Single-Phase Pole-Mounted Oil-Immersed Transformer

For distribution contractors, rural network upgrades and municipal projects: the ETENZ single-phase pole-mounted oil-immersed transformer covers twelve capacity steps from 5 to 160 kVA in a fully sealed tank hung straight on the pole, used singly for single-phase load or in groups of three run as a three-phase set.

Distributed Node Power Supply

Key Metrics

5–160kVA

Capacity

3.5%

Impedance

650kg

Weight 160 kVA

II0 / II6

Vector group

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Product Features

Pole mounted

A cylindrical fully sealed tank clamped straight onto the pole, with no foundation, fence or transformer platform. At 160 kVA the total weight is 650 kg and at 5 kVA only 135 kg, which a single pole carries, so the civil works come to almost nothing.

Pole mounted

Shorter LV radius

Small size and low cost mean more siting points, placed closer to the load. Shorter low-voltage runs bring the voltage drop and the line loss down with them — that is the main source of gain from scattered siting against one large central three-phase transformer.

Self-protected type

The self-protected version integrates the high-voltage fuse, the low-voltage circuit breaker and overload protection into the unit itself, clearing a fault locally rather than waiting for upstream protection to act. It comes first for lines where pole-top maintenance is awkward and inspection intervals are long.

Two core materials

At the same rating the amorphous core has about a third the no-load loss of silicon steel — 0.10 kW against 0.37 kW at 160 kVA. A pole-mounted transformer is energised year-round at a low load factor, so no-load loss takes a large share of the annual energy and the difference is worth calculating.

One unit or three

A single unit can feed single-phase load, or three can be grouped and run as a three-phase set. The second lets capacity be set per phase, so a line with uneven load distribution need not enlarge a whole three-phase transformer for the peak on one phase.

Product Details

Clamp mounting and high- and low-voltage terminations of a single-phase pole-mounted transformer

A cylindrical fully sealed tank is clamped directly to the pole, with two bushings on the high-voltage side and the low-voltage side brought out from the tank wall. Foundation, fence, transformer platform and earthing grid construction all fall away, and the civil scope is essentially removed. Weight rises gently with rating: 135 kg at 5 kVA, 350 kg at 50 kVA, 650 kg at 160 kVA. A standard single pole carries the whole capacity range, and pole type and burial depth follow the local distribution standard. In the fully sealed construction the oil never meets air, so no topping-up or filtering is needed in service and there is no conservator or breather. Where maintenance access at the top of a pole is awkward, one fewer item to inspect periodically is worth more than it would be at ground level. Where the units are supplied against a network upgrade schedule, ETENZ confirms pole type, clamp spacing and the outgoing direction with the line design before manufacture.

The low-voltage side comes in two arrangements: a 2×(0.22–0.24) kV dual winding brought out, or a single 0.22–0.24 kV winding. The dual winding can be connected in series for 0.44–0.48 kV, in parallel to double the current, or brought out as two independent 0.22 kV circuits, settled against the local low-voltage system and the way the load is connected. The vector group is II0 or II6 and the short-circuit impedance is 3.5% across the whole series — the same value on all twelve capacity steps, unchanged by rating, which is not how a three-phase unit behaves. Where three units are grouped and run as a three-phase set, their ratings need not be equal and can be chosen per phase against the real load. Matching impedance is the condition for parallel operation, met naturally when the three are the same type and rating; where the ratings differ, the resulting unbalance has to be calculated.

Delivery Scope Options

Scope 3

Inspection and Document Package

Scope 3

Inspection and Document Package

Routine tests are completed before dispatch; the test items and the manner of witnessing follow the contract, and customer or third-party witnessing can be arranged. The accompanying documents are organised to the requirements of the destination country and comprise product drawings, test records, the packing list and the installation and maintenance instructions; where a version in the language of the destination country is needed, it is raised at the ordering stage.

Scope Includes:

Routine tests before dispatch

Manner of witnessing per contract

Documents organised by destination country

Language version settled when ordering

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Scope 1

Single Unit or Complete Package Supply

Scope 1

Single Unit or Complete Package Supply

Transformers are supplied as single units against the order schedule, or as a complete package together with the protective enclosure, the temperature controller and the cooling fans. The active part is wound, assembled and routine-tested at the works and shipped as a complete unit; the assembly interface for the accessories follows the transport conditions. Where the transformer is to arrive together with a prefabricated power module, the E-House line takes on the enclosure, the internal arrangement and the foundation fixing, and the transformer is delivered as equipment housed within it.

Scope Includes:

Single unit or complete package

Complete-unit shipment and assembly interface

Foundation and fixing interface

In-cabin delivery handled by the E-House line

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Scope 2

Accessories and Component Platform

Scope 2

Accessories and Component Platform

Temperature controller, cooling fans, tap changer, protective devices and outgoing busbars are configured to the makes and types named by the project; where the project names none, a confirmed component platform applies and the schedule is submitted for confirmation at the drawing review. For on-load tap-changing transformers the switch type, the direction it is arranged in and the position of the operating mechanism are settled at the same stage.

Scope Includes:

Configured to project-named makes

A confirmed platform where none is named

Schedule confirmed at the drawing review

On-load tap changer arranged at the same stage

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Scope 3

Inspection and Document Package

Scope 3

Inspection and Document Package

Scope Includes:

Routine tests before dispatch

Manner of witnessing per contract

Documents organised by destination country

Language version settled when ordering

Inquire

Scope 1

Single Unit or Complete Package Supply

Scope 1

Single Unit or Complete Package Supply

Scope Includes:

Single unit or complete package

Complete-unit shipment and assembly interface

Foundation and fixing interface

In-cabin delivery handled by the E-House line

Inquire

Technical Specifications

Product form

Single-phase fully sealed oil-immersed transformer, pole-mounted

Rated capacity

5, 10, 16, 20, 30, 40, 50, 63, 80, 100, 125, 160 kVA

Rated high voltage

6, 6.3, 10, 10.5, 11 kV

Rated low voltage

2×(0.22–0.24) kV or 0.22–0.24 kV

Off-circuit tapping range

±5% or ±2×2.5%

Vector group

II0 or II6

Short-circuit impedance

3.5% across the series, unchanged by rating

No-load loss (silicon steel core)

0.04 kW at 5 kVA to 0.37 kW at 160 kVA

Load loss

0.15 kW at 5 kVA to 2.37 kW at 160 kVA

No-load loss (amorphous core)

0.02 kW at 5 kVA to 0.10 kW at 160 kVA

No-load current

4.0% at 5 kVA falling to 1.7% at 160 kVA

Total weight

135 kg at 5 kVA to 650 kg at 160 kVA

Product version

Standard or self-protected

Core material

Silicon steel or amorphous alloy

Tank construction

Cylindrical fully sealed; no topping-up or filtering in service

Mounting

Clamped to the pole; no foundation or transformer platform

Operating arrangement

One unit single-phase, or three grouped as a three-phase set

Product standards

GB 10318, IEC 76, ANSI C57.12.00, ANSI C57.12.20

Cooling

ONAN oil-immersed natural cooling

Service conditions

Outdoor; maximum +40 °C, minimum −25 °C, altitude not above 1000 m

Parameter	Specification
Product form	Single-phase fully sealed oil-immersed transformer, pole-mounted
Rated capacity	5, 10, 16, 20, 30, 40, 50, 63, 80, 100, 125, 160 kVA
Rated high voltage	6, 6.3, 10, 10.5, 11 kV
Rated low voltage	2×(0.22–0.24) kV or 0.22–0.24 kV
Off-circuit tapping range	±5% or ±2×2.5%
Vector group	II0 or II6
Short-circuit impedance	3.5% across the series, unchanged by rating
No-load loss (silicon steel core)	0.04 kW at 5 kVA to 0.37 kW at 160 kVA
Load loss	0.15 kW at 5 kVA to 2.37 kW at 160 kVA
No-load loss (amorphous core)	0.02 kW at 5 kVA to 0.10 kW at 160 kVA
No-load current	4.0% at 5 kVA falling to 1.7% at 160 kVA
Total weight	135 kg at 5 kVA to 650 kg at 160 kVA
Product version	Standard or self-protected
Core material	Silicon steel or amorphous alloy
Tank construction	Cylindrical fully sealed; no topping-up or filtering in service
Mounting	Clamped to the pole; no foundation or transformer platform
Operating arrangement	One unit single-phase, or three grouped as a three-phase set
Product standards	GB 10318, IEC 76, ANSI C57.12.00, ANSI C57.12.20
Cooling	ONAN oil-immersed natural cooling
Service conditions	Outdoor; maximum +40 °C, minimum −25 °C, altitude not above 1000 m

Product FAQs

In distribution areas where load is scattered, individual points are small and low-voltage runs are long. Several small single-phase transformers sited near the load shorten the low-voltage supply radius, and voltage drop and line loss come down with it; the longer the line and the more scattered the load, the clearer the gain. Where three-phase load dominates or load is concentrated, a three-phase unit is still the answer. The inputs for the judgement are low-voltage line length, conductor cross-section, load distribution and annual consumption.

It follows the inspection and maintenance conditions. The self-protected version integrates the high-voltage fuse, the low-voltage circuit breaker and overload protection into the unit, clearing an internal fault or a low-voltage overload locally rather than depending on an upstream operation — which suits long rural feeders with long inspection intervals and difficult fault location, and keeps a fault confined to one unit. The standard version is the transformer alone, with protection mounted separately on the pole or covered upstream; where inspection is easy and upstream protection is thorough, it is both more flexible and cheaper.

In no-load loss: at the same rating the amorphous core is about a third of the silicon-steel one — 0.10 kW against 0.37 kW at 160 kVA — while load loss is essentially the same. A pole-mounted transformer stays energised all year at a low average load factor, so no-load loss takes a large share of the annual energy, and with many units in service the cumulative difference is substantial. The payback follows directly from the number of units, the annual energised hours and the tariff.

The three ratings need not be equal and can be chosen per phase against the real load — that is exactly the value of grouping, since a whole three-phase transformer need not be enlarged for the peak on one phase. The condition is the impedance requirement for parallel operation: met naturally when the three are the same type and rating, and where the ratings differ, three-phase unbalance and neutral current have to be calculated. Connection arrangement and low-voltage system are settled together at the design stage.

A dual winding is brought out, with three ways to connect it: in series for 0.44–0.48 kV, in parallel to double the current, or as two independent 0.22 kV circuits. The choice follows the local low-voltage system and the way the load is connected. A single 0.22–0.24 kV winding is available as an alternative. State the low-voltage system, the connection and the termination arrangement together when ordering.

The single-phase capacity range is narrow, 5 to 160 kVA, and the design carries one impedance value through the whole series rather than stepping it with rating as a three-phase unit does. In practice the low-voltage short-circuit current then varies essentially in proportion to rating, and impedance matching for units in parallel or in a group is simple. Take this value when setting low-voltage protection.