The ambient temperature is the highest temperature which may surround the transformer under normal circumstances. If the transformer is built into a box, it is not alloed to go beyond the permissible ambient temperature, otherwise the load has to be reduced

The transformer can be operated as long as desired at nominal load. The power ratings apply with us for continuous operation.

Rated Output Voltage

The rated output voltage is the output direct voltage ( arithmetic mean ) in case of average load and rated  input voltage.

Rated Power

The maximal permissible output power in W ( watt ) is called the rated power and is stated as product of rated output direct voltage, and rated output direct current.

Residual Ripple (RW )

The proportion of the superimposed power-frequency voltage to the direct voltage. The value is stated as percentage.

Limiting Values According to DIN 19240 for 24 V – Direct Current Power Supplies
Upper limit of output voltage:

(The arithmetic mean can rise to the peak value, if a capacitor is used as protective element.)

Lower limit of output voltage:

The transformers contained in this catalogue are designed for 50 / 60 Hz. Losses, efficiency, and voltage drop are related to the frequency of 50 Hz. The reted power changes, if the frequency deviates from 50 / 60 Hz.

This expression represents the ambient temperature and the insulation class.
 

e.g.: T 40/B

(In this case „40“ means the ambient temperature of 40°C and „B“ represents the insulation class.)

The duty cycle (DC) is specified. In the operational pause, the temperature does not fall on the value of the environment.

The stated powers are valid for one primary and one secondary voltage. Tappings up to 5 % do not require a larger core power. Secondary tappings are measured for the current of the highest voltage step.

Several primary voltages, secondary tappings for full power, and some secundary windings with the necessary insulations require a larger core power.

Vector Group: YNyn0 resp. YNyn6

To avoid displacements of the neutral point and additional losses, it is only allowed to load the neutral point with the full rated current if the neutral conductor of the supply system is connected with the transformer-neutral point of the supply side. Does this not come true, only a load of 10 is permissible.

The same is valid for the star-delta economy connection (YNa0).

Vector Group: Dyn5 and Dyn II

The neutral point can be loaded with the full rated current in case of these vector groups.

Vector Group: Yzn5 or Dzn0

The neutral point is also fully loadable. These vector groups are to recommend, if the load of the phases is unbalanced. But the additional expense for wirings and connection requires an extra charge.

Generally, built-in transformers are not protected against overload and short-circuit.

Because of the high inrush current, which can be, possibly, the fiftyfold of the nominal input current, a protection by means of fuses or automatic ciruit-breakers is only possible in case of short-circuit but not in case of overload.

A better protection can be achieved by using a circuit-breaker with a thermomagnetic release (starting circuit-breaker, power breaker), which can be adjusted to the primary rated current. As a result of increased winding temperature in case of  short-circuit or overload, another possibility is to insert temperature-controlled sensors in the windings. In this case an external switching device turning off (e.g. thermistor protection, thermal cut-outs, temperature controllers). To use or starting current limiters is also recommendable.

The temperature caused by the specific heat capacity of the transformer under fixed operating conditions is called overtemperature. The difference between the nominal- resp. Ambient temperature and the temperature of the insulation class is the highest permissible overtemperature. The possible overtemperature has to be reduced because of hot spots and the reduction is dependent on the insulation class. Therefore, the permissible overtemperatures in case of an ambient temperature of 40° C are as fallows:

Temperature Class of Insulation

E = 75° C

B = 80° C

F = 100° C

H = 125° C

The stated protection class specifies the protective measures which secure a device against inadmissible touch voltage.

Protection Class I

Protection Class I characterizes devices, whose touchable metal parts, wich can be energized in case of a fault in the basic insulation, are connected to the safety earth terminal the connection of the safety earth terminal charcterizes the protective measure „protective earthing“.

Protection Class II (totally insulated)

Protection class II charcterizes devices, whose touchable metal parts are separated by means of an additional insulation from other parts, which can be energized in case of a fault in the basic insulation. They have no earth connection.

Open transformers (IP 00) designated  for the installation in a device are only prepared for a special protection class. Transformers prepared for protection class II can also be used in devices of protection class I.

Line-and Commutating Reactors

These reactors are installed between line and converter installations in order to increase the natural impedance of the line, to limit the commutation current, and to damp the interference voltage. A reac-tive voltage drop of 8.8 V/phase in case of 380 V, resp. 9,25 V/phase in case of 400 V corresponds to an impedance voltage ( Uk) of 4 %.

Smothing- and Filter Reactors

Reactors of this type are inserted in the direct current side of converter installations in order to reduce the ripple, to damp the harmonic waves, to limit the currents, and to damp the noise of the driving mechanism.

Magnetic Energy Content of a Reactor

The transformers are classified with regard to their capability to withstand short circuit as follows:

Inherentlay short-ciruit-proof

Non-inherently short-ciruit-proof

Non-short-circuit-proof

Inherently short-circuit-proof transformers have no protective device. The capability to withstand short circuit is achieved by internal voltage drop. This can be realized by design, e.g. high-reactance transformers.

Non-inherently short-circuit-proof transformers have a protective device which opens or limits the electric circuit in case of short circuit or overload. Fuses, excess-current circuit-breakers,thermal cut-outs, and PTC thermistors are customary protective devices.

Non-short-circuit-proof transformers have no built-in protective device and have to be protected against overload by means of protective measures within the incoming line or the outgoing cable.

The load time is so short that the maximum end temperature is not reached. In the operational pause, the temperature drops to the value of the environment.

Size, loadability and lifetime of a transformer are determined substantially by the used insulating materials.

According to IEC85 the temperature clsses of insulation are classified as follows:

E  =  120° C

B  =  130° C

F  =  155° C

H  =  180° C

Mains Transformers and Power Transformers                                

Transformers for general use with separate windings and a basic insulation between primary- and secondary winding.

Isolating Transformers According to DIN/VDE 0551

secure electrical separation the protective measure ,,protective separation” is fulfilled

reinforced or double insulation

rated output voltage: > 50 V

Safety Isolating Transformers According to DIN/VDE 0551

secure electrical separation the protective measure ,,safety extra-low voltage” is fulfilled

reinforced or double insulation

rated output voltage: = 50 V ( no-load operation )

The vector group indicates the winding connections and the ciruit arrangement of their phase angle to each other. Ist symbol consists of a capital letter for the input voltage, a small letter for the output voltage, and a code number. In case of brought-out neutral point „N“ resp. „n“ is added, for example YNyn0 – Dyn5 – YNa0.

The following table represents a range of the most customary vector groups. Our standard types are designed according to vector group YNyn0 resp. Dyn5 in case of separate windings and according to vector group YNa0 in case of autotransformers.

Three-phase transformers