On-Load Tap Changers

Dual Canopy Mechanic Electrical Engineering Co., Ltd. is one of the leading manufacturers and suppliers of On-Load Tap Changers in China. Please feel free to wholesale discount products for sale here and get quotation from our factory. Customized orders are welcome.

Anyone who has worked transformer maintenance knows the on-load tap changer is the only mechanical assembly inside the tank that actually moves during normal operation. Every tap change forces current through transition resistors and sliding contacts. When those resistors crack, contacts burn, or the drive mechanism sticks-causing a skipped step or an open-circuit moment-the result is usually an internal arc. In the worst cases, the tank pressure rises fast enough to rupture the casing.

For years, the accepted way to test an OLTC was to pull the core, strip all leads, and bench-test the switch bare. That still works, but nobody has time for a full disassembly during a tight outage window. The modern approach is wound-on-winding testing: you leave every connection in place and measure through the transformer inductance itself. The instrument drives enough current to overcome the winding impedance and captures the transition waveform as the switch moves from one tap to the next. That trace shows exactly how long the resistors carry current, whether the contacts make and break in the right sequence, and where any hesitation or arcing occurs. You get the same diagnostic picture without the crane, the gasket kit, or the three-day outage.

Inductance-resistant digital filtering algorithm (core feature): During winding testing, a large inductor can "smooth out" sudden current changes, making the transition resistance invisible. Our software incorporates a dedicated inductance compensation and differential filtering algorithm that automatically reconstructs the true transition waveform, clearly presenting "single-resistance" or "dual-resistance" transition steps.

One-click intelligent analysis: No need for manual mouse-based point selection. The software automatically identifies waveform characteristics, calculates transition time, bridging time, three-phase asynchrony, and transition resistance values, and uses red, yellow, and green colors to indicate whether values ​​exceed limits.

1. For winding testing, non-test phases must be short-circuited and grounded! If testing phase A, the leads of phases B and C must be short-circuited together and reliably grounded. Failure to do so will cause waveform distortion and numerous spikes due to inter-phase coupling capacitance and mutual inductance.

2. The clamps must engage with the bare copper! Paint, rust, and oxide layers on the bushing terminals are the culprits for waveform fluctuations. Before wiring, the metal at the clamp engagement point must be polished to a shine with sandpaper or a wire brush.

3. Perform a few "no-load" cycles before testing! Long-term operating OLTCs have oil films and carbides on the contact surfaces. Before formal testing, manually or electrically switch back and forth 3-5 times to clean the contact surfaces, ensuring accurate transition resistance measurements.

4. Observe the waveform carefully before drawing conclusions!

Interruption (waveform dropping to zero): A fatal defect! This indicates the contacts are not connected or the transition resistance is broken; operation is strictly prohibited.

Numerous burrs: Insufficient contact spring pressure or surface ablation.

Excessive transition time: Mechanical jamming or spring fatigue.

Clean the instrument surface and interface in time after each test;

Keep the instrument clean to avoid the accumulation of dust and oil stains;

Turn off the power after use and cover with a dust cover if necessary.

Dual Canopy Mechanical Electrical Engineering Co., Ltd. stands as a preeminent high-tech enterprise at the forefront of electrical system automation and precision testing.

Our comprehensive product portfolio encompasses a diverse range of essential electrical equipment. This includes Oil-immersed and Dry-type Transformers, which are designed to meet the varying needs of different applications; the Transformer Oil Test Series, which ensures the quality and reliability of transformer oil; the Transformer Test Series, which provides comprehensive testing solutions for transformers; and the High Voltage Tester Series, which is essential for ensuring safety and performance in high-voltage environments. These products are specifically tailored to serve a broad spectrum of industries, such as power systems, electrified railways, shipbuilding, telecommunications, municipal management, and other large-scale enterprises, where reliability and precision are of utmost importance.

How To Cooperate With Us?

 

Our address

Baoding Cloud Center, Hebei, China

Phone Number/whatsapp

+86 13483219412

E-mail

Salesm@dualcanopy.com

1. Q: Are the data from winding-on testing and core-removal (wire disconnection) testing the same?

A: Yes, there are differences. Core-removal testing measures the bare OLTC switch, providing the clearest waveform and most accurate data-it's the "gold standard." Winding-on testing is affected by the transformer winding resistance and inductance; the measured transition resistance will be higher, and the waveform steps will be gentler. On-site winding-on testing is mainly used for "longitudinal comparison" (comparing with the factory or last maintenance waveform) to see trend changes, rather than rigidly adhering to absolute values.

2. Q: Is it serious if there's a "current interruption" (current drops to 0) in the middle of the waveform?

A: Extremely serious! During normal resistance OLTC switching, it's crucial to ensure "connection before disconnection"-the current must not be interrupted. If a current interruption occurs in the waveform, it indicates the circuit broke at the moment of switching. This will generate extremely high operating overvoltage inside the transformer, causing arcing, burning contacts, and even leading to an explosion. If a current interruption is detected, power must be immediately cut off and the core removed for inspection!

3. Q: What is "three-phase asynchrony"? What is the standard?

A: During switching in a three-phase OLTC, the operating times of phases A, B, and C cannot be perfectly synchronized. The difference between the maximum and minimum operating times of the three phases is called "three-phase asynchrony." Standard procedures typically require a three-phase asynchrony of ≤ 3ms or 5ms (refer to the manufacturer's manual for specific requirements). If this limit is exceeded, it indicates inconsistent adjustment of the three-phase mechanical linkages, which can cause one phase to experience unbalanced current for an extended period.

Hot Tags: On-Load Tap Changers, China On-Load Tap Changers manufacturers, suppliers, factory, transformer tap changer test equipment oltc tester, Transformer On Load Tap Changer Tester, on load tap changer switch tester