Corona cages are used in overhead power line studies to investigate physical mechanisms involved in corona discharge and to predict radio noise generation. In this paper, we design a small laboratory corona cage to investigate wideband radio noise generation on practical HVac conductor bundles. We introduce and describe cage design criteria including the insulation of the cage mesh. Our measurement method generates data that can be used to calculate the characteristics of both fair-weather and foul-weather radio noise for interference studies over a wide bandwidth. We achieve this through time-domain measurements obtained on an 8-bit, 100-MHz sampling card. Single and multiple corona pulses are studied and we propose a single corona pulse source excitation function for small cages.

Small Corona Cage for Wideband HVac Radio Noise Studies: Rationale and Critical Design

The corona, electric field and ion- current performnance of a 6 x 406-cm conductor bundle, chosen for use on a ±900-kV bipolar HVDC transmission line, was studied on a test line for a period of over 18 months The results obtained provide a statistical evaluation of radio interference (RI), audible noise (AN), corona loss (CL), electric field and ozone generated by the line at the nominal voltage as well as furnishing data on the frequency spectra of AN and on the lateral profiles of RI, AN and ion-current density at ground level In addition, the results were analyzed to obtain the influence of atmospheric variables such as air density, humidity and wind velocity on the corona performance characteristics and to draw conclusions about the influence of the test duration on the statistical significance of the results

Long-Term Statistical Study of the Corona Electric Field and Ion-Current Performance of a ±900-kV Bipolar HVDC Transmission Line Configuration

Various conductor corona test methods have been used to predict corona performance of HVAC transmission lines. Due to the formation and build-up of space charge, it is unclear whether the same methods can be used for corona performance of HVDC conductors. We investigate the use of a large corona cage, a short test line, and a small corona cage at high altitude to generate RI data. Wideband excitation functions are derived using time- and frequency-domain techniques. These generation functions are compared to CISPR standard narrowband measurements as well as published empirical RI prediction formulas. We find that a small corona cage cannot be used to accurately predict the RI performance of HVDC transmission lines at high altitude.

Wideband and Narrowband HVDC Conductor Corona Test Methods for Radio Noise Prediction

An algorithm for calculating electromagnetic interference from power line corona for a range of frequencies from 100 kHz to 30 MHz is demonstrated. It can be used for calculations at any distance or direction from the line. The algorithm incorporates an existing generation function which has been optimized by comparison to long term electromagnetic interference measurements. >

A method for calculating wide band electromagnetic interference from power line corona

Prior to construction of the Manitoba Hydro Nelson River DC system, the HVDC corona performance of the transmission lines was predicted from test line measurements made at NRC Ottawa in 1967-69. Radio interference, corona power loss and the effect of drag stringing were studied [1,2]. Since completion of the two 895 km (556 mile) lines in Manitoba in March 1971, radio interference measurements were made at various system voltages. This paper gives radio interference results and compares them with test line predictions. Measurements of combined corona and insulator leakage loss on the 895 km line were made also in April 1978. The results of loss tests are presented and compared with 1967-69 predictions.

The Corona and Radio Interference Performance of the Nelson River HVDC Transmission Lines

The radio interference from high voltage transmission lines is generally measured using either the CISPR or the ANSI type of instrument to give the quasipeak value and in some cases also the peak and average values, of the interference. However, because of the random and uncorrelated nature of corona generation on the transmission lines, the analysis of radio interference propagation can be made only in terms of rms quantities. In order to resolve this apparent inconsistency between the measurement and analysis of radio interference, the response of the conventional radio noise meters to random pulses is investigated using digital computer simulation. Some results are verified using a hybrid computer simulation, which represents more closely the detector output circuit of a radio noise meter. The results show that as the degree of randomness, both in amplitudes and separation intervals, of the pulses increases, the quasi-peak value becomes roughly proportional to the rms value. It is also shown that it is possible to predict, even with greater accuracy, the rms response of the radio noise meter from the measured quasi-peak and average responses.

Nguyen T. Chinh

Papers

Radio Noise Meter Response to Random Pulses by Computer Simulation