltage and under voltage relay
Digital relay
Comparators
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Comparator
Phasors are fundamental quantities in the analysis of
ac systems.
A comparator is a design element used in relays to
compare two phasors either in magnitude or phase.A distance relay will always have a phase comparator
or magnitude comparator regardless of the technology
used, i.e., electromechanical, solid-state, and
microprocessor-based relays.
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Cont..
A comparator will give the relay system an output when
the conditions for operation are satisfied.
Two types comparator- phase and magnitude
Phase comparators are used widely in distance relaydesigns.
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Phase Comparator Phase comparators are used to detect when one a.c.
input is more or less than 90 out of phase with a
second a.c. input.
Phase-angle comparator logic circuitry produces anoutput when the phase angle between two quantities
is within certain critical limits.
Either of these two quantities, the polarizing (or
reference quantity) and operating quantity, may becurrent or voltage.
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Phase Comparator
In Figure, given two arbitrary phasors, S1 and S2, the
output of a phase comparator is a logic 1 (the
comparator has operated) if
0901
2
jS Me
S
0 01 290 90S S
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Cont..
The quantity
for the condition to be met and it does not
affect the operation of the phase comparator.
is any arbitrary magnitude
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Characteristic of phase
comparator
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Phase comparator
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Generalized Use of Phase Comparators
Phase comparators are used widely in distance relay
designs The input phasors are generally a combination of
voltages and currents. From these inputs, the ratio
V/I, or impedance, is proportional to the distance to
the fault
In general the input a phase comparator is given by
Constants k1, k2, k3, and k4 are design constants
that may be complex and introduce a phase shift.
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Cont..A general procedure to derive the impedance
characteristic of the comparator on the Z=V/I planewill be developed.
In most applications, k1
and k3 are real numbers
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Cont..
The quantities a and b are vectors and do have the same
units as Z, i.e., they are impedances as well.
In general, a and b will be sufficient to define the operating
characteristics of the unit
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Basic Application Example of a Phase
Comparator
For this purpose, let V and I be the voltage and
current input to the relay and the inputs to the phase
comparator be
where Zc is the relay setting
k1 =1, k2 =Zc, k3 = 1, k4 = 0.
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Characteristic of directional relay on the R-X plane
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Directional property of mho relay
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Cont
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Inputs to cosine-type phase comparator
resulting in trip output
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Inputs to cosine-type phase comparator
causing it to restrain
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Inputs to cosine-type comparator causing it to
be on threshold
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The Sine-type Phase Comparator
00 180m pS S then trip; else restrain
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The Sine-type Phase Comparator
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The Sine-type Phase Comparator
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Magnitude Comparator
Given two arbitrary phasors, SAand SB, the output of
a magnitude comparator is a logic 1 (the
comparator has operated) if
jrA
B
SCe
S
A BS S
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Characteristics of amplitudecomparator
1A Bif S S theoutput is
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Inputs to amplitude comparator resulting intrip output
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Inputs to amplitude comparator causing it torestrain
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Inputs to amplitude comparator causing it to
be on the threshold
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Generalized Use of Magnitude
Comparators
If the inputs SA and SB are expressed in terms of
impedances, either the power-system or relay setting
impedances
with C=1, the operating characteristic of thecomparator in the R-X diagram can be defined.
jrA
B
SCe
S
AS
BS
A BS S
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compare the above with the general equation for the circle
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Basic Application Example of a Magnitude
Comparator
Let V and I be the voltage and current input to the
relay, and the inputs to the magnitude comparator be
where Zc is the relay setting
For a magnitude comparator, the characteristic is
determined by
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Mho unit derived from a magnitude
comparator