Switching Actions in undisturbed cases

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

• 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
(disconnector)

• switching under no-load (i lt 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

Mech.pole no. Pole switch no. Pole switch no. Normal switch no.
Mech.pole no. Under normal load Breaking curent Normal switch no.
1000 20 2 1...2 /a
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
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 dont
  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
Np. Of mech. Switches Switching with Switching with Normal switching no.
Np. Of mech. Switches At nominal load Breaking current Normal switching no.
10.000 10.000 5 - 100 -
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
17
Freischalten einer Ortsnetzstation II
1. step Which open point must be closed?
18
Freischalten einer Ortsnetzstation III
1. step Which open point must be closed?
2. step Supply of the substation from the LV side
19
Freischalten einer Ortsnetzstation IV
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
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 31

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
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
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
L1
L2
L3
1U
1V
1W
Test
L1 N
Display 230 V
2U
2V
2W
2N
L2 N
L3 N
L1
L2
L3
N
28
Testing of the Phase Sequence with a voltage meter
L1
L2
L3
1. Test
1U
1V
1W
L1 L2
Test
Display 400 V
L1 L3
L1 L1
L2 L3
NO display
L2 L2
2. Test
L3 L3
L1 N
2U
2V
2W
2N
Display 230 V
L2 N
L3 N
L1
L2
L3
N