Frankfurt (Germany), 6-9 June 2011

Romanens – CH – S3 – 0220

Impact of Distributed Generation on Grid Protection

BKW FMB Energie AGSwitzerland Florian Romanens

Paper n° 0220

Frankfurt (Germany), 6-9 June 2011

Content

Introduction BKW FMB Energie AG and its grid Changes in existing distribution grids

Some requirements considered by BKW

Protection concept Short-circuits and earth-faults Frequency

Conclusion

Frankfurt (Germany), 6-9 June 2011

Introduction BKW FMB Energie AG and its grid

Swiss utility company based in Bern

Generation, transport and distribution of electricity

Grid: Transmission grid: 380kV, 220kV Over-regional distribution grid: 132kV, 50kV

Regional distribution grid: 16kV, 0.4kV

Interconnected

topology

radial topology

Frankfurt (Germany), 6-9 June 2011

Introduction Changes in existing distribution grids

Existing distribution grids are often built only for load flow DG can create a change in the power flow

DG

HV HV

MV MV

DG DG DG

DG

Standard distribution grid

Distribution grid with DG

by BKW:- 16kV- star point isolated

Frankfurt (Germany), 6-9 June 2011

Some requirements considered by BKW DG-protection systems have to recognize:

earth-f. and short-c. in case of fault on the DG-side quickly trip the DG-circuit breaker

earth-f. and short-c. in case of fault in the grid normally allow sufficient time for the grid to clear the fault. If the fault is

not cleared after a certain time, trip the DG-circuit breaker

over / under frequency and over / under voltage have to stay connected if f>47.5Hz and U>80%

Normally, a communication between substation and DG is used to realize an “intertrip” from the protection of the bay (in the

substation) to the DG-circuit breaker

Frankfurt (Germany), 6-9 June 2011

Short-circuits and earth-faults Protection zones

Each zone is defined by the CBs and CTs (beginning / end)

Paper n°0220 shows the protection concept for each zone

DG

Substation

DG16kV

0.4kV

0.4kV

50kV

load

16kV switchgearLine between substation and DG

Other parts of the grid

DG-zone

Frankfurt (Germany), 6-9 June 2011

Short-circuits and earth-faults Example: fault in the 16kV GIS in the substation

GIS have a rated arcing duration of 1.0s Faults in the GIS have to be cleared within 1.0s

Ipu

t

1/X

"

Iss

40msExample of WT short-

circuit behaviour

GIS

G

Relay

On the BB: cleared by the reverse interlocking busbar prot. with special “BB-intertrip”

Between CB and cable termination, the “intertrip” to the circuit breaker of the DG is used

inte

rtri

p

Simple over current functions are not appropriated

Frankfurt (Germany), 6-9 June 2011

Frequency Example with the frequency

DG have to stay connected if f>47.5Hz & U>80% Important for the stability of the grid in case of a large

disturbance

Under Frequency Load Shedding (UFLS) If the load is bigger than the generation, the frequency will fall. In

this case, a certain amount of load has to be shed, but the production has to stay connected to support the grid.

generation load

Frankfurt (Germany), 6-9 June 2011

Conclusion DG are / will be connected to the distribution grid

Due to DG, the power flow-direction can change

Grid configuration has to take DG into account

Especially protection concept have to be adapted for DG

The sum of a lot of small generation units can impact on the stability and reliability of the grid

Some requirements mentioned are difficult to fulfill. Therefore, the collaboration among the partners involved in projects with DG is very important

Frankfurt (Germany), 6-9 June 2011

Thank you for you attention!