Patent Grant
11415619
This application relates to active-monitoring systems for high-voltage bushings, transformers, reactors, and related equipment with high-voltage insulation and methods of making and using the same. The embodiments described herein may be used on any such equipment in a de-energized or energized condition.
High-voltage equipment such as bushings, transformers, reactors, and related equipment, with high-voltage insulation systems, may be constructed with solid, liquid, or a combination of solid and liquid dielectric insulation materials. The dielectric strength of the components and physical dimensions of the insulation system can be evaluated by the capacitance and power-factor values of each part of the system. Active-monitoring systems allow more complete testing of energized equipment by injecting low-energy signals into the energized equipment, while effectively isolating the low-energy signals from the high-voltage, high-current signals in the energized equipment, and measuring the magnitudes and phase angles of the resulting signals to determine the capacitance and power-factor values of the various parts of the component insulation system.
Examples of active-monitoring systems for measuring integrity of insulation components in electrical systems are described in U.S. Pat. No. 9,945,896 (Watson). The entire disclosure of U.S. Pat. No. 9,945,896 is incorporated herein by reference.
According to one aspect of the present disclosure, an active monitoring system may include: a modulating portion for generating a digital signal by modulating an input signal, and for injecting the digital signal into a high-voltage device; and a demodulating portion for receiving a digital output signal from the high-voltage device, and for demodulating the digital output signal to determine the power factor and capacitance values of an insulation system for the high-voltage device.
According to another aspect of this disclosure, the complete system assesses the health condition of electrical power equipment by measuring the power factor of the equipment insulation structure by injecting a modulated low-energy signal in real time at different points at high frequency (for example, a sinusoidal signal in the 10 kHz to 100 kHz range), into a power transformer energized at electrical grid voltages to 1500 kV or greater at a 50 or 60 Hz signal frequency and measure the magnitude and phase angle of the resulting signals at multiple other points in the transformer to evaluate transformer condition and the health of the components of the insulation system.
According to another aspect of this disclosure, the use of modulated input signals and demodulated output signals improves the quality of the measured signals by reducing interference from high-voltage noise and increases the accuracy of the measured and calculated results. At the same time, the lower-energy modulated signal may have an insignificant, or at least manageable, effect on the operation of the transformer or other device.
If desired, a system in accordance with this disclosure may have a multi-channel signal generator and measurement device, with connections to input and output sensors for the tested component. The system may provide a series of injected signals into each available port and measure the resulting signals from each available port. Although systems constructed in accordance with this disclosure may be configured differently for different types of equipment being tested, the systems may operate on similar principles. In operation, input signals may be used as the effective carriers for the modulated high-frequency, low-energy signals that pass through the equipment through each electrical path and the resulting voltage and current signals are measured at each available point, and the high-frequency, low-energy component of the signals are demodulated as a series of complex variables to model the insulation system components and determine their capacitance and power factor values.
If desired, for a complete transformer with condenser-type bushings, a system constructed in accordance with the present disclosure may includes sensors on each bushing test tap, sensors on an internal current transformer for each bushing and an external current transformer for each bushing, as well as a connection to the tank ground.
An active monitoring system constructed in accordance with the present disclosure may provide superior signal measurement and phase angle shift determination compared to sinusoidal signal measurement systems, with a lower-energy input signal.
Referring now to the drawings, where like elements are designated by like reference numerals or other characters,
System voltage 60 and system impedance 62 are electrically connected to first and second ends of the high-voltage winding 52 by suitable first and second conductive lines 68, 70. The first conductive line 68 is electrically insulated from ground by a first bushing H1, while the second conductive line 70 is electrically insulated from ground by a second bushing H0. The bushings H1, H0 have outer and inner bushing sections H1C1, H1C2, H0C1, H0C2, and test taps 72, 74 located between the respective bushing sections H1C1, H1C2, H0C1, H0C2. If desired, the first and second bushings H1, H0 may be constructed like the condenser-type bushings illustrated in U.S. Pat. No. 9,945,896, although this disclosure should not be limited to the examples shown and described herein or in U.S. Pat. No. 9,945,896.
First and second ends of the low-voltage winding 54 are electrically connected to first and second ends of a system load 80 by suitable conductive lines 82, 84. The third conductive line 82 is electrically insulated from ground by a third bushing X1, while the fourth conductive line 84 is electrically insulated from ground by a fourth bushing X0. The third and fourth bushings X1, X0 have outer and inner bushing sections X1C1, X1C2, X0C1, X0C2, and test taps 106, 108 located between the respective bushing sections X1C1, X1C2, X0C1, X0C2. If desired, the third and fourth bushings X1, X0 may be constructed like the condenser-type bushings illustrated in U.S. Pat. No. 9,945,896.
In operation, a test voltage signal XH(t) is supplied by a test voltage source 120. The test voltage signal xH(t) is modulated by a modulation device 10 such that a modulated digital signal mi(t) is applied to the test tap 72 of the first bushing H1. A demodulation device 12 is connected to the test tap 106 of the third bushing X1 to generate a demodulated signal xL(t) (where IL(t) is proportional to VL(t)). Thus,
In the example illustrated in
In operation, a modulated input signal mi(t), referenced to ground, may be injected into the test tap 72 of the first bushing H1 by the modulation portion 10 (“M” in
For each injection and measurement step in the complete cycle, the portion of the signal that goes to the external power system on the supply side is measured by a first current transformer CT1 and the portion that goes to the load side is measured by a fourth current transformer CT4. The portions of the injected signal that are distributed throughout the internal transformer circuit and the insulation structures (modeled as CH, CHL and CL) are measured by internal current transformers CT2, CT3, CT5, and CT6, and the resulting signals at each bushing H0, X1, and X0 are measured by the sensor on the test tap of each respective bushing. The sequence is repeated with the input sensor being changed to the third bushing X1, then to the second bushing H0, then to the fourth bushing X0, with the resulting signals measured by corresponding current transformer sensors and non-input bushing sensors.
The measured signals are demodulated by the demodulation portion 12 (“D” in
In the continuous time domain, a transformer is an electro-magnetic circuit which in its ideal form does not affect a change in the power factor between the primary and secondary circuit, i.e.
Cosine(θi)=Cosine(θo);
The noise is generally due to a combination of partial discharge, corona, radio interference voltage, and Barkhausen noise in the core at different mid-band frequencies of 150 kHz, 35 kHz and 1 MHz respectively. In the illustrated examples, a suitable filter may be provided for each measurement channel.
As illustrated in
Si(t)=X(t)+Nx(t) (Equation 1.4)
This noise can be assumed to be independent and identically distributed with a Gaussian distribution with mean zero and variance σx2 as:
Nx(t)˜N(0,σx2) (Equation 1.5)
Further, as illustrated in
MODULATED INPUT: Mi(t)=sp(t)·si(t) (Equation 1.6)
Let h(t) be the impulse response of the transformer under consideration. Then the output of the transformer may be given by:
MODULATED OUTPUT: Mo(t)=[input]*h(t) (Equation 1.7)
MODULATED OUTPUT: mo(t)=[sp(t)·si(t)]*h(t) (Equation 1.8)
Fourier Transform is applied to both the input as in Equation (1.6) and output as in Equation (1.8), which yields:
INPUT: MI(s)=SP(s)*SI(s) (Equation 1.9)
OUTPUT: MO(s)=[V(s)*SI(s)]·H(s) (Equation 1.10)
Thus, any changes in the power factor due to changes in the insulation structure caused by failures can be easily assessed after demodulation is conducted at points ‘b’ and ‘c,’ by retrieving the original injected signal and finding the changes in the phase angles of the input and output signals. The error in change in the phase angle at the input to the modulator and phase of the output of the demodulator may be tracked by a phase locked loop control circuit. When the error is zero, indicating no change, the power factor of this error is unity. When some error phase angle exists, then the power factor of this error is the error angle itself for a small angle change, for example when cos(θ)=θ. The above analysis is in the continuous time domain.
The same data is processed in the digital domain using suitable sensors and digital data acquisition circuits, i.e., analog-to-digital converter s or digital-to-analog quantities and digital filters to create the system. It is imperative to note that Equations (1.9) and (1.10) are in a matrix form and will include all parameters that are necessary to assess the condition of the transformer as a system at different points in the circuit, for example, as illustrated in
For a digital time domain formulation, the data must be obtained using a suitable sensor and then using a corresponding analog-to-digital converter. The analog-to-digital converter may require a minimum sampling rate of 20 kilo samples/sec or higher as the injected signal frequency increases up to 100 k Hz when the sampling rate will be 200 kilo samples per sec. The sensor will include a low pass filter that can acquire the power signal as in Equation (1.1) from the capacitor tap of the bushing on the respective side of the transformer and pass it on to the analog-to-digital converter. This will be given by:
Sp(k); k=1,2,3, . . . (Equation 1.11)
corrupted with white noise
Nv(k)˜N(o,σ2) independent and identically distributed; k=1,2,3 . . . (Equation 1.12)
The injected signal as in Equation (1.4) will be inserted using a suitable vector signal generator or a similar vector signal generator and modulated with the power signal passing through the transformer. The digitized injected signal in the illustrated circuit as introduced by the vector generator is given by:
Si(k); k=1,2,3,4 . . . (Equation 1.13)
corrupted with white noise
Nx(k)˜N(0,σx2) independent and identically distributed; =1,2,3, . . . (Equation 1.14)
This digitized signal as in Equation (1.11), whose continuous version is as in Equation (1.4), is then digitally modulated using phase modulation with the digitized version of the power signal as in Equation (1.13), whose continuous version is as in Equation (1.2). The digitized signals at appropriate measurement levels are obtained by the use of potential or current transformers at strategic points in the circuit as shown in
The present disclosure illustrates this for a general system for the phase change between points ‘a’ and ‘b’ in the circuit illustrated in
The modulation and demodulation of the power signal and the corresponding injected signals are obtained by using sensors suitable for the power signal at 60 Hz and injected signal at 10 kHz. Suitable filters may be incorporated in the design of the signals at suitable levels needed for measurements. The signals may be modulated using phase modulation scheme. The resulting evaluations of the change in phase angles at points ‘a’, ‘b,’ and ‘c’ yield data in the change in the transfer function in the digital domain generally obtained by Z-transforms of the digitized functions. A change in the phase angles Φp and Φi is obtained as in the continuous time domain analysis using phase locked loop (PLL) circuits 26, 28 in the digital domain and suitable digital-to-analog quantities 22, 24.
Equations (1.7-1.10) are affected in the digital domain to obtain information and characteristics of the change in the phase angle associated with the transformer system due to any change in the core-coil insulation structure caused by any insulation structural failure caused by different faults occurring in the transformer.
The following table lists variables and parameters mentioned in this application.
Ordinal numbers (“first,” “second,” “third,” etc.) are used herein only to provide clarity and context, and should not be considered limiting except to distinguish similar elements from each other in context.
What have been described above are examples. This disclosure is intended to embrace alterations, modifications, and variations to the subject matter described herein that fall within the scope of this application, including the appended claims. As used herein, the term “includes” means including but not limited to. The term “based on” means based at least in part on. Additionally, where the disclosure or claims recite “a,” “an,” “a first,” or “another” element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements.
This application claims priority to U.S. Provisional Patent Application No. 62/899,941, filed Sep. 13, 2019. The entire disclosure of U.S. Provisional Patent Application No. 62/899,941 is incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 20050261563 | Zhou | Nov 2005 | A1 |
| 20120322050 | Abassi | Dec 2012 | A1 |
| 20140119724 | Chi | May 2014 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20210190851 A1 | Jun 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| 62899941 | Sep 2019 | US |
