Title of Invention

"A REGULATOR FOR FEEDER LINES SUITABLE FOR INDUCTION MOTOR LOAD AND INDUCTION GENERATOR SOURCE"

Abstract

A regulator for feeder lines suitable for induction motor load and induction generator source characterized in that it comprises a series reactor (L1) of value 0.25 to 0.40 per unit reactance, a plurality of shunt reactors (L2.L3) having value between 0.25 to 0.40 pu, working in a closed loop with a plurality of capacitors (C1- C7) and an electronic controller wherein said shunt reactors (L2, L3) and said capacitors (C1-C7) are adapted to be switched on/off when output voltage Vo is beyon the desired normal voltage Vnom + 5% and when output voltage is less than Vnom-5%, a decoder counter is adapted to count up and switch on capacitors till Vo comes within said desired normal voltage limit, and wherein a decoder counter is adapted to count down when Vo exceeds Vnom+5% till Vo is within said desired normal voltage limited and wherein said output voltage is adapted to remain regulated within said desired normal voltage limits irrespective of input voltage variation from-30% to 20% and load variation from no load to full load.

Full Text

This invention relates to a regulator for feeder lines suitable for induction motor load and induction generator source. PRIOR ART Auto-transformer with on line static tap changer: Triacs are used for tap changing. Drawback is that it is not suitable for motor loads/inductive loads as tap changing takes at zero voltage and not zero current. Even if it was designed to change the tap at zero current, a break is expected in the current due to safety interval provided to avoid shorting of taps through commutating triacs. Also as triacs are in series and not in shunt path, it is not easy to make it fault tolerant or short circuit proof. Servo type buck/boost regulator: It gives a continuous voltage control. However, it has following deficiencies! 1. Very slow response 2. Lot of maintenance due to carbon brushes 3. Not suitable for motor loads. Constant voltage transformers Constant voltage or Ferro—resonant transformer has following deficiencies: 1. Very poor efficiency - 75 to 80V., very heavy in weight 2. Susceptible to frequency variation. Regulation becomes poor (+/-5% for +/-3%, frequency variation). 3. It is able to regulate only if load power factor is in 1-C to 0.9 lagging 4. Not suitable for motor loads due to fold back characteristics 3. Generates harmonics. Electronic type regulator with phase controlled thyristors or Triacst It also gives continuous control.However, it has following deficiencies: 1. Generates lots of current harmonics 2. It is difficult to make it short circuit proof 3. It is not good for motor loads as semiconductor device is in series path. An object of this invention is to propose a voltage regulator for feeder lines suitable for induction motor load and self excited induction generator source. Another object of this invention is to propose a voltage regulator for feeder lines suitable for induction motor load and self excited induction generator source which is fault tolerant. Vet another object of this invention is to propose a voltage regulator for feeder lines suitable for induction motor load and self excited induction generator source providing a soft start to motor loads. Further objects and advantages of this invention will be more apparent from the ensuing description. According to this invention there is provided a regulator for feeder lines suitable for induction motor load and induction generator source characterized in that it comprises a series reactor (LI) of value 0.25 to 0.40 per unit reactance, a plurality of shunt reactors (L2, L3) having value between 0.25 to 0.40 pu, working in a closed loop with a plurality of capacitors (C1-C7) and an electronic controller wherein said shunt reactors (L2, L3) and said capacitors (C1-C7) are adapted to be switched on/off when output voltage Vo is beyond the desired normal voltage Vnom ± 5% and when output voltage is less than Vnom-5%, a decode counter is adapted to count up and switch on capacitors till Vo comes within said desired normal voltage limit, and wherein a decoder counter is adapted to count down when V0 exceeds Vnom+5% till Vo is within said desired normal voltage limit and wherein said output voltage is adapted to remain regulated within said desired normal voltage limits irrespective of input voltage variation from -30% to +20% and load variation from no load to full load. The nature of the invention, its objective and further advantages residing in the same will be apparent from the following description made with reference to non-limiting exemplarly embodiments of the invention represented in the accompanying drawings: Fig. 1 circuit diagram of the regulator according to a first embodiment of the invention Fig.2 controller circuit flow diagram; Fig.3 circuit diagram of the regulator according to a second embodiment of the invention; In accordance with this invention the voltage regulator comprises a series reactor in combination with a plurality of switched reactors and capacitors working in closed loop. By way of example, the series reactor (Li ) can comprise #.375 to 0.4 per unit reactance in combination with a plurality of shunt capacitors (C1 - C7 ) each of approx. .2pu power, and •hunt reactors ( L2, L3 ) each of approx .2pu power, if switched sequentially in a voltage closed loop circuit based on output voltage sensing, regulates the output voltage within +/- 5% irrespective of input voltage variation of -30% and +205* and load variation from no load to full load independent of load power factor. By the present invention, it is possible to change number of switched capacitor or induction steps or their pu values to take care of any other combination of desired output voltage tolerances or input voltage variation limits. For voltage control (Fig.2) and soft start of induction motor, the value of series reactor can be reduced to increase starting torque if required. The capacitor and reactors may be switched by thyristors or triacs depending upon the magnitude of output voltage. If output voltage is less than desired (Vnom - 5%), a decade counter counts up and switches on the capacitors sequentially till Vo comes within the desired limit. A window generator is used for this purpose, it disenables the counting when V0 is with in window and thus output of BCD decoder gets latched. Similarly, a count down is initiated when Vo exceeds Vnom +5%. limit. When Vo is within VN+-5%, the counter rests. When VIn=Vn +/-5%. and also Vo is within limits, decoder output shall be at rest position and thus no switch shall be on. Out of decade counter is decoded by BCD decoder. BCD output is fed to triac gates using suitable logics. Opto couplers are used for isolation. Additional feature like settable initial power on delay is provided. Also gate of counting (clock signal frequency to decade counter) can be slowed down during starting giving adjustable timing for soft start for motor loads. Figure 3 illustrates a further improvement on the regulator depicted in Figure 1. In this embodimentJj capacitors instead of 7 capacitors and a permanently connected saturable reactor instead of two switchable reactors have been used. A third harmonic tuned filter (Lf, Cf) is connected to take care of harmonics generated by saturable reactor L2. A circuit breaker CB is added to enable tripping in case of faults.In the circuit given in Fig.3, the reactive currentd drawn by Cf and 12 cancel each other at V0=Vnom-5%, however, if output voltage exceeds above Vnom, the saturable reactor goes into saturable zone drawing high current, thus disallowing output voltage to rise beyond Vnom+5%. A Triac Tr5 is added across the output so that it can be triggered to protect the load in case of u/v, and earth fault. When u/v or earth fault is sensed. Tr5 is triggered, which makes approx 3 times current to flow in LI, thus tripping the breaker CB. In this configuration, the cost is reduced drastically and o/v protection is instantaneously provided by saturable reactor L2. It would be worthwhile to summarise the salient features of the Fault Tolerant L-l C Voltage Regulator according to the invention. 1. Short circuit proof, can recover from faults. Short circuit currant is limited to approx.2.5 times to 3.5 times. 2. It does not generate harmonics. 3. It can be used with motor loads, for example, a 3 KVA regulator can accommodate a 0.5 HP motor without causing much disturbance to other loads. 4. It works irrespective of load power factor - unity to 0 lagging.It is assumed that these small loads sum up to full load with a pf between 0.9 to unity. 3. It can be used as voltage regulator for induction generators. 6. It helps to overall power line regulation by supplying capacitive VAR when voltage is low and inductive VAR when voltage is high. 7. It discourages the consumers to over load the feeder,because the voltage droops steeply under overload conditions. 8. It has a very good efficiency - 97% to 99% depending on rating. The invention described hereinabove is in relation to a non-limiting embodiment and as defined by the accompanying claims. CLAIM: 1. A regulator for feeder lines suitable for induction motor load and induction generator source characterized in that it comprises a series reactor (L1) of value 0.25 to 0.40 per unit reactance, a plurality of shunt reactors (L2, L3) having value between 0.25 to 0.40 pu, working in a closed loop with a plurality of capacitors (C1-C7) and an electronic controller wherein said shunt reactors (L2, L3) and said capacitors (C1-C7) are adapted to be switched on/off when output voltage Vo is beyond the desired normal voltage Vnom ± 5% and when output voltage is less than Vnom-5%, a decoder counter is adapted to count up and switch on capacitors till Vo comes within said desired normal voltage limit, and wherein a daceder counter is adapted to count down when Vo exceeds Vnom+5% till Vo is within said desired normal voltage limit and wherein said output voltage is adapted to remain regulated within said desired normal voltage limits irrespective of input voltage variation from -30% to +20% and load variation from no load to full load. 2. A regulator as claimed in claim 1, wherein said shunt capacitors (C1-C7) have a range of 0.2 pu power (5pu impedance). 3. A regulator as claimed in claim 1 wherein said shunt reactors (L2, L3) are of 0.2 pu power (5pu impedance). 4. A regulator as claimed in claim 1 wherein the said shunt capacitors (C1 to C7) are adapted to be switched ON through triac in three steps to compensate for the voltage drop under variable loads upto full load condition. 5. A regulator as claimed in claim 1 wherein the shunt reactors (L2 , L3) are adapted to provide a limit to shunt circuit current making it fault tolerant and soft start to induction motor. 6. A regulator as claimed in claim 1 comprising a series reactor (L1), a permanently connected saturable reactor (L2); four capacitors (C1, C4) and an electronic controller, a harmonic tuned filter (Lf, Cf) which is operabiy connected to compensate harmonics generated by said saturable reactor (L2), and in that a circuit breaker (CB) is provided to the regulator to enable tripping in case of faults. 7. A regulator for feeder lines suitable for induction motor load and induction generator source as substantially herein described and illustrated with accompanying drawings.

Documents:

116-del-1996-abstract.pdf

116-del-1996-claims.pdf

116-del-1996-complete specification (granted).pdf

116-del-1996-correspondence-others.pdf

116-del-1996-correspondence-po.pdf

116-del-1996-description (complete).pdf

116-del-1996-drawings.pdf

116-del-1996-form-1.pdf

116-del-1996-form-2.pdf

116-del-1996-form-3.pdf

116-del-1996-form-4.pdf

116-del-1996-form-6.pdf

116-del-1996-gpa.pdf

116-del-1996-petition-124.pdf