A simple and novel approach in the design of an extended Kalman filter (EKF) for the measurement of power system frequency has been presented in this paper. The design principles and the validity of the model have been outlined. The performance of this filter has been compared with some of the existing methods for estimating the frequency of a signal under noisy conditions. The feasibility of the proposed filter has been tested in the laboratory under worst-case measurement and network conditions, which might occur in a typical power system. Also, the proof of the stability for the proposed filter has been discussed for a single sinusoid. It has been found that the proposed algorithm is suitable for real-time applications especially when the frequency changes are abrupt and the signal is corrupted with noise and other disturbances due to harmonics.

A novel Kalman filter for frequency estimation of distorted signals in power systems

A complete, three phase transformer model for the calculation of electromagnetic transients is presented. The model consists of a set of state equations solved with the trapezoidal rule of integration in order to obtain an equivalent Norton circuit at the transformer terminals. Thus the transformer model can be easily interfaced with an electromagnetic transients program. Its main features are: (a) the basic elements for the winding model are the turns; (b) the complete model includes the losses due to eddy currents in the windings and in the iron core; and (c) the solution of the state equations is obtained in decoupled iterations. For validation, the frequency response of the model is compared with tests on several transformers. Applications to the calculation of transients are given for illustration. >

/pdf/complete-transformer-model-for-electromagnetic-transients-3xyilbzg42.pdf

Complete transformer model for electromagnetic transients

With the fast-paced changing technologies in the power industry, new references addressing new technologies are coming to the market. Based on this fact, there is an urgent need to keep track of international experiences and activities taking place in the field of modern transformer design. The complexity of transformer design demands reliable and rigorous solution methods. A survey of current research reveals the continued interest in application of advanced techniques for transformer design optimization. This paper conducts a literature survey and reveals general backgrounds of research and developments in the field of transformer design and optimization for the past 35 years, based on more than 420 published articles, 50 transformer books, and 65 standards.

Transformer Design and Optimization: A Literature Survey

Partial discharges (PDs) generate wideband radio-frequency interference which can be used for noninvasive monitoring of discharges. This paper presents a novel method based on this principle for PD monitoring of substations. The significant advantage of this method lies in the ability to detect PD sources in energized equipment anywhere within a substation compound during normal operating conditions. The results obtained from the prototypes installed in the U.K. and U.S. substations are reported. Results include correlation with apparent charge and daily recordings obtained before, during, and after the failure of a 132-kV current transformer and 69-kV voltage transformer.

RF-Based Partial Discharge Early Warning System for Air-Insulated Substations

FRA tests in the frequency range up to 10 MHz were investigated using simulations and measurements. It was found that the FRA test was more sensitive to changes in the transformer at frequencies above 1 to 3 MHz than at lower frequencies. However, the effects of the conventional test circuits mask the changes at the higher frequencies. A new test method is proposed that is effective up to at least 10 MHz.

Improved detection of power transformer winding movement by extending the FRA high frequency range

Electromagnetic interference levels on sensitive electronic equipment are quantified experimentally and theoretically in air and gas insulated substations of different voltages. Measurement techniques for recording interference voltages and currents and electric and magnetic fields are reviewed and actual interference data are summarized. Conducted and radiated interference coupling mechanisms and levels in substation control wiring are described using both measurement results and electromagnetic models validated against measurements. The nominal maximum field and control wire interference levels expected in the switchyard and inside the control house from switching operations, faults, and an average lightning strike are estimated using high frequency transient coupling models. Comparisons with standards are made and recommendations given concerning equipment shielding and surge protection. >

Transient electromagnetic interference in substations

Measured electric and magnetic fields of switching transients are characterized in terms of their macroburst (series of transients) and micropulse (individual transient) properties and are classified according to substation voltage and type. Transient fields typical for 115-500 kV air-insulated substations (AISs) and gas-insulated substations (GISs) are reported. Macrobursts of up to 10000 individual transients with varying amplitudes and pulse repetition frequencies of 40 kHz or more can be produced during a single switch. The highest amplitude micropulse field transients are shown to scale with substation voltage. Peak vertical electric fields of 16 kV/m and horizontal magnetic fields of 212 A/m have been measured on the ground under the bus in 500 kV AISs during disconnect switching. Peak field component amplitudes are shown to double at several meters above ground and to scale approximately as 1/r with distance from the bus. Electric field enhancement above a grounded structure to many times the normal free-space value was measured. The dominant frequencies of switching transients are between 0.5 MHz and 120 MHz, vary inversely with substation voltage, and are highest in GISs. >

Switching transient fields in substations

The mechanical condition of a circuit breaker, i.e., whether the unit is in normal or abnormal condition, has been evaluated using noninvasive diagnostics, together with signal processing and decision-making techniques. Test procedures involved obtaining vibration signals from transducers placed along the external surfaces of (and, under certain conditions, within the interior of) a circuit breaker. Using the method, quantitative assessment of a circuit breaker can be carried out for any operating condition. Tests of oil and sulfur hexafluoride circuit breakers, under both normal and abnormal conditions, were carried out. In all cases, the abnormalities was detected. >

Mechanical failure detection of circuit breakers

An extensive set of switching transient EMI response measurements on several types of substation cables and internal cable wires is described in this paper. Measured and predicted cable/wire current and voltage transients at both air-insulated substations (AIS) and gas-insulated substations (GIS) are presented, for system voltages ranging from 115 kV to 500 kV. The maximum peak-to-peak amplitudes of measured wire transients are found to vary from around 1 A to almost 20 A (current in amperes), and from 0.3 kV to almost 7 kV (voltage in kilovolts). Predictive models for field-driven coupling, as well as for direct-driven coupling via current transformers or capacitively-coupled voltage transformers (CTs/CCVTs), are presented. Model predictions are compared to and validated against measured wire transients. >

Induced transients in substation cables: measurements and models

Frequency-dependent node-to-node impedance function (NIF) models of power system equipment based on systematic broad frequency range (50 Hz to 1 MHz) external driving point impedance measurements are described. Such models are needed to calculate and predict the radio frequency electromagnetic (EM) noise produced by the valve ignition of a converter station. The application of the transformer frequency-domain NIF model related to HVDC converter station EM noise calculations is demonstrated. Calculated performance data are compared with field measurements. >

S.E. Wright

Papers

Transient electromagnetic interference in substations

Switching transient fields in substations

Mechanical failure detection of circuit breakers

Induced transients in substation cables: measurements and models

Modeling of converter transformers using frequency domain terminal impedance measurements