Transformer On Load Tap Changer Tester

 

What is Transformer On Load Tap Changer Tester

The switch on a transformer that allows voltage levels to be adjusted while the system is energized is called an on-load tap changer (OLTC). It switches the winding taps without interrupting power to the transformer, thereby changing the turns ratio and stabilizing the output voltage. This switch has a complex internal structure, including transition resistors, contacts, springs, and mechanical mechanisms. It operates extremely quickly (within tens of milliseconds) during switching; if a fault occurs, it can cause the contacts to burn out and damage the transformer.

1. Transient Resistance

Measures the resistance value during the switching process, typically ranging from 0.4 Ω to 100 Ω. Used to assess contact wear and contact condition.

2. Transient Time

Records the time required for a switch to complete a single switching operation, generally ranging from a few milliseconds to several hundred milliseconds. Used to determine whether the mechanism operates smoothly.

3. Three-Phase Synchronization

Compares the time differences in the switching actions of a transformer’s three phases, with an accuracy of up to 0.1 ms, to ensure synchronized three-phase switching.

4. Transient Waveforms

Records the entire switching process at a high sampling rate of 20 kHz to 30 kHz, generating waveform diagrams for technicians to analyze anomalies (such as waveform breaks, oscillations, etc.).

• Resolving “Inaccurate Testing” Issues: Traditional methods filter out transient abnormal signals (such as contact bounce) that occur during switch operation, leading to misjudgments. Dedicated testers, however, use high-speed, unfiltered data acquisition to accurately and unambiguously reflect the switch’s status, thereby preventing missed detections and disputes.
• Eliminating “Untestable” Blind Spots: Traditional methods are limited by transformer connection configurations (such as delta connections), resulting in testing blind spots. Dedicated testers (particularly those using the AC method) are not subject to these limitations and are universally applicable to transformers with various connection configurations ranging from 10 kV to 500 kV, achieving full coverage of all types.
• Detecting “Early-Stage” Defects: On-load tap changers are the weakest link in transformers (with a failure rate exceeding 50%). Dedicated testers can clearly detect early-stage defects at the microsecond level (such as minor wear or poor contact), issuing early warnings before faults escalate into serious accidents like explosions or burnouts.

1. Connect to both ends of the transformer’s tap-changing winding

 

2. The instrument outputs a small current to simulate load switching

 

3. High-speed acquisition of voltage, current, and time waveforms

 

4. Automatic calculation of transition resistance, switching time, synchronism, and waveforms

 

5. Store, print, and determine pass/fail

1. Constant Current Source Output

The instrument provides a stable DC constant current source (typically with 1A, 0.5A, and 5A settings), which is applied to the transition circuit of the tap changer.

Purpose of the constant current: To ensure the current remains essentially constant, so that changes in voltage directly reflect changes in resistance.

According to Ohm’s Law: R = U / I

2. Measurement of the Tap-Changing Process

When an on-load tap changer switches between tap positions, it undergoes the following steps:

Main contacts open

Transition resistor is engaged

Transition contacts operate

New tap position is closed

This process typically lasts only a few tens of milliseconds, requiring high-speed sampling to capture the complete waveform.

3. High-Speed Data Acquisition

The tester simultaneously acquires data at sampling rates of 10 kHz to 50 kHz or higher:

Three-phase voltages (A/B/C)

Circuit current

Time axis

This allows for the reconstruction of the complete switching waveform curve.

4. Waveform Analysis and Calculation

Based on the waveforms, the instrument automatically calculates:

1.Transition resistance

Voltage drops/transition segments in the waveform → converted to resistance values

2.Switching time / bounce time

Total time from initiation to completion of the switching operation, and durations of each phase

3.Three-phase synchronization

Time differences between phases A, B, and C during operation to determine if they are out of sync

4.Whether the operating sequence is correct

Identification of gear skipping, sticking, or contact burnout

5. Protection and Diagnosis

Overcurrent, overvoltage, and incorrect wiring protection

Automatic comparison against standard limits to provide a pass/fail conclusion

Data storage, printing, and uploading

Oil-immersed power transformers (on-load tap-changing type)

 

Distribution transformers, main transformers, plant service transformers

 

Rectifier transformers, electric furnace transformers, and other special-purpose transformers

 

Reactors, on-load tap-changing switchgear

I. Internationally Renowned Brands

Megger (U.S. / U.K.)

• Representative Models: TTRX Series, OLTC-8000
• Advantages: A century-old brand with high sampling accuracy and strong interference resistance; suitable for ultra-high voltage systems and large transformers; high global market share
• Applications: Power grids, electric power research institutes, large transformer manufacturers, overseas projects

OMICRON (Austria)

• Representative Models: CT Analyzer, TC3000
• Advantages: Modular design, integrated multi-parameter measurement, powerful software analysis, compliant with IEC/GB standards
• Applications: High-end testing, research, export projects

SebaKMT (Germany)

• Representative Models: OTL Series
• Advantages: Portable, highly adaptable to field conditions, stable data
• Applications: On-site testing at substations, retrofitting of older substations

II. Leading Domestic Brands

Wuhan Goldhome Hipot

• Representative Models: HM5008, HM5008A
• Advantages: High cost-effectiveness, user-friendly operation, compliant with DL/T 846.8, compatible with mainstream domestic OLTCs
• Applications: Power companies, power plants, transformer manufacturers, on-site testing

Shanghai Siyuan Electric

• Representative Models: SYTC Series
• Advantages: Primary supplier for power grid centralized procurement, excellent stability, comprehensive service network
• Applications: State Grid / China Southern Power Grid tenders, large-scale projects

Wuhan Huadian High-Tech

• Representative Models: HDT-9000 Series
• Advantages: Dual-channel synchronous sampling, time accuracy of ±0.2 ms, exceeding IEC standards
• Applications: High-precision testing, scientific research comparisons

· On-Load Tap Changer Tester

· OLTC Tester

· Transformer Tap Changer Analyzer

· On-Load Tap Changer Analyzer

· Tap Changer Test Set

· OLTC Analyzer

· Transformer On-Load Tap Changer Tester

· Tap Switch Tester

· OLTC Test Equipment

· Resistance & Timing Tester for OLTC

· 3-Phase On-Load Tap Changer Tester

· Portable OLTC Tester / Analyzer

· Automatic Transformer Tap Changer Tester

· High Precision OLTC Analyzer

· OLTC = On-Load Tap Changer

· Tap Changer Tester

· OLTC Test Set

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