Power Quality

Power Quality:

• In the present scenario of power utilization and consumption, the importance of power quality is vital for a continuous and effective power supply. The features of power quality play a major role in the effective power utilization along with the control & improvement measures for various factors affecting it.
• Power quality is defined as the ability of a system to

1.     Deliver electric power service of sufficiently high quality so that the end-use equipment will operate within their design specifications and

2.     It should be of sufficient reliability so that the operator of end-use equipment will be continuous.

• In other words it may be defined as the concept of powering, grounding and protecting electric equipment in a manner that is suitable to the operation of that equipment.

Why is it a concern?

• Power Quality has been a problem since the conception of electricity, but only over the last 2 decades has it gotten considerable attention with the introduction of large numbers of computers & microprocessors in business and homes; and the network revolution and ever increasing equipment capability and speed.
• There are various factors that really make us think about it.

1.     Power quality problems can cause equipment malfunctions, excessive wear or premature, failure of equipment, increased costs, increased maintenance, repair time and expense & outside consultant expense.

2. Electronic equipments are more sensitive to minor fluctuations. We rely on the equipment more and have higher expectations. New electronic devices are more sensitive than the equipment being replaced as well.

Power Quality Affecting Factor:

• Many electronic devices are susceptible to power quality problems and a source of power quality problems. Some of the important concerns are

1.     Waveform Distortions like Harmonics

2.     Transients

3.     Voltage Fluctuations such as Voltage Sags & Swells

4.     Interruptions e.g. Outages & Blinks

1. Waveform Distortions -Harmonics

• Due to substantial increase of non-linear loads such as the use of power electronics circuits and devices, the ac power system suffers from harmonic problems. In general, we may classify sources of harmonics into three categories i.e.

1.     Domestic loads,

2.     Industrial loads,

3.     Control devices.

• A harmonic is “a sinusoidal component of a periodic wave or quantity having a frequency i.e. an integral multiple of fundamental frequency”. Pure or clean power is referred as those without harmonics. But this only exists in laboratories. The frequencies of the harmonics are different, depending on the fundamental frequency. Due to high harmonic voltage and/or current levels, there are a number of equipments that can have miss operation or failures.
• The main sources of harmonic current are the phase angle controlled rectifiers and inverters.
• Although the applied voltage to a transformer is sinusoidal, the magnetization current related to the flux through the lamination magnetization curve is non-sinusoidal. These harmonics have their maximum effect during the first hours of the day (when the system is lightly loaded and the voltage is higher).

2. Transients

• Transients occur in Distribution System due to factors like Lightning, Switching Operations, and Fault Clearing/Breaker Operations etc. The various causes of transients in Customer System are Lightning, Arcing Devices, Starting & Stopping Motors, Breaker Operations, and Capacitor Switching etc.

3. Voltage Fluctuations such as Voltage Sags & Swells

• In Sags, Voltage falls below 90% of normal but stays above 10% of normal for any amount of time. In Swells, Voltage rises above 110% of normal but below 180% of normal for any amount of time. If it’s long enough, you notice lights dimming or getting brighter. Sags are much more common than swells.

4. Interruptions e.g. Outages and Blinks

• Interruptions may be defined as the interrupts that hampers the normal flow of voltage or power quality. When Voltage falls below 10% of normal circuit voltage for any length of time the power supply is off. The outages can be of microseconds to hours or days. When interruptions occur there is a chance of blinking as well.

Control & improvement of The System:

• In order to overcome the various affecting factors, we need to implement some control and improvement measures. They are discussed as follows:

1. Harmonics

• Several techniques are adopted to minimize harmonic effects like increasing pulse number, passive filters and active filters. By use of these techniques we get higher pulse, trap the harmonics and convert the non-linear ac line current into a sinusoidal wave respectively.
• Power quality analysis is really a matter of concern as it is quite evident how important supply of power is especially in organizations where critical loads need continuous supply of clean power and that too without any disruption.
• Technological advancements are developing in this sector in order to manage the advanced and sophisticated power systems with utmost proficiency.

2. Transients

• We can use power enhancers like Surge Suppressors, Lightning Protection/Arrestors, Power Conditioning, Line Reactors/Chokes etc. Power Synthesizers such as Standby Power Systems, UPS & Motor Generator Set can be utilized. Simplest, least expensive way to condition power by clamping voltage when it exceeds a certain level and sending it away from the equipment it protects.
• Transient voltage surge suppressors (TVSS) can be installed at the terminals of the sensitive electronic loads. Power line filters limit noise and transients to a safe level by slowing down the rate of change of these problems and keeping electronic systems safer than surge protectors can.

3. Voltage Fluctuations such as Voltage Sags & Swells

• Use of Power Enhancers like Reduced Voltage Starters on large offending motors, Voltage Regulators, Constant Voltage Transformers (CVTs), Power Conditioners; as well as Power Synthesizers like UPS, Motor-Generator Sets can minimize voltage fluctuations.
• Voltage Regulators can be utilized to maintain voltage output within a desired limit or tolerance regardless how much input voltage varies. They can also be utilized for protection against swells or noise and limited protection from fast voltage changes depending upon the response time of the regulator. Voltage regulators respond best to slow changes in voltage.
• Constant Voltage Transformers (CVT’s), also known as Ferro resonant transformers are used for sags, swells, longer term over and under-voltages, especially attractive for constant, low-power loads like electronic controllers (PLC’s) where they provide ride-through capability. Variable loads, especially those with high inrush currents, (Drives) present more of a problem for CVT’s.