Voltage Control in Distribution System

Capacitor Banks

Distribution systems are the networks that transport the electric energy from bulk substation to many services or loads, thus causes more power and energy losses. Hence there is a need to reduce the system losses. By minimising the power losses, the system may acquire longer life span and has greater reliability.

Loss minimization in distribution systems has assumed greater significance recently since the trend towards distribution automation will require the most efficient operating scenario for economic viability. Studies have indicated that as much as 13% of total power generated is consumed I²R as losses at the distribution level. Reactive currents account for a portion of these losses. However, the losses produced by reactive currents can be reduced by the installation of shunt capacitors. Effective capacitor installation can also release additional Kvar capacity from distribution apparatus and improve the system voltage profile. Reactive power compensation plays an important role in the planning of an electrical system.

As Distribution Systems are growing large and being stretched too far, leading to higher system losses and poor voltage regulation, the need for an efficient and effective distribution system has therefore become more urgent and important. In this regard, Capacitor banks are added on Radial Distribution system for Power Factor Correction, Loss Reduction and Voltage profile improvement. The amount of compensation provided is very much linked to the placement of capacitors in the distribution system, which is essentially determination of the location, size, number and type of capacitors to be placed in the system

Capacitor Bank benefits to

• ·         Increase power transmission capability
• ·         Reduce system losses
• ·         Improve voltage profile on the lines
• ·         Improve power factor, voltage stability

The demand of this reactive power is mainly originated from inductive load connected to the system. These inductive loads are generally electromagnetic circuit of electric motors, electrical transformers, inductance of transmission and distribution networks, induction furnaces, etc. On the other hand, the user will be paying for much more than what is actually being used. And hence reactive power compensation becomes so important. This is commonly done by addition of a capacitor bank.

Method	Advantages	Disadvantages
Individual capacitors	Most technically efficient, most flexible	Higher installation & maintenance cost
Fixed bank	Most economical, fewer installations	Less flexible, requires switches and/or circuit breakers
Automatic bank	Best for variable loads, prevents over voltages, low installation cost	Higher equipment cost
Combination	Most practical for larger numbers of motors	Least flexible

Types of Capacitor Bank

Distributed Generator

DGs usually use different modular technologies which are located around a utility’s service area. Distributed generation is a technique, which minimizes the amount of power loss in transmission lines by generating the power very close to load center.

In present times, use of DG systems in large amounts in the different power distribution systems have become very popular and is growing on with fast speed. Some of the main advantages while installing DG units in distribution level are peak load saving, enhanced system security and reliability, improved voltage stability, grid strengthening, reduction in the on-peak operating cost, reduction in network loss etc.

Many technologies are used for DG sources such as photo voltaic cells, wind generation, combustion engines, fuel cells etc. Usually, DGs are attached with the already existing distribution system and lot of studies are performed to find out the best location and size of DGs to produce highest benefits. The different characteristics that are considered to identify an optimal DG location and size are the minimisation of transmission loss, maximisation of supply reliability, maximisation of profit of the distribution companies etc.

The DG size is limited to 40% of the total power demand of the system to avoid power quality and system protection issues, which might arise as DG size increases.

Benefits of Distributed Generator

• High peak load can manage
• Distribution losses decreases
• Faster response to New load connection
• Maintain Power quality and reliability
• Easy Load management
• Remote area become active
• Load shedding decrease

Issues with Distributed Generator

• Bi-directional Power flow
• Update Protection system needed
• Need to maintain Reactive power with Operation

	Capacity	Efficiency	Fuel
Gas turbine	1-20 MW	21-40%	Gas-kerosene
Micro turbine	30 kW-1 MW	25-30%	Biogas-Natural gas
Fuel cell	50 kW-1 MW	35-60%	Methanol-hydrogen gas
Photovoltaics	1-25 kW	25-30%	Sun Light
Wind Generation	200 kW-3 MW	30-40%	Wind

Types of Distributed Generator