US 12,282,073 B2
Inter-turn fault detection in current transformers
Mahdi Davarpanah, Tehran (IR); Mohammad Rasoul Noori, Tehran (IR); Abbas Torkamani, Tehran (IR); and Hossein Dadashi Ilkhechi, Tehran (IR)
Assigned to Electronic Sazan Fan Aria Company, (IR)
Filed by Mahdi Davarpanah, Tehran (IR); Mohammad Rasoul Noori, Tehran (IR); Abbas Torkamani, Tehran (IR); and Hossein Dadashi Ilkhechi, Tehran (IR)
Filed on May 23, 2023, as Appl. No. 18/321,815.
Claims priority of provisional application 63/344,640, filed on May 23, 2022.
Prior Publication US 2023/0288498 A1, Sep. 14, 2023
Int. Cl. G01R 31/62 (2020.01)
CPC G01R 31/62 (2020.01) 19 Claims
OG exemplary drawing
 
1. A method for inter-turn fault detection in a current transformer (CT), the method comprising:
obtaining a first normalization factor at an initial time, comprising:
coupling an AC power supply to a secondary winding of the CT;
generating, utilizing the AC power supply, a sinusoidal voltage;
setting an amplitude of the sinusoidal voltage equal to a knee-point voltage of the CT;
setting a frequency of the sinusoidal voltage equal to a measurement frequency of the knee-point voltage;
setting the amplitude of the sinusoidal voltage and the frequency of the sinusoidal voltage responsive to the knee-point voltage being higher than a first voltage threshold, according to a set of operations defined by the following:
fT1=f1×Vth1/Ukp
VT1=Vth1
where:
f1 is the measurement frequency,
Vth1 is the first voltage threshold,
Ukp is the knee-point voltage of the CT,
fT1 is the frequency of the sinusoidal voltage, and
VT1 is the amplitude of the sinusoidal voltage;
obtaining, utilizing one or more processors, an initial hysteresis curve of the CT from the sinusoidal voltage; and
calculating, utilizing the one or more processors, the first normalization factor according to an operation defined by the following:
IFI1base=AhHYS×IhT1-max
where IFI1base is the first normalization factor, AhHYS is a size of an area surrounded by the initial hysteresis curve, and IhT1-max is a zero-crossing of the initial hysteresis curve;
obtaining a second normalization factor at the initial time, comprising:
generating, utilizing a current source, a sinusoidal current;
setting a frequency of the sinusoidal current equal to the measurement frequency;
injecting the sinusoidal current to a primary winding of the CT;
measuring an initial open-circuit voltage waveform of the secondary winding responsive to injecting the sinusoidal current to the primary winding;
reducing the amplitude of the initial open-circuit voltage waveform to lower than the second voltage threshold responsive to an amplitude of the initial open-circuit voltage waveform being higher than a second voltage threshold by reducing the frequency of the sinusoidal current;
adjusting an amplitude of the sinusoidal current until the amplitude of the initial open-circuit voltage waveform satisfies a condition defined according to the following:
Kmin×√2×Ukp≤VHpeak≤Kmax×√2×Ukp
where VHpeak is the amplitude of the initial open-circuit voltage waveform and Kmin and Kmax are constants where Kmin<Kmax; and
calculating, utilizing the one or more processors, the second normalization factor according to an operation defined by the following:

OG Complex Work Unit Math
where IFI2base is the second normalization factor, VHh1 is an amplitude of a first harmonic of the initial open-circuit voltage waveform and VHh3 is an amplitude of a third harmonic of the initial open-circuit voltage waveform;
obtaining a first inter-turn fault index of the CT at a test time after the initial time, comprising:
applying the sinusoidal voltage across a secondary winding of the CT by coupling the AC power supply to the secondary winding;
measuring, utilizing a voltage sensor, the AC voltage;
measuring, utilizing a current sensor, an electric current passing through the AC power supply responsive to applying the sinusoidal voltage across the secondary winding;
obtaining, utilizing the one or more processors, a hysteresis curve of the CT from the sinusoidal voltage and the electric current; and
calculating, utilizing the one or more processors, the first inter-turn fault index according to an operation defined by the following:
IFI1=AHYS×IT1-max/IFI1base
where IFI1 is the first inter-turn fault index, AHYS is a size of an area surrounded by the hysteresis curve, and IT1-max is a zero-crossing of the hysteresis curve;
obtaining a second inter-turn fault index of the CT, comprising:
injecting, utilizing the current source, the sinusoidal current to the primary winding;
measuring the open-circuit voltage waveform of the secondary winding responsive to injecting the sinusoidal current to the primary winding; and
calculating, utilizing the one or more processors, the second inter-turn fault index according to an operation defined by the following:

OG Complex Work Unit Math
where IFI2 is the second inter-turn fault index, Vh1 is an amplitude of a first harmonic of the open-circuit voltage waveform, and Vh3 is an amplitude of a third harmonic of the open-circuit voltage waveform; and
detecting, utilizing the one or processors, an inter-turn fault in the CT responsive to at least one of:
the first inter-turn fault index being larger than a first fault threshold; and
the second inter-turn fault index being larger than a second fault threshold.