Grid Impact Study

 

What is Grid Impact Study?

Technically definition of grid impact study is a study of impact in capacity and load of the main grid when being connected to a new or another source of electricity energy. In more complex term, grid impact study meaning is studies to provides an analytical framework for power system stakeholders to make decisions about interconnecting between different sources of electricity. Grid impact analysis study sometimes is also called as grid integration or interconnection study. The grid integration study can be done by a variety of power sector decision makers and analysts.  —Omazaki Engineering is a consultant serves grid impact or interconnection or integration studies and assessment consulting services and analysis.  Contact Omazaki Engineering if you are looking for grid impact or connection study consultant for your project in Indonesia and South East Asia by sending an email to cs@omazaki.co.id or filling in the form in contact.

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Why We Need Grid Impact Study?

In order to guarantee the stability of the electric grid which the installation with the necessary constructive capacities and performance required by the grid code. While electric power utilities are interested in implementing renewable generation and reducing diesel fuel consumption, they must continue to meet standards to provide safe and reliable power to customer.

A grid impact study is conducted in order to provide a source of electrical energy. The grid impact study builds confidence among stakeholders (policy makers, regulators, system operators, distribution utilities, and others) in achieving goals related to electricity supply. It is also to be able to identify the necessary policy, regulatory, infrastructure and operating power system engagements to achieve these targets and objectives in a cost-effective manner and without compromising the reliability of electricity services.

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When Need Grid Integration Impact Study?

The potential barriers for any isolated system have been identified to be: energy balance (including steady-state voltage profile), small signal stability. Transient stability, protection coordination, harmonic analysis.

When a power plant is put into operation, which will impact the power system around this power plant

• Changes the grid diagram and structure.
• Changes the load flow on transmission lines.
• Affects short circuit current.
• Affects energy loss, power loss of the power system around the project.
• Affects the power quality.
• Affects the power grid stability.
• Affects the power supply reliability.

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Proposed Analytical Approach

Grid impact study are performed with power system simulation software including ETAP, DigSILENT, PSS-E.

The analysis of the potential impacts of grid on the power plant system will be divided into two main parts, focusing on generation and transmission, with a series of studies:

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The Study in Grid Impact Study

There are several electrical engineering studies that must be carried out before connecting a new generator to an existing interconnection system.

Load flow analysis

A load flow study is fundamental analysis module for demand evaluation, power flow analysis, power factor corrections and voltage drop calculations.

Carrying out a load flow study assists in designing electrical system which work correctly. This study also help to find sufficient power supplied by the power grid, where equipment is correctly sized, reactive power compensation is correctly placed and transformer taps are optimized.

Short circuit analysis

Perform device duty study using electrical power software which allows you to determine fault currents and automatically compare these values against manufacturer short circuit current ratings.

Analyze the effect of balanced and unbalances fault current are following below

• 3-phase or 1-phase
• Line-ground
• Line-line
• Line-line-ground

Reactive power capability and power factor

The reactive power limits defined at rated MW at lagging power factor will apply at all active power output levels above 20% of the rated MW output. The reactive power limits defined at rated MW at leading power factor will apply at all active power output levels above 50% of the rated MW output, and will reduce linearly below 50% active power output.

Reactive power is the power consumed in a AC circuit that does not perform any useful work, caused by inductors and capacitors. Reactive power counteracts effects of real power.

For the most part, wind plants use doubly fed asynchronous generator or full conversion machines with self-commutated electronic interfaces, which have considerable dynamic reactive and voltage regulation capability. Currently, inverter-based reactive  capability is more costly compared to the same capability supplied by synchronous machines.

For solar PV, it is expected that similar interconnection requirements for power factor range and low voltage rid-through will be formulated in the near future. Inverters used for Solar PV and wind plants can provide reactive capability at partial output, but any inverter-based reactive capability at full power implies that converter need to be sized larger to handle full active and reactive current.

• Reactive capability of synchronous generator

When reactive capability of variable generation resources is specified for transmission interconnections, it is done at the point of interconnection (POI), which is the point at which power delivered to the transmission system.

• Reactive capability for wind and solar PV Generator.

PV Generator and some types of wind generator use power converter. The ractive capability of converters differ from those of synchronous machines because they are normally not power-limited, but limited by internal voltage, temperature and current constraints.

This section will be explore in PV power plant Study, next.

Electrical energy losses

It is fact that the unit of electric generated by Power Station does not match with the units distributed to the customers. Some percentage of the units is lost in the distribution network.

There are two types of transmission and distribution losses:

• Technical losses

The technical losses are due to energy dissipated in the conductors, equipment used for transmission line, transformer, and distribution line and magnetic losses in transformers.

Technical losses are normally 20 % and directly depend on the network characteristics and the mode of operation

The major amount of losses in a power system is in primary and secondary distribution lines. While transmission and sub-transmission line account for only about 30% of the total losses. Therefore the primary and secondary distribution system must be properly planned to ensure within limits.

• The unexpected load increase was reflected in the increase of technical losses above the normal level
• Losses are inherent to the distribution pf electricity and cannot be eliminated.

There are two type of technical losses, there are permanent/fixed technical losses and variable technical losses.

• Non technical losses (commercial losses)

Non- the technical losses are the result to fraudulent actions on networks. Utilities have been able to identify several origins to fraud

• Meter and circuit-breaker manipulation
• Pricking out upstream from the meter
• Illegal connection
• Equipment theft

Harmonic distortion study

Large penetration of rooftop solar PV at the LV distribution grid has a significant effect on harmonic levels in the network. Power quality issues related to the low power factor of nonlinear loads and high harmonic current emissions from solar PV inverters at he LV network greatly affect the network performance. The power electronic converter/inverters that do not produce pure sinewaves introduce harmonics into the system when connected to the LV grid.

Transient Stability Study

Transient stability is study and analysis of the response of a system to disturbances such as loss of generation, line-switching operations, faults, and sudden load changes in the first few second after a disturbance. The stability of the power system is mainly divide into two types depending upon the magnitude of disturbances.

• Steady state stability
• Transient stability

The preceding look a steady-state stability serves as background for an examination of the more complicated problem of transient stability. This is true because the same three electrical characteristics that determine steady-state stability limits affects transient stability.

Transient stability is conducted when new transmitting and generating system are planned. Stability studies are helpful for the determination of critical clearing time of circuit breakers, voltage levels and a transfer capability of the system

Frequency Control

Frequency control is a process of maintaining the stability of a power system. In the power system, the frequency of the loop gets deviate from the steady-state value under the action of load perturbation. Load frequency  controller is employed to regulate the power generation level to match the load profile to keep the area frequency at its nominal value (±2.5% of nominal value)

The generating unit is able to increase or decrease the production based on changes in the frequency, and can therefore not easily be transferred to PV or wind plant. Since that plant is intermittent, it is possible to obtain a continual increase beyond the available PV/Wind energy.

For grid frequency stability, the generation capacity should be equivalent to the required load; otherwise, frequency problems may occur and thus lead to service disconnection. Conventional generators (such as steam, diesel and gas), which are generally equipped with the governor control, can stabilize the deviation in grid frequency (50 or 60 Hz) by reducing their output power through active power control. Consequently, the demanding efforts to replace conventional power generators with PV systems necessitate embedding such features for stable renewable power generation.

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Economic Evaluation Criteria

The economic indicators that need to be evaluated in a network impact study are as follows:

• Simple payback period (SPP)
• Net present value (NPV)
• Internal rate return (IRR)