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Switch on three-phase transformer gently

Pre-magnetizing transformer, transformer starting switch, transformer switching relay, TSR, for three-phase transformers are called TSRL or TSRDF

 

TSRD in cabinet of 50kVA isolating transformer, switches the transformer on with only the no-load current.

Real three-phase transformers

Soft starting of three-phase transformers in no-load operation or under load.
 

Real three-phase transformers are:

These transformers consist of a three-legged iron core with a winding package on each leg. The magnetic flux in the iron core is distributed evenly in all three legs of the iron core.

Real three-phase transformers up to a size of 45 kVA can be switched on with a TSRD, transformers up to 1000 kVA can be switched on with the so-called three-phase transformer switching relays, TSRDF, without inrush current even under load. The magnetization is balanced before full switch-on by influencing it with voltage pulses.

With two single-phase TSRL for 32A, even small three-phase transformers up to approx. 20 kVA can be switched on smoothly.

Large transformers with more than 40kVA, even with many megawatts, including those for 690V or medium voltage, can be switched on in no-load operation via a small inductive premagnetizing device without an inrush current. The premagnetizing device is bypassed after a short time. 

TSRD for real three-phase transformers

Application circuit diagrams for TSRD

 

Data sheets from TSRD

Economy circuit with 2 TSRL for soft switch-on of a small three-phase transformer

Description with measurement curves and switching suggestions for three-phase transformer soft start up to 20kVA with 2 TSRLs

 

with TSRDF control module for real three-phase transformers

The TSRDF module can control solid state relays or thyristor modules and a bypass contactor.

 

It can be used to build transformer switching relays for up to 500A and more and also to clock transformers with pulse groups. This saves an expensive thyristor controller.

TSRDF application switching examples:

TSRDF data sheets, control module:

Switching on large transformers with a premagnetizing unit

Pre-magnetizing before switching on fully avoids the inrush current.

 

Avoid inrush currents without electronic soft starters

Three-phase transformers without inrush current

A transformer equipped with an auxiliary winding no longer has an inrush current

 

The first step is to switch on at least two additional auxiliary wraps

Soft-start unreal or composite three-phase transformers consisting of 3 single-phase transformers

Unbalanced or composite three-phase transformers are transformers that consist of three separate single-phase transformers that are electrically connected together as a three-phase transformer at the output.

 

These transformers can be switched on smoothly with one TSRD or three TSRLs when they are idle, or with three individual TSRLs for single-phase transformers when they are loaded.

TSRL(F) applications for composite three-phase transformers.

All PDF documents are only available in German