KTP, KTPN, KTPM: which transformer substation to choose

Author: Viacheslav Yurdyk, Quality Engineer at LK Energy Group.
He checks that the switchboard equipment of our own manufacture complies with DSTU EN IEC 61439 — from incoming inspection of components to the acceptance testing of finished products.

KTP (package transformer substation) is a fully factory-built electrical installation that takes in 6 or 10 kV, steps it down to 0.4 kV with a power transformer and distributes the electricity among consumers. The letters in the designation — KTPN, KTPM, BKTP — denote the constructional version: outdoor kiosk, pole-mounted, or concrete block-type. It is the version that determines where the substation can be installed, what capacity it will actually provide and how much its installation will cost. In this article we compare the four main types and look at the criteria for choosing yours.

What a KTP is and why it is needed

Distribution networks operate at 6–10 kV — transmitting energy at such voltages is economically efficient. But consumers — machine tools, pumps, lighting, sockets — are supplied at 0.4 kV. It is the 10(6)/0.4 kV transformer substation that provides the transition between these levels.

Any KTP consists of three functional parts:

• the high-voltage (HV) device — receives the 6–10 kV line: a disconnector or load-break switch, fuses or a vacuum circuit breaker, surge arresters;
• the power transformer — steps the voltage down from 6–10 kV to 0.4 kV; its rated capacity in kVA is what is meant by “the capacity of the substation”;
• the low-voltage (LV) switchgear — a 0.4 kV RUNN cabinet or panel with an incoming device, outgoing lines, metering and, where required, street lighting.

The word “package” means that all of this is assembled and tested at the factory as a single product. What remains on site is to place the substation on a foundation or a supporting structure, connect the HV and LV lines and carry out commissioning — without erecting a full substation building and installing apparatus piece by piece in place.

Types of KTP by version

Indoor KTP (workshop type)

An indoor KTP 10(6)/0.4 kV is installed in a room: in an enterprise’s workshop, in a built-in or attached switch room, or in a separate substation building. The enclosure protects personnel from touching live parts but is not rated for rain and snow — the room provides that protection. This is the most flexible version in terms of scheme and capacity: the HV device is made up of KSO cubicles, the transformers follow the standard capacity range, and the RUNN is assembled for any number of outgoing lines. Typical applications are industrial enterprises, pumping stations, the main substations of buildings, and also KTP units for solar power plants.

KTPN — outdoor

The letter “N” in the designation historically stands for outdoor installation. KTPN is a substation in an insulated kiosk-type metal enclosure that is placed in the open air on a foundation. The enclosure, with its higher degree of protection, withstands precipitation, dust and temperature swings; maintenance is carried out through doors with interlocks. The 6–10 kV incomer is overhead or cable, and in the standard radial version the capacity is up to 250 kVA. KTPN is chosen when there is no separate room and building one is not worthwhile: villages and settlements, street networks, small production facilities and construction sites.

KTPM — pole-mounted

KTPM is the simplest and cheapest version: the equipment is mounted on a supporting structure (a pole), and no foundation or kiosk enclosure is needed. The incomer is overhead, from a 6–10 kV line; the transformer is protected by fuses, and the RUNN cabinet is of the outdoor type. The standard capacity range is from 25 to 400 kVA, in a radial configuration. This is the working solution for rural networks, farms, street lighting and remote or seasonal facilities — anywhere consumption is modest and an overhead line runs nearby.

BKTP — concrete block-type

A BKTP is a substation in a reinforced concrete enclosure made of separate block modules. The concrete enclosure provides vandal resistance, fire resistance and durability, while a layout with separate compartments for the 10 kV switchgear, the transformers and the 0.4 kV switchgear makes it possible to build two-transformer and through (transit) schemes with sectionalising. The incomer is cable. BKTP units are installed in dense urban development: residential complexes, retail and office centres, municipal infrastructure — where high capacity, two sections and a presentable appearance are required.

Comparison: what to install where

* The capacities are given for standard versions; the specific configuration — the transformer, the HV scheme, the set of outgoing lines — is determined by the questionnaire sheet.

How to choose: three questions

1. Where will the substation stand? There is a suitable room, or one is envisaged by the design — an indoor KTP. There is no room and the plot is out of town — KTPN or KTPM. Dense urban development with cable networks and requirements for appearance — BKTP.
2. What capacity is needed? The transformer capacity is chosen from the calculated load of the site with a margin for growth. All versions cover up to 250 kVA; 250–400 kVA is already beyond the standard KTPN; above 400 kVA it is an indoor KTP or a BKTP. For consumers of reliability categories I–II, two incomers and two transformers are provided — that is a two-transformer KTP or BKTP.
3. What is the high-voltage incomer? If an overhead 6–10 kV line runs to the plot, KTPM or KTPN with an overhead incomer are the logical options. If the network is cable, then KTP, BKTP or KTPN with a cable incomer. Clarify the scheme separately: a radial substation is the end point of the line, while a through substation passes the line on in transit and allows the network to be sectionalised.

These three answers plus the 0.4 kV single-line diagram effectively make up the questionnaire sheet — the document the manufacturer uses to configure the substation for the specific site.

Turnkey manufacturing of KTP units

A KTP is not a catalogue item off the shelf: the HV device scheme, the transformer capacity, the composition of the RUNN and even the dimensions of the enclosure are different in every project. That is why it matters who manufactures the substation. LK Energy Group produces KTP, KTPN and KTPM units at its own plant in Odesa: metal cutting and bending, powder coating, assembly of HV devices based on KSO cubicles, and of RUNN cabinets and panels — plus acceptance testing of every product before shipment. The design office adapts the standard solution to your site: non-standard dimensions, a layout to fit an existing foundation, additional metering compartments. Where required we also take on the installation and commissioning.

Frequently asked questions

LK Energy Group is a manufacturer of 6(10)/0.4 kV package transformer substations: indoor KTP, outdoor KTPN and pole-mounted KTPM. The full catalogue with specifications is in the “Equipment” section. Send us a single-line diagram or a completed questionnaire sheet — we will select the version and price the substation for your site.

See also

• Package concrete transformer substation (BKTP)
• KTPMM (sandwich panels)
• Case study: pole-mounted KTPM-400 10/0.4 kV in version U1
• Case study: KTPGS-1000 + UKM 230 kvar as a single package
• Standard solution: KTP 10/0.4 kV with RUNN