|Title of Invention||
"A MEASURING SYSTEM OF CAPTURING THE RADIO FREQUENCY (RF)SIGNALS"
|Abstract||A PC based monitor for turbogenerators in which the system measures the RF emission levels at the 3 phases and the neutral of the generator, analyses the data and gives current status of the machine insulation like abnormal, danger or shutdown on the PC screen. The RF emission from the 3-phases and neutral are measured using HV capacitor couplers and RF current probe. The emission is detected by the spectrum analyser and a RF multiplexer. The spectrum analyser is provided with a plotter. The RF data is sent to PC via GPIB communi¬cation link. The present invention has incorporated an algorithm in the software by which the operator views the various conditions of the generator on the PC screen.|
|Full Text||The invention relates to ameasuring system of capturing the Radio
Frequency (RF) signals, particularlyPC based RF monitor
for turbogenerators for monitoring the current status pf the machine insulation like abnormal, danger or shutdown.
Generator reliability is a vital factor for electric power generating units. Failure of a single unit in peak load period can cause serious service interruptions, leading to purchase of power from neighbouring utilities. Sometimes generator failure may require rewinding, which can take a minimum of 6 months and cost heavily in repairs and revenue losses. An important sub-system of the generator that is prone to deterioration and eventual failure is the insulation system.
Faults at incipient stage are often revealed by electrical discharges or arcing, before they cause serious short circuits. These discharges produce current pulses, which have broad frequency spectrum ( Radio frequency).
In the past generator insulation failures were difficult to detect, and any abnormal behaviour of the machine resulted in shut down of the particular unit. It took a long time sometimes even a few days to locate the fault. If it was a serious insulation failure and if the stator winding was to be replaced, it took 3 to 6 months and resulted in heavy revenue loss.
After several years of development, Radio Frequency Monitoring (RF Monitor) has emerged as one of the leading diagnostic methods used on electrical machines. RF Emissions are associated with numerous abnormalities like brush arcing, partial discharges, slot discharges and arcing due to broken conductor strands. Slowly monitoring of RF Emission from turbogenerators has become one of the best on-line diagnostic method for predicting the insulation deterioration well in advance.
There are disadvantages associated with the present system of monitoring turbogenerators.
The main disadvantages associated with present system of monitoring turbogenerator is that as RF emission measurements are made only in neutral, it is not possible to identify the exact location ( or phase) where insulation failure has occurred. This leads to spending considerable time in observing the various windings to locate the faults.
Therefore the main object of the present invention of a PC based RF monitor for turbogenerators is to measure the RF emission levels at the three phases and neutral of a turbogenerator, which analyses the data and gives current status of the machine insulation like abnormal, danger or shut down on the PC screen.
Another object of the present invention of a PC based monitor for turbogenerator is to provide detailed operator guidance as main menu on the monitor screen.
Yet another object of the present invention of a PC based monitor for turbogenerators is to identify incipient arcing or discharge source, as well as an estimate of its location so that repairs can be effected with minimum search time.
Still another object of the present invention of a PC based monitor for turbogenerators is to record RF data for routine shut down at specific RF levels or trends for repairs or preventive maintenance.
Further object of the present invention of a PC based monitor for turbogenerators is to develop a prediction system for determining of the remaining life of the stator coil insulation when RF monitoring becomes more widespread, and RF history of machine insulation is recorded ...
According to the present invention there is provided a PC based monitor for turbogenerators comprising a personal computer with a printer, said PC is connected to a spectrum analyser with a plotter through IEEE-488 port, said spectrum analyser is connected to a multiplexer/ Scanner to receive an input of RF emission from 3 phases and neutral.
The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non -limiting
exemplary embodiments of the invention represented in the accompanying drawings.
Figure 1 shows a block schematic diagram of RF monitor for turbogenerators;
Figure 2 shows graphically spectrum data for R-phase and Base level
Figure 3 shows graphically spectrum data for Y-phase and base level. SUMMARY OF THE PRESENT INVENTION
In the present invention of a Personal Computer (PC) (1) based RF MONITOR for Turbogenerators, the system measures the RF emission levels at the 3 phases (6, 7, 8) and neutral (9 ) of a turbogenerator, analyses the data, and gives current status of the machine insulation like abnormal, danger or shutdown on the PC Screen. Detailed operator guidance also is given in the Main Menu on the screen. This system apart from spectrum analysis of RF data, identifies incipient arcing or discharge source, as well as an estimate of its location so that repairs can be effected with minimum search time. As RF data are recorded and confidence gained, it is anti¬cipated that machines will be routinely shut down at specific RF levels or trends so that repairs or preventive type of maintenance can be carried out. As RF monitoring becomes more widespread, and RF history of machine insulation is recorded, then prediction of the remaining life of the stator coil insulation will be possible.
DESCRIPTION OF THE PRESENT INVENTION
A Block Schematic of the RF Monitor developed by BHEL is given in Fig. 1 .
The RF emission from the 3-phases ( 6,7,8) and neutral (9) are measured using HV capacitor couplers and a RF current probe. The emission is detected by the spectrum analyser
(3) and a RF multiplexer (5). The RF data is sent to the
PC (1) via GPIB communication link, necessary software
for which has been developed. This software sends commands from PC (1) to analyser (3) as regards reset, frequency ranges, sweeptime, reading of different peak amplitudes etc_. Acquisition of data in the PC (1) is achieved by the GPIB link and the associated software.
The spectrum analyser (3) is provided with a plotter
(4) and the PC (1) is provided with a printer (2).
Guidelines for the safe operation of the generator has been built in the PC screen, based on the current RF levels and the base level RF emission.
The RF phase measurement system uses discharge free HV coupling capacitors and suitable protection devices for protecting the system against HV transients and over voltages, A RF current transformer (CT) having frequency response upto 100 MHz and also insulation strength of 5KV is used for RF emission measurement from neutral.
The Multiplexer (5) used has 4 input channels and one output channel which goes to the Spectrum Analyser (3). The Analyser (3) has a frequency response of 1000 MHz and easy selection of frequency ranges and amplitude units
and reference levels. The PC (1) acquires the RF data through IEEE-488 ports and GPIB link and necessary software which has been developed.
Figs 2 and 3 shows the spectrum data for R-phase and Y-phase respectively.
The PC screen formats contains the following informa¬tion ( graphical plus text):
1) Current RF emission spectrum of the 3-phases (6,7,8)
(R,Y and B) and the neutral (9) for different frequency ranges ( viz, 10-150 kHz-lMHz, lMHz-10 MHz, 10 MHz-30 Mhz and 30 MHz- 100 MHz).
2) Corresponding base level spectrum for the 3-phases
(6,7,8) and neutral (9) for different frequency ranges.
3) RF emission spectrum for the entire frequency range
( 10 KHz to 100 MHz) along with base level data.
4) Comments on the performance/status of the generator
i. e. Normal, Abnormal, Danger level and shutdown alarm. All these texts are displayed on the same page where RF spectra is available. Deterioration of the performance is also indicated by change of colour of the RF spectra. These features will
enable the operator to take suitable decision
depending on the comments.
At any instant, a hard copy of the PC screen output
can be obtained from the plotter (4) for detailed
analysis and comparison.
5) A list of generator parameters like rating, load,
speed, grid frequency, type of insulation system,type
of cooling system, type of excitation system etc.
are also indicated on the screen.
6) Operator Guidance for carrying out comments and
instructions on the PC screen.
The invention described hereinabove is in relation to non - limiting embodiments and as defined by the accompanying claims.
1. A measuring system of capturing the Radio Frequency
(RF) signals, which are emanated from electrical
discharges/arcing inside a turbo generator, directly from all the high voltage terminals (6,7,8) and the neutral point (3) which comprises of a high voltage capacitor coupler, a spectrum analyser 2. A measuring system as claimed in claims 1 or 2 wherein
said emission is detected by the spectrum analyser (3) and a RF
mu11 i plexer 3. A measuring system as claimed in claim 2 wherein the RF
data is communicated to the said PC through a GPIB communication
link and ' IEEE-488 ports.
4. A measuring system as claimed in claim 1 wherein said
HV capacitor couplers are discharge free and are with suitable
protection devices for protection against HV transients and over
5. A measuring system as claimed in claim 1 wherein the RF
current probe for said RF emission measurement from neutral is a
6. A measuring system as hereinabove described and
illustrated in the accompanying drawings.
|Indian Patent Application Number||507/DEL/1999|
|PG Journal Number||01/2011|
|Date of Filing||05-Apr-1999|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LIMITED|
|Applicant Address||BHEL HOUSE, SIRI FORT, NEW DELHI - 110 049, INDIA|
|PCT International Classification Number||G06F 19/00|
|PCT International Application Number||N/A|
|PCT International Filing date|