he HVcompact is a high voltage meter with an auto-ranging oscilloscope display of the voltage waveform. The unit displays the peak voltage Û, Û/√2, Urms, frequency, and the crest factor. To improve the readability, one selected measurement is displayed using larger characters. To protect test specimens, the unit offers a pre-settable voltage limit, which trips a relay output. The divider ratio is widely adjustable and is kept with a non-volatile memory.
Mainly, the HVcompact is used in case of modernisation or upgrade of high voltage test sets. With conventional analog or digital panel meters, usually, solely the voltage is displayed. The HVcompact adds several valuable functions.
Oscilloscopic Display
The input voltage is sampled in high resolution, and one cycle is displayed as an oscilloscopic trace. Any distortion of the high voltage due to transformer core saturation or power frequency harmonics, for instance, is clearly identified with this display. The screen is automatically synchronised with the measured voltage, and an auto-range function controls the amplitude deflection.
Measurements
Usually, the instrument connects to the capacitive or resistive divider. With larger high voltage transformers, the capacitance of the condenser bushing can be used. Within the menu of the HVcompact, the divider ratio can be adjusted. It is kept with non-volatile memory. The nominal input range of the HVcompact is 100 Vrms. Peak voltages of up to 200 V are accepted and sampled to cover even strong harmonics correctly,
The instrument calculates the characteristic quantities of the high voltage signal based on the preset divider ratio by using the sampled voltage. With the upper two lines of the display, the peak voltage Û, Û/√2, and the effective voltage Urms are shown. Additionally, the crest factor is calculated and displayed. With the bottom line of the display, the frequency of the captured voltage signal is shown. This bottom line further indicates the scaling of the Y-axis grid of the oscilloscopic display. One selected value is displayed using larger characters for improved readability.
Safety Features
A voltage limit can be set with the instrument to avoid a test specimen being stressed above its allowable voltage. In case the voltage then exceeds this limit, a relay is tripped. This relay can block the 'UP' button of the control circuit or disconnect the main circuit breaker. Additionally, the instrument detects incipient breakdown or flashover. Therefore, a maximum permissible voltage change per second (dU/dt) can be set. Then, each cycle of the high voltage signal is analysed. Especially with long-term voltage endurance tests, this feature can minimise the thermal destruction of the breakdown channel and, thus, improve the defect's analysis.
Optional REC OUT
The HVcompact is available with an optional recorder output. A connector carries a re-converted analog (DC) signal of 0-10 V, which corresponds to the high voltage signal. This signal can be fed to a paper recorder, for instance. In addition, a screw terminal carries the optional relay output signals for voltage limit and break down detection.
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