Standards Development

Scope

To issue a new standard for star point reactors, that follows the IEC 61869 layout and leans on the main IEC 61869-1 standard for the dielectric requirements, majority testing requirements and appendices as these are common. Specific features of these prod ucts should then be defined in their standalone standard. Multiple parts of the IEC 60076 -6 standard are to be addressed or incorporated (e.g. inductance measurements, magnetizing characteristic measurements, etc.). Specific clauses and tests need to be written to adequately describe these units. As a first draft, these include:

• Definition and tolerances on required parameters (unsaturated and saturated inductance, resistance, fault current, allowed continuous DC current, simultaneous current, losses…) and performance requirements

• Definition of proprietary routine tests (e.g. unsaturated inductance measurement, saturated inductance measurement, DC capability test, etc.)

• Definition of proprietary type and special tests (e.g. temperature rise under simultaneous AC and DC excitation, fault current tests, operation under superimposed 3rd harmonic, etc.)

Purpose

Background:

 Star point reactors (also known as HVDC reactors, HVDC discharge transformers, HVDC neutral reactors, etc.) are devices used in symmetrical monopole HVDC VSC installed between the DC and AC voltage connection. They are configured in a way that they represe nt a current path with a high impedance for the fundamental component of the AC current (generally 50 or 60 Hz) and a low impedance for DC current. Their purpose is to conduct the parasitic leakage currents which accumulate on the DC side (predominantly insulator surfaces) into the ground and to prevent a voltage drift between two poles at a floating potential, thus having approximately equal values of voltage in respect to the ground potential.

That being said, these devices are defined by rated parameters of unsaturated inductance, saturated inductance and winding resistance. They are also intended to be used with simultaneous AC and DC excitation, where the DC component can be several times hig her than the AC component. They are also exposed high fault currents of short duration (comparatively to typical values of inductive voltage transformers) as a result of a direct lightning strike to the DC line.

Since these units are specified with different values of saturated and unsaturated inductance, they typically have a magnetic core, which needs to be designed to avoid premature saturation under AC and DC excitation. These units are phase-to-ground insulated, with the applicable voltages ranging from 36 – 550 kV (or even more), depending on the substation topology and power transformer connection.

In addition, the requested values of both AC and DC currents are in an approximate realm of 50 mA – 1 A. For those reasons, these units are based on the design of inductive voltage transformers covered by the IEC 61869 series under TC 18, and not “conventi onal” reactors covered by the IEC 60076-6 standard under TC 14. This is supported by the fact that the production technology of such units, and insulation systems (liquid and gas) is similar to the production of instrument transformers. Consequently, the manufactures of these units are typically companies that manufacture instrument transformers.

Justification:

Firstly, given the number of HVDC projects, the majority of which utilize the symmetrical monopole technology, which consequently leads to an increased number of specifications for star -point reactors, the need for a standardized approach is apparent.

Secondly, given the requirements for this type of equipment and the expected performance, which is different than conventional voltage transformers, these cannot be covered adequately by the IEC 61869-3 standard.

Similarly, based on their general design, these also cannot be covered adequately by the IEC 60076 -6 standard.

Since the existing standards do not cover these units adequately, their direct interpretation may cause a wrong specification, tolerance, or a test that does not adequately prove the performance characteristics or may even result in a failure (e.g. if sepa rate source from IEC 60076-6 is applied directly on the HV winding).

In addition, these units exhibit performance features atypical for either of the above -mentioned standard groups. These features include, simultaneous AC and DC excitation, very high fault currents and operation with superimposed 3rd harmonic.

Since these units do not “fit” in either of the existing standard groups, there is the need to issue their standalone standard, which will adequately address all the intricacies these units exhibit.