Rural Electrification Project, Cabo Delgado, Mozambique

Mozambique is committed to extending its electrical grid to rural spaces. However, this puts the existing infrastructure under great pressure, which can lead to blackouts and low power. Advanced power management solutions in addition to network expansion are being deployed to strengthen the grid, improving the quality and reliability of electricity.

Challenge

In recent years there has been a high rate of new grid connections in Mozambique. Existing substations have been operating at the upper limit of their capacity and consequently there have been increasing problems with grid performance.

Mozambican energy company EdM appointed RXPE to improve the reliability and efficiency of its 220 kV substation in Nampula through provision of a dynamic reactive power compensation system.

Early investigations by RXHK (then part of RXPE) identified that the power grid at Nampula substation was very weak. The low-load short circuit level at the 220kV busbar was only 175MVA. In this context, meeting the technical requirements to improve the performance of the substation would be extremely challenging.

Solution

Initially the contract scope was to provide and install a Static Var Compensator (SVC) to enhance the network performance. However, once the low-load short circuit level had been determined by our engineers we recommended the high-power Maxivar™ Static Synchronous Compensator (STATCOM). This next generation Flexible AC Transmission System solution offers much better potential for weak electrical grids.

Advantages over traditional SVC solutions include faster response times (20ms), reduced overshoot in weak network conditions and better resonance performance. SVC systems typically have an overshoot 10-20% higher than that of the Maxivar™ STATCOM which can result in equipment failure. Furthermore, in weak grid conditions an SVC can cause net resonance or harmonic amplification; with a high-power STATCOM resonance is minimal.

Additional benefits include full redundancy, which enables equipment to remain in operation should one of the power modules fail. It also has a modular design, so faulty power modules can be replaced in less than 30 minutes. Total investment for a Maxivar™ STATCOM is on par with an SVC. The upfront equipment cost is higher, but associated civil and installation costs are lower. Efficiencies can also be made in the reduced ongoing maintenance requirements and lower system losses.

Summary of Advantages

Description	SVC	MAXIVAR™ STATCOM
Reactive power compensation effect	Good	Very good
Voltage compensation effect	Good	Better (5% closer to 1.0pu)
Fault response time and adjustment time	Good	Better (faster than SVC)
Resonance and harmonic characteristic	Average	Very good
Induction motor recovery	Good	Very good
Losses	Average	Low (low reactive power and in normal mode)
Maintenance	Good	Better
Availability	Good	Better (built in redundancy and will bypass H-Bridge)
Size of area	Large Footprint	1/3 smaller
Investment	Similar	Similar

Current status

The Maxivar™ STATCOM for the Nampula substation underwent extensive Factory Acceptance Testing and Real Time Digital Simulator testing, witnessed and verified by EdM and other representatives. The solution satisfied all project requirements for reactive compensation support and voltage control.

Commissioning was completed in December 2015.

Successful installation of this solution in place of an SVC adds to mounting evidence surrounding the efficacy of voltage source converter STATCOMs. These next generation FACTS are likely to replace traditional utility grade reactive compensator technologies as the demands placed on electrical grids continue to escalate.