Please enable JavaScript.
Coggle requires JavaScript to display documents.
Short Duration Voltage Variation: Voltage Sag (G4: Source of voltage sag…
Short Duration Voltage Variation: Voltage Sag
G4: Parameters
voltage magnitude
0.1 to 0.9 pu
depth of voltage sag
the difference between the reference voltage and the residual voltage
Radial System - Voltage Divider Model
Meshed Systems - Matrix Calculations
(Thevenin’s superposition theorem and node impedance matrix.)
duration in time or cycle
Instantaneous 0.5 to 30s
Momentary-30 cycles to 3 secs
Temporary- 3 secs to 1 minute
time between the instant at which the voltage at a particular point on a supply system falls below the voltage sag start threshold
G2: Area of Vulnerability
DEFINITION
Equipment voltage sag immunity or susceptiblity limit.
To evaluate the likelihood of sensitive equipment being subjected to voltage lower than its minimum sag ride through capability
determined by:
Total circuit miles of exposure to fault - that can cause voltage magnitude at end-user to drop
AREA
Inside area of vulnerability, the voltage will drop below 0.5pu
Outside area of vulnerability, the voltage will not drop below 0.5pu
G4: Source of voltage sag
Starting of induction motor
Short circuit fault in electrical network
Fault on own feeder
Fault on parallel feeder
External Factor
P=VI (Current inversely proportional to voltage. eg: current increase, voltage drop)
Lightning
Crane encroachment
Animal encroachment
Copper theft
Internal Factor
Ohm's law, V= IR, current proportional to voltage, eg: current increase will leads to voltage increase)
Cable fault
Transformer short circuited
Fault on transmission system
L to G Fault (less severe but most occurrence)
L-L-L fault-(most severe but less occurrence)
Electrical Load changes
Transformer energizing
Loose electrical connection
Failure of voltage regulator
G1: Effect of voltage sag
Delayed delivery
Reduced customer satisfaction
Impacted equipment due to Sag
Induction motors - Loss of torque
Synchronous motors - Loss of torque, loss of excitation current
Contactors and relays - Nuisance disconnection
Variable speed drives - Loss of control supply to the control supply, loss of torque
IT equipment and control system - Affects CPU & I/O card. Process interruption
High-pressure discharge lamp - reduce voltage <45% during cooling and restart
Decrease power delivery
Cost of restarting process
Loss of production
G2: Voltage Sag Indices
DEFINITION
Indicator of the quality and reliability of the services
Compare power quality in different network
INTENT OF INDICES
Individual Customer Level
Utility System Level
TYPE OF INDICES
Single-event index
Single-site index
SARFI-x
SARFI-90 - Referring to below than 90% of Vref
SARFI-110 - Referring to above 110% of Vref
SARFI-Curve
SARFI-CBEMA
SARFI-ITIC
SARFI-SEMI
SEMI F47
Formula:
System index
G1: Voltage Sag standard
IEC 61000-2-8 - Environment - Voltage dips and short interruptions on public electric power supply systems with statistical measurement results
ITIC
CBEMA
SEMI F47 & IEC 61000-4-34
G3: Mitigation technique
solution in the manufacturing process itself
solution between the process & the public electric grid
solution in the grid
Method
reduction of the number of fault
replacing overhead lines with cables
the use of insulated conductors on overhead lines
regular tree cutting in the area of the transmission line
fencing against animals
shielding overhead conductors with additional sheath wires
increase frequency of overhaul & periodic maintenance cleaning insulators etc
increase insulation level
reduction of the fault clearance
use of current limiting fuses
modification of the supply system configuration
installing generator close to sensitive load
increasing the number of substation & busbar
installing current limiting reactors at strategic points of the system
supplying sensitive customer busbar from several substation
voltage stabilizers
energy storage system
UPS
super conduting magnetic energy storage (SMES)
rotating machine flywheel, motor generator system etc
no energy storing capability
CVT (constant voltage transformer)
static fast transfer switching (SFTS)
static generators of the fundamental harmonics current & voltages
improvement in equipment immunity
acquiring information on system operation
acquiring information equipment sensitivity
determination of the potential effect
G3: Equipment Sensitivity to voltage sag
magnitude
device such as under voltage relays, process control, motor drive control etc
sensitive to the min/ max voltage magnitude experience during
sag / swell
other than magnitude and duration
RMS variation performance indices defined are focused on the more common magnitude & duration characteristics
impact are much more difficult to generalize
phase unbalance during sag event or any transcient oscillation occur during the disturbance
magnitude and duration
important characteristic :-
duration the rms voltage is below a specified threshold at which the equipment trips.
misoperates or fail when the power supply o/p voltage drop below specified value.
virtually or equip. uses electronic power supplies
Reduction of the number of faults
