09-07-2012, 03:30 PM
Industrial Power System Protection against Transmission System Blackouts
Industrial Power System.pdf (Size: 6.81 MB / Downloads: 311)
INTRODUCTION
Complex industrial power systems that include significant
on-site power generation are usually at risk when the
transmission system they are interconnected to experiences
large perturbations such as a blackout. The interconnection
with the transmission system exposes the on-site generation
to severe stresses during the blackout situation that may cause
inadvertent tripping of the on-site generators and even plant
shutdown. For continuous processes that have expensive
consequences following a shutdown, the impact of a
transmission system blackout has to be mitigated through the
selection of appropriate protection schemes that will separate
the industrial system from the transmission system when
signs preceding the onset ofa blackout are detected.
OVERVIEW OF BLACKOUT MITIGATING MEASURES
The risk of experiencing blackouts became a concern for
the electricity transmission industry since the first
interconnections between power systems were completed.
The continuous development and increasing complexity of
the interconnected power systems means that that more
complex patterns of cascaded events are now causing
blackouts than in the past [5]. More complex prevention tools
are therefore being deployed in both the transmission and
distribution networks.
COMBINEDUNDERVOLTAGE ANDUNDERFREQUENCY
SEPARATION SCHEME
For industrial customers with on-site generation seeking
protection against being dragged into a transmission system
blackout the separation scheme should incorporate both
undervoltage and underfrequency detection. The scheme
should be set so as to avoid false operation when other
common events cause significant voltage deviations that may
trigger the undervoltage component of the scheme. Slightly
different timescales for the undervoltage and underfrequency
phenomena were confirmed by observations of earlier events
indicating that undervoltages had been present for up to a
couple of minutes before the frequency deviation started
(which is a fast phenomenon that happen within seconds) [2].
The simultaneous detection of the two phenomena is
therefore problematic because of the detection times for the
typical industrial relays and the operation times of the
separation equipment.
CONCLUSIONS
The complex patterns of cascaded events leading to power
system blackouts indicated that a suitable protection for
industrial customers with onsite generation should include a
combination of undervoltage and underfrequency separation
schemes. Such a scheme is discussed in this paper
The proposed combined scheme does not involve an
interlocking between the two individual schemes because of
the different timescales for the undervoltage and
underfrequency phenomena.