Power Quality Aspects


One important contributing factor to Pakistan’s slow pace of industrial growth is the poor quality and reliability of the electrical power. Poor power quality is hurting industrial competitiveness and our efforts to become a global supplier of goods and services. The sensitive electronic devices/products need clean and reliable power from the utility.

 

Power Quality:

Good power quality is not easy to define because what is good power quality to a refrigerator motor may not be good enough for a PC. For example, a shor (momentary) outage would not noticeably effect the motor, lights etc, but could reset a computer. However, it may be defined as: “Power quality is the degree to which both the utilization and delivery of electric power affact the performance of the electrical equipment.”

In this blog, I am going to describe the definitions of some typical aspects of power quality.

  1. Outages (Interruptions):
    An outage is complete loss of voltage usually lasting from as short as 30 cycles up to several hours. Outages are usally caused by the fault-induced operation of circuit breakers or fuses. Some of these interruptions might be classified as permanent while others might be classidfied as temporary (momentary).

  2. Surges:
    A surge is a transient voltage or current, which is of extremely short duration and high magnitude. Typically, surges are caused by switching operations or lightning. Surges can be generated by customers due to the switching of their own loads or may be caused by utility switching operations (capacitors, breakers etc). Surges have always existed on power systems but it is only in recent years that they received attention, mainly due to the sensitivity electronic devices like VCRs and PCs.

  3. Under Voltages (Voltage drop):
    A customer who experiences a long duration (several seconds or longer) service or utilization voltage less than the proper nominal operating low voltage limit can be considered to be experienceing an under voltage situation. Such a consideration may be caused by a number of factors, such as overloaded or poor house wiring, poor connections and voltage drop on the utility system.

  4. Harmonics:
    These are the non fundamental frequency components of a distorted 50 Hz power wave. They have frequencies, which are integral multiple of the 50 Hz fundamental frequency. Harmonics are not mostly produced by the utility but rather by the customer’s equipment. For example, Industrial, commercial and residential loads which draw non-sinusoidal currents generates harmonics. These nonlinear loads are a form of electrical “pollution” which results in decline in the quality of the electrical supply. An emerging power electronic solution to the harmonics problem has been termed the active power filter (APF).

  5. Voltage Sags:
    A momentary voltage dip that lasts for a few seconds or less is classified as a voltage sag. Voltage sags may be caused by faults on the transmission or distribution system or by the switching of loads with large amounts of initial starting/inrush current (motors, transformers, large dc power supplies). Voltage sags may be sufficiently severe, especially in the case of faults, to cause sensitive loads (computers, VCRs etc) to reset.

  6. Voltage Swell:
    When a fault occurs on any phase of a three phase, 4 wire system, the other two phases rise in voltage relative to ground. This steady state rise in voltage is referred to as a Swell.

  7. Over Voltage:
    Any steady state voltage, delivered to the customer which is above the standard upper servive voltage limit is classified as an over voltage. Over voltages usually occur as a result of improper regulation practices.

Normal Power

Power Outage

Voltage Surge

Under Voltage

Voltage Sag

Voltage Swell

Over Voltage


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