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Preamplifers & Preacquisition Units

Preamplifiers and preacquisition units serve to condition, filter, and amplify the partial discharge signal to be measured. Because the frequency range in which PD signals are measured is strongly dependent on the preamplifier used, proper selection of a preamplifier is an important part of noise mitigation and can have a strong effect on the appearance of the partial discharge pattern itself.

Preamplifers & Preacquisition Units

Power Diagnostix provides a complete line of modular preamplifiers for various testing applications. The most significant difference among the preamplifiers is the frequency range in which they detect partial discharge signals. Other features that distinguish one preamplifier from another are: options for transparency and on/off switching, unipolar vs. bipolar charge detection, and the possibiltiy of galvanic isolation in the test setup.

All of the Power Diagnostix external signal conditioning modules and preamplifiers are remote supplied and remote controlled through a simple coaxial signal cable (RG58). This technique allows placement of these units close to the sensor or signal source. Furthermore, as these modules act as impedance converter and line driver, the weak signal source, such as voltage divider or coupling impedance, is not loaded by the cable capacitance or impedance.

This technique also provides enhanced over-voltage protection. All preamplifiers of the RPA series can drive a 50 W cable up to 50 m long.

The RPA1 is the standard preamplifier for measurements in the low frequency range according to standards such as the IEC 60270. The RPA1D, RPA1E, RPA1F, and RPA1G are variations on the RPA1.

The RPA1D and RPA1G are suited to connect directly to ultra-sonic acoustic sensors. To simplify connection, the they provide selectable power supply for the sensor (15 V or 28 V DC).

The RPA1L and RPA1H are intended primarily for measurements on medium and high-voltage power cables using the ICMcompact.

The RPA2 is primarily for measuring the PD signal spectra found with rotating machines, while the RPA2B is used with capacitive sensors to monitor cables and cable accessories at a higher sensitivity.

The RPA3 module is well-suited for measuring PD signal spectra, detected by sensors and antennas installed with gas insulated switchgear (GIS).

The RPA4 is a preamplifier set with fiber optic transmission, offering outstanding isolation properties.

The RPA6 allows selecting one of three frequency ranges according to the particular application. The logarithmic RPA6 is mainly used with monitoring applications, and as a versatile preamplifier for noise gating.

The frequency converter unit FCU is an ultra-wide band preaquisition unit, covering 100 to 1800 MHz. It has a logarithmic output and is mainly used for GIS applications.

The UHF1 and UHF2 offer an amplification of 27 dB in the range from 200 MHz to 1 GHz resp. 300 MHz to 2 GHz, and are suitable for boosting weak signals from GIS sensors.

The HST1B is an impedance converter for the measurement of voltages. The input impedance is as high as 10 MW and ideal to measure the low-voltage wave from e.g. a voltage divider. The output is to be connected to the SYNC IN of the ICMsystem.

Type Frequency
Roll-Off Bipolar Remarks
RPA1 40 kHz–800 kHz 10 kΩ//50 pF <200µV 40dB/dec Yes Standard preamplifier
RPA1D 40 kHz–800 kHz 10 kΩ//50 pF <200µV 40dB/dec Yes Built-in sensor supply,
switchable (15/28 V)
RPA1E 40 kHz–800 kHz 10 kΩ//50 pF <200µV 40dB/dec Yes 0/20 dB attenuation
RPA1F 40 kHz–800 kHz 10 kΩ//50 pF <200µV 40dB/dec Yes For the AIAcompact only
RPA1G 40 kHz–800 kHz 10 kΩ//50 pF <200µV 40dB/dec Yes Built-in sensor supply,
switchable (Off/15/28 V)
RPA1H 40 kHz–20 MHz 1 kΩ//50 pF <400µV 40dB/dec Yes Oil/paper cable, DSO
RPA1L 40 kHz–20 MHz 1 kΩ//50 pF <200µV 40dB/dec Yes Cable, DSO
RPA2 2 MHz–20 MHz 50 Ω//50 pF <800µV 40dB/dec No Online measurements on rotating machines
RPA2B 2 MHz–20 MHz 50 Ω//50 pF <200µV 40dB/dec No Cable sensors
RPA3 200 MHz–1 GHz 50 Ω//50 pF <300µV 40dB/dec No GIS sensors
RPA3D 50 MHz–400 MHz 50 Ω//50 pF <300µV 40dB/dec No Nearfield detection
RPA3E 20 MHz–200 MHz 50 Ω//50 pF <300µV 40dB/dec No Nearfield detection
RPA4 40 kHz–800 kHz 10 kΩ//50 pF <200µV 40dB/dec Yes Fiber optic isolation
40 kHz–800 kHz 10 kΩ//50 pF <200µV 40dB/dec No For gating, selectable frequency range, logarithmic output
RPA6 2 MHz–20 MHz 50 Ω//50 pF <200µV 40dB/dec No For gating, selectable frequency range, logarithmic output
200 MHz–500 MHz 50 Ω//50 pF <200µV 40dB/dec No For gating, selectable frequency range, logarithmic output
FCU 100 MHz–1.8 GHz 50 Ω//50 pF <200µV 40dB/dec No Logarithmic output
UHF1 200 MHz–1 GHz 50 Ω//50 pF No GIS, sensors
UHF2 300 MHz–2 GHz 50 Ω//50 pF No GIS, sensors
HST1B 20 Hz–400 Hz 10M Ω//200 pF No ICMsystem, SYNC IN