A common method for measuring pulsed high voltages using a voltage divider

Author： GOZ Electric Time：2014-04-24 09:30:30 Read：17

      Common methods for measuring pulse high voltage are measurement systems with voltage dividers and digital storage oscilloscopes as main components, measurement systems with calculus links and digital storage oscilloscopes as main components, and photoelectric measurement systems. Pulse voltages with low voltage peaks (several kilovolts to 50 kilovolts) can be measured directly with commercial high-voltage probes or attenuators and general-purpose digital storage oscilloscopes. However, when the peak value of the measured pulse voltage is very high, the peak value and waveform must be measured through a conversion device such as a voltage divider and an impact high-voltage voltage dividing system composed of multiple other components.

         Pulse voltage dividers can be divided into resistor dividers, capacitor dividers and resistor-capacitor series voltage dividers. The resistor divider has a simple structure, high measurement accuracy, and good long-term stability. However, in order to pursue high response performance, its resistance cannot be too high, generally not greater than 10kΩ. Therefore, in order to prevent overheating, the measured peak voltage cannot be higher than 2MV. The error generated by the resistor divider when measuring the transient pulse voltage is related to the product of the resistance and the stray capacitance to ground, so the size and influence of the stray capacitance to ground should be minimized. Usually, in addition to minimizing the size of the voltage divider, technologies such as supply-type or collection-type distributed capacitance compensation and inductance compensation can also be used to improve the response performance of the voltage divider. Capacitive voltage dividers consume no energy and do not have the trouble of heating. They are more advantageous than resistive voltage dividers for measuring pulse waves with longer wave fronts and half-peak times. Due to the problem of loop spurious oscillation, the rated voltage cannot be too high for measuring steep wave pulses. And when there is a high-voltage lead, its response characteristics are not as good as a resistive voltage divider. In order to damp the oscillation of the capacitor divider loop, a resistor-capacitor series voltage divider was developed, and its performance is related to the degree of compensation and damping.

         Differentiating-Integrating measuring systems (D/I system for short) began to emerge in the early 1980s due to the development of digital measurement. The advantage of the D/I system is that it has minimal load effect on the high-voltage source. , has sufficiently high response characteristics. Its disadvantage is that the requirements for the integrator are high, and the non-inductive requirements for the resistance of the differential part are much higher than those of the general resistor divider.

         Photoelectric measurement system is a system that uses various electro-optical effects or optical communication methods to measure. Among them, the good insulation properties of optical fiber transmission lines can be used to isolate high-voltage equipment from highly sensitive measuring instruments and computers, and to reduce the impact of radio frequency interference and stray parasitic signals on the measurement loop. However, compared with traditional measurement systems based on high-voltage voltage dividers or shunts, the stability of photoelectric measurement systems is poor.

  Measurement of pulse current

         For the measurement of high pulse current, a system consisting of a shunt and a digital oscilloscope is commonly used, and a Rogowski coil is also commonly used as a transducer device. In addition, photoelectric measurement systems are also available. Three factors should be considered when designing a shunt: the residual inductance should be as small as possible; the effective impedance of the shunt must be a constant in the widest possible frequency band; for good anti-interference performance, the current flowing through the outer conductor of the cable should be minimized . When measuring pulse current with a shunt, the measured current will produce thermal and force effects in the shunt. If the current to be measured reaches hundreds of kiloamps, there will be certain difficulties in manufacturing the shunt. At this time, Rogowski coils are often used to measure the current. The Rogowski coil uses the voltage induced in the coil by the magnetic field generated by the current to be measured to measure current. It is actually a current transformer measurement system. Compared with the shunt method, the Rogowski coil has no direct electrical connection with the circuit under test, which can avoid or reduce the interference effect caused by the instantaneous increase in the ground potential of the current source grounding point. Since the voltage signal obtained at the coil output port is proportional to the derivative of the measured current with respect to time, in order to directly obtain a signal proportional to the current, an integration link needs to be added to the measurement system. The integration method of Rogowski coil can be divided into two types: LR integral form (self-integrating form) and RC integral form. Regardless of the integration method, the response characteristics must meet the requirements during parameter selection and system construction. The rise time of the self-integrating square wave response can be less than 1ns.

         At present, the most commonly used measurement methods are: (1) measuring the ball gap; (2) a measurement system composed of a voltage divider and a digital storage oscilloscope; (3) a measurement system composed of a differential integration link and a storage oscilloscope; (4) photoelectric measurement system .

         The ball gap can only be used to measure voltage peaks, not voltage waveforms. The differential-integral measurement system began to emerge in the early 1980s due to the development of digital measurement. Its advantages are: it has minimal load effect on high-voltage sources and has sufficiently high response characteristics. The disadvantages are: when the capacitance value of the differential link is very small, the measurement error of the static voltage dividing ratio is often large; the non-inductive requirements of the resistance of the differential link are very high; when the rising edge of the measured pulse is very steep, the resistance of the differential link rises Extremely high spike voltages can occur. The photoelectric measurement system is a system that uses various electro-optical effects to measure. Its outstanding advantages are less intervention in the measured object and strong anti-electromagnetic interference ability. However, the system is complex, and the reliability of the measurement depends on optics and electronics. The actual performance of the system, therefore these technologies are still under development. This chapter mainly discusses the principle and production of high-voltage pulse capacitor divider.