Abstract: The present invention relates to a method and monitoring device, for monitoring N number of transformer bushings operating in substantially the same environment. N being any number more than 1. The method comprises estimating an absolute value for the capacitances of each of the bushings, the absolute values for the capacitances being denoted Cx, and estimating an absolute value for the loss factor or the power factor of each of the bushings, the absolute values for the loss factors or the power factors being denoted Fx. X is a number representing which bushing the value is associated to and X larger than 1. The method further comprises calculating ?-values for all C values and ?-values for all F values, according to: ?CX=CX?CX+1, for all values up to, and including, ?CN?1, ?CN=CN?C1, for ?CN, ?FX=FX?FX+1, for all values up to, and including, ?FN?1, ?FN=FN?F1, for ?FN, and determining whether the ?-values are within predefined ranges.

Abstract: Embodiments are disclosed for determining states of electrical equipment using diagnostic parameter prediction error. A prediction error value is determined for a plurality of predicted diagnostic parameter values over a predetermined time period for at least one component of an electrical equipment. The prediction error value suppresses variations observed in behavior of the at least one component. The determined prediction error value is compared to an expected prediction error value. An indication of a state of the at least one component is selectively generated based on the comparison.

Abstract: There is provided mechanisms for monitoring substation equipment. A method is performed by a SCADA system. The method comprises obtaining data/signal values of parameters monitored in the substation equipment. The method comprises associating each data/signal value with at least one attention indicator. The method comprises determining one attention indicator value for each of the attention indicators by processing those data/signal values that are associated with the respective attention indicators. All attention indicators for all monitored parameters have one and the same nominal attention indicator value acting as a threshold for abnormal behavior of the substation equipment. The method comprises providing an alert indication to a human machine interface (HMI) when at least one of the attention indicator values is above the nominal attention indicator value.

Abstract: The present invention relates to a method and monitoring device, for monitoring N number of transformer bushings operating in substantially the same environment. N being any number more than 1. The method comprises estimating an absolute value for the capacitances of each of the bushings, the absolute values for the capacitances being denoted Cx, and estimating an absolute value for the loss factor or the power factor of each of the bushings, the absolute values for the loss factors or the power factors being denoted Fx. X is a number representing which bushing the value is associated to and X larger than 1. The method further comprises calculating ?-values for all C values and ?-values for all F values, according to: ?CX=CX?CX+1, for all values up to, and including, ?CN?1, ?CN=CN?C1, for ?CN, ?FX=FX?FX+1, for all values up to, and including, ?FN?1, ?FN=FN?F1, for ?FN, and determining whether the ?-values are within predefined ranges.

Abstract: A method of determining the capacitance and loss-factor of each of a plurality of capacitive components of an electrical power device, wherein the method includes: a) obtaining for each capacitive component a respective capacitance value and loss-factor value, and b) processing the capacitance values and the loss-factor values, wherein the processing involves removing a common influence of temperature on the capacitance values from the capacitance values and removing a common influence of temperature on the loss-factor values from the loss-factor values to obtain for each capacitive component a temperature-compensated capacitance value and a temperature-compensated loss-factor value.

Abstract: A method of determining the capacitance and loss-factor of each of a plurality of capacitive components of an electrical power device, wherein the method includes: a) obtaining for each capacitive component a respective capacitance value and loss-factor value, and b) processing the capacitance values and the loss-factor values, wherein the processing involves removing a common influence of temperature on the capacitance values from the capacitance values and removing a common influence of temperature on the loss-factor values from the loss-factor values to obtain for each capacitive component a temperature-compensated capacitance value and a temperature-compensated loss-factor value.

Abstract: The invention is concerned with a monitoring device, method and computer program product for monitoring a transformer having a tap changer. The transformer has at least two magnetically coupled windings and a tap changer having impedance elements and a changeover switch configured to gradually pass the impedance elements when changing between two tap changer positions during a tap change operation. The method is performed in the monitoring device and including: obtaining waveforms of measured power transmission properties recorded at the first and second transformer sides, processing the recorded waveforms for obtaining at least one waveform (Ploss) representing a tap change operation, and extracting information indicative of the performance of the tap change from the at least one waveform that represents the tap change operation.

Abstract: A system and a method for determining the power loss of a transformer. The method includes measuring voltage and current at the primary side of the transformer, calculating input power by multiplying the measured current and voltage on the primary side of the transformer; measuring voltage and current at the secondary side of the transformer, calculate a nominal error ratio, calculating output power by multiplying the measured current and voltage on the secondary side of the transformer. The method further involves calculating a first corrected power loss by means of multiplying the input power with the nominal error ratio and subtract the output power.

Abstract: The invention is concerned with a protection device, method and computer program product for protecting a transformer including a tap changer and a transformer arrangement including a transformer and a protection device. The transformer has at least two magnetically coupled windings with terminals (MT1, MT2, MT3, MT4) at which power enters and exits the transformer and a tap changer having impedance elements and a switch configured to gradually connect the impedance elements when changing between two tap changer positions during a tap changing operation.

Abstract: The invention is concerned with a protection device, method and computer program product for protecting a transformer including a tap changer and a transformer arrangement including a transformer and a protection device. The transformer has at least two magnetically coupled windings with terminals (MT1, MT2, MT3, MT4) at which power enters and exits the transformer and a tap changer having impedance elements and a switch configured to gradually connect the impedance elements when changing between two tap changer positions during a tap changing operation.

Abstract: A system for monitoring transformer bushings sensors, wherein first and second bushing sensors are connected to a common first phase of a high voltage source, and the third and fourth bushing sensors are connected to a common second phase of the high voltage source. A first time series is generated from the first and second bushing sensors during a predetermined time interval. A second time series, is generated from the third and fourth bushing sensors during the predetermined time interval. A correlation model for the first and second time series for determining a difference between a measured signal and an estimated signal, and generating a signal indicative of a bushing problem the difference is larger than a threshold.

Abstract: The invention is concerned with a monitoring device, method and computer program product for monitoring a transformer having a tap changer. The transformer has at least two magnetically coupled windings and a tap changer having impedance elements and a changeover switch configured to gradually pass the impedance elements when changing between two tap changer positions during a tap change operation. The method is performed in the monitoring device and including: obtaining waveforms of measured power transmission properties recorded at the first and second transformer sides, processing the recorded waveforms for obtaining at least one waveform (Ploss) representing a tap change operation, and extracting information indicative of the performance of the tap change from the at least one waveform that represents the tap change operation.

Abstract: A method of determining phasor components of a periodic waveform, wherein the method includes: a) sampling the periodic waveform, b) determining a frequency spectrum of the sampled periodic waveform by means of a frequency transform utilizing a Gaussian window function, wherein a ratio np defined by the duration of the sampling of the periodic waveform divided by the width parameter of the Gaussian window function is at least 5, c) selecting a region of the frequency spectrum containing a frequency peak defined by a group of consecutive frequency bins each being defined by a frequency value and a magnitude value, and d) determining phasor components of the periodic waveform based on the group of consecutive frequency bins.

Abstract: A system and a method for determining the power loss of a transformer. The method includes measuring voltage and current at the primary side of the transformer, calculating input power by multiplying the measured current and voltage on the primary side of the transformer; measuring voltage and current at the secondary side of the transformer, calculate a nominal error ratio, calculating output power by multiplying the measured current and voltage on the secondary side of the transformer. The method further involves calculating a first corrected power loss by means of multiplying the input power with the nominal error ratio and subtract the output power.

Abstract: A method of determining phasor components of a periodic waveform, wherein the method includes: a) sampling the periodic waveform, b) determining a frequency spectrum of the sampled periodic waveform by means of a frequency transform utilizing a Gaussian window function, wherein a ratio np defined by the duration of the sampling of the periodic waveform divided by the width parameter of the Gaussian window function is at least 5, c) selecting a region of the frequency spectrum containing a frequency peak defined by a group of consecutive frequency bins each being defined by a frequency value and a magnitude value, and d) determining phasor components of the periodic waveform based on the group of consecutive frequency bins.

Abstract: A system for monitoring transformer bushings sensors, wherein first and second bushing sensors are connected to a common first phase of a high voltage source, and the third and fourth bushing sensors are connected to a common second phase of the high voltage source. A first time series is generated from the first and second bushing sensors during a predetermined time interval. A second time series, is generated from the third and fourth bushing sensors during the predetermined time interval. A correlation model for the first and second time series for determining a difference between a measured signal and an estimated signal, and generating a signal indicative of a bushing problem the difference is larger than a threshold.

Abstract: A transformer diagnosis apparatus and method which can advantageously be used for on-line diagnosis of a transformer, and by which transformer properties may be monitored and/or determined. The diagnosis method includes collecting, for at least two different transformer loads, measurements of a current being indicative of the transformer load, as well as measurements of at least one further transformer AC signal. The method further includes deriving, from the collected measurements, at least two values of a quantity which depends on a transformer property as well as on transformer load; and determining, from the derived values, a set of coefficient(s) of a relation for how the quantity is expected to vary with transformer load. The method further includes using the determined coefficient(s) in performing a diagnosis of the transformer.

Abstract: A transformer diagnosis apparatus and method which can advantageously be used for on-line diagnosis of a transformer, and by which transformer properties may be monitored and/or determined. The diagnosis method includes collecting, for at least two different transformer loads, measurements of a current being indicative of the transformer load, as well as measurements of at least one further transformer AC signal. The method further includes deriving, from the collected measurements, at least two values of a quantity which depends on a transformer property as well as on transformer load; and determining, from the derived values, a set of coefficient(s) of a relation for how the quantity is expected to vary with transformer load. The method further includes using the determined coefficient(s) in performing a diagnosis of the transformer.