Wideband measurement system for mixed-connected capacitive voltage transformer based on optical voltage sensor

A wideband measurement system for mixed-connected capacitive voltage transformer (CVT) based on an optical voltage sensor, comprising a CVT power frequency measurement section and an optical wideband measurement section;

• wherein the optical wideband measurement section comprises a low-voltage capacitor, an optical voltage sensor, a signal processing unit, and a monitoring and analysis host;
• wherein the CVT power frequency measurement section comprises a voltage divider, and the voltage divider comprises a series connection of a high-voltage capacitor and a mid-voltage capacitor;
• the low-voltage capacitor is connected between a lower end terminal of the mid-voltage capacitor and a grounded junction of the optical wideband measurement section;
• the optical voltage sensor is connected in parallel to two ends of the low-voltage capacitor;
• the optical voltage sensor, triggered by a superluminescent diode (SLD) light source in the signal processing unit, splits a light signal modulated by the low-voltage capacitor into two beams and directs the two beams into the signal processing unit;
• the signal processing unit converts the two incoming light signals into two voltage signals being uo1 and uo2, and obtains a voltage signals in a medium-to-low frequency range uoL (f1) and a voltage signal in a high-frequency range uoH (f2);
• and
• the monitoring and analysis host captures the voltage signals in the medium-to-low frequency range uoL (f1) and the voltage signal in the high-frequency range uoH (f2), and calculates to obtain a wideband voltage signal;
• wherein the signal processing unit comprises:
• a low-pass filter circuit, a 1 #bandpass filter amplifier circuit, a 2 #bandpass filter amplifier circuit, a 1 #divider, a 2 #divider, a 3 #divider, a 4 #divider, a 1 #subtractor, a 2 #subtractor, the SLD light source, a 1 #photodetector, and a 2 #photodetector;
• the SLD light source serves as a triggering light source for the optical voltage sensor;
• the two beams of light emitted from the optical voltage sensor are respectively converted into the voltage signals uo1 and uo2, by the 1 #photodetector and the 2 #photodetector;
• the low-pass filter circuit extracts a direct-current (DC) bias voltage Us1 from the voltage signal uo1 and extracts a DC bias voltage Us2 from the voltage signal uo2;
• the 1 #bandpass filter amplifier circuit performs bandpass filtering and amplification on the voltage signal uo1 to obtain a medium-to-low frequency voltage signal u1L (f1) and performs bandpass filtering and amplification on the voltage signal uo2 to obtain a medium-to-low voltage signal u2L(f1);
• the 2 #bandpass filter amplifier circuit applies bandpass filtering and amplification to the voltage signal uo1 to obtain a high-frequency voltage signal u1H (f2) and applies bandpass filtering and amplification to the voltage signal uo2 to obtain a high-frequency voltage signal u2H (f2);
• the 1 #divider calculates a quotient A between the medium-to-low frequency voltage signal u1L (f1) and the DC bias voltage Us1;
• the 2 #divider calculates a quotient B between the medium-to-low frequency voltage signal u2L (f1) and the DC bias voltage Us2;
• the 3 #divider calculates a quotient C between the high-frequency voltage signal u1H(f2) and the DC bias voltage Us1, while the 4 #divider calculates a quotient D between the high-frequency voltage signal u2H (f2) and the DC bias voltage Us2;
• the 1 #subtractor takes a difference between the quotient A and the quotient B to obtain the voltage signal in the medium-to-low frequency range uoL(f1);
• the 2 #subtractor calculates a difference between the quotient C and the quotient D to obtain the voltage signal in the high-frequency range uoH(f2);
• and wherein the monitoring and analysis host calculates the wideband voltage signal according to following equation:
• uoL(f1)=G1kKCu1(f1),
• uoH(f2)=G2kKCu1(f2),
• wherein G1 and G2 are amplification factors of the 1 #bandpass filter amplifier circuit and the 2 #bandpass filter amplifier circuit, respectively;
• u1(f1) and u1(f2) represent a low-frequency voltage component and a high-frequency voltage component, respectively;
• u1 denotes the wideband voltage signal loaded on a voltage monitoring terminal, wherein the voltage monitoring terminal is a high-voltage end of the voltage divider;
• k is an electro-optic constant, and KC is a voltage division ratio of the low-voltage capacitor.