Industrial Grade 3Phase 50kVA 20kV/0.4kV Off Circuit Tap Changing Distribution Transformer for Construction Sites, Municipal Utilities, and Commercial Centers
50 kVA distributietransformator met 20 kV/0,4 kV-verhouding, off-circuit kraanwisselaar voor spanningsaanpassing en conformiteit met IEC60076. Verkrijgbaar in droge of in olie ondergedompelde versies voor bouwplaatsen, gemeentelijke nutsvoorzieningen en commerciële centra. Beschikt over een robuuste constructie, tolerantie voor overbelasting en aanpasbare opties.
3 Phase 50kVA Distribution Transformer
,20kV/0.4kV Distribution Transformer
,Industrial Grade Distribution Transformer
This three phase double wound distribution transformer combines heavy duty construction with flexible voltage adjustment to serve the demanding power needs of construction sites, municipal utilities, and commercial centers. Rated at 50kVA and providing step down transformation from 20kV to 0.4kV, it creates a stable and safe low voltage supply directly at the point of use. The manually operated off circuit tap changer allows the voltage ratio to be preset during commissioning, compensating for permanent deviations in the primary feeder voltage without relying on complex automation. Built to withstand frequent relocation, outdoor exposure, and continuous operation, this unit covers temporary site boards, permanent pump stations, street lighting networks, and indoor commercial distribution with equal reliability. Custom engineering ensures every project receives the exact vector group, protection features, and enclosure finish required.
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Tough Construction for Harsh Sites and Outdoors:
A reinforced structural frame, corrosion resistant enclosure finish, and internally braced active parts withstand transport vibration, construction site handling, and all weather exposure.
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Simple Field Voltage Matching:
The off circuit tap changer lets site technicians quickly set the correct high voltage tap without energized work. This avoids the cost and complexity of on load equipment while ensuring a correct 400V output under actual site voltage conditions.
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Dual Configuration for Any Location:
Choose dry type construction for indoor commercial installations where fire safety and low noise are essential, or hermetically sealed oil immersed construction for outdoor pad or pole mounted municipal and site applications.
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Excellent Overload Margin for Hard Starting Loads:
Generous thermal design tolerates the motor starting currents and periodic overloads typical of construction machinery and pump sets, extending active insulation life.
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EPC Ready Customization on Standard Lead Times:
Vector group, bushing orientation, paint specification, cable box layout, and monitoring accessories are configured to your project drawings, eliminating field modifications.
| Technical Feature | Specification and Description |
|---|---|
| Rated Capacity | 50 kVA, three phase, double wound, continuous duty. |
| Voltage Ratio | 20 kV (primary) to 0.4 kV (secondary), galvanic isolation between medium and low voltage. |
| Off Circuit Tap Changer | Manually operated device on the high voltage side. Voltage ratio adjustment is permitted only when the transformer is fully de energized and isolated. |
| Tapping Range | ±2x2.5% giving five positions. For a 20kV nominal, typical available taps are 21kV, 20.5kV, 20kV, 19.5kV, and 19kV, each maintaining a 0.4kV secondary when set correctly. |
| Core Material and Design | Low loss grain oriented silicon steel, assembled with step lap joints to reduce no load loss and magnetically induced sound. |
| Winding Conductor | Electrolytic copper or aluminum, arranged in layer or disc type windings. Double wound construction ensures complete electrical separation. |
| Dry Type Cooling and Insulation | Natural air cooling (AN) with forced air (AF) option. Insulation system rated Class F (155°C) or Class H (180°C), with vacuum pressure impregnation (VPI) or encapsulated windings for excellent moisture and chemical resistance. |
| Oil Immersed Cooling and Fluid | Natural oil circulation (ONAN) inside a hermetically sealed, corrugated steel tank. Dielectric fluid options include mineral oil or biodegradable natural ester for enhanced fire safety and environmental performance. |
| Standard Impedance | Typically 4% at principal tap, providing a balance between fault current limitation and secondary voltage regulation. |
| Sound Performance | Low noise generation achieved through precision core stacking and internal damping measures. Suitable for noise sensitive commercial and residential adjacent installations. |
| Temperature Rise | Oil immersed: winding rise limited to 65K above ambient. Dry type: winding rise limited to 100K. Generous cooling surfaces maintain hot spot temperature well within safe margins under normal cyclic loading. |
| Enclosure Protection | Dry type available from IP20 upward. Oil immersed tanks with weatherproof cable boxes and anti corrosion coating system up to C5 class for outdoor durability. |
| Standards and Testing | Fully compliant with IEC 60076. All units undergo routine testing including separate source AC voltage withstand, induced overvoltage, and temperature rise type tests on representative units. |
| Customizable Features | Vector group (commonly Dyn11), terminal exit direction, anti condensation heaters, surge arrester brackets, winding temperature indicators, and specific paint systems can all be specified at order stage. |
Construction power requires fast setup, frequent relocation, and the ability to withstand harsh surroundings while powering motor driven plant and tools.
Voltage Matching for Long Site Feeders:
Temporary site cables and shared utility transformers can depress the primary voltage at the point of connection. Using the off circuit tap changer, the commissioning electrician selects a tap (e.g., 19.5kV position) so the secondary stays at a healthy 400V even if the incoming supply is permanently low. This prevents undervoltage dropouts on crane hoists and sensitive electronics.
Mobile and Vibration Proof Structure:
The transformer base incorporates structural skids and heavy lifting eyes for forklift or crane hauling. Internal windings are rigidly braced to endure transport shocks and vibration from adjacent piling or compaction equipment without movement or abrasion.
Outdoor Weather Hardiness:
For open air site substations, the oil immersed tank is fully welded with a sealed cover, and cable terminals are housed in gasketed, water shedding boxes. The anti corrosion paint system resists cement dust, rain spray, and prolonged UV exposure.
Motor Load Starting Capability:
Machinery such as mixers, winches, and saws imposes short but intense starting currents. The transformer’s thermal mass and cooling design allow these repetitive overloads without pushing the internal hotspot beyond the insulation limit, maintaining site productivity.
Water and wastewater plants, street lighting, traffic signals, and public building services need continuous availability and adherence to long term voltage profiles with minimal operator attendance.
Managing Seasonal Primary Voltage Drift:
Urban and suburban 20kV loops often see a gradual voltage rise at night or a steady decline during irrigation season. By setting the off circuit tap at an optimal fixed position during regular maintenance, utility crews ensure the 0.4kV bus remains within specification all year, protecting programmable logic controllers, UV treatment lamps, and communications hardware from voltage stress.
Hermetically Sealed Reliable Oil Chamber:
The corrugated tank design has no rubber gaskets exposed to oil, so there is zero risk of leakage over decades. The sealed air cushion above the oil eliminates moisture and oxygen ingress, meaning the insulating fluid needs no routine filter breathing replacement. This directly cuts field service visits.
Low Noise Operation Near Public Space:
Parks, residential streets, and pedestrian zones demand silence. The step lap core and damping elements reduce emitted sound to a level that blends with background urban noise, preventing annoyance and municipal complaints.
Compact Pad Mounted Footprint:
A 50kVA unit sized pump house or lighting kiosk requires minimal civil works. The transformer’s reduced external dimensions often allow drop in replacement of legacy units onto existing pads without rebuilding the transformer plinth.
Malls, office towers, retail outlets, and mixed use complexes require invisible, fire safe power distribution integrated into basement switch rooms or mechanical floors.
Ultra Low Acoustic Signature for Tenant Adjacent Areas:
By using premium steel grades and careful joint construction, the magnetic noise remains exceptionally low. In a dry type indoor version, this means the transformer does not transmit any hum to floors above or to adjacent meeting rooms and boutiques.
Fire Safe Dry Type Construction:
The indoor version uses Class F reinforced insulation and VPI encapsulation. In the event of a building fire, the materials are self extinguishing and produce very limited smoke, complying with strict commercial fire codes and eliminating the need for bunded oil containment in the plant room.
Compact Assembly for Restricted Electrical Closets:
The core and coil assembly is dimensionally optimized to pass through standard doors and fit into tight rooms alongside LV switchboards. Vented enclosures or optional forced air cooling keep the unit within footprint yet thermally stable.
Enduring Repetitive Daily Load Swings:
Commercial complexes start with a base load elevator and lighting profile, then peak sharply at opening hours. The insulation thermal time constant absorbs these repeated cycles so that the winding hot spot never exceeds the design limit, resulting in a transformer service life that matches the building’s own design horizon.
Full Specification Matching for EPC Delivery:
From the exact Dyn11 vector connection to specific cable gland plates and monitoring sensors, the transformer leaves the factory fully aligned with the project’s single line diagram and installation manual. This removes the need for on site retrofitting and speeds up handover acceptance tests.
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Q1: Can this 50kVA transformer be used for both temporary construction power and then later as a permanent building supply?
A1: It can, provided the permanent load profile does not exceed 50kVA. For such dual purpose use, we recommend a hermetically sealed oil immersed version on a skid, as it can serve outdoors during construction and then be relocated to a permanent outdoor pad position once the building is completed.
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Q2: How do I select the correct tap position on site?
A2: The tap changer is purely mechanical and accessed under a bolted cover only when the transformer is completely de energized. Measure the average primary voltage at site during commissioning, then consult the internal connection chart. Move the bridging link to the position that corresponds to your measured voltage, so the secondary sits at 0.4kV. This is a one time setup unless the grid voltage later undergoes a permanent shift.
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Q3: What is the benefit of an off circuit tap changer compared to an on load one for a municipal pump station?
A3: In municipal applications, primary voltage tends to shift seasonally rather than minute by minute. Off circuit tap changers are inherently simpler, more rugged, and have no moving parts in oil that need frequent servicing. A brief scheduled shutdown during low demand hours allows the adjustment, which perfectly aligns with typical pump station maintenance windows.
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Q4: We need to install the transformer inside the basement of a shopping mall. What safety provisions are included?
A4: For such basements we supply the dry type version with Class F insulation, low smoke materials, and a ventilated IP20 enclosure. It requires no oil basin and meets fire protection standards for this kind of occupancy. For additional safety, we can integrate PTC thermistors for winding temperature monitoring that link directly to your building management system.
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Q5: What maintenance inspections are truly necessary after commissioning?
A5: The inspection schedule is modest. We advise checking all bolted electrical connections for correct torque after one month. Thereafter, annual visual inspections of the enclosure, cable gland seals, and tap changer contacts are sufficient. Oil immersed designs benefit from a dielectric fluid test every two to three years. The sealed tank system removes the need for periodic oil filtration.
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Q6: Our EPC contract specifies a unique paint color and cable entry from below. Can you accommodate this?
A6: Absolutely. Custom paint RAL numbers, cable box configurations (bottom or side entry), specific bushing spacing, and additional accessories like surge counters or pressure relief devices are all part of our built to order service. We take your data sheet and deliver a transformer that matches the project equipment schedule exactly.
Submit your specifications now and receive a custom quotation with a clear delivery timeline.
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