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10.2.2 Voltage
surges due to utility power-factor/voltage-regulation capacitor
switching
Utilities often find it necessary
to add/subtract capacitance to their ac transmission and
distribution system to achieve reasonable power factors and
voltage levels. When these capacitor banks are switched on and off
the ac distribution system, they create phase-voltage surges.These
surges appear as decaying-oscillatory surges to the user. Examples
of the impact of these surges follow.
CASE HISTORIES
Problem 3:
Intermittent
shutdowns of ASDs in a manufacturing plant-over voltage.
This case involves a manufacturing
plant, located in the southern U.S., where 5 hp ASD motors
frequently would trip-out intermittently. The result of these
disruptions, on a multistage continuous-processing line, was
considerable material loss and excessive line restart time.
The ASD diagnostic code typically
would indicate an "over voltage on the ac power" feeding the
system.
Steady-state, true rms voltage
readings on the 480 V, three-phase line were on the low side at
452 - 479 V. Further measurements correlated voltage surges with
utility-level power factor correction capacitor switching.
Solution.
Consultation with the ASD
manufacturer revealed that the ASD protection circuitry was
sensitive to ac over voltage conditions for extremely short time
periods (e.g., 800 V for 40 μs). The manufacturer solved the
problem with the addition of transient voltage surge suppressors,
which clamped the ac voltage to less than 750 V.
Stop the Damage
Toronto Transformer
Fire Causes Province-wide Voltage Dip
Power Surges Can Fry Your Sensitive Electronics
Toronto Hydro Recommends Surge Protection Equipment
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