Power system studies are conducted to
cover key principal design aspects of
a power distribution network. These are
classified into
Load Flow
Studies
Load-flow studies are performed to determine
the steady-state operation of an electric
power system. The studies cover aspects
such as voltage gradient across downstream
equipments, the voltage profile at each
bus system, power trends in all branch
and feeder circuits. Total system losses
contributed by individual system components
are also calculated.
Load-flow studies determine if system
voltages remain within specified limits
under various loading conditions, and
if transformers, generators, cables and
switchgear are overloaded. Load-flow studies
identify the need for additional installed
capacity, assess redundancy, capacitive,
or inductive VAR support to maintain system
voltages within specified limits.
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Short
Circuit Studies
Short-circuit studies are performed to determine
amplitude of currents that flow in a power
system during electrical faults. Faults
may occur at any location within a power
network and fault currents contributed by
each such location; namely utility service
entrance, transformers & generators,
UPS, Motors, cables, etc are estimated.
Before upgrade of installed capacity of,
say a transformer, existing & projected
fault levels must be verified in order to
assess suitability of breaking capacities
of switchgear, cable, etc. Since occurrence
of a fault results in associated drop in
voltage of the fault zone, effect on associated
equipments is also estimated.
Short circuit studies calculate network
impedances and form basis for protection
co-ordination studies. Effect of paralleling
and synchronizing are also considered from
view of increased fauld levels.
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Protection
co-ordination
Protection co-ordination studies are performed
to ensure faster clearance of faults and
avoidance of nuisance tripping of feeders
for faults occurring out of their respective
zone; thus allowing neighboring equipments
to perform without interruption. Protective
relaying requires periodic calibration,
servicing, testing and upgrade, which is
also reviewed.
Although common protections are against
overload, short circuit and earth fault
each equipment may require different scheme
of protection. Transformers, generators,
motors, cables, bus bars, switchgear are
provided with distinct protection schemes
and yet these must be co-ordinated with
up stream protection schemes so that faults
are limited to their location and upstream
protection works as back up if downstream
protection fails or delays in operation.
Protection co-ordination studies also review
various requirements such as inrush currents
of transformer, motor, capacitor, nominal
and full load conditions of plant, pre-load
and ambient temp compensation for fuse,
hot & clod load pick up, auto re-closing
schemes, motor staring & locked rotor
curves, etc. Characteristic curves such
as thermo-mechanical damages to transformers
& alternators, motors, cables, switchgear,
etc are generated & plotted against
performance characteristics curves for verifying
time/current setting of protective relaying.
IEEE 242-2001 standards referring to Recommended
Practice for Protection and Coordination
of Industrial and Commercial Power Systems
may be followed in certain cases.
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Insulation
co-ordination
Insulation co-ordination studies are generally
covered during principal design of plant
and may continue to be valid provided no
changes take place for a few years. Insulation
review becomes essential when one of more
of conditions take place, namely sudden
rise in frequency of faults, frequent equipment
failures, rise of utility voltage levels,
upgrade of utility of customer's installed
capacity, installation of new type of load,
i.e. a number of LV motor of large size
with star-delta start are replaced with
that of VFDs or HV motors are replace with
VFDs.
Similarly, process plant with established
corrosion & air contamination levels
exhibit rapid deterioration of insulation
properties. Installation with dissimilar
insulation material for identical voltage
levels may find frequent failures that call
for co-ordination studies.
Insulation co-ordination studies are conducted
at all voltage levels existing in a plant.
Upstream equipments such as lightening arrestors,
and distribution schemes incorporating Transient
Voltage suppressers, Surge arrestors in
VCBs are also reviewed.
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ARC Flash Hazard
Electrical arcs resemble deadly weapons
stored within an electrical installation
and could prove extremely hazardous to human
life and property. Electric arc could lead
to explosion with release of very high energy,
could result in serious injury or sudden
death, electrical fires and other consequent
damages.
All switching equipments undergo arcing
during normal operation and are designed
to withstand and quench the arc on continuous
basis. However, under abnormal conditions
like short circuits, fault energy may initiate
an arc that could not be controlled by the
switchgear, may propagate and escape to
outside; injuring an unprotected working
personnel nearby.
Arc flash hazard analysis is conducted
with following objectives
1. To calculate fault energy at key locations
within a power distribution network.
2. To establish arc flash boundaries at
these locations.
3. To recommend appropriate protective gear
for operating personnel.
4. To design warning labels to be installed
at such locations.
Personnel working in the vicinity of electrical
equipments such as High & Low Voltage
Switchboards, Outdoor switchyards, Transformers,
Large Motors are under constant threat of
arc flash hazards and must therefore be
trained in protective measures.
A typical arc flash hazard program
comprises of
1. Field survey and power system studies
reviewing protective relaying, equipment
aging, insulation levels and thermal imaging.
2. Establishment of arc flash energy levels,
risk levels and protective boundaries at
various locations generally referred to
IEEE 1584.
3. Generation of warning labels and brief
training program.
4. Selection of appropriate protective gear
at these levels.
When to perform arc flash hazard
studies
When one or more of conditions listed below
apply to an installation, it is recommended
to get the study conducted
1. Change in Electric Utility Installation
including upgrade of installed capacity,
change in voltage level, etc.
2. Protective relaying is not calibrated
/ tested for a few years.
3. Recent fault occurrence.
4. Addition of transformers or motors within
an installation.
5. Facility not supported with appropriate
O & M practices.
Critical
Load / Disaster Management
Critical load may be defined as that set
of primary equipments that support the process
of the business and shutdown of which would
result in substantial losses.
Critical load management applications are
found in all major business; airport, shipping,
logistics, continuous process plants, server
farms & data centers, ATMs, hospitals,
telecom installations, Cellular units, etc.
The basis of critical load management lies
in identifying single point of failure in
the electrical scheme and creating redundancy
to compensate for should the failure occurs.
Energy Integra offers services that cover
various aspects in critical load / disaster
management.
- Field survey, study of scheme and identification
of critical load scheme.
- Identification of single point of failure
and devise means to create redundancy.
- Formulation of solution, assistance
for implementation.
- Field testing to ensure of success
of scheme.
- Continued support.
Field testing comprises of review of existing
scheme for reliable operation of raw power
back up / auto changeover, UPS & static
bypass, synchronization and load shedding,
etc.
Existing scheme may undergo modification,
extension or installation of additional
equipments may be recommended to enhance
reliability and redundancy.
O & M practices and inventory are reviewed
and suggestions offered for improvement.
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