Automatic Power Factor Controller

                FIRST TIME IN INDIA
                This is 3rd Generation of Development in the APFC Field.

Till today –APFC manufacturing was exposed to the SECOND GENERATION units that are RELAY TYPE akin to RELAY TYPE STABILISERS in Voltage stabiliser field.. This is Servo type APFC Controller – Continuously correcting type . This will upgrade your concept of Power factor correction. The unbalanced type APFC provided ideal correction to individual phases .

This objective & advantage is not possible from RELAY TYPE Power Factor Panels. Your next purchase can be this type of of panel . Cost wise - competitive. At existing sites of Relay Type Power Factor installations, – a small sized Unbalanced Type unit will further correct Power Factor of individual phases by correcting PF of Individual phases from Average figures of say say 0.92-0.97 to 1 & thus further saving 3-4 % on Electricity Bills. Say add 10 KVAR or 20 KVAR Constantly variable capacitors in Individual phases.

An Innovative product : The innovative character of this APFC controller can be best understood from the anomaly with the Voltage stabiliser field.

There are three STAGES of development in the field of voltage stabilisers. The latest is a Servo type voltage stabiliser – that maintains Voltage of any establishment to + 1 % or so accuracies.

Earlier – 1st Stage was when – a Voltage Regulator of MANUAL ROTARY TYPE was used to adjust the voltage as is still being done on Voltage regulators for TV etc. There is ONE 4,6 or 8 POSITION rotary switch that is rotated to adjust output voltage.

In 2nd stage of this development, RELAY TYPE STABILISERS like those used with Air Conditioners etc. came in. There are Steps ( 2,3,4 or 5 ) – and we call them in the Regulating Transformers that are Switched ON and OFF to keep output voltage to say +10 % or so accuracy.

In the 3rd Stage – the Servo stabilisers came in that maintain output voltage accuracy of +1 % or so by using a Motor Driven Variable Transformer.

Similarly in Power Factor Controllers, in the 1st Stage – fixed value capacitors are added in parallel to individual motors or loads. This is a Crude method of Power Factor Correction. In the 2nd Stage – is the conventional Power Factor Controller that incorporates a Set of Discrete value capacitors that are switched ON & Off to the value required through a set of Contactors & a POWER FACTOR SENSING RELAY. This operation is similar to the Voltage Stabilisers of Air Conditioners that contains steps & cannot switch on and off the capacitors to any definite value required. The switching IN & OUT of the Capacitors is in steps of say 2 KVR or so.

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In the 3rd stage, similar to SERVO STABILISERS – there is no APFC that can continuously feed VARIABLE CAPACITANCE in the line. GREEN DOT is only ONE & ONE COMPANY in INDIA that has perfected the technology of continuously varying capacitance and has thus introduced STEP LESS POWER FACTOR CONTROLLERS.

Furthermore, the existing system has some serious disadvantages. You cannot have ideal compensation to reactive power as because of the steps only a near about compensation to Power Factor is available. The System will always be over compensated or under compensated. The degree of compensation deviates undesirably from the ideal values. When using six capacitors – the deviation could be to 1/12 of the compensate value.


  • There exists a fear of over improvement and a name is given to this as ‘power factor correction better than 0.9’. With combination of increments in sizeable capacitor steps, and abrupt full current switching, , over improvement could cause over voltages of as much as 40 % on affected power lines and subsequent damage to motor driven equipment under certain conditions of operation.
  • With every capacitive switching of capacitors, a surge or spike like, results, thus causing a perceivable flicker which is extremely detrimental to sensitive electronic switching loads connected to line. In fact - the capacitor switching is primary cause of trouble in computer receiving power from lines. True in the Capacitive switching circuits, today switching is made at ZERO VOLTAGE CROSSING, but this feature achieves a little because in capacitors, when voltage curve is at zero, the current curve is at peak and vice versa.
  • Even in the absence of Sensitive Electronic loads, the operation of contactors is a rough & violent physical action – resulting in frequently blowing of fuses. This results in watt losses & in this interim period, the kilowatt demand increases operational expenses until those fuses are replaced.
  • If the load in power lines consists of rectifiers and particularly of rectifiers with forced communication, which as it is known, it generates a substantial reactive power component, and also very substantial 5th, 7th and 11th harmonics. With rectifier transformer winding, a resonant circuit develops whose frequency closely coincides with frequency of said 5th Harmonic, making the current seriously dangerously uncontrollable.
  • The capacitors used have to be furnished with discharging resistances. When there is a power failure, a Power Disconnection or a fuse blowing and – fuses blow frequently – the circuit has no path of discharge anywhere , and without discharge resistors, the capacitors would explode at next energization, when added to existing charge. These discharge resistances have certain cost and also consume power incessantly.


The capacitors work at all time at full rated voltage and at certain switching instances the peak voltage is enhanced beyond the rated peak voltage of capacitors – which can destroy or reduce the life time of these components.

Since the switching of multiple capacitors through contactors is involved, plethora of harmonics gets introduced in the line & thereby LINE FILTERS of suitable rating have to be installed. It is like first introducing the NOISES & HARMONICS & then putting circuits & chokes to mitigate their evil effects.


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Green Dot Electric Limited has developed a Variac Based Power Factor Panel. A Motorised Variable Transformer ( the Motorised Dimmer Dot ) is used a source of Variable Voltage that is applied to the required value of Capacitance rated for 440 Volts or so. The varying voltage applied to the Fixed value capacitance-makes the Fixed value Capacitance to Continuously Variable capacitance that is used to correct the Power Factor without steps. There are no switching of Contactors or interruption of CAPACITIVE CIRCUITS and thus no harmonics get introduced. The costly harmonics filters are also avoided. In case the supply goes off & comes in – delay is provided to give time for discharge of capacitors and then to start again at zero voltage input from the Dimmer Dot. There is further advantage in our system that the power change is proportional to the square of applied voltage to the capacitors whereas by comparison to Switching In, and or out Capacitors – the affect is only to the first power of the capacitor size.

The Power Factor Sensing relay has been developed from an advanced Micro Controller that senses the existing Power Factor & rotates the Variable Transformer forward or backward – increasing or decreasing the output voltage of the Variable transformer, to provide required voltage across the capacitor so that the adjusted & the required power factor is always maintained with respect to ever varying load of the establishment. The LED Read out panel of the Relay Box reads Input Voltage & adjusted Power Factor Thus there is step less Varying capacitance that is made available to suit the varying load. There is no switching surge & Power factor is maintained accurately. There are no contactors & no complicated wiring.


Automatic Power Factor Controller 4