LAAKSONEN Hannu – Finland – RIF Session 3 – Paper 0431

Frankfurt (Germany), 6-9 June 2011

In the future, traditional fuse based over-current protection of LV networks will not be applicable for LV microgrids with island operation capability Because high fault currents are not present

during island operation Therefore, new protection approach is needed

In this paper novel adaptive protection system for LV microgrids is proposed

LAAKSONEN Hannu – Finland – RIF Session 3 – Paper 0431

PROTECTION SYSTEM FOR FUTURE LV MICROGRIDS


Adaptivity means that protection system takes into account The operation state of the LV microgrid and The number, type and fault current feeding

capability of DG units

Fast and selective operation is achieved by utilization of high-speed communication




In the development of the new protection scheme for LV microgrids many things must be considered such as

1) The number of protection zones in LV microgrid Which defines the needed amount of protective devices (PDs)

2) Speed requirements for the microgrid protection in different operation states and configurations Two main reasons for the speed requirements are stability and

customer sensitivity

3) The protection principles for parallel and island operation of the microgrid




In this figure the LV microgrid protection zones and types of protective devices (PD 1-4) chosen for the new LV microgrid protection system are presented

The needed protection devices (PD 1-4) are PD 1: Protection in connection

point of LV microgrid PD 2: LV feeder protection PD 3: Customer protection PD 4: DER unit protection




In the proposed LV microgrid protection system for example the PD 2s of LV feeders are able to adapt to the current configuration and operation state

Change of settings and pick up limits of PD 2s could be done by Microgrid Management System (MMS) when microgrid configuration changes

Fast real-time communication is needed for microgrid protection purposes between PDs and also between MMS and DER units during microgrid island operation




Based on extensive simulation studies with PSCAD, also the pick-up limits and operation curves for PDs are defined in the paper

In this figure for example the operation curves for PD 1 and PD 4 are presented




Operation curves of PDs




The idea was that the operation curves of different PDs could be the same during normal and island operation as far as possible

However, during island operation the operation curve and principle of PD 2 needed to be changed to be adaptive and multicriteria based




Also few additions to the proposed protection system were defined in the paper to take into account for example:

1) Protection of long LV feeders with section CBs,

2) Connection of large DG units (e.g. > 50 kVA) to LV microgrid and

Directly connected SGs should be connected either 1) directly or 2) with own LV feeder to the MV/LV distribution substation

3) Protection issues related to possible ring operation of LV feeders




In this paper novel protection system for LV microgrid, including the operation curves for PDs, during normal and island operation has been presented

Realization of LV microgrids as integrated part of future Smart Grids needs new grid codes where the protection requirements and settings for LV microgrids are clearly determined

The proposed new LV microgrid protection system also revealed the need for fast, accurate, low-cost, and programmable PDs with high-speed communication capability in future smart LV networks


CONCLUSIONS



Thank you for your attention

LAAKSONEN Hannu – Finland – RIF Session 3 – Paper 0431

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