Unsa ang mga rason sa kaipuhan sa insulasyon sa low-voltage side sa usa ka dry-type transformer?

Hi everyone, I’m Felix, and I’ve been working in electrical equipment fault repair for 15 years.

Over these years, I’ve traveled across factories, substations, and distribution rooms all over the country, troubleshooting and repairing all kinds of electrical equipment. Dry-type transformers are among the most common devices we deal with.

Today, a friend asked me:

“What does it mean when the low-voltage side of a dry-type transformer has low insulation resistance?”

Great question — especially for maintenance personnel. So, I’ll explain this in simple terms, based on real-life cases I've worked on over the years.

1. Ano ang ibig sabihin ng “Mababang Insulation sa Low-Voltage Side”?

Let’s start with a quick overview:
Ang dry-type transformer ay isang air-cooled, oil-free, at insulated na transformer na karaniwang ginagamit sa mga gusali, malls, ospital, data centers — mga lugar kung saan mahalaga ang fire safety.

Ang low-voltage side nito ay karaniwang naglalabas ng 400V o 230V at direktang nagpapatakbo ng mga load.

Kapag sinabi natin na “mababang insulation sa low-voltage side”, ibig sabihin ang insulation resistance sa pagitan ng low-voltage winding at ground (core o enclosure) ay mas mababa kaysa sa normal — ang ibig sabihin, ang insulation performance ay nabawasan.

Sa simpleng salita: ang dating fully non-conductive barrier ay ngayon ay pinapayagan ang maliliit na leakage currents na lumampas. Ito ay maaaring magresulta sa tripping, arcing, o kahit short circuits!

2. Karaniwang Dahilan (Lahat mula sa mga totoong kaso na nafi-fix ko)

Batay sa aking karanasan sa field, ang pangunahing dahilan ng mababang insulation sa low-voltage side ng dry-type transformers ay nasa mga sumusunod na kategorya:

2.1 Moisture / Condensation

Ito ang pinakakaraniwang dahilan, lalo na sa mga mapagligo na lugar tulad ng southern China o coastal regions, o sa mga bagong installed na transformers na hindi pa ganap na nadry out.

Halimbawa: Noong nakaraang taon, nacheck ko ang isang bagong dry-type transformer sa isang factory sa Xiamen. Ang insulation sa low-voltage side ay lang nang ilang puluhin megaohms — way below standard (dapat ≥500MΩ). Kapag binuksan namin ang cabinet, may condensation sa loob! Tumukoy pala ang unit ay nagsimulang umabsorb ng moisture sa panahon ng transport at dahil sa mataas na humidity.

Solutions:

• Check for water ingress;

• Use a heat gun or infrared lamp to dry it out;

• Send back to the factory for vacuum drying if necessary;

• Install a dehumidifier or space heater as prevention.

2.2 Dust or Foreign Material Buildup

Ang dry-type transformers ay umiiral sa air para sa cooling, kaya may maraming vents — na nagbibigay din nito ng prone sa dust accumulation sa huling bahagi.

Ang dust ay maaaring conductive — lalo na metal dust o salt particles — at kapag pinagsama sa moisture, maaari itong makabawas ng insulation levels.

Isang beses akong nakita ang puting crystalline deposits sa low-voltage terminals ng isang transformer sa isang chemical plant. It was caused by corrosive gases, and the insulation was clearly compromised.

Solutions:

• Clean regularly, especially around terminals and windings;

• Install filters in dusty environments;

• Use specialized insulating cleaners — never wash with water;

• Check for clogged ventilation openings.

2.3 Winding Aging or Partial Discharge Damage

Ang mga winding sa dry-type transformers ay karaniwang encapsulated sa epoxy resin — durable, pero hindi indestructible.

Ang long-term operation under high temperatures, overloads, o harmonic conditions ay maaaring makabawas, crack, o carbonize ang insulation layer, leading to partial discharge at eventually reduced insulation.

Isang beses, nirepair ko ang isang dry-type transformer na nasa serbisyo na ng 8 years. Ang low-voltage insulation nito ay bumaba mula 1000MΩ hanggang 20MΩ. Sa inspection, nahanap namin ang clear signs of carbonization sa surface ng winding.

Solutions:

• Check operating temperature records for long-term overheating;

• Measure partial discharge levels (if possible);

• Replace damaged windings or the entire unit;

• Improve ventilation, reduce load, and avoid frequent overloads.

2.4 Loose or Oxidized Terminal Connections

Ang loose terminal connections ay maaaring magresulta sa localized heating, na pagkatapos ay nakakaapekto sa surrounding insulation materials.

Halimbawa, isang beses akong naging parte ng isang dry-type transformer na konektado sa isang UPS system. Ang low-voltage insulation ay bigla na lang bumaba sa ibaba ng 100MΩ. Inspection revealed a loose copper busbar bolt — ang contact area ay nasunog at even smoked before.

Solutions:

• Regularly tighten all terminal connections;

• Use a torque wrench according to specifications;

• Check for oxidation, discoloration, or burn marks;

• Polish or replace heavily oxidized terminals.

2.5 Poor Enclosure or Grounding

Ang enclosure at core ng dry-type transformer ay dapat maayos na grounded. Kung ang grounding ay poor, maaari itong mag-create ng floating voltages, leading to incorrect insulation readings.

Isang beses, noong commissioning check sa isang new site, nahanap kong ang low-voltage insulation ay lang nang ilang hundred kiloohms. Turns out, ang ground wire ay nasira ng construction workers, causing the core to become energized — falsely indicating low insulation.

Solutions:

• Check for broken or loose ground wires;

• Test ground resistance (should be ≤4Ω);

• Ensure the core is well connected to the enclosure;

• Avoid misdiagnosis due to grounding issues.

2.6 Measurement Errors / Improper Testing Methods

Sometimes, the problem isn't with the equipment itself, but how the test was conducted.

Examples include:

• Using a 500V megohmmeter instead of a 2500V one;

• Not disconnecting secondary cables or other connected devices;

• Failing to discharge before testing, causing residual charge interference;

• Ending the test too early before the reading stabilizes.

I’ve made this mistake before — almost condemned a perfectly good transformer.

Solutions:

• Use the correct megohmmeter (2500V for dry-type transformers);

• Disconnect all external wiring;

• Discharge for at least 1 minute before testing;

• Record R15 and R60 values, calculate absorption ratio (R60/R15 ≥ 1.3);

• Consider dielectric loss tests for further confirmation.

3. How to Test and Diagnose
Here's the step-by-step process I use for diagnosis:

4. Repair Suggestions & Preventive Measures

Repair Suggestions:

• If moisture is the issue, drying may restore insulation;

• If dust or debris is the cause, cleaning often restores performance;

• If windings are aged or damaged, send for factory repair or replacement;

• If terminal connections are the problem, tighten or replace them;

• All operations must be done with power off, lockout-tagout applied!

Preventive Measures:

• Regular inspections (quarterly), using infrared thermography to detect hotspots;

• Periodic cleaning (annually), paying attention to hidden corners;

• Install dehumidification systems (especially in humid areas);

• Monitor load to avoid long-term overloading;

• Consider online monitoring systems (for high-end users);

• Keep detailed equipment records and track changes over time.

5. Final Thoughts

Low insulation resistance on the low-voltage side of a dry-type transformer may sound technical, but in most cases, it can be identified and resolved using basic tools and procedures.

As someone who has worked in electrical equipment repair for 15 years, I want to emphasize:

“Insulation doesn’t fail suddenly — it deteriorates slowly over time.”

With regular checks and timely maintenance, most problems can be caught early and prevented from becoming serious.

If you're dealing with a similar issue on-site and aren't sure how to proceed, feel free to reach out — we can work through it together and find the best solution.

Remember this key message:

“Prevention is better than cure — catch it early, fix it early.”

Stay safe, keep the lights on!

— Felix