Electricity is the main driving force of industries today. The reason behind it is electricity can be easily converted to other forms of energy, regardless of the industrial types electricity is used all over the world in industrial sectors.
Poor power quality in the industry will cost money in the form of equipment damage, production loss, raw material loss, greater down time and goodwill loss. To survive the today’s global competitive market productivity is the key. Thinking about the basic inputs to production—time, labor, and materials it is very much clear that there isn’t much room for optimization. Power efficiency is definitely the sector where industry can focus to mitigate losses such as down time, production loss and equipment damage.
There is a wise saying “If you can measure it, you can manage it”. So it’s time to break down “Power Quality” term to its sub-sectors for better understanding so that you can measure each of the problematic parameters in your facility to control and mitigate all the power related issues.
Power Quality is a set of parameters which have to meet a standardized requirements. Parameters
- Voltage Unbalance.
- Total Harmonics Distortion.
- Voltage Dips/Sags and Voltage Swells.
- Power Factor/Reactive demand.
Unbalanced voltages are unequal voltage values on 3-phase circuits that can exist anywhere in a power distribution system. Unbalanced voltages can cause serious problems, particularly to motors and other inductive devices.
Unbalanced voltages typically occur because of variations in the load. When the load on one or more of the phases is different from the other(s), unbalanced voltages will appear. As a consequence, the resulting current unbalance is caused not only by the system voltage unbalance but also by the system impedance, the nature of the loads causing the unbalance, and the operating load on equipment, particularly on motors.
When a motor continues to operate with unbalanced voltages its resistance increased. The increase in resistance and current “stack up” to contribute to an exponential increase in motor heating which eventually leads the motor to burn out. Also, Mechanical stresses in motors due to lower than normal torque output can damage the motor.
Fig-1: Motor Losses and Heating Vs Voltage Unbalance
Some of the more common causes of unbalanced voltages are:
- Unbalanced incoming utility supply.
- Unequal transformer tap settings.
- Large single phase distribution transformer on the system.
- Open phase on the primary of a 3 phase transformer on the distribution system.
- Faults or grounds in the power transformer.
- Open delta connected transformer banks.
- A blown fuse on a 3 phase bank of power factor improvement capacitors.
- Unequal impedance in conductors of power supply wiring.
- Unbalanced distribution of single phase loads such as lighting.
- Heavy reactive single phase loads such as welders.
Here I mentioned just some of the common issued but for your factory it may not be applicable. To identify and solve the issue expert opinion is required. Previously, finding voltage unbalance was a tedious work but currently smart auto analyzers are available which can detect and calculate voltage unbalance quickly and accurately without hampering the process. By identifying the proper causes of voltage unbalance and taking corrective actions as per an expert personnel, it can be reduced to a tolerable range (Less than 2%).
Total Harmonics Distortion
Harmonic is multiple of the fundamental frequency and as AC current is a sinusoidal wave, harmonic is applicable for voltage and current. When fundamental frequency and single harmonic are present at the same time we get the resultant of those two frequency, this frequency is completely different from those two individual frequencies and distortion is created in the process. If several numbers of harmonic are present in the line then the resultant we get is call Total Harmonics Distortion.
Fig-2: Distortion Waveform by Harmonic
Harmonic distortion can have detrimental effects on electrical equipment. Following common and harmful effects can be observed due to Higher Frequency Harmonic present in the power system.
- High current to flow in neutral conductors.
- Motors and transformers to run hot, shortening their lives byadditional core loss.
- Increased susceptibility to voltage sags, potentially causing spurious resets.
- Reduced efficiency of transformer — or, a larger unit is required to accommodate harmonics.
- Audible noise.
Voltage distortion (THD) should be investigated if it is over 5 % on any phase. Some current distortion (THD) is normal on any part of the system serving electronic loads. Total Harmonics Distortion (THD) can be reduced from the system by taking some corrective measures and modifications. Expert opinion is advised before taking any steps for correcting THD from your power system.
Voltage Dips/Sags and Voltage Swells.
A voltage sag happens when the RMS voltage decreases between 10 and 90 percent of nominal voltage for one-half cycle to one minute. Voltage swell is the opposite of voltage sag. Voltage swell, which is a momentary increase in voltage, it may happen when a heavy load turns off in a power system. The most likely kind of power quality problem is the voltage sag.
Fig-3: Voltage Sags Fig-4: Voltage Swell
The sensitivity of today’s electronic equipment make it susceptible to Voltage Sags and can cost a lot for any factory such as computers or controllers by spurious resets. Sags on one or two phases of 3-phase loads causing the other phase(s) to draw higher current in an attempt to compensate. This may trip the facility by overcurrent protection.
Power Factor/Reactive demand
In AC circuits, the power factor is the ratio of the real power that is used to do work and the apparent power that is supplied to the circuit. The power get lost in the system is called reactive power (measured in kVAR). This is the non-working power.
Mostly industries having low power factor faced some common issues like Large Line Losses, Poor Voltage Regulation and Large Voltage Drop, Low Efficiency and most importantly Penalty from Electric Power Supply Company due to Low Power factor. Nevertheless, equipment damage and production loss are two inevitable scenarios occurred due to low power factor.
Power factor higher than 0.97 is considered efficient for any factory. Inductive loads such as motors, transformers, and high-intensity lighting introduce reactive power (kVARs) into a power system. To run a factory these inductive loads could not be eliminated but capacitors may be applied on individual loads to improve power factor to the desire level. It takes a lot of expertise to give a right plan and calculation to overcome the low power factor issue.
In Bangladesh, some industry already identified Electrical Power Quality issues but rest are in the total darkness. Without knowing the actual cause of their problem they are just blaming their equipment, maintenance team and personnel those are involved in using the equipment.
All the issues described in this article can be taken care off by an electrical expert personal who has the in-depth knowledge on the industrial level, who can measure parameters using proper device, who can do proper modification based on pure calculation and give a proper guidance to an industry for its growth and prosper. Fortunately, this type of service firms are available in the Bangladeshi market, so any kind of change or modification in the power generator and distribution sector of your industry is not advised by your own.
Benchmark Solutions can provide you the smart analyzed data through auto analyzer and expertise you need to smoothen your business. For any query, you may contact us.