SYSTEM RESPONSE CHARACTERSTICS power quality.pptx

Power quality

1. SYSTEM RESPONSE CHARACTERSTICS

2. EFFECT OF RESISTANCE AND RESISTIVE LOADS The resonant harmonics align with a common harmonics align with a common harmonics source is not always cause for alarm. The damping provided by resistance in the system is often sufficient to prevent catastrophic voltage and currents. In the graph, the parallel resonant circuit impedance characteristics for various amount of resistive load in parallel with the capacitance. The significant length of line or cables between the capacitor bus and the nearest up line transformer ,the resonance will be suppressed. Lines and cables can add a significant amount of the resistance to the equivalent circuit.

3. PARALLEL RESONANCE All circuit containing both capacitances and inductances have one or more natural frequencies. A resonance may develop in which the voltage and current at that frequency continue to persist at very high values. This is the root of most problem with harmonics distortion on power system The perspective of harmonic source the shunt capacitor appears in parallel with the equivalent system inductance at harmonics frequencies. Parallel resonance occur when the reactance of Xc and distribution system cancel each other.

4. Q – quality factor of resonant circuit Less than 5 on distribution feeder and more than 30 on the secondary bus of a large step down transformer. A small resonance a small amount harmonic current can cause a large v oltage drop across the apparent impedance

5. At resonance ,the current flowing in the capacitor bank or into the power can be expressed as,

6. The extent of voltage and current magnification is determined by the size of the capacitor bank. The effect of varying capacitor size in relation to the transformer on the impedance seen from the harmonic source and compared with the case in which there is no capacitor.

7. The resonant harmonic ‘ hr ’ based on fundamental frequency impedence and ratings can calculated using the following expression

8. Series resonance There are certain instances when a shunt capacitor and inductance of a transformer or distribution line may appear as a series LC circuit to source of harmonics current. If the resonant frequency responds to a characteristics harmonics frequency of the non-linear load The LC circuit will attract a large portion of harmonics current that is generated in the distribution system.

9. During resonance , the power factor correction capacitor forms a series circuit with transformer and harmonic source. The simplified circuit represents the total harmonics produced by other loads. Service extrance transformer . The voltage at the power factor correction capacitor is magnified and highly distorted.

10. In many system problem occur in arises due to circuit topology The resulting parallel resonant frequency is always smaller than its series resonant frequency due to the source inductance contribution .