Operational Aspects In Reactive Power And Voltage Control:

 Operational Aspects In Reactive Power And Voltage Control:

Operational Aspects In Reactive Power

In the power system networks, EHV transmission lines are interconnected with the other lines in a way such that the generators, transformers, reactors, capacitors etc. are directly or indirectly needed for rendering uninterrupted supply to consumers at a desired voltage level.

All the series elements in the system has a reactance which has power loss proportional to the square of the current passing through it.

Series winding having an inductance, server as a sink for reactive power while the capacitance of EHV lines and cables charge the reactive power in the system.

During the light load periods, the reactive power surplus due to high charging and low series reactive loss may affect the system operation by causing over voltage in the system.

Under a specific operating condition, frequency is uniform throughout the system, the voltage levels can vary at different points of the network due to the reactive power problem.

Voltage control problem may also cause voltage instability problem which is basically a reactive power mismatch in a power system.

1. System MVAR Mismatch:

Two possibility exist for the occurrence of reactive power mismatch

1. Reactive power surplus
2. Reactive power deficit

(1) Reactive Power Surplus :

When there is a surplus reactive power, there is a problem of over voltage.

The duration of these overvoltages affect the instability of system. Thus there is an essential need for fast counter measures, this can most effectively be achieved by taking at each nodes.

Shunt reactors are located as a counter measure at various locations at sub-stations to provide an effective handling of reactive power surplus. an effective handling of reactive power surplus.

(2) Reactive Power Deficit :

The voltage reduction draws on inherent stabilizing factors which initially counter act a

reactive power deficit.

Counter measures for the problem are:

• Generator terminal voltage increase.
• Generator transformer tap changing.
• Reactive power boost
• Quick acting load transformer tap changing.
• Load shredding.

2. Vulnerable System Disturbance :

A lost of system failures have occurred due to reactive power mismatch.

These events are initiated from sudden small disturbance in EHV or HV grids, leading to reactivate power mismatch.

These events are succeeded by trippings and ultimately fragmented the  inter-trippings and ultimately power system into sections, thus, destroying he system reliability.

It spreads very fast, leaving no time for operators to act.

After cascade tripping and when the system is on the verge of collapse, the co-ordination between numerous control centres became ineffective and uncertainty among the operators led to further failure of the system.