For satisfactory operation of motors, lamps and alternative masses, it’s fascinating that buyers area unit equipped well constant voltage. Too wide variations of voltage might cause erratic operation or perhaps amiss of consumers’ appliances. To safeguard the interest of the customers, the govt has enacted a law during this regard. The statutory limit of voltage variation is declared voltage at consumers’ terminals. The principal reason for voltage variation at consumer’s premises is that the amendment in load on the provisioning system. once the load on the system will increase, the voltage at the consumer’s terminals falls thanks to the increased free fall in
- Alternator synchronous impedance
- Transmission line
- Transformer impedance
- Feeders and
This is achieved by putting in voltage regulation instrumentality at appropriate places within the grid. the aim of this chapter is to influence vital voltage management instrumentality and its increasing utility during this quick developing grid.
Importance of Voltage Contr voltage Control:
When the load on the provisioning system changes, the voltage at the consumer’s terminals additionally changes. The variations of voltage at the consumer’s terminals square measure undesirable and should be unbroken inside prescribed limits for the subsequent reasons :
- In the case of the lighting load, the lamp characteristics square measure terribly sensitive to changes of voltage.
- In case of power load consisting of induction motors, the voltage variations could cause erratic operation.
- Too wide variations of voltage cause excessive heating of distribution transformers. This may cut back their ratings to a substantial extent.
- It is clear from the higher than the discussion that voltage variations in an exceedingly grid should be unbroken to the minimum level so as to deliver smart service to the shoppers.
With the trend towards the larger and bigger interconnected system, it’s become necessary to use acceptable strategies of voltage management.
Methods of Voltage Contr voltage Control:
There are many strategies for voltage management. In every technique, the system voltage is modified in accordance with the load to get a reasonably constant voltage at the consumer’s finish of the system. the subsequent are the strategies of voltage management in associate a.c. power system:
- By excitation control
- By using tap changing transformers
- Auto-transformer tap changing
- Booster transformers
- Induction regulators
- By synchronous condenser
Location of Voltage Contr voltage Control Equipment:
modern facility, there are many components between the generating station and therefore the shoppers. The voltage management instrumentation is employed at quite one purpose within the system for 2 reasons. Firstly, the ability network is extremely intensive and there’s a substantial drop in transmission and distribution systems. Secondly, the varied circuits of the ability system have dissimilar load characteristics. For these reasons, it’s necessary to produce individual means that of voltage management for every circuit or cluster of circuits.
- generating stations
- transformer stations
- the feeders if the drop exceeds the permissible limits
Excitation Contr Excitation Control:
When the load on the availability system changes, the terminal voltage of the generator additionally varies because of the modified dip within the synchronous electrical phenomenon of the coil. The voltage of the generator is often unbroken constant by ever-changing the sector current of the generator in accordance with the load. this can be called associate excitation management methodology.
- Tirril Regulator
- Brown-Boveri Regulator
These regulators square measure supported the “overshooting the mark †principle” to change them to reply quickly to the speed fluctuations of the load. once the load on the generator will increase, the regulator produces a rise in excitation over is ultimately necessary.
This is achieved by the speedy gap and shutting a loop across the exciter variable resistor. For this reason, it’s additionally called moving kind transformer. Construction. the essential elements of a Tirril transformer. A variable resistor R is provided within the exciter circuit and its worth is about to grant the desired excitation. This variable resistor is placed in and out of the exciter circuit by the regulator, therefore variable the exciter voltage to take care of the required voltage of the generator.
- Main contact. There square measure 2 levers at the highest that carry the most contacts at the facing ends. The left-hand lever is controlled by the exciter magnet whereas the right-hand lever is controlled by AN a.c. magnet is understood as the main management magnet.
- Exciter magnet. This magnet is of the standard magnet kind and is connected across the exciter mains. Its exciting current is, therefore, proportional to the exciter voltage. The equilibrize force for the exciter magnet is provided by four coil springs.
- A. C. magnet. It is additionally of magnet kind and is energized from a.c. bus-bars. It carries series additionally as shunt excitation. This magnet is therefore adjusted that with traditional load and voltage at the generator, the pulls of the 2 coils square measure equal and opposite, so keeping the right-hand lever within the horizontal position.
- Differential relay. It basically consists of a U-shaped relay magnet that operates the relay contacts. The relay magnet has 2 identical windings wound differentially on each the limbs. These windings square measure connected across the exciter mains–the mitt one for good whereas the right-hand one has its circuit completed only if the most contacts square measure closed.
- Operation. In this position of main contacts, the relay magnet remains energized and pulls down the coil carrying one relay contact. Consequently, relay contacts stay open and therefore the exciter field variable resistor is within the field circuit.
When the load on the generator will increase, it’s terminal voltage tends to fall. This causes the series excitation to predominate and therefore the a.c. magnet pulls down the right-hand lever to shut the most contacts. Consequently, the relay magnet is de-energized and releases the coil carrying the relay contact. The relay contacts square measure closed and therefore the variable resistor R within the field circuit is short-circuited. This will increase the exciter-voltage and thence the excitation of the generator. The augmented excitation causes the generator voltage to rise quickly. At constant time, the excitation of the exciter magnet is It is worthy to say here that exciter voltage is controlled by the speedy gap and shutting of the relay contacts. because the regulator is worked on the overshooting the mark principle, therefore, the terminal voltage doesn’t stay completely constant however oscillates between the utmost and minimum values. augmented thanks to the rise in exciter voltage.
In this sort of regulator, exciter field resistor is varied ceaselessly or in tiny steps rather than being initial utterly cut in and so utterly cut out as in Tirril regulator. For this purpose, a regulation resistance is connected asynchronous with the sphere circuit of the exciter. Fluctuations within the generator voltage are detected by an impact device that actuates a motor.
Construction. the schematic diagram of a Brown-Boveri transformer. It conjointly works on the “overshooting the mark principle” and has the subsequent four necessary components :
- Control system. The system is constructed on the principle of the induction motor. It consists of 2 windings A associate degreed B on a rounded core of laminated sheet steel. The winding A is worked up from 2 of the generator terminals through resistances U and U′ whereas a resistance R is inserted within the circuit of winding B. The magnitude relation of resistance to the electrical phenomenon of the 2 the 2}windings are fittingly adjusted thus on produce a section distinction of currents within the two windings.
- Mechanical control torque. The electric force made by this within the split section winding is opposed by a mixture of 2 springs (main spring and auxiliary spring) that turn out a continuing mechanical force regardless of the position of the drum. below the steady deflected state, mechanical force is equal and opposite to the electrical force.
- Operating system. It consists of a field resistor with the contact device. The resistor consists of a combination of resistance parts connected to the stationary contact blocks CB. These 2 resistance sectors R are connected asynchronous with one another and so asynchronous with the sphere circuit of the exciter. On the within the surface of the contact, blocks roll the contact sectors metallic element. once the terminal voltage of the generator changes, the electrical force acts on the drum.
- Damping torque. The regulator is formed stable by damping mechanism that consists of associate degree atomic number 13 disc O rotating between 2 permanent magnets m. The disc is double-geared to the rack of associate degree atomic number 13 sector P and is mounted to the atomic number 13 drum C by means that of a versatile spring S acting because of the recall spring. If there’s an amendment within the generator voltage, the eddy currents induced within the disc O turn out the mandatory damping force to resist fast response of the moving system.
Operation. Suppose that resistances U and U′ square measure thus adjusted that the terminal voltage of the generator is traditional at position one. during this position, the electrical torsion is counterpoised by the mechanical torsion and also the moving system is in equilibrium. it’s assumed that electrical torsion rotates the shaft in a very dextral direction.
Now imagine that the terminal voltage of the generator rises thanks to a decrease in load on the provisioning system. the rise within the generator voltage can cause a rise in electrical torsion that becomes bigger than the mechanical torsion. This causes the drum to rotate within the dextral direction, notify position three. As a result, additional resistance is inserted within the exciter circuit, thereby decreasing the sector currently and thence the terminal voltage of the generator.
Sometimes it’s desired to regulate the voltage of a line at some extent secluded from the most electrical device. this may be handily achieved by the employment of a booster electrical device as shown in Fig. 15.7. The secondary of the booster electrical device is connected nonparallel with the road whose voltage is to be controlled. the first of this electrical device is provided from a regulation electrical device *fitted with on-load tap-changing gear. The booster electrical device is connected in such how that it’s secondary injects a voltage in section with the road voltage.
The voltage at AA is maintained constant by tap-changing gear within the main electrical device. However, there is also a substantial dip between AA and pellet thanks to the fairly long feeder and sound of hundreds.
An induction regulator is actually a continuing voltage electrical device, one winding of which might be moved w.r.t. the other, thereby getting a variable secondary voltage. the first winding is connected across the availability whereas the coil is connected asynchronous with the road whose voltage is to be controlled. once the position of 1 winding is modified w.r.t. the other, the secondary voltage injected into the road additionally changes.
- Single-phase induction regulator. A single section induction regulator is illustrated in construction, it’s the same as one section induction motor except that the rotor isn’t allowed to rotate incessantly however is adjusted in any position either manually or by the tiny low motor. the first winding A B is wound on the stator and is connected across the availability line. The coil CD is wound on the rotor and is connected asynchronous with the road whose voltage is to be controlled.
- Three-phase induction regulator. In construction, a 3-phase induction regulator is comparable to a 3-phase induction motor with wound rotor except that the rotor isn’t allowed to rotate incessantly however is controlled in any position by suggests that of a gear wheel. the first windings either in star or delta square measure wound on the mechanical device and square measure connected across the availability. The secondary windings square measure wound on the rotor and therefore the six terminals square measure brought out since these windings square measure to be connected asynchronous with the road whose voltage is to be controlled.