Hey everyone, let’s talk about something that keeps popping up in our service calls lately: partial discharge (PD) test equipment acting wonky. I’m not here to throw around super technical jargon that makes your eyes glaze over—just the real, on-the-ground stuff I’ve seen as a PD test equipment supplier for the last 8 years, troubleshooting everything from 10-year-old portable units in a hydro plant to new setups in a substation being commissioned last month. Partial Discharge Test Equipment
First off, if your PD test gear is doing something off that you didn’t expect, it’s probably not “just a quirk”—it’s a malfunction, and ignoring it can lead to wasted time, wrong data, or even worse: missing a real fault in your high-voltage gear. I’ve had clients brush off weird readings once, then come back a week later saying their transformer blew because they relied on bad PD data. So let’s break down the most common signs I see, no fancy lab talk required.
1. Readings That Jump Randomly for No Reason
This is the #1 red flag that’s so easy to miss if you’re just glancing at your screen between readings. Let’s say you’re testing a medium-voltage cable at a steady voltage, right? You expect PD levels to hover around a consistent baseline—maybe 50 pC, give or take 10. But if suddenly it spikes to 500 pC, drops to 0, then jumps to 300 pC without you changing any settings, that’s not a real fault in the cable. I once had a client tell me their new 11kV cable had “random PD spikes every 2 minutes” during testing. Turns out their oscilloscope cable was loose, wiggling every time a tech leaned against the test bench, so the equipment was picking up electrical interference, not real PD. Another angle: if your baseline reading drifts wildly when you haven’t even connected the test object, that’s definitely a hardware issue—your sensor or amplifier’s not calibrated right, or there’s a short somewhere in the signal path.
2. No Reading at All (When There Should Be One)
Sometimes the problem isn’t chaos—it’s silence. You hook up the PD test equipment to a known bad component (say, a transformer with a confirmed internal void), crank up the voltage, and… flat line. No PD peaks, nothing. I’ve seen this happen a lot with older equipment where the current sensor is worn out, or the signal filter is clogged with dust. Wait, no—don’t assume the component is perfect just because you get no reading. I had a client test a 33kV power transformer that a factory audit had already found had a void, and their PD unit gave 0 pC. Turned out their coupling capacitor (super important for picking up PD signals) was corroded on the terminals, so the signal never reached the detector. Pro tip: always test your equipment against a known standard before you use it on site—we send out little PD calibration sources to all our clients, and if yours doesn’t pick that up, you know you’ve got a problem before you waste hours on a field test.
3. Weird, Unfamiliar Noise or Feedback
If your PD test unit starts making sounds it never made before, that’s a big tell. I’m not talking about the faint hum from the high-voltage source—think static, popping, or even a high-pitched whine that gets louder when you adjust the sensitivity. Last year, a client brought their portable PD unit in for servicing because it was making a clicking sound every time they applied voltage, and it turned out the relay inside the unit was failing. The clicks were causing tiny electrical blips that the equipment was misinterpreting as PD, so their readings were garbage. Also, if you feel a tingle or get electric feedback on your test leads when you’re handling them, that’s not normal PD—it’s the equipment’s shielding failing, which means it’s picking up external interference way too much. That noise is your equipment’s way of saying “I can’t tell real PD from static, fix me.”
4. Off-Screen Anomalies in Data Shape
Most PD equipment plots readings on a phase-resolved partial discharge (PRPD) pattern, right? That little graph where PD pulses line up with specific points on the AC voltage cycle. If that pattern doesn’t look like it’s supposed to—like, say, it’s shifted 90 degrees from where it should be, or there are random small pulses all over the place that don’t match the typical shape for your test object—that’s a malfunction. I’ve seen this with equipment that has a faulty phase synchronization module. One time, a utility tech was using an old PD unit on a circuit breaker, and the PRPD pattern looked like it was from a void in epoxy, not a breaker contact issue. We checked the phase sync and found the unit’s clock was misaligned, so it was plotting all pulses at the wrong phase, leading them to misdiagnose the actual fault. Don’t just look at the numbers—glance at the graph every time, that’s where the hidden malfunctions hide.
5. Unresponsive or Glitchy Controls
This one might seem obvious, but I’ve had clients brush this off as “user error” instead of a hardware or software glitch. If your buttons stick, the touchscreen freezes mid-test, or the settings you adjust (like sensitivity or voltage level) don’t actually change when you press them, that’s a problem. For example, if you set the sensitivity to 10 mV/pC, but the equipment is still picking up every little external electrical signal because the setting didn’t save, you’re going to get way too many false positives. I had a client in the solar industry tell me their PD unit kept switching from “cable test” to “transformer test” on its own—turns out the internal memory card was failing, so the settings were randomly switching. Next thing you know, they’re testing a cable at transformer-level voltage, and they almost damaged the unit and the cable. Never ignore glitchy controls—they’re the most immediate sign that your equipment can’t be trusted to do what you tell it to.
6. Frequent Overheating or Error Codes (Even in Cool Spaces)
Modern PD equipment has temperature sensors, so if it’s overheating and throwing error codes, that’s built-in safety kicking in to stop a bigger problem. But I’ve seen this happen to units in cool control rooms too—last quarter, a client’s fixed PD monitoring unit in a substation kept throwing an “amplifier overtemp” error, even though the room was 22°C. We took it apart and found dust had built up in the cooling fan, so it couldn’t dissipate heat, and the amplifier was starting to degrade. If your unit is constantly shutting down mid-test or giving error codes that you can’t find in the manual, don’t just reset it and keep going—look for the root issue. Overheating is a slow-burn malfunction that will eventually take out a component entirely if you don’t fix it.
A Quick Note on Interference vs. Actual Equipment Malfunction
Wait, I should clarify something real quick: not all weird PD readings are equipment malfunctions. Sometimes it’s external interference—like a nearby radio tower, another high-voltage line, or even a loose power cord in the test area. How do you tell the difference? If you move the equipment 10 feet away and the weird readings go away, that’s interference, not your unit. But if the readings stay the same no matter where you move, or you get that same random spike pattern when you test against a known calibration source? That’s 100% your equipment.
At the end of the day, PD test equipment is only as good as its ability to pick up real, small PD signals and ignore noise. If you’re noticing any of these signs—random spikes, flat lines, weird noises, glitchy controls, or off patterns—don’t guess your way through the test. A bad reading is worse than no reading, because it might make you miss a critical fault or waste time fixing something that’s not broken.
If you need a second pair of eyes to check out your PD test equipment, whether it’s a quick troubleshooting call, a full calibration, or you’re looking to upgrade to a reliable unit that won’t give you these headaches, feel free to reach out. We’re here to make sure your PD testing is accurate and stress-free.
References
Lead Acid Battery Regenerator IEC 60270:2000, High-voltage test techniques – Partial discharge measurements
IEEE Std 433-2009, IEEE Guide for Partial Discharge Testing of Rotating Machinery
Wuhan Goldhome Hipot Electrical Co., Ltd.
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