HZ-3320D 3 Channel DC Winding Resistance Tester
HZ-3320D DC Winding Resistance Tester 20A 3 channels
Product Overview
The HZ-3320D Transformer DC Winding Resistance Tester is a high-current, multi-channel precision instrument designed for measuring the DC resistance of transformer windings, a mandatory test item in transformer manufacturing, factory acceptance, commissioning, and preventive maintenance. By injecting a regulated DC current into the winding and measuring the resulting voltage drop across the four-terminal Kelvin connection, the HZ-3320D detects critical defects - including poor-quality welded joints, loose connections, broken conductor strands, shorted turns, and tap-changer contact degradation - long before they escalate into catastrophic failures.
Built around an advanced switch-mode power supply and a single-chip microcontroller, the HZ-3320D delivers up to 20A of test current across 9 selectable current gears (10mA–20A plus automatic), covering a measurement range from 0 µΩ to 20 kΩ with a best-in-class accuracy of 0.2% ±0.2 µΩ. The instrument supports seven measurement modes - including YN three-phase simultaneous, YN three-phase compensation (with O-phase resistance), YND11 magnetic assist, and transformer demagnetization - making it the most versatile DC resistance tester in its class for both routine and diagnostic field testing.
Product Value
Eliminate Unplanned Outages: DC resistance testing is the gold standard for detecting winding defects that thermal imaging and ratio tests cannot reveal - loose clamping plates, brazed joint fatigue, and tap-changer contact erosion - enabling predictive maintenance before failures occur.
3× Faster Than Single-Phase Testing: YN three-phase simultaneous measurement tests all three phase windings in one cycle. For on-load tap-changer (OLTC) transformers, tap positions can be switched without discharge, reducing total test time to one-third of traditional single-phase methods.
Field-Ready Intelligence: Automatic current selection, data stabilization assist (5"/15"/30" deviation analysis), material-based temperature conversion (copper/aluminum), and one-touch three-phase balance rate calculation eliminate manual calculations and interpretation errors.
Built for Substation Environments: AC380V misconnection protection, anti-back-EMF protection, automatic discharge with acoustic alarm, and a rugged dustproof/moisture-proof enclosure ensure safe, reliable operation in the harshest field conditions.
Tech Data
| Parameter | Specification |
|---|---|
| Model | HZ-3320D |
| Output Current | Auto, 20A, 10A, 3A, 1A, 300mA, 100mA, 30mA, 10mA (9 gears) |
| Measurement Range (Single-Phase) | 0 Ω – 20 kΩ (10mA gear: 20 Ω – 20 kΩ; Auto: 0 Ω – 600 Ω) |
| Measurement Range (Three-Phase) | 0.001 Ω – 360 Ω (Auto); gear-dependent up to 0.6 Ω (20A) |
| Accuracy | ±(0.2% of reading + 0.2 µΩ) |
| Minimum Resolution | 0.1 µΩ |
| Measurement Modes | Single channel, YN three-phase, YN three-phase compensation, YND11 magnetic assist, HV phase selection, LV phase selection, demagnetization |
| Stabilization Assist | 5s / 15s / 30s deviation percentage display |
| Temperature Conversion | Copper (T=234.5) and aluminum (T=225) material selection |
| Balance Rate | Automatic three-phase resistance unbalance rate calculation |
| Display | 6-inch true-color touch LCD, Chinese/English bilingual |
| Data Storage | 100 groups with perpetual calendar timestamp, non-volatile |
| Printer | Built-in thermal micro-printer |
| Data Export | USB flash drive plus dual RS485 interfaces; optional Bluetooth wireless module |
| Demagnetization | AB phase / BC phase / ABC sequential; automatic alternating-polarity pulse sequence |
| Safety Protections | AC380V misconnection protection, anti-back-EMF, automatic discharge with acoustic alarm, discharge interlock, fuse-protected input (5A) |
| Power Supply | AC 220V ±10%, 50Hz ±1Hz |
| Operating Temperature | –20°C to 40°C |
| Operating Humidity | ≤ 80% RH, non-condensing |
| Dimensions (L × W × H) | 420 × 320 × 200 mm |
| Net Weight | 13.8 kg |
| Packing List | Main unit, test cable set, three-core power cord, fuse (5A × 2), operation manual |
Common Problems And Solution Methods
1. Don't start and buzzer continues sound
Firstly check whether power supply is connected with AC380V or voltage of input power supply is too low under such condition.
2. Crystal screen can't be lit when machine is started.
Firstly check whether power supply is normal in case of this situation, then check whether fuse is broken. If it is broken, replace new fuse.
3. Liquid crystal screen for starting machine is lit but display is abnormal or not display
Firstly start again and press re-set key once under such condition.
4. Testing data isn't stable or error is too great
Firstly check testing wire whether it is virtually connected and loose under such condition. If it isn't still solved, check whether the sample is corroded.
5. Always display "Charging …." during testing process
Firstly exclude magnetic circuit problem of the transformer in case of this situation. If the current isn't changed for long time and it is always around zero, check whether there is short circuit phenomenon in the circuit. If current isn't always charged, check whether measurement scope is exceeded.
6. "Exceed measurement scope". If resistance value is greater than 50Ω during testing process, it will inform "Exceed measurement scope", the instrument will not stop testing, and it will continue display testing result. But the measurement result may be inaccurate, it belongs normal phenomenon.
7. "Overheat protection" Temperature may rise up because the power supply in the instrument works for long time or is damaged, it will inform "Overheat protection". Start the machine and don't carry out testing, let the air fan work for 10 minutes and let internal temperature drop down as soon as possible, and then carry out testing. If it can't be tested, power supply may be damaged.
FAQ
Q1: Why is DC winding resistance testing mandatory? Finds bad joints, strands, tap wear. IEC required.
Q2: How does it stabilize readings so fast? 20A saturates core fast. Mag assist for YND11.
Q3: How to ensure accurate measurements? YN comp. <0.1% deviation = stable. Auto current.
Q4: Tap switching during test? Demagnetization? OLTC: live tap. Off-load: stop first. Demag after.
Q5: What if 380V is connected by mistake? Auto disconnect + alarm. Self-resetting. No fuse.
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