The Ideal Voltage-regulated Power Supply

Topics: Alternating current, Direct current, Electrical engineering Pages: 10 (1436 words) Published: May 24, 2014
Why use regulated power supplies?
The ideal voltage-regulated power supply would have the following features: 1. Zero output impedance at DC and at all frequencies
2. Zero regulation (constant DC output voltage) for a wide range of AC line voltages and over the entire range of load currents that are required by the powered circuitry. 3. Zero power dissipation.

4. Instantaneous recover from changes in line voltage and load current. 5. Overload protection so that normal operation is automatically restored when the excessive current demand is removed.

Power line disturbances and Sources of Power line Disturbance. Blackout - Sustained lack of AC line voltage.
Brownout - Sustained period of low AC line voltage.
Fluctuation - A surge, sag or brownout condition.
Line Noise (EMI/RFI) - Electromagnetic Interference and Radio Frequency Interference. Can be caused by a variety of sources, including: static electricity, household appliances, radio stations or other broadcast facilities, military or civilian radar, faulty electrical fixtures and power transformers. Under-Voltage (Sag) - A low voltage condition of short duration.

Voltage-Spike - Instantaneous over voltage condition superimposed on the AC line. Large scale spikes from a thunderstorm, smaller spikes generally result from appliances. Over-Voltage Surge - Sustained period of over-voltage.

Line Conditioners - A general term referring to any device designed to decrease AC line related problems. UPS - Uninterruptible Power Supply uses batteries to provide backup power in the event of a blackout, or provide stable voltage during a brownout or fluctuation if the unit also features voltage regulation. Voltage Regulator - A device designed to stabilize line voltage. Many different types exist, some are more accurate than others

What are the sources of Under-Voltage (sags)?
The sources of sag can be classified broadly into: starting or energizing electrical equipment, natural causes and equipment/component breakdown. When electrical motors are started, the starting currents can be as high as 6 times the full load currents (for full voltage starting). This current comes from the source of the power supply passing through all the series impedances of the line between the source & the point of utilization. The voltage drop will be higher and all the buses connected to this source will be affected faced with an undervoltage situation (sag). For this reason a motor starting analysis (profile) is conducted to calculate the starting current, the voltage drop & its duration.

How electrical equipment can be protected against the Under-Voltage (sag) phenomena? Solving the problems that cause sags in power systems, may eliminate or reduce such phenomena & its negative impacts on the different connected loads in an electrical power distribution system. The use of additional components may alleviate this problem, though they would require additional operation knowledge & maintenance. Example for such equipment are: capacitors, voltage regulators, transformers with tap changers, the use of reduced voltage induction motor starters, reclosers. Using capacitors at point of application will assist boosting the voltage by supplying lagging reactive power locally, thus relieving the source from supplying such power (that cause voltage drops). At times when the reactive power consumption is low, the voltage may excced the nominal value if the capacitors are not installed at the load, but at the bus, for example, thus cautious must prevail when using capacitors (shunt or series). Voltage regulators can be used to regulate the voltage within the acceptable range when voltage fluctuations, including sags are common in certain area or location.

What are the sources of transient overvoltage?
The sources of transient overvoltage can be either due to internal or to external causes. The internal causes producing a voltage rise are: resonance, switching operation, insulation failure &...
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