
TR 60909-4 © IEC:2000 – 3 –
CONTENTS
Page
FOREWORD ...............................................................................................................................7
Clause
1 General................................................................................................................................11
1.1 Scope and object........................................................................................................11
1.2 Reference documents.................................................................................................11
1.3 Definitions, symbols and indices, and equations........................................................13
2 Positive-sequence, negative-sequence and zero-sequence impedances of electrical
equipment............................................................................................................................13
2.1 Overhead lines, cables and short-circuit limiting reactors..........................................13
2.2 Transformers..............................................................................................................15
2.3 Generators and power-station units............................................................................27
3 Calculation of short-circuit currents in a low-voltage system Un = 400 V............................37
3.1 Problem .....................................................................................................................37
3.2 Determination of the positive-sequence impedances ..................................................37
3.2.1 Network feeder..............................................................................................37
3.2.2 Transformers .................................................................................................41
3.2.3 Lines (cables and overhead lines)..................................................................41
3.3 Determination of the zero-sequence impedances........................................................43
3.3.1 Transformers .................................................................................................43
3.3.2 Lines (cables and overhead lines)..................................................................43
3.4 Calculation of "
k
I and ip for three-phase short circuits ...............................................45
3.4.1 Short-circuit location F1................................................................................45
3.4.2 Short-circuit location F2................................................................................47
3.4.3 Short-circuit location F3................................................................................49
3.5 Calculation of "
k1
I and ip1 for line-to-earth short circuits............................................49
3.5.1 Short-circuit location F1................................................................................49
3.5.2 Short-circuit location F2................................................................................53
3.5.3 Short-circuit location F3................................................................................55
3.6 Collection of results...................................................................................................55
4 Calculation of three-phase short-circuit currents in a medium-voltage system –
influence of motors..............................................................................................................57
4.1 Problem .....................................................................................................................57
4.2 Complex calculation with absolute quantities ............................................................59
4.3 Calculation with short-circuit reactances of electrical equipment ..............................67
4.4 Calculation with per-unit quantities...........................................................................71
4.5 Calculation with the superposition method ................................................................75
This is a preview - click here to buy the full publication