Transcript Online Monitoring Applications of Power Transformer

ONLINE
MONITORING
APPLICATIONS
OF POWER
TRANSFORMER
Deepak Subedi
Why monitoring of Power
Transformer is required
 Critical Assest of Power System (Transmission & Distribution System)
 Transformer failure leads to power outage, financial loss, environmental
hazards
 Good tool to reduce power outage caused by Transformer failure
 Can enhance the life time of the Transformer
 Reduces the loss encountered due to Transformer failure
 Can supplement to diagnose the reasons behind the Faiure
Methods
for
Condition
Monitoring
 Offline Monitoring
o Accurate and useful information of the Transformer
condition.
o Transformer isolated from the network and may use
intrinsive methods for measurement
o Return Voltage Measurement, dielectric frequency
response, gas analysis of oil sample
 Online Monitoring
o Temperature measurement, oil status, partial discharge
o Winding movement, dielectric frequency response, load
tap changers
o Censors are used for the measurement
o Censors may include optical fibers, vibration sensors,
temperature sensors, UHF antennas, gas censors,
capacitive censors and etc.
Temperature Measurement
 Overload and malfunction in cooling system may lead to increase in temp.
 Increase may temp. may cause ageing of insulation
Thin Film Sensor
• Advanced technique to measure
temperature.
• More accurate and reliable than
traditional Pt100 thermocouple devices
• Thickness of film from 12 to 50nm,
significantly smaller than Pt100 devices.
• No air gap and changing of flux inside the
core.
• Can be used in crictical installation
locations.
Enhanced Fibre Optic Sensor
• More accurate and reliable than
traditional Pt100 thermocouple devices
• Sensing probe integrated with a plastic
cladding large-core (200 m) optical fiber
• Temperature detection is based on analog to
digital processing hardware to monitor the
power output of the optical fiber.
• The resolution is 0,2 C and accuracy is
0,5 C for the measurement system
Gas Analysis
• Electrical and thermal stresses such as arching, partial discharges and overheating cause degradation
of dielectric oil and solid dielectric cellulose materials.
• Different degradation mechanisms generate different gases thus making it possible to determine the
degrading part of the transformer
Online DGA
• Traditionally DGA carried out using
off-line measurements.
• Recently, better techniques for gas
analysis using a membrane or vacuum
extraction.
• Semiconductor sensors, infrared sensors,
combustible gas detector and gas
chromatography are commercially available.
• Methods applied to DGA can be used
to reveal apparent fault conditions.
Online Gas Phase
Monitoring
• Carried out using infrared spectroscopy
measurements
• One application is to use a Clemet TM Fourier
transform infrared spectroscope (FTIR) to
measure the free gases in the inert gas
blanket above the transformer oil.
• FTIR can detect all hydrocarbons and
even Furans too.
• Measuring free gas quantities can provide
helpful information on insulation status
more readily than DGA.
Partial Discharge Measurement
• Power transformer breakdowns are most frequently preceded by partial discharges (PD).
• Every partial discharge occurring inside the transformer generates an electrical pulse, a mechanical pulse
and electromagnetic waves which can be detected by using various sensors and techniques.
UHF PD Detection
• Partial discharges occurring inside the transformer excite electromagnetic waves with resonance at
frequencies 500 – 1500 MHz.
• Possible causes of PD: temporary overvoltage, weakness in the insulation introduced during
manufacturing or due to various aging effects
• Different types of data handling layers are used in this on-line application.
• Four data layers: data monitoring layer, interpretation layer, corroboration layer and information layer.
• PD sensor data can be analysed using these methods: time-energy mapping and clustering of PD data,
time-frequency analysis combined with feature extraction and clustering and phase-resolved data
representation.
P.D. Contd……
New techniques for online PD Measurement:• On-line PD measurements of HV equipment suffer from heavy noise caused by various origin which effects the
measurement accuracy.
•
Hardware and software approaches used to reduce the noises.
• New sensors introduced with PD coupler board and multi channel PD detector.
• Sensing board installed near of the HV conductor and the stray capacitance acts as a coupling capacitor.
Vibration Measurement
• Two major reasons: Core vibration and Winding Vibration
• Core Vibration caused by excitation by magnetostriction and excitation generated in the air gaps.
• Winding Vibration generated by Lorenz force due to correlation of leakage flux and winding current.
• Piezoelectric accelerometer is positioned at different locations on the transformer tank wall.
• On-line measurements are conducted under load and no-load conditions.
• Spectrum of the signal is calculated for analysis.Spectrum of winding vibration can be found by subtracting the noload results from the loaded results
• Different characteristics of the spectrum of the measured vibration of a power transformer in a good condition can be
used as a reference during on-line monitoring.
On-Load Tap Changer Monitoring
• Tap changers are the mechanical switching devices of the power transformer.
• OLTC malfunction can destroy the complete transformer.
• OLTCs cause more failures and outages than any other component of a power transformer.
On-line monitoring of OLTCs
• OLTC possible failures include: motor malfunction, loss of power and flaw in controlling circuits may cause
the tap change to stop before its completion.
• The tap changer needs 5 – 6 seconds to finish its operation. During this time, different sensors are used for
on-line monitoring.
• High sampling rate is needed. The system consists of a 30 kHz accelerometer, clamp-on current
transformer and pair of thermocouples
• Monitoring of OLTCs is carried out using measurements on vibration of the contact movements,
temperature of the insulation oil, voltage and current of the drive motor.
• The system is triggered by operation of the OLTC and above-mentioned measurements are conducted
together with detection of the tap position.
Others Measurement and
Monitoring
• FURFURALDEHYDE MEASUREMENTS:
–
•
On-line FFA measurements using optical sensor
MECHANICAL FAULT DETECTION USING FREQUENCY RESPONSE ANALYSIS
• On-line low voltage impulse test method
– Low voltage impulse (LVI) also known as FRA is used to monitor possible winding movement on-line.
• TAN- ON-LINE MONITORING
– Measurement of the tan- of power transformer insulation used to determine the quality of the
insulation as a standard test before initial installation.