ENGINEERING ARTICLES

An electrical power substation is a conversion point between transmission level voltages (such as 138 KV) and distribution level voltages (such as 11 KV). A substation has one or more step-down transformers and serves a regional area such as part of a city or neighborhood. Substations are connected to each other by the transmission ring circuit. An electrical grid station is an interconnection point between two transmission ring circuits, often between two geographic regions. They might have a transformer, depending on the possibly different voltages, so that the voltage levels can be adjusted as needed. The interconnected network of grid stations is called the grid, and may ultimately represent an entire multi-state region. In this configuration, loss of a small section, such as loss of a power station, does not impact the grid as a whole, nor does it impact the more localized neighborhoods, as the grid simply shifts its power flow to compensate, giving the power station o...

MEASUREMENT: The set of operations having the object of determining the value of a quantity. MEASURAND: A quantity subject to measurement. METROLOGY: The field of knowledge concerned with measurement. This term covers all aspects both theoretical and practical with reference to measurement, whatever their level of accuracy, and in whatever field of science or technology they occur. ACCURACY: The closeness of agreement between the result of a measurement and the true value of the measurand. SYSTEMATIC ERROR: A component of the error of measurement which, in the course of a number of measurements of the same measurand, remains constant or varies in a predictable way. CORRECTION: The value which, added algebraically to the uncorrected result of a measurement, compensates for an assumed systematic error. RANDOM ERROR: A component of the error of measurement which, in the course of a number of measurements of the same measurand, varies in an unpredictable way. UNCERTAINTY OF...

Generally, Fixed Shunt Reactors are designed and located in a way to be connected to the network most of the time. However, lately it is often required by the electrical utilities to perform automatic switching in/out operations on Switchable Fixed Shunt Reactors by monitoring the bus-bar voltage level. Figure 8-1 illustrates a typical Switchable Fixed Shunt Reactor control scheme. Figure 8-1: Typical On/Off switching control of a Fixed Shunt Reactor As seen in Figure 8-1, the normal operating range is 85% to 125% of bus-bar nominal voltage. For voltages higher than 125% of the nominal voltage, the switch-in (On) command is issued. Likewise, for voltages lower than 85% of the nominal voltage, the switch-out (Off) command is issued. This control system is interlocked with a zero voltage detection which is considered as voltages very lower than 20-80% of the nominal voltage; in this case, the bus-bar will be assumed dead and the control function will be blocked. As shown, this sw...

Compared to shunt reactors with a fixed rating, Variable Shunt Reactors provide several benefits to the operators. Customer values and applications of VSRs are as follows. To reduce voltage spikes in the network resulting from switching in and out the Fixed Shunt Reactors; especially in networks with low short circuit power. Generally, switching Fixed Shunt Reactors in and out is a non-optimal compensation which leads to voltage steps and also wearing out the breakers. It is possible to avoid switching actions by using a VSR and regulate it to its minimum power tap position. VSRs reduce voltage jumps during switching operation. In substations with SVC equipment and rotating phase compensators, the VSR has the capability to be coordinated with the SVC/phase compensators in order to maximize the dynamic capacity of the network during failure. For wind park generation applications, a VSR may be used by the operator of the wind park to control reactive power fluctuations. An impo...

The Shunt Reactor is a consumer of reactive power. In some applications there is a need to consume the inductive reactive power in steps. In such a case, several shunt reactor units are needed to connect and disconnect frequently which requires more circuit breakers and foot prints at substation. Instead of having several units, one unit that covers the entire power range could be an economical solution. A Variable Shunt Reactor (VSR) is a reactor where the inductance can be varied in steps. The reactive power consumption can increase up to twice its initial value over the whole regulating range. The regulation speed is determined by the operation time of the tap changers used; and it is in the order of seconds. VSRs are based on the same concept as a Fixed Shunt Reactor. However, the design requires special attention and the VSR is considered as a separate product type. Generally, when there is a slow variation of the load, the VSR works as an efficient reactive power compen...

Fixed Shunt Reactors have been traditionally used in transmission and distribution systems for many years. The reason that it is called Fixed Shunt Reactor is that its rated reactive power consumption is approximately constant; in other words, it has a fixed reactance (XR). The inductive reactive power which is consumed by Reactor can be calculated as follows: Where: Q IR  is the 3‐phase inductive reactive power consumed by the Shunt Reactor in VAR V  is the phase‐to‐phase voltage at the point the reactor is connected to the network in Volts X R  is the total inductive reactance of the Shunt Reactor in Ohms L R  is the equivalent inductance of the Shunt Reactor in Henry, I is the flowing current into the Reactor’s branch in Amperes As seen in equation 6-1, the consumed reactive power is only a function of the line voltage and is not affected by the load current of the line. The Reactor is characterized by the following.  Rated power Rated system voltag...

Viewed externally in the substation yard, a large high voltage Reactor does not differ much from a transformer. The easiest way to distinguish a Reactor from a transformer is to observe its terminals and bushings on top of the device. To explain more, contrary to a 3-phase transformer which has three primary and three secondary voltage terminals, a 3-phase Shunt Reactor has only three voltage connections. Figure 6-1 illustrates a 3-phase Shunt Reactor. Figure 6-1: Schematic of a 3-phase Shunt Reactor The shunt reactor is the most cost efficient equipment for maintaining voltage stability on the transmission lines. It does this by compensating for the capacitive charging of the high voltage AC-lines and cables, which are the primary generators of reactive power. The reactor can be seen as the voltage control device which is often connected directly to the high voltage lines. Figure 6-2 shows how the generated capacitive reactive power of the line is consumed by the reactors. ...