Fault Types and Magnetic Sensor Introduction
-
Upload
modithasilva -
Category
Documents
-
view
13 -
download
0
description
Transcript of Fault Types and Magnetic Sensor Introduction
Faults Of Power System
• 3 major fault occurs usually.• All faults can be solved using
symmetrical component.• We are not going to analyze it
now. Take an overview .
Faults in Power systemFaults Types
◦ Balanced 3Ø faults (Symmetrical). 3Ø direct connect(LLL) 3Ø to ground(LLLG)
◦ Unbalanced 3Ø faults (Asymmetrical). Single line to the ground (SLG) Line to Line (LL) Double line to ground (DLG)
◦ Series Faults. One line open (OLO) Two line open (TLO)
Faults in Power systemFaults Can occur anywhere in
the power system.For the time being consider 33kV
network.Recover faults are more critical.Proper detection of faults helps
to fast recovery.Placing fault indicators over the
network helpful for recover mission.
Fault IndicatorsWhen fault occur, both voltage
and current changes undesirably.By measuring voltage and
current ,can identify faults.Current can measure in various
ways◦By using current shunt◦By using current transformer.◦By measuring magnetic field around
conductor.
Fault IndicatorsCurrent shunt is more suitable for low
voltage applications.We are more prefer for non-contact
method.So current shunt is not suitable.Current transformer is more accurate &
reliable but it suitable up to some extent.It is suitable for bus bars & transformers.Since CT are bulky and main conductor go
through the CT ,its not applicable.
Fault IndicatorsNext method is measure current
by measuring magnetic field.There are several methods to
measure magnetic field.◦Flux gate◦SQUID◦Hall effect◦Magnitoresistance◦Proton precession◦Optical pump
Magnetic Field Sensor
Figure: Magnetic field sensors are divided into two categories based on their field strengths and measurement range: magnetometers measure low fields and gaussmeters measure high fields.
Magnetic Field Sensor
Table: Field Strength Instrument Characteristics
Hall Effect SensorHall sensors uses well known phenomena
called ‘Lorentz force’ ,force acting on moving charge in magnetic field.
To make charge moves ,use constant current.
Hall Effect SensorUnder external magnetic field, charged partials
are moving they tends to concentrate on one side.That creates electrical field perpendicular to
moving direction
Hall Effect SensorHall effect occurs in both
conductors and semiconductors.Compare to conductors,
semiconductors has considerably large VH.
Predominantly use n-type silicon.But there are other materials too.
◦GaAs◦InAs◦InSb
Hall Effect SensorHall voltage is linear function of
◦Applied Current (I)◦Magnetic field (B)◦Separation between sensor points
(d)◦Carrier density (N)
VH =
Hall Effect SensorCompare wit others ,InSb has
large VH.
Hall Effect SensorBut InSb is highly sensitive to
temperature variations.
Hall Effect SensorSince VH is in mV & µV
range ,amplification is required.VH measures between two points.
So it requires differential amplifier.
Hall Effect SensorFinal output is linearly behave
with applied magnetic field.
Hall Effect Sensor
Hall Sensor
Power line
Core
Magnetoresistive Sensors There are two basic types.
◦Giant Magnitoresistance Sensor (GMR)
◦Anisotropic Magnitoresistance sensor (AMR).
Magnitoresistance is the property of a material to change the value of its electrical resistance with an externally applied magnetic field.
Magnetoresistive Sensors Magnetoresistive Sensors available in
market uses MR element in balanced wheatstone bridge configuration.
All four elements are identical but two of them are covered with magnetic shield.
Magnetoresistive Sensors It helps to minimize the effect of
temperature coefficient of resistive elements.
Under external magnetic field only two of them vary accordingly.
It causes the unbalance of bridge.
Unbalanced voltage can be measured using differential amplifier.
Magnetoresistive Sensors
Magnetoresistive Sensors Output voltage is linearly vary
with applied magnetic field.AMR - can identify magnetic pole
typeGMR – equally response to both
poles
Comparison of Magnetic Sensors
• GMR sensors are more suitable for DC current sensing application.
• For AC ,AMR is more prefer than Hall sensor.