Series Compensation (SC)
- Description
- Details
- Applications
- References
Series compensation is defined as insertion of reactive power elements into transmission lines and provides the following benefits:
- Reduces line voltage drops
- Limits load-dependent voltage drops
- Influences load flow in parallel transmission lines
- Increases transfer capability
- Reduces transmission angle
- Increases system stability
For these tasks, Siemens offers various solutions that have already been proven in numerous applications. Applications are the Fixed Series Capacitor (FSC), the Thyristor – Controlled Series Capacitor (TCSC) and the Thyristor - Protected Series Capacitor (TPSC).
The task of series compensation is to reduce the transmission lines inductivity. This means, that the line length is "virtually" shortened. As a consequence, the transmission angle is reduced and thus the power transfer can be increased without reduction of the system stability.
Applications
Series compensation makes use of capacitors, reactors or power electronic devices offering high flexibilty.
Depending on the application three different types of Series Compensation are provided. The most common application is the Fixed Series Capacitor (FSC). Thyristor-Valve Controlled Systems (TCSC) and Thyristor-Valve Protected Systems (TPSC) may also be installed.
Fixed Series Capacitor (FSC)
The simplest and most cost-effective type of series compensation is provided by Fixed Series Capacitors (FSCs). FSC installations are protected against overvoltages using MOVs and self/forced triggered gaps.
Due to its benefits like
- Increase in transmission capacity and
- Reduction in transmission angle
Fixed series compensation is a proven solution to optimize power transmission.
FSCs comprise the actual capacitor banks and parallel arresters (metal oxide varistors, MOVs), spark gaps, and a bypass switch. Surge arresters, spark gaps and bypass switch have a protecting function in a Fixed Series Capacitor bank installation. The bypass switch protects the spark gap which defends the arrester from excessive energy absorption. The surge arresters in turn protect the capacitor from overvoltages during and after transmission system failures. Three high-voltage switches serve to integrate the FSC into and isolate it from the transmission line (e.g., for maintenance purposes).
A damping circuit is connected in series with the triggered spark gap and is not always stressed by the ac-line current. In parallel to the spark gap the bypass-breaker is located to provide current commutation for times when the current capability of the Spark gap or MOV is exceeded.During internal faults (faults occuring on the HV-line to which the capacitor bank is connected to) the spark gap and the bypass-breaker are allowed to operate and to protect capacitor and MOV from overload.
In some cases a MOV only protection scheme is used (i.e. no spark gap) however this usually requries a much higher MOV energy which is more costly than a Spark Gap Solution. A typical single line diagram for a FSC is shown below.
Thyristor – Controlled Series Capacitor (TCSC)
Reactive power compensation by means of TCSCs can be adapted not only to brand-new installations but also be implemented in a wide range of existing systems. The TCSC provides, in addition to the conveniences of a conventional Fixed Series Compensation, some further benefits. It also controls the current and thus the load flow in parallel transmission lines, which simultaneously improves system stability. Further applications for TCSC include power oscillation damping and mitigation of subsynchronous resonance (SSR), which is a crucial issue in case of large thermal generators.
- Local mitigation of subsynchronous resonance (SSR) permits higher levels of compensation in networks where interactions with turbine-generator torsional vibrations or with other control or measuring systems are of concern.
- Damping of electromechanical (0.5-2 Hz) power oscillations often arises between areas in a large interconnected power network. These oscillations are due to the dynamics of interarea power transfer and often exhibit poor damping when the aggregate power transer over a corridor is high relative to the transmission strength.
A typical single line diagram of a TCSC is shown in the figure below.
Thyristor – Protected Series Capacitor (TPSC)
When direct-light-triggered thyristors are used, there is no need to install conventional spark gaps or surge arresters. Due to the very short cooling times of the light-triggered thyristor valves, thyristor protected series capacitors can be quickly returned to service after a failure, allowing the transmission lines to be utilized to their maximum capacity.
TPSCs are the first choice whenever transmission lines must be returned to maximum carrying capacity as quickly as possible after a failure.
Siemens supplies Fixed Series Capacitors as well as Thyristor-Controlled SC´s and of course, Protected Series Capacitors. Series Capacitor installations made by Siemens increase power transfer capacity on existing transmission systems all over the world.
The selected references offer detailed information about interesting projects:
| In Operation since ... | Country | Project Name | Application |
|---|---|---|---|
| 2009 | India | East-West | FSC |
| 2008 | Brazil | North South Interconnector III | FSC |
| 2006 | China | Fengjie | FSC |
| 2006 | USA | Eldorado-Lugo & Eldorado-Moenkopi | TPSC |
| 2003 | USA | Lexington and Valley | FSC |
| 2003 | Mozambique | Maputo-Barberton | FSC |
| 1999 | Canada | Montagnais | FSC |
| 1993 | Brazil | Serra da Mesa | TCSC |
| More: | FACTS - Reference List |
Please use the following link for a overview of our references.