IEEE 1036:2010 pdf free download – IEEE Guide for Application of Shunt Power Capacitors
During system contingencies,when parts of the transmission system are unavailable, increased loading onthe remaining system causes additional voltage drop.Shunt capacitors are required to support the systemvoltage during these contingencies. The lack of available shunt capacitors can (and has) lead to systemvoltage collapse.
Most power system loads and delivery apparatus (e.g.,motors，lines and transformers) are inductive innature and therefore operate at a lagging power factor. When operating at a lagging power factor, powersystem loads require reactive current from the system, which results in reduced system capacity, increasedsystem losses, and reduced system voltage.
Figure 1 illustrates how the application of shunt power capacitors increases system capacity and reducessystem losses by reducing reactive power needs from Q., to Q.a through the addition of Q.As a result, thesystem load is reduced from S to Sas shown in Figure 1.
Table 1 gives a summary of benefits derived from shunt power capacitors as they apply to transmission anddistribution systems. Var support and voltage control are the primary benefits for a transmission systemwhile the distribution system benefits may be more varied depending upon whether the system belongs to agenerating utility, a nongenerating utility, or an industrial power user. The following subclauses describeeach of these benefits in more detail.
4.1.1 Voltage support
Applying shunt capacitors to a system results in a voltage rise. This voltage rise is caused by the flow ofcapacitor current (or the reduction of inductive current) through the inductive reactance of the system fromthe point of installation back to the generation. The voltage rise at the capacitor location is approximatelyequal to the capacitor current Ic times the inductive reactance of the system to the capacitor location X.There is a voltage rise all the way back to the voltage source, the magnitude depending on the inductivereactance between the source and the location. In a radial system, there is also an increase in the voltagebeyond the capacitor location resulting from the increase at the capacitor location.
There are a number of formulas that can be used to estimate the voltage rise that capacitors will produce.Based on the capacitor current and the inductive reactance of the system to the capacitor location:
For systems with a reasonably high X/R ratio, where the short-circuit impedance to the capacitor location isabout the same as the inductive reactance, the X of Equation (1) is the impedance that determines thesystem short-circuit current available at the capacitor location. This short-circuit current is useful incstimating the voltage rise.A commonly used estimate is as follows in Equation (2).
Capacitor banks are typically installed on the transmission system at major buses to provide voltage supportfor a large area. They are also installed at distribution buses and directly on customer delivery buses toprovide voltage support to smaller areas and to individual customers.Capacitor banks installed ondistribution lines support voltage along the entire length of line.
Capacitor banks that are installed for voltage support are generally switched on during the peak loadingperiods or low-voltage conditions and switched off during light loading periods or high-voltage conditions.
Capacitors have also been used on distribution feeders to keep the feeder voltage constant (acceptable, butlow) during substation voltage reduction contingencies. Voltage reduction can decrease feeder power andcurrent during peak load conditions.