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    FAQ CVT
 
     
  1. Why CVT  
  2. How & Why Elent  
  3. Technical Highlights  
  4. Factors Affecting Performance, Queries, Notes  
  5. Servicing of Elent CVT  
  6.Comparison Between Servo Voltage Stabilizer & Elent CVT  
 


 
 

1. Why CVT

Electronic Instruments, Machines, computers and other microprocessor-based equipment are designed to operate on steady stream sine wave of 220/230 V RMS. The Nature of utility power is such that very frequently the equipment encounters electrical disturbances and voltages which are beyond the range of these equipment. The quality of power has deteriorated so much without encountering disturbances. Equipment using microprocessors are especially vulnerable due to the degradation of the utility power. The equipment when plugged into the wall socket outlet are normally located a good distance from the building service centre [the place where the power meters are located]. Thus in order to reach the equipment potentially damaging impulses generated outside your location travel through the impedance of lot of copper wire. Although this barrier serves to dampen out many of these disturbances, the real problem occurs along the electrical path from the point the power enters your premises to your equipment. Between these points are all kinds of devices, such as Lifts, Air conditioners, Florescent tube chokes, photocopiers and in case of factories the Machines. Any equipment that arcs, cycles on off, or draws excessive bursts of current becomes the cause of potential hazard to your microprocessor-based equipment.

The utility power has also been so much overloaded that the demand far exceeds the supply. Coupled with that is the fact that although the wiring in your area/building/location was initially designed to handle lets say "x" amount of power the actual power being handled by these wires could be as much as "3x". On top of this is the poor/negligible/nil maintenance of the junction boxes located near your premises. All this results in either very low voltage during Off load hours Microprocessor based equipment are normally designed to operate on very narrow voltages bands and when they are subject to large variation in voltages they get damaged.

 
Solution
ELENT CVT has been designed to give you total protection against power related problems and to condition the power to suit the needs of your microprocessor based equipment. It effectively regulates voltage variation, suppresses transients [ISOLATION] and bridges short interruptions/dips.


 
 
2. How & Why Elent

Voltage Variations/Fluctuation & Principle of Operation:

The phenomenon, which makes the CVT special, is "Ferro Resonance". This is achieved by resonating of the output secondary coil with selected high stability capacitors. This resonant circuit is so dimensioned that the secondary part of the transformer core is saturated during each half cycle. In this way the output voltage of the transformer is nearly constant even for large variation in the input voltages. By design ELENT CVT has sinusoidal waveform. All problems related to variation / fluctuation in Voltages are effectively handled because of this principle and a constant voltage output of & 1% is given by ELENT CVT.

Transients/Noise (Spikes):
In Elent CVT the primary and secondary sides are separated by large air gap and a magnetic shunt. The combined inductance and capacitance are radically reduced because of this and thereby it gives an effective protection against asymmetric voltage transients. There also exists a phase difference between the Input and Output Voltage in ELENT CVT. The phase shift varies with the magnitude of the load and change in line voltage and helps in suppression of noise. The Isolation between the primary & secondary strips away the high frequency components of the Normal Mode Noise and the neutral to ground bonding on the secondary side cause a short circuit for the Common Mode Noise.

Short Interruption & Dips:
The output of the CVT is taken from the saturated secondary section of the transformer, which has an energy reserve close to 5 to 10 ms at full load. This feature is responsible for bridging the small interruption and large dips in line voltage. i.e. for small duration of power breaks [caused because of phase compensation, switching in the distribution network, lightning, switching On/Off of heavy electrical equipment] the ELENT CVT continues to deliver power from its own energy reserve.
The ELENT CVT combines the features of three different line conditioning / protection equipment, viz. Line Filters/ Surge Suppresser, Servo stabilizers and Isolation Transformers. A comparison chart is given at para 6. This gives the comparison between Servo stabilizers and ELENT CVT's.


 
3. Technical Highlights

Input Voltage :
180 V to 260V at the rated power. At lesser loads, the "Low Voltage" limit is increased automatically.
Short term high Input Voltages shall not affect the load side. ELENT CVT can handle upto 300 Volts for 10 minutes and shall delivery the rated output voltage during this period.
A fuse has been incorporated on the input side of the CVT so that in case of persistent high current (normally caused because of high voltages occurring on account of a weak neutral) the same shall protect the CVT. The CVT ensures that even if more than the specified Input Voltages are applied the equipment does not ever see damaging high voltage.

Output Voltage : 220V to 225V from No load to Full load or a line voltage swing from 180V to 260V.

Line Frequency : 50 HZ 1%
All specifications relates to 50HZ. For every 1 % change in the line frequency the output voltage changes by 1.6% the special feature incorporated in the ELENT CVT is that it has a very wide tolerance of the load power factor within the specified line frequency limits.

Output Wave Form : The output waveform of ELENT CVT is sinusoidal and the waveform distortion is limited to 5% under full load conditions at typical input.

Voltage Correction Speed : Changes in supply voltage are normally corrected within half cycle i.e. within 10 ms.

Output Step Load Response : 2 cycles (30 to 40 ms)

Isolation : Since the Input & Output voltages are separated not only electrically, but physically also, by a magnetic shunt, ELENT CVT has a stronger isolation effect then a normal transformer. The Isolation effectively strips away the high frequency component of the normal mode noise and the neutral to ground bonding creates a short circuit path for the common mode noise.

Short Circuit Protection : Instantaneous and intrinsic.

Ambient Temperature : ELENT CVT is rated for continuous operation at an ambient upto 50 deg.C.


  4. Factors Affecting Performance, Queries, Notes

Selection of CVT : The CVT power rating should match the maximum power of the load including the initial surge rating. The rating should also take into account the future expansion of the load viz. addition of extra drive in a computer, extra lines on an EPABX exchange etc. As there are a large variety of machines like FAX/Computers/EPABX available in the market with different features and power ratings it is essential to carefully select the CVT instead of generalizing that "A" rating of CVT is suitable for "B" equipment. Under-specification of the load may result in collapsing of the CVT voltage under over load conditions (starting inrush) and the consequent "hanging" of computers/microprocessor systems. In case of doubt it is advisable to select the next rating of CVT.

CVT Voltages :
All specifications of the CVT are referred to the true RMS Voltage, hence all measurements (in case of testing by user) must be made by using a TRUE RMS meters, ELENT CVT has a specially designed shielded and calibrated voltmeter.

No Load Operation/Heating : CVT functions at a very high level of flux density and the resonating tank circuit is working all the time whether the load is connected or not. The no load current of the CVT are as high as 40% and therefore it heats up under no load condition. It is therefore recommended that at least 25% of the rated load be connected at all times or, as with most equipment, The CVT switched off when not in use. ELENT CVT is designed to work under the worst condition, i.e. from no load to full load and from minimum to maximum voltage Continuously at ambient's uptill 50 deg. Centigrade. The CVT should be kept in a manner so that heat dissipation is possible. (Do not keep it in an enclosed cabinet).

Monitor Screen Shaking : CVT is a frequency dependent system. At frequencies other than the specified range (49.5 to 50.5 HZ) the CVT's resonance circuit always tries to lock on to the basic frequency. Monitors which have the scan frequency locked to the line frequency, may result in the continuous shaking of the raster. This phenomenon shall not be observed in monitors which have their raster scan frequency locked to the internal crystal.
Monitor shaking may also be observed in case, where the CVT is kept in close proximity of the monitor. This is because the leakage flux from the CVT interferes with the Electro magnetic deflection of the CRT. The CVT must therefore be kept approximately 1 meter away from the CRT and so oriented that the effect of leakage flux is minimum.
Caution: Because of the high leakage it is recommended that magnetic storage media/component/display devices be kept away from the CVT.

Computer/Keyboard "Hanging" : In some computers, after connecting it to the CVT, during switch-on of heavy loads like Printers etc. the computer "Hangs". This is due to malfunctioning of the SMPS of the Computer. SMPS have a present threshold on the 5 Volts DC bus for "Power Good" signal. If the SMPS units are marginal in their power rating then a normal heavy load switch on will "Disable" the "Power Good" signal, which causes the Computer to "Hang". To overcome this problem the "Power Good" threshold of the SMPS need readjustment. Even after this if the problem persists the SMPS rating needs to be looked into.

Audible Noise : All CVT produce audible noise because of the fact that its secondary section is in resonance while in operation, and hence the core (lamination) also tend to vibrate at the basic resonance frequency. The intensity and the frequency of this noise depend on the geometry of the core and it's mass. The intensity of this noise is also directly proportional to the power rating of the CVT. The audible noise also increase for CVTs having a very close regulation tolerance & vice versa. ELENT CVT not only has a very good regulation under extreme load & voltage conditions but also ensures that this does not interfere with the normal working environment.

Wider Input Line Voltage Range : In order to control a wide line voltage fluctuation (beyond the specified range), a CVT of higher rating may be used.

Operation With Motor Loads : Because of the current limiting effect special attention should be given when used with motor application. In general the CVT must have a load rating nearly equal to the maximum power drawn during the starting cycle. In case of very high inductive motors the starting currents may vary from two to eight times the normal running rating of the motors.

Effect Of Temperature : The output voltage may show a small change as the unit warms up to stable operating temperature. The change is approximately 1% for each 40 deg. C of temperature range.

Output Voltage Setting : Because of the fact that the normal incoming frequency commonly prevalent is around 49.5 Hz. and because of the change in voltage as the CVT reaches its stable operating temperature the CVT is adjusted at the factory to within plus 2%, minus 0% of the rated value, with rated nominal voltage at 50HZ applied at the Input and the full rated load at unity power factor applied at the output at room temperature.

Neutral To Ground Bonding : This is factory provided and is optional. The user may remove this bond and create his own neutral or use it in the floating output mode. In the floating output mode the CVT output also becomes shock proof

Effect Of Load Power Factor : The output voltage may vary from the name plate values at different power factors.

Applications : Telemetry equipment & Systems, Supervisory control and data acquisition (SCADA) systems, CNC machines, Computers, Data processing machine, Colour photography Labs, PA system, Telecommunication, Telex, TV, VCR, Electronic typewriters FAX, EPABX systems, Desk top publishing & Pre-print systems, Biomedical equipment like Ultra sound machines. Centralized Monitoring systems, Computerized medical equipment, Embroidery machines etc. etc.


 
5. Servicing of Elent CVT

In normal working conditions, ELENT CVT is designed for years of trouble free service. It is tolerant to a number of extreme conditions, since it has no moving part and / or sensitive solid state devices.
The only electrical component, which may (if at all) deteriorate over a period of time, is the capacitor of the resonating circuit. The known major cause of capacitor failure is the high line frequency, which makes the capacitor voltage to exceed its rating and results in "Spark" Over. Since the capacitors used are "Self Healing" type they are normally in a position to retain their value. If, However the capacitors are subjected to very high frequency continuously the frequent "Spark Over" results in reduction of the capacitor's basic value and hence, lower output voltage. The known sources of higher frequency are the low power gensets.
In all ELENT CVT's it is ensured that within specified operating conditions, the capacitor voltages are well within the marked operating values. (A typical ELENT CVT's capacitor operates at 430 V under worst condition whereas the rated working voltage of the capacitor is 440V).
The other components, which are susceptible to failure in transit/extended use, are external hardware viz. Voltmeter, Switch & Sockets. All these are field replaceable.


  6. Comparison Between Servo Voltage Stabilizer & Elent CVT

 
 
FEATURES SERVO VOLTAGE STABILIZER ELENT CONSTANT VOLTAGE TRANSFORMERS (CVT)
Isolation Nil Transients are passed on to the load side. The brush movement on the Auto Transformer itself is a source of Micro Sparks and hence noise. Exhibits a high degree of isolation between Input/Output and hence excellent Noise Rejection & suppression of Transients. Very effective protection against asymmetric Voltage Transients which are not handled effectively even by Line Filters.
Reliability Constant movement or servo Motor and wear & tear of Carbon Brushes reduces reliability Semiconductor switching is prone to failure under extreme voltage conditions Extremely Reliable and rugged as there are no moving parts.
Heavy Voltage Dips & Short Interruption Nil Tank Circuit (resonance) effectively Bridges short Interruptions and heavy Dips, which are usually encountered because of Phase Compensation. Switching in distribution Network, Lightening, arid Heavy Load shedding.
Regulation Good regulation, However Hunting Phenomenon is observed if sensitivity is increased. Excellent Voltage Regulation under extreme Line & Load conditions.
Input Voltage Control Range Fixed Controlling range Capable of Controlling a higher Input Voltage Range at lesser loads
Response Time Sluggish response (Typically 25 Volts/Sec) Very Fast (Typically 10 ms)
Short Circuit & Overload Protection MCB's have slower response to overload and have to be rest manually. Intrinsic and Instantaneous with automatic recovery on removal of Short Circuit/Overload conditions.
     
     
 

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