David Pommerenke

ESD: Transient Fields, Arc Simulation and Rise Time Limit

Abstract ESD is simulated by the combination of arc resistance laws and a method of moment algorithm. Simulated results are backed up by quantitative near-field measurement on model structures, real equipment and IEC 1000-4-2 ESD simulators. It is shown that the arc resistance law by Rompe and Weizel and an electron avalanche model can be applied in ESD simulations. Other arc resistance laws fail. Disturbances by ESD are dominated by the arc length, not directly by voltage. Arc length is controlled by voltage, speed of approach and time lag. For approaching objects ultimately field emission initiates sparking if the breakdown has not been initiated earlier by other processes. The onset of field emission can be calculated by evaluation of the Fowler-Nordheim equation. Using the resulting minimal arc length and an arc model a lower rise time limit of approx. 20 ps can be calculated.

Numerical modeling of electrostatic discharge generators

The discharge current and the transient fields of an electrostatic discharge (ESD) generator in the contact mode are numerically simulated using the finite-difference time-domain method. At first the static field is established. Then the conductivity of the relay contact is changed, which initiates the discharge process. The simulated data are used to study the effect of design choices on the current and fields. They are compared to measured field and current data using a multidecade broadband field and current sensors. The model allows accurate prediction of the fields and currents of ESD generators, thus it can be used to evaluate different design choices.

ESD: WAVEFORM CALCULATION, FIELD AND CURRENT OF HUMAN AND SIMULATOR ESD

Abstract Currents, current derivatives and transient fields of human ESDs are compared to currents and fields caused by commercial simulators. The results point at undefined but influential parameters of simulators and the standardized setup used. Suggestions for possible improvements of ESD test standards are given. A calculation method for the ESD current is provided. This method includes an arc model. Possible high peak current values ( > 10 A/kV) are validated by a simple physical model of the hand-metal piece geometry. By calculation it is shown under which circumstances human ESD currents come close to the standardized waveform of simulators.

Computer simulation of ESD from voluminous objects compared to transient fields of humans

Computer simulation of electrostatic discharge (ESD) for simplified objects is described and compared to measured transient fields of human/metal ESD. The simulation algorithm uses the method of moments in time domain, coupled with nonlinear arc resistance model. Transient currents and fields are analyzed from the electromagnetic compatibility (EMC) point of view. Validation of the numerical simulation is done by comparison to experimental data. The simulated structure models the human/metal ESD in its peak current and field values and their derivatives reasonably well.

Numerical calculation and measurement of transient fields from electrostatic discharges

The paper compares measured and numerically calculated results of currents and transient fields caused by electrostatic discharges (ESDs). An algorithm based on the magnetic field integral equation was combined with an arc model. It takes the nonlinearity of the arc and the dependence of the breakdown process on the arc length into account. It can calculate the discharge currents and the transient fields for perfectly conducting bodies of revolution.

Discrimination between internal PD and other pulses using directional coupling sensors on HV cable systems

On-site partial discharge (PD) measurement is required to ensure proper installation of extra high voltage (EHV) cable systems accessories. To achieve high sensitivity and good localization, two problems have to be overcome. First, the strong high frequency in long XLPE cables requires that the sensors be located along the cable, preferably directly at the accessories. Secondly, the detection system must be able to distinguish internal PD from other pulses. This paper describes a solution based on directional coupling sensors and a data visualization system, which displays phase-amplitude diagrams for individual PD sources which are identified by the direction of pulse propagation. It has been applied to on-site measurements, type and routine testing of HV cable joints and stress cones. Due to the reliable discrimination between internal PD from the accessory measured and from other pulses, testing can be done in unshielded rooms even using terminations with internal PD and corona. The method works independently well on line voltage, resonance sources, oscillating voltages and 0.1 Hz cosine-square voltage. It has been used to verify the cable accessories installed in the 6.3 km long 380 kV cable system in Berlin, Germany.

Numerical simulation of partial discharge propagation in cable joints using the finite difference time domain method

In this second of a series of three papers, the authors investigate partial discharge (PD) detection and propagation in cable joints. The complex nature of cable joints leads to errors when PD analysis is carried out using conventional equivalent circuits. The authors use the finite difference time domain method to determine the transient electromagnetic fields caused by simulated PD in model cable joints.

Broadband measurement of ESD risetimes to distinguish between different discharge mechanisms

Different discharge mechanisms are possible for ESD (electrostatic discharge) below 2 kV breakdown voltage as a function of the parameters gap distance, breakdown voltage, electrode material and gas pressure. In this paper, risetime measurement data of electrostatic discharges, measured at about 8 GHz bandwidth, are presented as a function of these parameters. Electrode SEM photographs (scanning electron microscope) helps to understand the influence of electrode surface. This provides information about the development of ESD and helps to increase their reproducibility.

To what extent do contact-mode and indirect ESD test methods reproduce reality?

Currents, current derivatives and transient fields of ESDs of humans are compared to currents and fields caused by simulators. A method for the simulation of the discharge current is provided. This method includes an arc model. The resulting high peak current values (>10 A/kV) are validated by a simple physical model of the hand geometry. Investigations of transient fields from simulators point to differences between simulators from different manufactures and between the transient fields caused by humans compared to the fields from simulators. Suggestions for possible improvements of the ESD test standard are given.

Partial discharge on-line monitoring for HV cable systems using electro-optic modulators

A technique for the remote inspection and monitoring of partial discharge (PD) activity using an optical network is described. The network uses a LiNbO/sub 3/, modulator to modulate the intensity of the transmitted laser light approximately proportional to the voltage applied across the modulator. The laser light is transmitted along an optical fibre and measured remotely by a high-speed optical receiver. A capacitive coupler has been used to detect partial discharge activity and act as the modulators input voltage source. The electro-optic modulator is passive and does not require a power supply at the site of the PD detection sensor. The system has the additional advantages of being immune to electromagnetic interference, having very little signal transmission attenuation, with good sensitivity, compact size, as well as being convenient to use and safe. Both simulation experiments and practical PD tests on two cable systems have indicated that the optical system provides a feasible remote PD monitoring technique for high voltage cable systems.