Power Quality and Facts

Previous Page Next Page    Unit 03 –  Electrical Transients Syllabus:   Source of Transient Over Voltages: Atmospheric and Switching transients, motor starting transients, pf correction capacitor switching transients, ups switching transients, neutral voltage swing, etc. Devices for over Voltage Protection. Transients: Transients are disturbances that occurs for a very short duration of time (even less that a cycle) and electrical circuit is quickly restored to original operation provided no damages due to the transients. Sources of Transient Over Voltages: 1. Atmospheric Phenomena: Lightning is a powerful source of impulsive transients. Figure shows some of the places where lightning can strike that results in lightning currents being conducted from the power system into loads. The most obvious conduction path occurs during a direct strike to a phase wire, either on the primary or the secondary sid...

Previous Page Next Page  Active Series Compensator: These are one of the new technologies using power electronic component that can boost the voltage by injecting a voltage in series with the remaining voltage during a voltage sag condition. They are available in size ranges from small single-phase devices (1 to 5 kVA) to very large devices that can be applied on the medium-voltage systems (2 MVA and larger). When a disturbance to the input voltage is detected, a fast switch opens and the power is supplied through the series-connected electronics. This circuit adds or subtracts a voltage signal to the input voltage so that the output voltage remains within a specified tolerance during the disturbance. The switch is very fast so that the disturbance seen by the load is less than a quarter cycle in duration. This is fast enough to avoid problems with almost all sensitive loads. The circuit can provide voltage bo...

Previous Page Next Page  6. Static VAR Compensator: A static VAR compensator (SVC) is a set of electrical devices for providing fast-acting reactive power on high-voltage electricity transmission networks. SVCs are part of the FACTS device family, regulating voltage, power factor, harmonics and stabilizing the system. 7. Line drop Compensator: The line-drop compensator comprises an 'artificial line' circuit consisting of adjustable resistances and reactance connected into the voltage relay operating-coil circuit. UPS: UPS stands for Un-interrupted Power Supply, also known as Un-interrupted Power Source. It is a power system provide continuous power supply or a battery backup which maintain a continuous supply to connect equipment by supplying power from a separate source when utility power is not available. a. Static UPS: The static UPS is called “static” because, throughout its power path, it has no moving p...

Previous Page Next Page  3. Magnetic Synthesizers: Magnetic synthesizers use a similar operating principle to CVTs except they are 3-phase devices and take advantage of the three-phase magnetics to provide improved voltage sag support and regulation for three-phase loads. They are applicable over a size range from about 15 to 200 kVA and are typically applied for process loads of larger computer systems where voltage sags or steady-state voltage variations are important issues. Energy transfer and line isolation are accomplished through the use of nonlinear chokes. This eliminates problems such as line noise. The ac output waveforms are built by combining distinct voltage pulses from saturated transformers. The waveform energy is stored in the saturated transformers and capacitors as current and voltage. This energy storage enables the output of a clean waveform with little harmonic distortion. Finally, three...

Previous Page Next Page  1. Isolation Transformer: Isolation Transformer are used for other purposes like breaking a circuit into a primary and a secondary, so direct current noise can’t get through. It can prevent capacitance build-up by high-frequency noise. It also prevents unconditional ground connection between the primary and secondary and thus prevents high voltage discharge. It is used mostly in sensitive equipment as power supply. It can be used to protect people against the dangers of electric shocks. 2. Ferro-resonant Transformers: Ferro-resonance is a non-linear resonance phenomenon that can affect power networks. The abnormal rates of harmonics and transient or steady state over voltages and over currents that it causes are often dangerous for electrical equipment. Ferro-resonance is different from resonance in linear system element. In linear system, resonance results in high sinusoidal voltage and ...

Previous Page Next Page  Solutions at the End-User Level: 1. Protection for small loads (less than 5kV): This usually includes protection for equipment controls or small, individual machines. 2. Protection for individual equipment or group of equipment up to about 300 kVA: Protection of critical equipment by using power conditioning technology. This technique is very economical method as every equipment does not requires protection. 3. Protection for large groups of loads or whole facilities at the low-voltage level: These includes protection of large portion of the facility. 4. Protection at the medium-voltage level or on the supply system: If the whole facility needs protection or improved power quality, solutions at the medium voltage level can be considered. Voltage Regulation: Voltage regulation is the measure of change in voltage magnitude between sending end and receiving end of a component. It is commonly...

Previous Page Next Page  Utility Distribution system sag Performance Evaluation: The utility protection scheme plays an important role in the voltage sag and momentary interruption performance. There are two possible locations for faults on the distribution systems. a. On Parallel Feeder The voltage at the end-user facility can be due to a fault on parallel feeders can be estimated by calculating the expected voltage magnitude at the substation. The voltage magnitude at the substation is impacted by the fault impedance and location, the configuration of the power system, and the system protection scheme. The voltage sag performance for a specific sensitive equipment having the minimum ride through voltage of can be calculated as: E(parallel) = N1Ep1 + N3Ep3 Where, N1 and N3 are the fault performance data for SLG (Single Line to Ground) and 3PF (3-Phase Fault) faults in faults per miles per month, and Ep1 and Ep3 ...