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Switching Actions in undisturbed cases

Switching Actions in undisturbed cases. It is important to understand the switching capabilities to find out the right switching sequences: Circuit breakers, load breakers and disconnectors have to be handled in a different way with respect to the right switching sequence.

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Switching Actions in undisturbed cases

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  1. Switching Actions in undisturbed cases It is important to understand the switching capabilities to find out the right switching sequences: Circuit breakers, load breakers and disconnectors have to be handled in a different way with respect to the right switching sequence.

  2. Switching Protection: Interlocking Schemes Switch, as there would be no switching protection • Disconnectors should not be switched under load • (guaranteed by logical, topological or optical interlocking mechanisms) • Earthing breakers should be switched on only, if the part to be earthed has no voltage • (hard to detect for ring main units) • Circuit breakers should not be switched on, if an isolator is in intermediate/disturbed position • Circuit brealers at bus ties should not switched off until more than disconnector at another feeder is on or one of them is disturbed. • (every bay must be controled and its position information must be provided to the bus tie bay via ring lines) Interlocking program

  3. Trennschalter Siwtch pole (disconnector) • switching under no-load(i < 0,5 A) • are able to carry short-circuit currents • represent a visible disconnection (i.e. for work at downstream parts) OFF-state ON-state

  4. Lasttrennschalter (switch disconnector) • siwtching under normal load (up to p.f. = 0,7) • are able to carry short-circuit currents • represent visible disconnection Principle of arc distinction

  5. Arf Distinction II Arc distinction with switch disconnector Foto: Driescher, Wegberg Switching at nominal load! Foto: Driescher, Wegberg

  6. Types of Switch Disconnectors Foto: Peters & Thieding Vacuum switch disconnector with HH-fuse and high-speed grounding switch Name plate

  7. Load breaker – Fuse Combination Switching Area Itake-over Itransfer 50 100 VDE 0671 Part 105 Ims I3 I1 Forbidden area HH-fuse Load breaker Tested area transfer current: values of the symmetrical current, where the switching task changes from breaker to HH fuse Transfer area affected by tolerances of the fuse characteristic, The fuse which trips at first, releases the load breaker. Afterwards the next fuse or the load breaker are interrupting the current. For current highet than Itransfer , all fuses have to trip before the load breaker.

  8. Circuit Breaker Circuit breakers are able to interrupt load and short-circuit current without damage. They don‘t have a visible disconnection. They can switch currents up to 16 kA (in 20 kV) and are able to draw such currents for some seconds without damage. Circuit Breakers are able to store siwtching sequences.

  9. Circuit-breaker 10-kVVacuum Circuit breaker

  10. Switching of a circuit breaker 2) Busbar disconnector OFF 1) Circuit breaker OFF

  11. Switching ON of a Circuit Breaker Feeder 1) busbar disconnector ON 2) circuit breaker ON

  12. Switching ON of a Transformer: For primary as well as distribution transformers it is recommended to switch on the HV side at first and then the low voltage side. Reason: inrush current because of the magnetic remanence of the iron core. Those high currents can be handled better by the HV network than the LV network.

  13. Switching ON of a Transformer ← 1) MV load breaker ON ← 2) LV circuit breaker ON

  14. Switching OFF of a Transformer: Switching off requires a different switching sequence: If the transformer is switched off at the HV side at first, than big inductive transient currents disturbes the power quality of the LV side with a possible danger for the equipment of LV clients.

  15. Switching OFF of a Transformer ← 2) MV load breaker OFF ← 1) LV circuit breaker OFF

  16. Freischalten einer Ortsnetzstation I Order: De-energizing NSt. Juistweg 33 Stat.-Nr. 509

  17. Freischalten einer Ortsnetzstation II Order: De-energizing NSt. Juistweg 33 Stat.-Nr. 509 1. step: Which open point must be closed?

  18. Freischalten einer Ortsnetzstation III Order: De-energizing NSt. Juistweg 33 Stat.-Nr. 509 1. step: Which open point must be closed? 2. step: Supply of the substation from the LV side

  19. Freischalten einer Ortsnetzstation IV Order: De-energizing NSt. Juistweg 33 Stat.-Nr. 509 1. step: Which open point must be closed? 2. step: Supply of the substation from the LV side 3. step: Switching of separation point, De-energizing of the substation

  20. Freischalten einer Ortsnetzstation V Order: De-energizing NSt. Juistweg 33 Stat.-Nr. 509 NSt. Juistweg 33 is de-energized and earthed Substation can be released for work

  21. Switching Sequences in undisturbed StateNetwork Coupling Network couplings are necessary for: connection of one 20 kV switchgear to another network area without interruption of power supply for the supply of on partial network via an spare bus for the maintenance of a primary transformer Such couplings require single busbars or multiple busbars with bus ties.

  22. The system voltages have to be synchronized before the coupling to avoid high transient currents, which have to be switched off immediately by the network protection. If the short-circuit power exceeds the rated short-circuit power of the switchgears during the coupling, no people are allowed to stay at the switching rooms of the affected switching of primary substations.

  23. Operation of Distribution TransformersParalleling of Transformers • same voltage, same frequency • Same vector group (otherwise transfer currents even during normal operation) • Same transformer ratio • Impedance voltages should not differ more than 10 % of the average value of the two units • ratio of nominal power lower than 3:1

  24. Paralleling of 3 Transformers Transformer 1: SN1 = 100 kVA ukN1 = 4 % Transformer 2: SN2 = 250 kVA ukN2 = 6 % Transformer 3: SN3 = 500 kVA ukN3 = 4,5 % Total nominal power S = 850 kVA With: The resulting impedance voltage is: The final load of each transformer is: S = 850 kVA

  25. Testing of the Phase Sequence with a voltage meter V L1 L2 L3 1U 1V 1W Test: L1 – L1 No Value L2 – L2 L3 – L3 2U 2V 2W 2N L1 L2 L3 N

  26. Testing of the Phase Sequence with a voltage meter V L1 L2 L3 Test: 1U 1V 1W L1 – L2 Display 400 V L1 – L3 L2 – L3 2U 2V 2W 2N L1 L2 L3 N

  27. Testing of the Phase Sequence with a voltage meter V L1 L2 L3 1U 1V 1W Test: L1 – N Display 230 V 2U 2V 2W 2N L2 – N L3 – N L1 L2 L3 N

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