16-07-2012, 02:36 PM
Characteristics of the SCFCL in parallel with a resistor and a ZnO device by the numerical analysis
[attachment=27742]
Introduction
In recent years, deregulation of electric power industries
advances in Japan, and distributed generators (for example
wind power, solar cell system, micro gas-turbine system,
and so on) are introduced to load system sides. Therefore
the electric power system has been getting more
complicated. Consequently a fault current is getting larger
and the load to a circuit breaker is increasing. In the power
system, when a fault occurs, the fault point is rejected from
the power system by circuit breakers not to expand the
influence of the fault. However the capacity of the circuit
beaker has reached to the limit and further increase of the
capacity will not be expected. Therefore the recent power
system is designed to suppress the fault current flow
through the circuit breaker less than the capacity of the
circuit breaker. Under this condition, it is expected to install
superconducting fault current limiters (SCFCLs) to power
systems in order to solve both of the fault current problem
and the stability problem.
Modeled SCFCL
The Modeled SCFCL contains three SCFCLs of
transformer type in one cryostat. The SCFCL consists of
two superconducting coils (NbTi wire for AC use)
magnetically coupled coaxially. Schematic configuration is
shown in Fig. 1. The inner (primary) coil will be connected
to a power line. The outer (secondary) coil is
short-circuited.
Characteristics of the SCFCL system
To investigate the fundamental characteristics of the
SCFCL in parallel with a resistor and a ZnO device, a
numerical analysis using single-phase circuit was carried
out with EMTP (Electro-Magnetic Transients Program).
Simulation model of SCFCL with EMTP
The SCFCL turns into secondary coil. Since the AC
critical current of the secondary coil is 246.1 A (= 174.0
Arms), the SCFCL is designed to turn into the current
limiting mode when the current I2 exceeds 246.1 A in the
numerical analysis. The equivalent circuit of the SCFCL is
shown in Fig.4. If it is assumed that all of the loss generated
in the SCFCL in the current limiting mode is caused by the
resistive component RFCL of the impedance of the SCFCL
ZFCL, the loss PFCL is calculated from Eq.(1)
The characteristics of the SCFCL system
The results of the numerical analysis using single-phase
circuit are shown in Fig.8-right. Fig.8-left shows the
experimental results. [6] These graphs represent the data in
the case of using a ZnO device of 22 V of varistor voltage
and a resistor of 2 Ω. The simulation results agree well with
the experimental results. It found that when the value of Vfcl
is lower than varistor voltage, the current don’t flow the
resistor and the Ifcl is the peak value.
Numerical analysis method
an experimental power system, which is a
target of the simulation. A three-phase synchronous
generator was connected to an infinite bus (210V
commercial power line) through parallel artificial
transmission lines. Three-line shorted fault was simulated in
the lower line (fault line) by closing the switch Sw3. The
switch Sw1 and Sw2 simulated circuit breakers, and the
SCFCL in parallel with a resistor and a ZnO device was
installed in the fault line.
[attachment=27742]
Introduction
In recent years, deregulation of electric power industries
advances in Japan, and distributed generators (for example
wind power, solar cell system, micro gas-turbine system,
and so on) are introduced to load system sides. Therefore
the electric power system has been getting more
complicated. Consequently a fault current is getting larger
and the load to a circuit breaker is increasing. In the power
system, when a fault occurs, the fault point is rejected from
the power system by circuit breakers not to expand the
influence of the fault. However the capacity of the circuit
beaker has reached to the limit and further increase of the
capacity will not be expected. Therefore the recent power
system is designed to suppress the fault current flow
through the circuit breaker less than the capacity of the
circuit breaker. Under this condition, it is expected to install
superconducting fault current limiters (SCFCLs) to power
systems in order to solve both of the fault current problem
and the stability problem.
Modeled SCFCL
The Modeled SCFCL contains three SCFCLs of
transformer type in one cryostat. The SCFCL consists of
two superconducting coils (NbTi wire for AC use)
magnetically coupled coaxially. Schematic configuration is
shown in Fig. 1. The inner (primary) coil will be connected
to a power line. The outer (secondary) coil is
short-circuited.
Characteristics of the SCFCL system
To investigate the fundamental characteristics of the
SCFCL in parallel with a resistor and a ZnO device, a
numerical analysis using single-phase circuit was carried
out with EMTP (Electro-Magnetic Transients Program).
Simulation model of SCFCL with EMTP
The SCFCL turns into secondary coil. Since the AC
critical current of the secondary coil is 246.1 A (= 174.0
Arms), the SCFCL is designed to turn into the current
limiting mode when the current I2 exceeds 246.1 A in the
numerical analysis. The equivalent circuit of the SCFCL is
shown in Fig.4. If it is assumed that all of the loss generated
in the SCFCL in the current limiting mode is caused by the
resistive component RFCL of the impedance of the SCFCL
ZFCL, the loss PFCL is calculated from Eq.(1)
The characteristics of the SCFCL system
The results of the numerical analysis using single-phase
circuit are shown in Fig.8-right. Fig.8-left shows the
experimental results. [6] These graphs represent the data in
the case of using a ZnO device of 22 V of varistor voltage
and a resistor of 2 Ω. The simulation results agree well with
the experimental results. It found that when the value of Vfcl
is lower than varistor voltage, the current don’t flow the
resistor and the Ifcl is the peak value.
Numerical analysis method
an experimental power system, which is a
target of the simulation. A three-phase synchronous
generator was connected to an infinite bus (210V
commercial power line) through parallel artificial
transmission lines. Three-line shorted fault was simulated in
the lower line (fault line) by closing the switch Sw3. The
switch Sw1 and Sw2 simulated circuit breakers, and the
SCFCL in parallel with a resistor and a ZnO device was
installed in the fault line.