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Abstract- Directional overcurrent relaying (67) refers to
relaying that can use the phase relationship of voltage and
current to determine direction to a fault. In this paper,
directional overcurrent relay SPAS348C is introduced. At
first structure of this relay is reviewed then with regard to
characteristics of SPAS348C, this relay is modeled and
this model is added to DigSILENT library. In this paper,
one method was presented that in this method each relay
can be modeled and applied in simulation project. Finally,
we can apply this model to simulation of power system.
I. INTRODUCTION
An overcurrent relay in a looped or networked system
needs a directional element to determine fault direction
and supervise the overcurrent element to provide more
performance that is precise. Directional overcurrent relays
are used to protect interconnected power systems and
looped distribution systems. The fault direction may be
forward (between relay and grid), or reverse (between
relay and source), the normal power flow being from
source to the grid. Known directional overcurrent relays
rely on a reference voltage phasor for estimating direction
of the fault, requiring both current and voltage sensors.
The DigSILENT software is very effective in design,
calculation, and simulation of power system but there are
some restrictions in these simulations projects. For
example, models of all types of relays that are used in
power systems are not available in DigSILENT library.
The aim of this paper is presenting a method that by using
it we can modeling of intended relay and add to
DigSILENT library. Finally, we can apply all types of
relays in simulation of protection schemes. In this paper
directional overcurrent relay SPAS348C is considered.
II. CHARACTERISTICS AND APPLICATION OF
SPAS348C
The feeder protection relay SPAS348C is designed for
applications that require to directional phase overcurrent,
directional short-circuit and directional earth-fault
protection. Typically, this relay is used for overcurrent and
earth-fault protection of feeders and busbars in distribution
substations provided with multiple feeders supplied from
the same high voltage busbar system via power transformers [1]. In addition, these relays are applied for
the selective short-circuit and earth-fault protection of
parallel feeders between substations and for feeder
protection in ring-type and meshed distribution networks.
Further, the directional relay is used for the protection of
radial feeders with a small back-feed of energy from a
generator in the consumer end feeder. This relay includes
three protection relay modules as Two directional
overcurrent relay modules SPCS4D11 and SPCS4D12,
and one directional earth-fault relay module type SPCS
2D26.
Relay Module SPCS2D26
This relay module has two overcurrent stages:
1- Directional or non-directional low-set neutral
overcurrent stage I01> with definite time characteristic.
2- Directional or non-directional high-set neutral
overcurrent stage I02> with definite time characteristic.
When required, both directional neutral overcurrent stages
of directional earth-fault protection can be configured to
operate as residual voltage stages. Then relay module
includes three separate adjustable residual voltage stages.
The directional earth-fault unit measures the neutral
current I0, the residual voltage U0 and phase angle between
residual voltage and neutral current. An earth-fault stage
starts if all of three criteria below are fulfilled at same time:
-The residual voltage U0 exceeds the start level set for the
U0> stage. The setting is same for stage I01> and stage I02>.
- The neutral current I0 exceeds the set start value of stage
I01> or stage I02>.
- If the phase angle between residual voltage and neutral
current falls within the operation area ϕb ±∆ϕ, where ϕb is
the characteristic basic angle of the network and ∆ϕ is the
operation sector.
The setting value of the characteristic basic angle ϕb of
the network is selected according to the earthing principle
of the network, that is, 90° in an isolated neutral network,
and 0° in a resonant-earthed network, earthed through an
arc suppression coil (Petersen coil), with or without a
parallel resistor. The basic angle can be set at -90°, -60°,
-30°, or 0° via the SGF switches [1, 2].
III. MODELING OF DIRECTIONAL
OVERCURRENT RELAY SPAS348C
The DigSILENT has a section (block/frame diagram)
that modeling of relay is performed in this section. This
section has a tool called “Slot” that can create required
block (CT, VT, measurements, etc.) to modeling of relay.
For example, creating CT block has been illustrated in
Figure 4. At first three different modules of relay are
modeled separately then final model of SPAS348C is
presented.
A. Modeling of SPCS4D11
Figure 5 shows the block diagram of SPCS4D11. This
block diagram is obtained according to the specification
and application of SPSC4D11 (section II-A). Current
Transformer (CT) and Voltage Transformer (VT) send
three-phase current and voltage to measurement unit.
Measurement makes required signals of directional unit
and current comparator units. Current Comparator units
are used to create trip signal. Directional unit and logic
units (AND) are used to modeling directional protection.
The inputs of last logic unit (OR) are trip signals of
stage I >, stage I >> and stage I >>>. The output of last
logic unit (OR) is trip signal of SPCS4D11.
CONCLUSIONS
The DigSILENT software is widely used in simulation
of power system and protection schemes. In this paper, one
method has presented that in the method each relay can be
model and apply in simulation project. In this paper,
directional overcurrent relay SPAS348C has modeled that
was applied in simulation of a power system for validation
of relay model. One short circuit in this power system has
simulated, relay performance has evaluated, and
consequently accuracy of presented model has shown.