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Engineering >> Transformer >> Knowledge Base For Transformers
          
Direct Current Power Supplies

Rated Output Voltage
The rated output voltage is the output direct voltage ( arithmeticmean ) 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:
Peak value: <30,2 Vs in case of unloaded output and a
arithmetic mean: 28,8 V mains overvoltage of + 6%

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

Lower limit of output voltage:
Paek value: > 18,5 Vs in case of rated output current and a
arithmetic mean: 20,4 V mains undervoltage of - 10%
Residual ripple: < 5 % in case of rated output current

General Information

The transformers, reactors, and direct current power-supplies represented in this catalogue are produced according to DIN/VDE 0550 - 0551 - 0532 with greatest possible care.

Dynamo sheets according to DIN 46400 or electrical sheets with magnetic privileged direction are used as core materials.

This catalogue contains our standard- and stock program, considering the most customary applications. Due to our stock of standard materials and the possibility to produce boxes and sheet-metal parts in our factory, we are also able to realize designs deviating from our standard program.

The high-quality standard of our products is guaranteed by strict production control and final inspection and testing of each unit.

All windings are made of copper. The used insulation materials are chosen in accordance with the insulation class. An increased insulation resistance is achieved by impregnating the parts with resin. This measure also produces a corrosion protection, if the products are used in dry locations.

Reactors

according to DIN/VDE 0550 -2 kVAR - single-phase
suitable for the rated power - 10 kVAR - three-phase
according to DIN/VDE 0532 - 2 kVAR - single-phase
suitable for the rated power - 10 kVAR - three-phase

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 Reactorl

W = 0,5 x L x I² (Ws)
W = energy in watt-seconds (Ws)
L = inductivity in henry (H)
I = current in ampere (A)

Transformers

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

according to DIN/VDE 0550 < 1 kVA - single-phase
suitable for the rated power < 5 kVA - three-phaseq
according to DIN/VDE 0532 1 kVA - single-phase
suitable for the rated power 5 kVA - three-phase

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

rated power: up to 25 kVA - single-phase
up to 40 kVA - three-phase

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 )

rated power: up to 10 kVA - single-phase up to 16 kVA - three-p

rated power: up to 10 kVA - single-phase
  up to 16 kVA - three-phase

Control-power Transformers According to DIN/VDE 0550

Transformers with separate windings and a basic insulation between primary- and secondary winding. The dimensions of control-power transformers have to be designed sufficiently in order to keep the voltage drop within permissible limits even under unfavourable circumstances. The pickup power of all contactors switched on simultaneously results in the short-time rating of the control-power transformer. Additional power for other loads must be added to the rated power.

Autotransformers

There is an electrically conductive connection between the primary- and secondary winding. The power is transmitted partially inductively and partially by current conduction. The smaller the difference between primary- and secondary voltage, all the smaller will be the size or the model output.

according to DIN/VDE 0550 < 1 kVA - single-phase
suitable for the rated power < 5 kVA - three-phase

according to DIN/VDE 0532 > 1 kVA - single-phase
suitable for the rated power > 5 kVA - three-phase

Rated Input Voltage (PRI-voltage)
The rated input voltage is the line voltage (in case of three-phase lines the phase-to-phase voltage) for which the transformer is calculated.

Rated Output Voltage (SEC-voltage)

The output load voltage (in case of three-phase transformers the phase-to-phase voltage) of a transformer in case of rated input voltage, rated power, and rated frequency is called rated output voltage.

Rated Power (P)
The rated power of a transformer is the maximal permissible output power in VA and is staded as product of rated output voltage, rated output current, and power factor. In case of three-phase transformers this product is multiplied by 1,73.

Rated Frequency (f)
Operating frequency in Hz for which the transformer is designed.

No-load Voltage (U )
Output voltage of an unloaded transformer in case of rated input Voltage, and rated frequency.

No-load Current (I )
The input current of an unloaded transformer in case of rated input voltage, and rated frequency.

Impedance Voltage (U )
Voltage value on the input side of a transformer occuring in case of short-circuited output winding and the rated output current flowing there. The value is stated as percentage of the rated input voltage.

Ambient Temperature

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

Frequenzy

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 rated power changes, if the frequency deviates from 50 / 60 Hz.

Insulation Class

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.)

Multi-winding Transformers and Tappings

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.

Neutral Point Load

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.

Operating Modes

Continous operation (DB)
The transformer can operate under rated load as long as you like. The rated powers stated in the catalogue are valid for continous operation.

Short-time operation (KB)
The admissible final temperature is not reached because the load period is so short. In the intervals between the load periods the temperature falls to the degree of the ambient temperature.

Intermittent operation (AB)
The operating time (ED) is stated. In the intervals between the load periods, the temperature does not fall to the degree of the ambient temperature.

Definition of the operating time (ED)
The proportion of load period to cycle duration in case of intermittent operation. The cycle duration is composed of the load period and the interval between the load periods.

Overload - and Short - circuit Protection
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.

Overtemperature
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:

E = 75° C
B = 80° C
F = 100° C
H = 125° C

Protection Class

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, which 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.

Protection Type (DIN 40050/IEC 144)

IP 00 Open frame Without any protection against water and dust
IP 23 protection against spray water Protection against particles > 12mm dia.
IP 55 protection against water jets (all directions) Protection against dust coverage


Short-circuit Withstand Capability

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

Inherently 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.

Temperature Class of Insulation

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

Vector Group (three-phase transformers)e

The vector group indicates the winding connections and the ciruit arrangement of their phase angle to each other. Its 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

YNyn0 primary = connection with neutral point
  N = neutral point accessible
  Secondary = connection with neutral point
  n = neutral point accessible
   
Dyn5 primary = connecting without neutral point
  secondary = connection with neutral point
  n = neutral point accessible

Autotransformers

YNa0 primary and secondary = connection with neutral point
  n = neutral point accessible

 


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