How to reduce system failures for improved power supply

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 centers 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.

Investigations conducted over recent global blackouts has indicated 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 privatized Genco’s and Disco’s 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 down 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.

Two factors promote power generation that is remote from load centers necessitating frequent grid system failures: a) The economics of purchasing power from lower-cost remote sources rather than more expensive local generation
b) The public’s reluctance or refusal to permit new generating plants to be built in urban high- load areas, causing utilities/IPPs to build these plants remote from these load centers

The above identified fundamental changes applicable to operations of the Nigerian power grid system results in the transmission of power over long distances. This makes the power grid very dependent on the transmission system to deliver power to the load centers. It also results in increased reactive power losses when transmission lines trip

Using a basic power system with the remote generators supplying a significant amount of power (Ps) over a considerable distance to the remote load center to illustrate, we find that the load is comprised of resistive load and motor load. During a voltage dip, resistive load current will decrease and help limit the need for local reactive support. Motor loads are essentially constant kVA devices. The lower the voltage, the more current they draw, increasing the need for local reactive (VAr) support. Power system loads consist of both resistive loads as well as reactive motor loads. During hot weather, however, air conditioning motor loads comprise a large portion of total load, thereby making the system more susceptible to voltage collapse.

With reference to the frequency of blackouts from system collapses in Nigeria, It is possible that demand for reactive power were unusually high because of a large volume of long-distance transmissions streaming through the southern states to Northern states, more than needed to import power to meet local demand. But the supply of reactive power is very often low because some generating plants are often out of service and, possibly, because other plants were not producing enough of it.”

Because Reactive power does not travel very far, it is usually necessary to produce it close to the location where it is needed. A power generation source close to the location of the need is in a much better position to provide reactive power compared to one that is located far from the location of need. Reactive power supplies are closely tied to the ability to deliver real or active power.

It is in the light of the above explanation, that we consider the recent completion and commissioning of the Geregu II Power plant as a progressive development that would appropriately contribute towards supplying the needed reactive power to mitigate tendencies for transmission and distribution grid system failures as well as ensure power supply reliability especially to Abuja and its environs.

There is therefore a compelling need to encourage investors to build more power generating plants especially from the non- fossil fuel based systems as an absolutely important mix that is readily derived from; small and medium capacity hydro power plants ( especially from waterfall sources and perennial rivers providing combined capacities in excess of 2000mw) excluding; biomass, thermal solar and waste-to-power options to be located specifically within the middle belt and Northern states of the country to provide a reactive power balance needed to guarantee overall national grid stability. Government should provide incentives that will encourage investors to take up projects in the mentioned renewable areas of power development in order to equilibrate the demand for reactive power and ensure power grid stability.

As part of measures to effectively attract investors to take on power infrastructure development in the areas enumerated above, the ministry of power is advised to look into the possibility of developing a compendium of renewable energy power generation resources in order to provide adequate information and available technology guide for intending investors. For instance, instead of deploying huge capital in building dams as conventionally required for constructing hydropower plants, investors should be made aware of the globally adopted using modern design of turbines based on hydro-matrix and straflo-matrix models to construct medium size (30-300)mw and even multiples on perennial flowing rivers requiring no real dams but just weirs to achieve such a feat.

As part of interim measure to stem the tide of grid system collapses, the ministry of power should recognize that power grid stability can only be guaranteed through investment in technology and therefore give serious consideration towards deploying smart grids and employing the services of competent consultants to undertake the relevant studies needed for effective deployment of digital smart grids which are most effective for stabilizing power grids where renewable mix power sources are to be grid connected.