Automatic Load-ratio Voltage Transformer
Rated Power: 4000Kva (Customized)
Rated-voltage: 35kV/10.5kV (Customized)
Tap Range: ±8×1.25% (Customized)
Vector Group: YNd11 (Customized)
Notes: This SZ transformer supports customisation on voltages, tap settings, parameters, accessories and standards, subject to technical validation upon customer requirements.
Zhejiang Tianrun Electric Co., Ltd. is one of the leading manufacturers and suppliers of automatic load-ratio voltage transformer in China. We are committed to providing high quality customized products with competitive price. We warmly welcome you to buy bulk advanced automatic load-ratio voltage transformer from our factory. Also, quotation is available.
Product Overview
The SZ13 is a 35kV-class two-winding oil-immersed vacuum voltage regulation of 3 phase transformer, with the built-in SYJZZ vacuum on-load tap changer. It performs continuous automatic voltage regulation under load without any power interruption, solving the bus voltage deviation (high/low) load fluctuations, and keeping the low-voltage side stable within the standard range. It is the primary voltage-stabilizing supply equipment for 35kV substations, new-energy booster stations and large industrial plants.
Model Designation
Technical Parameters
|
Parameter |
Standard Configuration |
Optional Customization |
|
Rated capacity |
4000kVA |
Non-standard capacity available |
|
Voltage combination |
HV: 35kV; Regulation ±8×1.25%; LV: 10.5kV |
LV 6.3kV / 6.6kV / 0.4kV |
|
Matched tap changer |
SYJZZ-40.5/200-11 vacuum OLTC |
Neutral-point type SYXZZ |
|
Connection group |
YNd11 |
Yyn0, Dyn11 on request |
|
Rated frequency |
50Hz |
60Hz export version |
|
Cooling method |
ONAN oil-immersed self-cooling |
ONAF with fans |
|
No-load loss |
3.15kW (better than national Grade-2) |
Grade-1 low-loss upgrade |
|
Load loss (75℃) |
30.8kW |
Low-resistance energy saving |
|
No-load current |
≤ 0.45% |
Ultra-low no-load current |
|
Short-circuit impedance |
7% ±5% |
6.5% / 7.5% on request |
|
Total tap positions |
17 (±8 taps) |
±4×2.5%, 9-tap simplified scheme |
|
Insulation level |
HV: LI200 AC85kV; LV: LI75 AC35kV |
Reinforced external insulation for polluted areas |
|
Temperature rise limits |
Top oil ≤ 55K; winding ≤ 65K |
Reinforced cooling for hot climates |
|
Noise level |
≤ 52dB |
Silent version ≤ 48dB |
|
Protection class |
Outdoor IP23 |
Indoor IP44 sealed tank |
|
Operating altitude |
≤ 1000m |
Reinforced insulation above 1000m |
Rated current reference (this unit): HV 35kV side ≈ 66A; LV 10.5kV side ≈ 220A. The matched SYJZZ switch rated at 200A provides a generous safety margin for continuous full-load and short-time overload operation.
Product Core Functions
Uninterrupted automatic voltage stabilization (core function): During load peaks, valleys, seasonal changes or new-energy output fluctuations, the SYJZZ switch automatically changes winding turns without power interruption, stabilizing the LV bus voltage and ensuring stable operation of motors, precision instruments and energy-storage equipment.
Grid power flow & reactive power optimization: The 35kV substation main transformer regulates bus voltage to optimize regional reactive distribution, reduce line voltage loss and overall grid losses, and raise transmission efficiency.
All-scenario intelligent control: Local automatic, remote background and local manual-motorized operation modes; the VQC controller can interlock with reactive compensation devices for integrated voltage/reactive regulation, ideal for unattended smart substations.
Multi-layer safety interlocking: On main-transformer overload, oil over-temperature, gas relay action, tap position limits or switching faults, the OLTC is automatically locked to prevent dangerous regulation and avoid winding/switch arc damage.
Wide duty-cycle adaptability: Stable voltage regulation under strong new-energy output swings (PV/wind booster stations); also suited to 24-hour continuous production lines in metallurgy and chemical plants, eliminating production losses from outage-based regulation.
Core Advantages
Low-loss Core System
High-permeability grain-oriented silicon steel, fully automatic 45° step-lap stacking with burr ≤ 0.01mm; multi-stage vibration-damping core clamping - remarkably reduced no-load loss and noise, lower long-term energy cost.
High-strength Oxygen-free Copper Windings
HV and LV windings use high-purity oxygen-free copper wire in multi-layer cylindrical structure; internal/external insulation spacers fully chamfered to optimize field distribution; ampere-turn balanced design passes national short-circuit withstand tests; whole winding vacuum-impregnated for moisture resistance and low partial discharge.
Fully Sealed Anti-leakage Tank
Heavy-duty steel plate one-piece welding with fully automatic kerosene leak detection; oil-resistant acrylic rubber gaskets stable from -30℃ to +40℃; corrugated/finned radiators with 15% higher heat-dissipation efficiency, suiting both southern heat and northern cold; anti-corrosion epoxy coating available for coastal projects.
On-Load Tap-Changing Transformer vs Conventional Transformer
|
Dimension |
This unit (with SYJZZ OLTC) |
Conventional off-circuit transformer |
|
Tap-changing operation |
Under full rated load, no power interruption; one tap change in 3–6 seconds |
Full station outage required; all loads disconnected; manual tap changing takes 30+ minutes |
|
Core component |
Built-in SYJZZ vacuum OLTC, independent oil chamber, motorized intelligent control box |
Only simple exposed tap terminals; no arc-extinction/transition mechanism, no motor drive |
|
Regulation accuracy & taps |
±8×1.25%, 17 fine steps, voltage stability ±0.5% |
Only ±2×2.5%, 5 coarse steps, poor voltage control |
|
Application fit |
Continuous-process chemical plants, PV/wind farms, urban hub substations, data centers - critical loads |
Rural distribution, stable loads, sites allowing short outages |
|
Maintenance cost |
Periodic check of SYJZZ oil chamber and vacuum bulbs; long intervals for main body |
No tap mechanism to maintain, but frequent regulation requires repeated outages - very high outage cost |
|
Cost |
25%–35% higher at same capacity (core cost: SYJZZ vacuum OLTC) |
Lower cost, suitable only for low-requirement distribution |
|
Grid value |
Real-time voltage stabilization, reactive power optimization, lower line losses, better supply quality |
Static coarse regulation only; cannot cope with day/night or seasonal swings - risks motor burnout (low voltage) or damage to precision equipment (high voltage) |
OLTC Technical Data
- Voltage regulation range: ±10%; Step voltage: 1.25% / 1.5% per tap; Number of taps: 17 / 19 / 33
- Operating levels: 11kV / 33kV / 132kV / 220kV; Control mode: manual / automatic (AVR)
- Protection & interlocks: OLTC oil surge relay (Buchholz type), motor overload protection, end-position limit switches, electrical & mechanical interlocks, tap position indicator
Why OLTC is critical: stable voltage = better equipment life, improved grid reliability, reduced losses, fewer consumer complaints. The OLTC may be a small part of the transformer, but it plays a huge role in power system stability.
Operating Environment
|
Item |
Requirement |
|
Ambient temperature |
Max. +40℃, min. -30℃ (low-temperature special insulating oil available for cold regions) |
|
Altitude |
≤ 1000m (above 1000m: reinforced insulation and derated temperature rise) |
|
Relative humidity |
Monthly average ≤ 90%, no condensation (anti-corrosion tank for coastal salt-fog areas) |
|
Installation site |
Outdoor open-air substations, indoor distribution rooms; no explosion hazard, corrosive gas or heavy dust |
|
Seismic intensity |
≤ 8 degrees (vibration-damping base optional) |
Application Scenarios
- Power industry: 35kV urban regional substations, county-grid hub main transformers, rural grid upgrade projects.
- New energy: PV plant 35kV booster transformers, wind farm booster stations, energy-storage supporting main transformers.
- Industry: large chemical parks, metallurgy & steel, mining, paper-making & textile continuous production lines.
- Infrastructure: data centers, hospitals, airports, rail transit - class-1 important uninterrupted loads.
- Export: 35kV grid new construction and expansion power projects in Southeast Asia, Central Asia and Africa.
Proccess of Transformer
1-Wire‑wound winding of transfomer
2-Foil‑wound winding of transfomer
3-Vacuum casting of transformer
4-Epoxy resin casting of transfomer
5-Coil assembling over core
6-HV porcelain bushings of oil immersed transformer
7-Lead insulation taping and welding of transfomer
8-Vacuum oil filling of transformer
9-Tank sealing of transformer
Testing of Transformer
1-Measurement of winding resistance testing of transformer
2-Measurement of voltage ratio and check of phase displacement testing of transformer
3-Separate‑source AC withstand voltage testing of transformer
4-Measurement of no‑load loss and no‑load current of transformer
5-Measurement of short‑circuit impedance and load loss of transformer
6-No load loss and no load current testing of transformer
7-Temperature‑rise test of transformer
8-Partial‑discharge measurement of transformer
9-Winding ressitant and voltage ratio testing of transformer
FAQ
Q: What is the voltage regulation of transformer?
A: Voltage regulation describes output voltage variation between no load and full load condition. On load tap changer (OLTC, e.g. SZ series) adjusts voltage under live load to keep secondary voltage within required range.
Q: What is an On-Load Tap Changer (OLTC)?
A: An on-load tap changer is a mechanism installed in power transformers that allows voltage regulation while the transformer remains energized and supplying load, without any interruption to power supply. Its primary role is to maintain a stable output voltage despite variations in input voltage or load conditions.
Q: The typical types of OLTC?
A: Resistor type (most common) · Reactor type; In-tank OLTC · External / compartment type OLTC.
Q: What is the Working Principle of On-Load tap changer?
A: 1, Tap selector pre-selects the next tap. 2, Diverter switch transfers current via transition resistance. 3, Arcing is confined inside the OLTC chamber. 4, Voltage changes smoothly. 5, No supply interruption.
Q: What are the key functions of OLTC?
A: Regulates secondary/output voltage; Compensates voltage drop due to load variation; Improves overall grid voltage stability; Eliminates shutdowns during voltage correction; Enables automatic voltage control via AVR.
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