Transformers Chokes, Passive filters.

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Technical data

TRAFECO’s range includes low and medium voltage transformers and chokes, designed for low and medium frequency circuits.

We manufacture equipment based on international, European and national technical standards. The standards are EN/IEC 61558, EN/IEC60076.

As standard, our transformers and chokes are made in temperature class F (Tmax=155OC). It is possible to manufacture the devices in other temperature classes, e.g. B (Tmax=130OC) or H (Tmax=180OC). Transformers and chokes are designed for vertical operation, unless otherwise specified in the offer and agreed with the customer.
If transformers and chokes are supplied without an enclosure with protection degree IP00, they are suitable for installation in control cabinets or enclosures with protection degree up to IP24. The intention to place a transformer or choke in a highly protected (sealed) enclosure should be consulted with the manufacturer. We can supply transformers and chokes in steel, powder-coated housings with protection levels IP23, IP44, IP54 or any other on request.

The specified values of primary and secondary voltages for transformers and three-phase chokes are interphase values. It is assumed that the standard power supply is sinusoidally alternating voltage with a frequency of 50Hz, and the ambient temperature of the working transformer or choke does not exceed 40 C degrees, unless the offer and the agreement with the customer state otherwise. Each transformer may have several primary or secondary windings. The windings may be equipped with additional voltage taps. The number of windings and taps and their load capacity is agreed with the customer at the quotation preparation stage.

We manufacture transformers and chokes for various climatic and environmental zones. Depending on the application of the transformer or choke, we use typical designs – land C1/E0 and marine C2/E1. By agreement, we can design and technologically adapt a transformer or choke to operate in other extreme climatic or environmental conditions.

Detailed technical data of the device groups can be found in the data sheets. In addition to standard equipment, we can design and supply non-standard transformers and inductive components with parameters tailored to customer requirements.

Operation types of transformers

Several standardised and mathematically described types of operation are used to describe the duty cycle of electrical machines and transformers. EN 60034-1 describes several types of operation of rotating electrical machines and associated equipment, which differ in the load pattern of the machines. Operation types are designated by the letter abbreviations S1 to S8. Below are the characteristics of the three most common operation types:

Continuous operation S1

Operation type with a load of a constant value for an indefinite period of time or at least until a fixed temperature rise of the device is reached.

Casual operation S2

Operation type over a period of time, starting from the cold state of the appliance, with intervals between periods of operation long enough to cool the appliance down to a temperature close to ambient temperature. Casual operation is described by the symbol S2 and the working time tp in minutes (e.g. S2- 15min).

Intermittent operation S3

A type of operation carried out in succession in defined equal cycles of time consecutively, where the periods of work are separated by equal periods of breaks. The designation of intermittent operation is e.g. S3-20%, where the numerical value indicates the percentage ratio of the working time tp to the duration of the period t0, i.e. the working time and the subsequent break.

Cooling types of transformers

Heat exchange between the transformer and the surroundings takes place via conduction, convection and radiation. When optimising transformer design, the aim is to improve the efficiency of the natural cooling mechanisms by additional measures to facilitate the exchange of thermal energy. The type of cooling for a particular appliance is described by a letter code depending on the refrigerant and the way it circulates. The method of heat dissipation from a transformer placed inside an enclosure is described by a code consisting of four letters, for a device without an enclosure the type of cooling is described by two letters.
EN 60076-11 introduces the following designations:

The first letter indicates the refrigerant of the appliance
The second letter indicates how the coolant is moved
The third letter identifies the external refrigerant
The fourth letter indicates how the external coolant is introduced

Coolant types

A air cooling
G gas cooling – other than gas
W water cooling

Method of setting the coolant into motion

N natural cooling
F forced cooling by artificially inducing movement of the refrigerant

Protection classes provided by enclosures

The EN 60529 technical standard defines the degrees of protection provided by enclosures against the ingress of solid objects and water. The code describing the degree of protection consists of two digits. The first digit indicates the degree of protection of the interior of the enclosure against the ingress of solid bodies and also the degree of protection of the user against direct contact with live components. The second digit defines the degree of protection against ingress of water into the housing. The additional letter A,B,C,D indicates the degree of protection of the user against direct contact with live parts.

First digit

IP0X no protection of the device
IP1X protection of the device against penetration of objects with a diameter of Ø≥50 mm, e.g.: a human hand
IP2X protection of the device against penetration of objects with a diameter of Ø≥12 mm e.g.: finger of hand
IP3X protection of the device against penetration of objects with a diameter of Ø≥12 mm e.g.: finger of hand
IP4X protection of the device against penetration of objects with a diameter of Ø≥1.0 mm
IP5X protection against penetration of any object and against dust deposits
IP6X dustproof

Second digit

IPX0 no protection of the device
IPX1 protection of the device against vertically falling drops of water
IPX2 protection of the device against water droplets falling at an angle ≤ 150 from the vertical
IPX3 protection of the device against water droplets falling at an angle ≤ 600 from the vertical (e.g.: rain)
IPX4 protection of the device against water splashes from all directions
IPX5 protection against strong jets of water falling from all directions
IPX6 protection against waves and strong jets of water coming from all directions
IPX7 protection of the device against damage from brief (up to 30 min.) immersion in water to a depth of H=1 m.
IPX8 protection of the device against damage from prolonged immersion in water to a depth of H>1 m.

Additional letter

A Protection against direct contact with an open hand of diameter Ø < 50 mm
B finger protection with a diameter of Ø < 12 mm, length < 80 mm
C protection against contact with a tool of diameter Ø <2.5 mm, length <100 mm
D protection against contact with conductors with diameter Ø <1.0 mm, length <100 mm

Protection against short-circuits and overloads

One of the causes of transformer failure is damage to the insulation of the current paths caused by excessive temperature rise during overloads and short circuits. An increase in the temperature of current paths or windings can be caused by electrical phenomena, as well as occur for non-electrical reasons, causing further damage to the device, which is already of an electrical nature. Such causes may be: insufficient air exchange in the enclosure, increase of ambient temperature, decrease of water flow – for water cooled windings or for devices cooled by air blowing, fans’ failure or soiling of the fan’s protective mesh.

Protection devices

Electrical equipment is usually protected against overloads or short circuits by fuses or circuit breakers. The rated current of the fuse- link installed on the supply side of the appliance shall be selected close to the rated current of the appliance and equal to the upper value of the nearest standardised fuse-link. To protect transformers, fuse links with the gG delayed characteristic are recommended. When selecting the fuse link, the switching current of the transformer must be taken into account. For low power transformers, miniature fuse disconnectors can be used. The popular S-type overcurrent circuit breaker can also be used as protection. Their versions with delayed characteristics are available with letter designations from B to D.

Temperature sensors

Fuses or circuit breakers protect transformers from the effects of overloads and short circuits by quickly switching off the current in the circuit. However, there are a number of non- electrical factors that can lead to overheating and damage to transformers and chokes. For this reason, various types of temperature sensors are additionally installed in the windings, depending on the application and user requirements.

Temperature sensors applied:

resistance type Pt100 or Pt1000
pTC solid-state posistors
miniature bimetallic NO switches normally open or NC normally closed

Sensors are placed in the windings and core of the transformer or choke at characteristic points. Some applications even require two types of sensors to be mounted in a single winding. Continuous temperature monitoring of the transformer can be implemented using a Pt100 type sensor. NO or NC bimetallic switches indicate exceeding of the permissible temperature.

Climate and environmental design

Climatic and environmental design in accordance with EN 60076-11

EN 60076-11 defines the climatic and environmental conditions for storage, transport and operation of transformers and chokes. The standard defines two climate classes:

Class C1 – The transformer can operate at a temperature of not less than -5OC, but can be transported and stored at a temperature of not less than -25 OC.
Class C2 – The transformer can be operated and can be transported and stored at temperatures not lower than -25 OC.

The environmental conditions for dry-type transformers are determined by the humidity, condensation present, contamination and ambient temperature:

Class E0 – No condensation appears on the transformer and contamination is negligible.
Class E1 – Condensation may occasionally appear on the transformer (e.g. when the power supply to the transformer is switched off). Limited pollution is possible.
Class E2 – There is frequent condensation and/or heavy contamination on the transformer.

Climatic design in accordance with PN-EN 60721-3-5

EN 60721-3-5 classifies the environmental conditions in which transformers and chokes are stored, transported and operated, among others in railway applications. Brief information about the classification system defined in this standard is given below. The identification system for the environmental conditions class designation is extensive and consists of the following designations:

The first digit indicating the place of application:

1 conditions at the place of storage
2 conditions during transport
3 conditions in places protected from the weather
4 conditions in places not protected from the weather
5 conditions in land vehicles
6 conditions in maritime environment
7 conditions during portable and non- stationary use of products

A letter indicating the type of environmental conditions to be considered:

K factor of a climatic nature (temperature, humidity, insolation, etc.)
B factors of a biological nature (e.g. attack by animals, termites, etc.)
C chemically active agents (various chemical agents)
S substances with mechanical action (sand, dust, etc.)
M factors of a mechanical nature (vibrations, shocks, vibrations)
Z from factors of a special nature

The number following the letter takes values from 1 to 7, indicating the intensity with which the factor occurs. A higher number indicates greater intensity.

In addition, the letters H(high) or L(low) may appear at the end of the designation to indicate the frequency of occurrence of a given condition, e.g. the temperature is usually low and never high.

An example of a full designation according to EN 60721 taking into account the occurrence of all environmental conditions in protected areas may be as follows: 3K3/3B1/3C2/3S1/3M4/3Z1

The most common classes of environmental conditions according to EN 60721:

Condensation

Environmental parameters	Unit	Class 3K3	Class 3K4	Class 3K7	Class 3K7L
The lowest air temperature	°C	+5	+5	-40	-40
Max. air temperature	°C	+40	+40	+70	+70
The lowest relative humidity	%	5	5	10	10
Maximum relative humidity	%	95	95	100	100
The lowest absolute humidity	g/m³	1	1	0,1	0,1
Maximum absolute humidity	g/m³	29	29	35	35
Temperature change rate	°C/min	0,5	0,5	1	1
The lowest air pressure	kPa	70	70	70	70
Maximum air pressure	kPa	106	106	106	106
Solar radiation	W/m2	700	700	1120	1120
Heat radiation	none	⁶⁾	⁶⁾	⁶⁾	⁶⁾
Ambient air movement	m/s	1,0 ⁵⁾	1,0 ⁵⁾	1,0 ⁵⁾	1,0 ⁵⁾
none	no	yes	yes	yes
Precipitation during wind	brak	no	no	yes	yes
Water from sources other than rain	none	no	no	⁶⁾	⁶⁾
Ice formation	none	no	no	yes	yes
5) – if applicable, the relevant value can be given according to table 2 of EN 60721-3-36) – existing location conditions can be determined according to table 2 of EN 60721-3-3