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Updates found with 'vfd drive suppliers'

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Updates found with 'vfd drive suppliers'

Servo Controlled Voltage Stabiliser The IE Rules 1956 stipulated that the supplier shall supply voltage at the commencement of supply limiting the variation to 6 % of the declared voltage in case of LV/MV distribution system and +6 % / -9 % in case of HV distribution system. But generally it is observed that very low voltage during the day & normal voltage during night in residential area and very low voltage during day and very high voltage during night in industrial areas. As most of the equipment are designed to operate for a voltage variation of ±10 %, automatic voltage regulator is required. Generally two types of regulators are available: STEP RELAY CONTROL: This type of AVR can generally maintain output voltage within ±10 % of the standard output voltage. For wide variation in the voltage, many steps are involved and it may complicate and may also result in voltage surges to the connected equipment. The losses in an electronic stabilizer can be reduced by use of toroidal core transformer. STEP-LESS SERVO CONTROLLED STABILISER This type of stabilizer can regulate the output voltage within ±1 % of the standard voltage and here the variation in the voltage is smooth without steps / interruptions. This type of stabiliser can be designed for wide variation of the voltage with ease. It also have reasonably quick correction time. The Servo Stabilizer find use in telecom equipment, photocopier machines, offset printing presses, AC plants, moulding and machine tools machine, Scientific equipment etc. The voltage regulators are selected based on the following requirements: Input Voltage Variation: Standard ranges are 300 - 460 V, 290 - 470 V, 245 - 470 V for three phase and 160 - 260 V, 170 - 270 V and 140 - 270 V for single phase systems. Output Voltage Variation: Generally taken as 240 ± 1 %. Capacity: Stabilisers are normally designed to take 20 % overload for 60 minute, 50 % overload for 30 minutes and 100 % overload for few minutes. This overloading can take care of short time overloads, transformer inrush currents, motor starting currents and handling of thyristor loads. Type of load: It may be balanced three phase or unbalanced three phase. In the Telecom Department generally unbalanced load condition and unequal input voltage is considered. SERVO STABILISER OPERATING PRINCIPLE: The schematic diagram of the servo is given in figure below. It consists of Step-less variable toroidal wound a motor driven auto-transformer also known as dimmer-stat or variac. Reversible, instantaneous start synchronous motor (Servo motor) Buck-boost transformer (Series transformer) Power contactor Electronic control system Metering and indication panel Protection and cutoff system ( if any) Housing suitable for air/oil cooling. The buck-boost transformer is a series control transformer interposed between input and output. The primary is fed through the Auto transformer output. Depending upon the variation in the input voltage variation, a voltage is induced in this transformer in-phase or out of phase with reference to the input voltage so as to regulate the voltage at a steady value. Thus both step up and step down voltages are obtained through the same transformer tapping. The electronic control system monitors the output voltage continuously and based on the variation of output voltage the servo motor is driven in the forward and reverse direction to vary the output of the Auto transformer which in turn changes the voltage compensation at the buck/boost transformers. The control system monitors the voltage between the phase and neutral for each phase and regulates the voltage on each phase. However the regulation of voltages between the phases may be slightly different based on the actual loading of the individual phases. The single phase stabilizer employs one variable Auto transformer driven by a servo motor and one sensing circuit. The balanced type three phase stabilizer also employs single control circuit. Here the three variable auto transformers are mechanically coupled and are driven by a single motor. The sensing is done in one of the three phases and the other two are corrected automatically. These stabilizers can be used with loads where unbalance is not much and lesser accuracy in output is acceptable. For the unbalanced load and unequal input voltages, the three phase servo voltage stabilizer consists of three sets of identical components each set corresponding to a single phase system with the corresponding control system and with a common output contactor housed in the same enclosure for smaller capacities and in separate enclosure for very high ratings. The main electrical systems are connected in Star to form a three phase system with a common neutral between input and output. In case of oil cooled system, the Auto transformer and buck-boost transformers are immersed in oil. STANDARD FEATURES: Output voltage regulation within ±1 % of the load voltage. A provision is also available to vary the settings to adjust the output voltage at the desired value within ±5 V of the rated voltage. To cutoff the output at high and low input voltages beyond the designated voltages with audio and visual alarm. Overload protection by isolating the load in the stabilizer with visual and audio alarm. Tripping arrangement in case of any phase failure. Auto/Manual provision for restarting the stabilizer after tripping due to any reason. Micro limit switches to cutoff the power supply to the servo motor while it reaches the extreme low voltage and extreme high voltage points.
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Voltage Stabilizer The figure below shows the working model of a Voltage Stabilizer that contains a step-down transformer (usually provided with taps on secondary), rectifier, operational amplifier/microcontroller unit and set of relays. Operation of Voltage Stabilizer In this, op-amps are tuned in such way that they could sense various set voltages such as lower cut off voltage, boost condition voltage, normal operating voltage, higher cut off voltage and buck operating voltage. A set of relays are connected in a manner that they trips the load circuit during higher and lower cut off voltages and also they switch buck and boost voltages to the load circuit. A step-down tap changing transformer has different secondary voltage tapping which are helpful for operating operational amplifier for different voltages and also to add-up and deduct voltages for boost and buck operations respectively. A rectifier circuit converts AC supply into DC to power-up entire electronic control circuit as well as relay coils. Let us assume that this is 1 KVA single phase stabilizer that provides stabilization for voltage range of 200 to 245 with a boost-buck voltage of 20-35 V for input voltage of 180 to 270 V. If the input supply is, say 195 V, then operational amplifier energizes boost relay coil such that 195 + 25 = 220V is supplied to the load. If the input supply is 260 V, corresponding op-amp energizes buck relay coil so that 260-30 = 225 V is supplied to the load. If the input voltage is below 180 V, corresponding op-amp switches lower cut off relay coil such that load is disconnected from the supply. And if the supply is beyond 270 V, corresponding op-amp energizes higher cut off relay coil and hence load is terminated from the supply. All these values are approximate values; it may vary depending on the application. By this way, a stabilizer operates under different voltage conditions. Servo Controlled Voltage Stabilizers In case of automatic voltage stabilizers, the speed of voltage correction is very less. The high speed voltage correction at a greater precision is achieved with servo controlled stabilizers. In servo controlled stabilizers, voltage correction is done very precisely, i.e., closer to the base voltage value. The main components of a servo stabilizer include servo motor driven continuously variable auto transformer, buck-boost transformer and solid state control circuit as shown in the figure below. Servo Controlled Stabilizer In this stabilizer, solid state control circuit sense voltage fall and rise from a predetermined value and correspondingly operates the servo motor. The primary winding of buck-boost converter is connected to the motorized auto transformer whereas its secondary is connected in series with incoming supply.Whenever motor operates the autotransformer, appropriate voltage is supplied to the primary of the buck-boost transformer and hence corresponding secondary voltage corrects the supply voltage to the load. Here comparators (nothing but op-amps) in solid state control circuit senses the voltage changes and activates servo motor to a desired location so that variable transformer increase or decrease the output voltage to the load. When the control circuit finds output voltage higher than a reference voltage, it feeds the positive signal to the servo motor controller and hence the arm rotates till the two voltages are equal. If the output voltage falls below the reference value, a negative signal goes to the servo motor such that arm rotates the contact in other way so as to reduce the voltage. Servo stabilizers can produce output regulation of ±0.5% with high efficiency about 98%.
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