03-10-2012, 05:10 PM
Influence of System Protection to Estonian Power System Security
Influence of System.pdf (Size: 508.41 KB / Downloads: 34)
ABSTRACT:
In this paper the current system protection
influence to Estonian power system security
is observed and future needs are discussed and analysed.
Due to the changes in Baltic region power
generation together with increasing demand and
changes in the directions of the power flows, but also
due to the planning and building of new interconnections
new solutions that consider different limitations
must be developed and thoroughly analysed in order
to secure the Estonian power system security. This
topic is extremely important and in this paper first
steps in this field from the perspective of Estonian
power system are covered.
Introduction
Monitoring and analysing the power system operation
considering different limitations, e.g. power lines thermal
limits, generation deficiencies, power market principles
etc. is a complicated task and needs complete understanding
about the system and its peculiarities. Estonian
power system is a one part of Russian IPS/UPS power
system and therefore its operation is closely related to
surrounding system behaviour. In order to protect Estonian
power system and to avoid possible blackout in
case of large contingencies in the IPS/UPS system,
appropriate countermeasures and remedial action
schemes have been developed. Different approaches and
clarification of principles for system protection are
available in [1], [2], [3], and [4].
When talking about system protection one must bear
in mind the influence of energy markets and reflected
power flows in the system. Baltic power market was
partly opened at the beginning of 2010 [5] and will be
completely opened at 2013 [6]. This brings additional
challenges to be considered when updating currently
used system protection. Additionally, increased consumption
over the years, relocation of power generation
and possible overload of certain power flow corridors
should also be considered.
Baltic Power System
Baltic power system is located at a crossroad between
three large synchronous networks – UCTE, Nordel and
IPS/UPS. Baltic interconnected power system includes
Estonian, Latvian, Lithuanian and Kaliningrad power
systems and it has strong connections to IPS/UPS power
system forming the so-called loop (Fig. 1). Therefore,
Baltic power system operation is strongly influenced by
the IPS/UPS system and in normal conditions cannot be
observed and analysed separately. For example, when
something happens in some part of the system e.g.
power plant or some line trip etc., all loop members and
their system operation is influenced. To avoid large
system contingencies co-ordinated system protection
and information exchange between concerned parties
must exist.
When analysing the power system operation one
must consider that Estonia and Lithuania have been
energy exporters and Latvia needs to import its energy
form neighbouring countries (Table 1). That results to a
situation where large amount of energy is transmitted
through different parts of the system, for example,
Latvian import from Russia, through Estonia and
Lithuania, but also power flows inside the loop. Those
power flows are influenced by generation placement
and network configuration at different locations in the
region. At the end of 2006, first HVDC interconnection
to Finland (365 MW) was commissioned and consequently
power flows were altered. Currently, second
interconnection to Finland (650 MW) is at its planning
stage and it will be in operation 2014. The described
situation is only one aspect that must be considered
when analysing and understanding the Baltic power
system operation. The second approach is related to the
future scenario where Baltic power system is connected
to the UCTE system. For that, new DC and AC connections
to Poland must be built and existing connection to
Russia and Belarus should be disconnected or/and replaced
by HVDC Back-to-Back connection. That situation
changes the current system operation enormously
and thus precise studies and exhaustive analysis is necessary.
Additionally, an approach where IPS/UPS power
system is directly connected to the UCTE could also be
possible, but certain criterions reduce the feasibility of
that solution [9]. Here, only the first approach is observed.
System protection principles
For maintaining operational reliability in the loop, wide
use of system protection automation exists. The main
purpose of system protections is to localize disturbances
by means of automatic redispatching of generation and
disconnection of local loads. If previously described
means are not sufficient, stressed parts of system are
separated to prevent spreading of disturbance all over
the loop.
Conclusions
In this paper current Estonian power system protection
principles are covered and new solutions to be included
during the system update are proposed. The main
system protection devices in use, in Estonia, are JAAF,
AGNA, under voltage and under frequency protection.
Development of the current system protection is
required due to changes in the production pattern and
location in the Baltic States and building of new interconnections
to Finland and Latvia.
Adequate and co-ordinated system protection enables
to use the current power system more efficiently, e.g.
more power can be delivered in same conditions. This
also means that the level security of the system is much
higher compared to the one where system automation is
not implemented.