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Power System Technology Navigator

Bottlenecks
Constrained transmission paths or interfaces in an interconnected electrical system
The term Bottlenecks is often interchangeable to congested transmission paths or interfaces. A transmission path or interface refers to a specific set of transmission elements between two neighboring control areas or utility systems in an interconnected electrical system. A transmission path or interface becomes congested when the allowed power transfer capability is reached under normal operating conditions or as a result of equipment failures and system disturbance conditions. The key impacts of Bottlenecks are reduction of system reliability, inefficient utilization of transmission capacity and generation resources, and restriction of healthy market competition.The ability of the transmission systems to deliver the energy is dependent on several main factors that are constraining the system, including thermal constraints, voltage constraints, and stability constraints. These transmission limitations are usually determined by performing detailed power flow and stability studies for a range of anticipated system operating conditions. Thermal limitations are the most common constraints, as warming and consequently sagging of the lines is caused by the current flowing in the wires of the lines and other equipment. In some situations, the effective transfer capability of transmission path or interface may have to be reduced from the calculated thermal limit to a level imposed by voltage constraints or stability constraints.

Power System Technology Navigator


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Asynchronous connection

The interconnected AC networks that tie the power generation plants to the consumers are in most cases large. The map below shows the European situation.
There is one grid in Western Europe, one in Eastern Europe, one in the Nordic countries. Islands like Great Britain, Ireland, Iceland, Sardinia, Corsica, Crete, Gotland, etc. also have their own grid with no AC connection to the continent. The other continents on the globe have a similar situation.
Even if the networks in Europe have the same nominal frequency, 50 cycles per second or Hertz (Hz), there is always some variation, normally less than ± 0.1 Hz, and in certain cases it may prove difficult or impossible to connect them with AC because of stability concerns. An AC tie between two asynchronous systems needs to be very strong to not get overloaded. If a stable AC tie would be too large for the economical power exchange needs or if the networks wish to retain their independence, than a HVDC link is the solution.
And in other parts of the world (South America and Japan) 50 and 60 Hz networks are bordering each other and it would be impossible to exchange power between them with an AC line or cable. HVDC is then the only solution.

Bottlenecks

Constrained transmission paths or interfaces in an interconnected electrical system
The term Bottlenecks is often interchangeable to congested transmission paths or interfaces. A transmission path or interface refers to a specific set of transmission elements between two neighboring control areas or utility systems in an interconnected electrical system. A transmission path or interface becomes congested when the allowed power transfer capability is reached under normal operating conditions or as a result of equipment failures and system disturbance conditions. The key impacts of Bottlenecks are reduction of system reliability, inefficient utilization of transmission capacity and generation resources, and restriction of healthy market competition.The ability of the transmission systems to deliver the energy is dependent on several main factors that are constraining the system, including thermal constraints, voltage constraints, and stability constraints. These transmission limitations are usually determined by performing detailed power flow and stability studies for a range of anticipated system operating conditions.

Harmonics

Harmonics are associated with steady-state waveform distortion of currents and voltages
Harmonics are components that make up a waveform where each component has a frequency that is an integral multiple of the fundamental frequency. The term Harmonic is normally applied to waveform components that have frequencies other than the fundamental frequency. For a 50 Hz or 60Hz system the fundamental frequency is 50HZ or 60Hz. A waveform that contains any components other than the fundamental frequency is non-sinusoidal and considered to be distorted.
 
Loop Flow

Unscheduled power flow on a given transmission path in an interconnected electrical system
The terms Loop Flow and Parallel Path Flow are sometimes used interchangeable to refer to the unscheduled power flows, that is, the difference between the scheduled and actual power flows, on a given transmission path in an interconnected electrical system. Unscheduled power flows on transmission lines or facilities may result in a violation of reliability criteria and decrease available transfer capability between neighboring control areas or utility systems.

 Power Oscillations

Periodic variations in generator angle or line angle due to transmission system disturbances
Oscillations of generator angle or line angle are generally associated with transmission system disturbances and can occur due to step changes in load, sudden change of generator output, transmission line switching, and short circuits. Depending on the characteristics of the power system, the oscillations may last for 3 -20 seconds after a severe fault. Drawn out oscillations that last for a few seconds or more are usually the result of very light damping in the system and are pronounced at power transfers that approach the line’s stability limit. During such angular oscillation period significant cycle variations in voltages, currents, transmission line flows will take place. It is important to damp these oscillations as quickly as possible because they cause mechanical wear in power plants and many power quality problems. The system is also more vulnerable if further disturbances occur