Initiatives for reducing recurrence of power grid system collapse in Nigeria (1)

Power systems today are much more susceptible to voltage collapses than they were 35 years ago (when frequency was the culprit) as we increasingly depend on generation sources that are located remotely from load centres as is typical with the Nigerian scenario.

However, the major factor that leads to rapid system voltage collapse is attributable to the nature of the loads that are being served by utilities. Many of today’s loads are single-phase small air conditioning motors.

This was not the case 35 years ago when air conditioning was not as prevalent. These small motors are prone to stall when subjected to voltage dips caused by transmission system short circuits. Therefore, during hot weather, these motors comprise a high percentage of the utility load.

The slow tripping of stalled motors and the relatively slow re-acceleration of more robust motors result in low system voltage after a transmission system fault is cleared. The voltage dip and its effect on these motors are exacerbated if the transmission system fault is cleared via a time delay backup relay or if it’s a multi-phase fault.

According to investigations conducted on recent global blackouts, there is an indication that the root cause of almost all of these major power system disturbances is voltage collapse rather than the frequency conditions which were prevalent in the blackouts of the 70s as already discussed above. This explains why voltage collapse is today the leading edge indicator of impending power system problems.

Bearing the above in mind, it is possible to examine other contributing factors to grid system collapses and proffer solutions on how best the problem can be tackled to ensure a hitch free electricity delivery to Nigerians especially with the recent hand over of the privatised Gencos and Discos to the new owners

Therefore, following from the above definitions and discourse, we can confirm and state as follows that “Reactive power (vars) is required to maintain the voltage to deliver active power (watts) through transmission lines. Motor loads and other loads require reactive power to convert the flow of electrons into useful work. When there is not enough reactive power, the voltage sags and it is not possible to push the power demanded by loads through the lines.” This occurrence is the major contributor to the frequent occurrence of grid system failures.

What is reactive power? Where does it come from? And why do we need it?

Reactive power (often referred to as imaginary power) actually refers to the circulating power in the grid that does no useful work and results from energy storage elements in the power grid (mainly inductors and capacitors). It has a strong effect on system voltages and it must balance in the grid to prevent voltage problems. Reactive power is present when the voltage and current are not in phase and as such have tremendous effect on voltage collapse.

Reactive power is also a by-product of alternating current (AC) systems, is measured in volt-ampere reactive (VAR) and is produced when the current waveform leads voltage waveform (Leading power factor) and is consumed when the current waveform lags voltage (lagging power factor).

While transformers, transmission lines, and motors require reactive power, transformers and transmission lines often introduce inductance as well as resistance because both oppose the flow of current.

Therefore reactive power must raise the voltage higher to push the power through the inductance of the lines unless capacitance is introduced to offset inductance. The farther the transmission of power, the higher the voltage needs to be raised. Reactive power is present when the voltage and current are not in phase.

Despite all these, the term “Power” normally refers to active power.

From the foregoing, we are inclined to agree with the opinion of experts that a severe shortage of reactive power, which ultimately caused power plant and transmission line failures, has been responsible for some of the grid system collapses that have resulted in the recent National blackouts.

By: GOODY DURU-OGUZIE