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Busbars

Breaker and internal busbar faults are generally accompanied by high-level short circuit currents and thereafter create very dangerous conditions for power system stability. That is why very fast tripping is absolutely required for busbar protection as well as its selectivity for detection of internal and external faults. 

The TOR 300 DPB devices provide reliable busbar differential protection for HV, EHV and UHV substations. The IED provides three (single-phase) differential zones and operates as low impedance centralized differential protection. Each differential zone within TOR 300 DPB consists of main differential protection function, sensitive current unit and differential current function for CT circuit supervision. Fine numerical equalization of the bay CTs rated currents is implemented. Differential protection follows automatically the connections of different bays to a certain busbar section and this way ensures dynamic bay selection within a certain differential zone. Sensitive current units are designed to automatically increase the sensitivity of busbar protection during busbar autoreclosing cycle, and for consecutive tripping of bays with smaller fault current. Sensitive current units may also be used for tripping the bay at switch-onto fault conditions. CT circuit supervision prevents unnecessary operation of busbar protection for different faults in CT secondary circuits.

Differential protection for busbars with more than 8 bays is implemented on per phase basis in each TOR 300 DPB device Each IED provides selective this way protection of one phase within sectionalized (two) busbar systems. It comprises for this purpose three single-phase differential zones: one check-zone and selective zones for the 1st and the second busbar section:

  • for busbars with up to 16 bays and max. 8 bays per section (one TOR 300 DPB in 3/4 of 19” case for all three phases)      
  • for busbar up to 18 bays (one TOR 300 DPB in 3/4 of 19” case for each phase)
  • for busbar up to 24 bays (one TOR 300 DPB in full 19” case for each phase)

One TOR 300 DPB device can provide three-phase restrained busbar differential protection and protect all three phases of small busbar up to 4 bays (TOR 300 DPB in 1/2 of 19” case) or busbar with up to 8 bays (TOR 300 DPB in 3/4 of 19” case).

Protected objects

  • double busbar system equipped with a bus coupler and transfer bus, with variable bay connection;
  • double sectionalized busbar system with bus coupler and transfer bus;
  • double sectionalized busbar system with double breaker configuration;
  • double bus system with double circuit breakers (similarly to “one-and-a-half-breaker” busbar system) etc.

Main functions

  • PBDF (87B) - busbar differential protection
  • RBFP (50 BF) - breaker failure protection for all bays
  • RREC (79)  - adjustable busbar autoreclosing functionality, operating after elimination of busbar faults
  • SOTF - switch-onto-fault logic
  • flexible software design permits implementation of additional protection functions and user adjusted logic

Main advantages

  • short operating time
  • up to 24 bays with configurable connectivity
  • simple current restraint calculation
  • built-in CT circuit supervision functions (fast and slow)
  • numerical equalization of CT ratio (50 - 500%)
  • reliable operations during external faults with CTs saturation are secured by patented innovation

Development of the centralized PAC technologies for substations is one of the most prospective directions for their further improvement. The centralized structure of PAC functionality provides high flexibility of their structure and amount of the real time signals, which can be processed in different algorithms. In addition to this, centralized PAC systems within substations allow obtaining high economic effects on capital investments and reduction of operating costs.

Relematika can provide two solutions for the centralized PAC system for down-up HV /MV substations:

  • solutions based on classical, but optimized design of primary and secondary circuits and wiring
  • digital centralized solutions based on IEC 61850 standard, including sampled values, GOOSE and MMS messaging

Protected objects

  • distribution down-up substation connected to single-power line
  • transit  down-up substation connected  as H scheme
  • two-winding transformers
  • three –windings transformers

Main functions (within one TOR 300 IED)

  • PBDF (87B) - busbar differential protection
  • PTDF (87T) - transformer differential protection
  • PIOC/PTOC (50/51) -  backup OC protections for transformer
  • PLDF (87 L)- line current differential protection as a main protection for HV line:
  • PDIS (21P) - distance protection for HV line
  • PDEF ( 67N) - directional EF OC protection for HV line
  • RBRF (50 BF) – breaker failure protection
  • PTOC (51)- OC protection for incoming feeder
  • RDRE - disturbance and event recorder
  • RFLO - fault location on lines
  • Buchholz protection
  • automatic breaker control: line circuit breakers, busbar sectionalizing circuit breaker as well as circuit breakers on MV side of power transformers
  • transformer and circuit breakers technological protections

Advantages

  • relay protection, control and automation on one single section in one device
  • 2 - 3 times reduced requirements on PAC hardware (less cubicles and copper cables)
  • reduction of expenses for substations upgrading (including survey and design, construction and installation works as well as commissioning)
  • major construction cost reduction (reduced substation footprint)
  • PAC system maintenance cost reduction
  • constructional design simplification: standard integrated design and engineering solutions
  • observability level increase
  • protection reliability increase (100% backup, high speed of operation)

Examples of centralized PAC implementation
HV_grids_Centralized_PAC.png

Substations should be provided with a full interlocking scheme to ensure that all disconnectors, fixed earthing switches (or other interlocked earthing devices) and, where required, circuit-breakers are operated in the correct sequence so that personnel do not endanger themselves and/or the integrity transmission against incorrect or inadvertent operation of equipment. Where necessary, such interlocking shall also be extended to cover limitation of access to areas where there is a risk that normal safety clearances may be infringed.

Interlocking schemes shall cover the following conditions:

  • interlocking between circuit-breakers and disconnectors to ensure that disconnectors do not close or disconnect load currents
  • interlocking between disconnectors and earthing switches to ensure that earthing switches cannot be closed on to a locally energized circuit  and cannot be energized, when closed by  disconnectors
  • interlocking between disconnectors and adjacent earthing switches to permit operation of the disconnectors when earthing switches are closed on both sides of the disconnectors
  • ensuring correct sequence of on load busbar transfer switching operations at multiple busbar substations
  • ensuring that a bus-coupler or bus-section circuit-breaker is only closed with its associated disconnectors both open or both closed

Relematika has different solutions to ensure reliable interlocking systems.

Local interlocking scheme is designed by using TOR 300 bay controller for a single bay unit. Position of disconnectors, earthing switches and breakers are transferred to the IED by their auxiliary contacts over copper cables. Two contacts are used within each primary unit - an open and a close contact to ensure the true position of switches. Interlocking logic is created by using the PCAP software and loaded into the bay controller. Data exchange between IEDs within substation (if necessary) is performed by using UniSCADA communication networks and EC 61850 standard (GOOSE) messages. 

Distributed interlocking scheme use separate bay controllers as a DMU (acquisition system) thereafter present information transferred to central unit (controller) or to SCADA by fiber optic or cooper cables. Interlocking logic is performed into the central controller or as one of applications of UniSCADA.

Centralized interlocking scheme is
designed according to technical requirements of customers by using PCAP
software and TOR 300 IEDs. Position of disconnectors, earthing switches and circuit breakers are
transferred to IEDs by their auxiliary contacts over cooper cables. Two
contacts (from each switching device) are used (open and close contact) to
ensure reliable information about position of switches. One or two TOR 300 IEDs
are applied according to the quantity of primary equipment.