2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC 60027(all parts), Letter symbols to be used in electrical technology
IEC 60633, Terminology for high-voltage direct current (HVDC) transmission
3 Symbols and abbreviations
3.1 General
The lists in 3.2 and 3.3 cover only the most frequently used symbols. The lists of symbols of the IEC 60027 series and IEC 60633 apply.
3.2 List of letter symbols
α(trigger/firing) delay angle
β(trigger/firing) advance angle
µcommutation overlap angle
γextinction angle
3.3 List of abbreviations
The following abbreviations are always in capital letters and without dots:
ETT electrically triggered thyristor
LTT light triggered thyristor
TCU thyristor control unit
HVDC high-voltage direct current
VBE valve base electronics
MVU multiple valve (unit)
BOD breakover diode
4 General terms related to converter circuits
4.1 converter arm
part of a bridge connecting two points of different potentials within a bridge, for example between an AC terminal and a DC terminal
Note 1 to entry: The main function of a converter arm is conversion.
4.2 converter bridge
equipment used to implement the bridge converter connection, if used SEE: Figure 1
Note 1 to entry: The term “bridge” may be used to describe either the circuit connection or the equipment implementing that circuit.
[SOURCE: IEC 60633: 201 5, 6.2, modified – The expression “and the by-pass arm” has been deleted from the definition.]
4.3 converter unit
indivisible operative unit comprising all equipment between the point of common coupling on the AC side and the point of common coupling on the DC side, essentially one or more converter bridges, together with one or more converter transformers, converter unit control equipment, essential protective and switching devices and auxiliaries, if any, used for conversion
SEE: Figure 1
Note 1 to entry: If a converter unit comprises two converter bridges with a phase displacement of 30 degrees, then the converter unit forms a 1 2-pulse unit.
5 Converter performance
5.1 forward direction
conducting direction
direction of current through a valve, when current flows from the anode terminal to the cathode terminal
5.2 reverse direction non-conducting direction
direction of current through a valve, when current flows from the cathode terminal to the anode terminal
6 Thyristor valve design
6.1 thyristor
bi-stable semiconductor device comprising three or more junctions which can be switched from the off-state to the on-state
Note 1 to entry: Devices having only three layers but having switching characteristics similar to those of four- layers devices may also be called thyristors.IEC 60700-2 pdf download.