HV voltage divider resistor 3-5kV - Page 1
Forum section: electronics / testgear

author: geggi1
author_rank: Frequent Contributor
timestamp: May 06, 2021, 08:09:54 pm
content: Im looking into doing a test for a customer of mine to test some shortcircuit timing on a VFD.The line to be tested is a line as this:MCCB 40A 440V > VFD > Transformer > abut 2500m ROV umbelical.The test is to check how long time it takes form a short on the end of the umeblcal until the VFD shut down.The plan is to use a Oscilloscope with a voltage divider for measuring the voltage and a rogowski coil for te current.The short will be done by a high current contactor to ensure that it has enough gap between in the contacts to withstand a voltage of 3000V but the current will only be a few amps. The contactor will only be used for a few shorts before going in the bin. We will just have a few contactors avalable at the test and replace as they break down.Can anybody recommend a voltage divider and rogowski coil for the test.The line voltage is 3000V and the current will probably be 100A or less. Accuracy is not very important because it is only the shut down time for the VFD that is important.

author: penfold
author_rank: Frequent Contributor
timestamp: May 06, 2021, 09:19:36 pm
content: PEM make nice rogowski coils. For voltage sensing, I would recommend an isolated or differential high voltage probe since the short circuit event can cause jumps in the ground potential, something like a tektronix THDP0100. I've had good results on double pulse tests running at similar voltages and currents as those you mentioned, just neither are exactly a cheap option.

author: geggi1
author_rank: Frequent Contributor
timestamp: May 06, 2021, 09:55:40 pm
content: The THDP0100 is close to the price of a cheep motorcycle and the PEM probes looks very nice.However I will probably have to rent the probes at rental.no that is a partner company with where I'm employed.The timing measurements will probably be done in an oscilloscope in one-shot mode.I have to figure out a test procedure and get it approved by the client.

author: threephase
author_rank: Regular Contributor
timestamp: May 07, 2021, 12:38:20 pm
content: You could hire in something like an Omicron CMC256 with the enerlyzer option installed that would be capable of carrying out the measurements.Why would you need a Rogowski coil, could you not do the current measurement with a standard 100:1A current transformer? For the voltage measurement, you would be safer electrically isolating the scope from the VFD output by either a differential probe as already suggested or a small step down transformer.Your contactor will need to be able to survive the let through energy of the VFD, not just the fault current.

author: geggi1
author_rank: Frequent Contributor
timestamp: May 07, 2021, 10:21:06 pm
content: Ill probably doing the measurement at the VFD. Its simpler because I dont have to deal with the high voltage. The measurement is to check the timing on the VFD for shut down and because it can be very short time its better to use a rogowsky coil and a lot of these got a frequency range up in the multiple Mhz. They also comes with a interface that is directly compatable with a oscilloscope.With an Iron core current transformer there are normally a frequency limit of 50Hz or 60Hz because of the iron core.Because this is timing measurement all involved sensors and probes must be very fast so they dont influence the measurement.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: May 09, 2021, 05:06:00 pm
content: Quote from: geggi1 on May 07, 2021, 10:21:06 pmRogowsky probes are good also LEM Makes nice sensors. You have not said the bandwidth you need?