Abstract
Contactless capacitive sensors are applied to monitor(over)voltages near the overhead line terminations of asubstation or at cable to line transitions. The sensor response isthe signal time derivative when loaded with a resistiveimpedance and the waveform is restored by integration. As partof this differentiating/integrating (D/I) measuring concept, theuse of open-air sensors results in excellent EMC characteristicsbut the inherent cross-coupling to other phases has to be dealtwith. Three applications are presented: 1) For a 150 kV cabletermination the partial discharge activity needs to be related tomomentary phase voltages; 2) Measured slow front overvoltageat a 380 kV cable termination from line energizationare compared with predictions from numerical simulation; 3)The perspectives of employing the D/I method for (very) fastfront overvoltages near a 380 kV circuit breaker are examined.
Highlights
Terminations at the end of a transmission line or at a transition between overhead line and underground power cable are critical components in electrical insulation
For partial discharge (PD) interpretation, one needs to distinguish internal discharges arising inside the terminations from corona discharges coming from the connecting overhead lines
The PD activity can be correlated to the momentary angle of the phase voltages
Summary
Terminations at the end of a transmission line or at a transition between overhead line and underground power cable are critical components in electrical insulation. For PD interpretation, one needs to distinguish internal discharges arising inside the terminations from corona discharges coming from the connecting overhead lines To this end, the PD activity can be correlated to the momentary angle of the phase voltages. Voltage monitoring can provide information on the exposure of the insulation to slow or fast front transient overvoltages Such overvoltage types arise e.g. from line energization and can cover a wide frequency spectrum ranging from power frequency to 100 MHz [1]. The major fraction drops over the highest impedance which is located at the sensor side, whereas at the measurement side only a small fraction arises This is different from a capacitive divider where, in order not to load the low-voltage branch of the divider, the receiving end impedance is taken relatively large. The discussed applications will make use of symmetries, reducing the total number of unknowns
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