condition monitoring for generator and transformer
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CONDITION MONITORING OF ELECTRICAL EQUIPMENTS full report
CONDITION MONITORING OF ELECTRICAL EQUIPMENTS report.doc (Size: 343 KB / Downloads: 160)
SEMINAR ON CONDITION MONITORING OF ELECTRICAL EQUIPMENTS
SUBMITTED BY: -
REPORT ON CONDITION MONITORING OF GENRATOR AND TRANSFORMER
Condition Monitoring (CM)
Condition monitoring, also known as predictive maintenance, uses primarily nonintrusive testing techniques, visual inspection, and performance data to assess machinery condition. It replaces arbitrarily timed maintenance tasks with maintenance scheduled only when warranted by equipment condition. Continuing analysis of equipment condition monitoring data allows planning and scheduling of maintenance or repairs in advance of catastrophic and functional failure.
Condition monitoring and condition assessment is a maintenance approach that is driven by financial, operational, and safety requirements. It must produce reliable information on plant condition to allow maintenance resources to be optimized and assist with the optimum economic replacement of the asset. The techniques of condition monitoring will form a vital part of future risk-based strategies.
The CM data collected is used in one of the following ways to determine the condition of the equipment and to identify the precursors of failure:
Â¢Trend Analysis: -
Reviewing data to see if a machine is on an obvious and immediate downward slide toward failure.
Â¢Pattern Recognition: -
Looking at the data and realizing the causal relationship between certain events and machine failure. For example, noticing that after machine x is used in a certain production run, component ax fails due to stresses unique to that run.
Â¢Tests against Limits and Ranges: -
Setting alarm limits (based on profession a intuition) and seeing if they are exceeded.
Â¢Statistical Process Analysis:-
If published failure data on a certain machine/component exists, comparing failure data collected on site with the published data to verify/disprove that you can use that published data.
Condition monitoring can be performed in two basic ways:
1. One can take spot readings with hand-held instruments.
2. One can install permanent data acquisition equipment and take repeated readings that are stored for future analysis.
Generally, taking spot readings provides sufficient information for making informed decisions regarding maintenance of facilities. Usually, the maintenance technician can keep a log of these spot readings and develop trends from these logs.
Permanent condition monitoring equipment is expensive to install, and the data bases created cost money to analyze and maintain.
Typically, permanent data logging equipment is installed only on super critical equipment used in production processes, equipment that - if it goes down - costs the facility money by the minute when it is not operating..
Use of Condition Monitoring (CM)
A variety of methods are available to assess the condition of systems/equipment, to determine the most effective time to schedule maintenance:-
vibration monitoring and analysis
lubricant and particle wear analysis (oil analysis)
electrical condition monitoring
Electrical Condition Monitoring: -
Electrical condition monitoring encompasses several technologies and techniques used to provide a comprehensive system evaluation. Electrical equipment represents a major portion of a facilityâ„¢s capital investment. From the power distribution system to
electric motors, efficient operation of the electrical systems is crucial to maintaining operational capability of a facility.
Monitoring key electrical parameters provides the information to detect and correct electrical faults such as high resistance connections, phase imbalance, and insulation breakdown. Since faults in electrical systems are seldom visible, these faults are costly (increased electrical usage), present safety concerns (fires), and involve life cycle cost issues (premature replacement of equipment). According to the Electric Power Research Institute, voltage imbalances of as little as 5 percent in motor power circuits result in a 50 percent reduction in motor life expectancy and efficiency in three phase AC motors. A 2.5 percent increase in motor temperatures can be generated by
the same 5 percent voltage imbalance accelerating insulation degradation.
High potential testing (HiPot)
Conductor complex impedance
Time domain reflectometry (TDR)
Motor current spectrum analysis
Power factor and harmonic distortion
Transformer oil analysis
Starting current and time
A hand-held generator (battery powered or hand cranked) is used to measure the insulation resistance phase-to-phase or phase-to-ground of an electric circuit. Readings must be temperature-corrected to trend the information. Winding temperatures affect test results. An enhanced technique compares the ratio of the
Megohmmeter readings after 1 minute, and then again compares the readings after 10 minutes. This ratio is referred to as the polarization index.
High Potential Testing (HiPot)
HiPot testing applies a voltage equal to twice the operating voltage plus 1000volts to cables and motor windings to test the insulation system. This is typically
a go/no-go test. Industry practice calls for HiPot tests on new and rewound motors. This test stresses the insulation systems and can induce premature failures in marginal motors.
Due to this possibility, HiPot is not recommended as a routinely repeated condition monitoring technique, but as an acceptance test. An alternative use of the equipment is to start with lower voltage
and increase the applied voltage in steps and measure the change in insulation rÃƒÂ©sistance readings.
Surge Testing uses equipment based on two capacitors and an oscilloscope to determine the condition of motor windings. This is a comparative test evaluating the difference in readings of identical voltage pulses applied to two windings simultaneously. Like HiPot testing, the applied voltage equals two times operating voltage plus
1000 volts. This test also in primarily an acceptance, go/no-go test. Data is provided as a comparison of waveforms between two phases indicating the relative condition of the two phases with regard to short circuits. The readings for a particular motor can be
trended, but the repeated stress of the insulation system is not recommended.
Conductor Complex Impedance
The total resistance of a conductor is the sum of its resistance, capacitive impedance, and inductive impedance. Accurate measurement of the conductor impedance allows minor degradations in a motor to be detected and addressed prior to motor failure. The condition of the insulation system can be determined by measuring the capacitance between each phase and
ground. The presence of moisture or other conducting substance will form a capacitor with the conductor being one plate, the insulation the dielectric, and the contaminate forming the second plate. Maintaining proper phase balance is imperative to efficient operation and toward realizing the full lifetime of electrical equipment.
Time Domain Reflectometry
In this test, a voltage spike is sent through a conductor. Each discontinuity in the conductor path generates a reflected pulse. The reflected pulse and time difference between initial pulse and reception of the reflected pulse indicate the location of the discontinuity.
Motor Current Spectrum Analysis (MCSA)
MCSA is a method of detecting the presence of broken or cracked rotor bars or high resistance connections in end rings. Motor current spectrums in both time and frequency domains are collected with a clamp-on ammeter and Fast Fourier Transform (FFT) analyzer. Rotor bar problems will appear as side-bands around the power supply line frequency. MCSA evaluates the amplitude of the sidebands that occur about the line frequency.
Radio Frequency (RF) Monitoring
RF monitoring was developed to detect arcs caused by broken windings in generators. It consists of establishing RF background
levels and the amplitude trend over a narrow frequency band.
Power Factor and Harmonic Distortion
Maintaining optimum power factor maximizes the efficient use of electrical power. Power factor is the ratio of real power to reactive power usage. Dual Channel data-loggers are used to determine the phase relationship between voltage and current, and
Histogram of RMS Average Transformer Loads
then calculate the power factor. If this detects a low power factor, subsequent engineering analysis will be required to devise a means of improving power system power factor.
Airborne (Passive) Ultrasonic
Airborne ultrasonic devices are highly sensitive listening guns (similar in size to the radar speed guns used by police at speed traps). The maintenance technician should use a piece of equipment to obtain a translation of the noise (into the range audible to human ears) produced by that piece of equipment.
It provides convenient, no intrusive means of testing equipment. It is especially easy and useful in testing remote.
Airborne ultrasonic devices can also detect the noise caused by loose connections as they vibrate inside of panels.
CONDITIONS MONITORED: -
Conditions to be monitored are: voltage, current, resistance, complex impedance, capacitance, insulation integrity, phase imbalance, mechanical binding and presence of arcing.
DETECTION INTERVAL: -
Monitoring intervals of several weeks to several months for various technologies will provide sufficient condition information to warn of degrading equipment
condition. Specific expectations of the length of warning provided should be factored into developing monitoring intervals for specific technologies. Several of the technologies outlined are also effective when used for acceptance testing and certification.
Accuracy depends on the technique applied and rating of instrument.
The technologies presented can be divided into two categories:
Those technologies that can safely provide information on energized systems and require the system be energized and operational. These technologies include IRT, Ultrasonic, Motor Current Readings, Starting Current, Motor Current Spectrum Analysis RF, Power Factor, and Harmonic Distortion.
Technologies that require the circuit to be de-energized for safe usage include Surge Testing, HiPot Testing, Time Domain Reflectometry (TDR), Megohmmeter, Motor Circuit Analysis, Transformer Oil Analysis, Turns Ratio, and Conductor Complex Impedance.
Equipment to be monitored
Specific equipment that can be monitored by electrical condition monitoring techniques are:-
1. Electrical Distribution Cabling â€œ
Megohmmeter, Time Domain Reflectometry, HiPot, IRT (if visible), and Airborne Ultrasonic
2. Electrical Distribution Switchgear and Controllers â€œ
Timing, Visual Inspection, IRT, and Airborne Ultrasonic.
3. Electrical Distribution Transformer â€œ
Oil Analysis, Turns Ratio, Power Factor, and Harmonic Distortion.
4. Electrical Motors â€œ
Current Draw, Motor Current Spectrum Analysis, Motor Circuit Analysis, Megohmmeter. HiPot, Surge Test, Conductor Complex Impedance, Starting Current, and Coast-Down Time.
5. Generators â€œ
Megohmmeter, RF, and Coast-Down Time.
6. Distribution System â€œ
HiPot, Ultrasonic, Power Factor, and Harmonic Distortion.â„¢
Generator condition monitoring benefits include:
Â¢ Maximized Generator Productivity:â€œ
Enables maintenance professionals to look within the machine and improve its basic operation.
Â¢ Improved Maintenance Scheduling:-
Planned maintenance/repair is less expensive and more efficient than unplanned repair. To quantify the effect, 'repairs' should include the 'time to repair' as well as the 'waiting time' or the time lost between time of failure, reporting, personnel assignment, machine documentation and parts procurement, as well as the time to repair. Information generated through generator condition monitoring enables users to reduce unplanned maintenance by predicting a part's failure well in advance.
Â¢ Improved Repair Time: -
Pre-planned repair/maintenance is inherently faster and smoother than crisis fixing.
Â¢ Improved Uptime/Reduced Unplanned Outages: -
Condition monitoring provides information that implements scheduling maintenance/repair on a needs only basis.
Â¢ Increased Machine Life: -
A well maintained generator lasts longer than a poorly maintained one. Condition monitoring provides a means to diagnose the cause of a deteriorating situation be it a mechanical failure in a rotor, retaining ring, fan, or bearing, or electrical failure from lack of adequate insulation protection, age, winding stress, surges, or short circuits.
Â¢ Improved Product Quality: -
Translates into reliability, availability and reduced cost to the customer.
TRANSFORMER CONDITION MONITORING
Transformers are generally reliable pieces of plant and cover a vast range of sizes on power stations. However, the outage of any transformer may be catastrophic especially for important and high rating power transformers that supply large number of loads. Faults are often difficult to diagnose locate in transformers due to complicated winding structures, but a multi- parameter CM approach gives valuable data to diagnose the fault and suggest its location. Where insecure pairs can then be made, both downtime and costs can be significantly reduced. CM can prevent transformer unplanned outages and catastrophic failures cause by faults. It allows ageing of the plant to be monitored and therefore controlled and possibly predicted and extended. According to old and recent research in the field transformer condition monitoring, it can be divided into five main categories. shows the main categories transformer CM techniques. In the remaining of this paper, each techniques of the transformer condition monitoring techniques will be explained and discussed.
Transformer Condition Monitoring Techniques:-
Vibration analysis dissolved gas analysis (DGA)
Frequency response analysis (FRA)
Thermal analysis of the transformers can provide useful information about its condition and can indicate any incipient inside it. Many of the incipient faults cause change in thermal behavior of the transformer. It is usually accepted that transformer life can be affected very much for a continuous maximum hotspot temperature of 98Ã‚Â°C on the paper insulation. Beyond this, it is assumed that the rate of ageing doubles for every increase of 6Ã‚Â°C.Also, the transformer subjected to degradation due to direct thermal effects, and enhanced oil temperatures are likely to accelerate other ageing processes. The condition of the oil can affect the ability of transformer to withstand emergency overloading.
The usage of the vibration signals in assessing the transformer health is relatively a new technique and its research is under development compared with the other methods of the transformer CM The health condition of the core and windings can be assessed using vibration signature of transformer tank.Also, vibration analysis used for assessing the health of the On Load Tap Changer
According to the tank vibration consists of two types; core and winding vibrations. These generated vibrations propagate through the transformer oil until reaching the transformer walls, at which the vibration signature of the transformer can be collected via vibration sensors. Accelerometers are used to collect the vibration signals by attaching it to the transformer walls. The collected signal can be found as a series of decaying bursts, each of the bursts the result of a combination of a finite number of decaying sinusoidal waveforms. The vibration signals collected and measured using accelerometers. The collected vibration signal was analyzed using Fourier transform to show that the transient vibration signals are concentrated in the range from 10 to 2000 Hz. The condition assessment of the transformer OLTC was successfully done using vibration signatures. Any OLTC has its
own vibration signature regarding the number of the rising edges of the vibration busts and the duration between each successive two rising edges. The features can be extracted from the collected data using many signal processing techniques. The continuous wavelet transform was used to analyze the vibration bursts generated from the operation of the OLTC due its reliable ability to extract the useful features from the non-stationary and fast transient signals. As a conclusion, the usage of the vibration analysis was used to assess the health of the transformer or some important parts of it such as OLTC. However, there is a good chance for development in this area because the research focused on using the vibration analysis for assessing the health of the OLTC only; therefore, more work is needed to assess the condition of all transformer parts.
PARTIAL DISCHARGE ANALYSIS
Partial discharges (PDs) occur in a transformer when the electric field strength exceeds the dielectric breakdown strength of a certain localized area in which, an electrical discharge or discharges partially bridge the insulation between conductors. The dielectric properties of the insulation may be severely affected if
subjected to consistent PD activity overlong periods of time. This may lead to catastrophic failure if the PD activity remains untreated. As the insulation system of the transformer is regarded as a critical aspect of a transformerâ„¢s condition, suitable safeguards are required to monitor and assess the condition of the insulation. Investigations into partial discharge phenomena in liquid dielectrics (such as oil) have been less common and subsequently less well understood than solid dielectrics. PD can be detected and measured using piezo-electric sensors. Also, optical fiber sensors were used to capture signal successfully. Ultra High Frequency (UHF) sensors are relatively newer than traditional PD measurement methods. UHF sensors were used to measure the PD occurred in power transformers.
DISSOLVED GAS ANALYSIS
The insulation of power transformers is generally very reliable. Insulation ageing in transformers is most commonly associated with long-term effects of the operating temperature, moisture and air. Since a significant proportion of transformers on the network are over 30 years old, it is necessary to assess the Ëœchemicalâ„¢ age of their insulations and, possible, to predict their rates of ageing
relative to their present and future loading conditions. Dissolved
Gas Analysis DGA) researchers sees that electrical measurements (partial discharge, dielectric loss, dc resistance, dielectric strength,
Etc.) Have no clear and strong correlation between electrical properties and the physical and chemical states of the oil-paper insulation. The thermal degradation of oil results in the production of hydrogen, methane, ethane, ethylene, acetylene, CO, CO2 and other products of oil breakdown include alcohols, organic acids, aldehydes, peroxides, etc. For any given oil sample, the absolute and relative concentrations of fault gas can be used to indicate the type, intensity and location of the fault. A variety of methods are available to achieve this, laboratories may rely upon defined critical levels of gases, rates increase in gas level (on a year by year basis), or one of the various methodologies associated with Rogers, Duvd or Dome berg. The recommended practice for oil sampling, extraction of the gases and methods of analysis are detailed in IEC 567. After analyzing the gas concentrations and using the gas ratio codes, the fault can be diagnosed using these key tables that relate the ratio of gases with the defect. Some artificial intelligent agents can be trained on the DGA ratio codes to classify some incipient faults, which have some irregular gas ratios that canâ„¢t be interpreted by the sample usage of the ratio
codes. The problem of the usage of DGA analysis in assessing the
condition of the transformer is that it needs special Arrangements to measure the dissolved gases.
Wireless Remote Monitoring & Control
(GPRS/GSM enabled Wireless SCADA)
Wireless SCADA i.e. Wireless Supervisory Control & Data Acquisition is a remote wireless data logger for industrial & process automation. This is a GPRS/GSM based SCADA system with 'Plug & Play' feature.
Softbit has launched a range of remote data loggers for wireless industrial & process automation. These wireless remote data loggers can be used for real time data acquisition, monitoring & control of remotely installed electrical systems, HT/LT electric motors, HV/LV transformers, generators, HT/LT distribution panels, boilers or any electrical machine & system. The micro-
processor based wireless remote data logger works on "Plug & Play" methodology i.e. this comes fully pre-programmed and you only need to connet it with a machine to be monitored & controlled from a remote location.
Advantages of Wireless Remote Data Logger: -
Following are the main advantages of Remote Data Logger.
a)- Energy Auditing/Management i.e., Energy Conservation
b)- Remote Condition Monitoring of Machines
c)- Remote Monitoring & Control of any machine &system
d)- Remote Power Monitoring & Management
e)- SCADA - Industrial Automation
g)- Security Applications
Data Monitoring - Wireless Remote Data Logger (Wireless SCADA): -
Once the remote data logger is connected & energized, the user can monitor the parameters in the following ways:
1) - LCD Screen: The various electrical parameters of machine can be monitored locally on the LCD screen of the data logger itself.
2) - SMS Alert: User can activate SMS alerts to receive messages on his/her mobile phone. This requires a GPRS/GSM enabled SIM card.
3) - Email Alert: User can activate Email alerts to receive messages on his/her mobile phone. This requires a GPRS/GSM enabled SIM card
4) - Remote Web Account (Optional): User can monitor all the parameters live in real time if he/she has activated the remote web account. This service requires activation and is on annual chargeable basis. If the user has activated his/her "Remote Web Account" then all the parameters can be monitored from a remote PC/Laptop. User can also do the switching operations from the remote PC/Laptop. An exceptionally low cost wireless GPRS/GMS based SCADA solution for remote industrial automation
Management of maintenance activities at facilities on military installations is a complex and expensive task. This report presents a variety of techniques thatcan monitor equipment condition and anticipates failure. For some noncritical, inexpensive, and easily replaced components, run-to-failure method may be an acceptable practice. For large, complicated, expensive, mission-critical items, run-to-failure may be unacceptable. Maintenance to maximize service life of equipment or components and surveillance of performance degradation can allow repairs/replacement without interruption of mission-critical activities. For certain installations, it may be more economical to use contract services to maintain Infrequent, complex, and expensive equipment and processes.[/size]