US3873807A

US3873807A - Power modulating arrangement for electric fluid heating apparatus

Info

Publication number: US3873807A
Application number: US321345A
Authority: US
Inventors: Glenn R Mohr
Original assignee: MOHR BAKER CO
Current assignee: MOHR BAKER CO
Priority date: 1972-10-25
Filing date: 1973-01-04
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25

Abstract

An apparatus and system for converting electrical energy to heat energy within a fluid conducting medium. A transformer means has its primary windings connected in series with a source and heating elements in the fluid medium while the secondary winding is also connected in series with heating elements in the same or another fluid medium. Each heating element may comprise two sets of electrodes, one of which is connected to a return line. By varying the effective area, distance and voltage between the sets of electrodes of the secondary winding or both sets of electrodes, the resistance through the fluid medium is varied to control the energy utilized from a minimum core magnetizing energy level to approximately four times the power rating of the transformer. Preferably, a 3 phase source delivers energy to a 3 phase transformer or 3 single phase transformers.

Description

United States Patent [1 1 Mohr [54] POWER MODULATING ARRANGEMENT FOR ELECTRIC FLUID HEATING APPARATUS [75] Inventor: Glenn R. Mohr, Linthicum, Md.

[73] Assignee: Mohr-Baker C0., West Chicago, 111. [22] Filed: Jan. 4, 1973 [21] Appl. No.: 321,345

Related US. Application Data [63] Continuation-in-part of Ser. No. 300,711, Oct. 25,

1972, abandoned.

[52] US. Cl 219/285, 13/23, 219/272,

219/288, 219/290, 219/295, 219/503, 323/85 [51] Int. Cl. 1105b 3/60, H05b 1/02 [58] Field of Search 2l9/27l276,

2 g 16 g E 1 a 20 g 1 T [451 Mar. 25, 1975 Williams 323/85 X Tanaka 219/295 X [57] ABSTRACT An apparatus and system for converting electrical energy to heat energy within a fluid conducting medium. A transformer means has its primary windings connected in series with a source and heating elements in the fluid medium while the secondary winding is also connected in series with heating elements in the same or another fluid medium. Each heating element may comprise two sets of electrodes, one of which is connected to a return line. By varying the effective area, distance and voltage between the sets of electrodes of the secondary winding or both sets of electrodes, the resistance through the fluid medium is varied to control the energy utilized from a minimum core magnetizing energy level to approximately four times the power rating of the transformer. Preferably, a 3 phase source delivers energy to a 3 phase transformer or 3 single phase transformers.

11 Claims, 8 Drawing Figures PATENTEDHARZSISYS sum 2 0r 3 Pmmmnmzsnws sum 3 5 73 FIG FIG.5

II lllllfli. 9L

"6 RESTRICTOR POWER MODULATING ARRANGEMENT FOR ELECTRIC FLUID HEATING APPARATUS CROSS-REFERENCE This application is a continuation-in-part of Application Ser. No. 300,711 filed Oct. 25, 1972, now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a system and apparatus for converting electrical energy into heat energy. More specifically, it relates primarily to a system and apparatus for heating water and other liquids to meet the needs of commercial buildings or industrial facilities. Such needs may relate to the usage of the fluid or the mere storage of heat energy for subsequent use.

Currently available electrical heating systems require switchgear to switch the system on and off the line as dictated by the temperature of the liquid or other control parameters. Additionally, they need protective devices which limit the amount of current which can be drawn in the event of a short circuit. Finally, available systems have limited control ranges and do not permit the desired variation in power utilization by the system.

An optimum electrical heating system would have the following desirable features:

I. An inherent current limiting feature which avoids the use of auxiliary protective devices. Such would be of substantial benefit for use in areas subject to brownout conditions;

2. A capability to remain on the line at all times regardless of the control parameters, thus eliminating the need for switch gear;

3. A capability to vary the power drawn and the voltage across the heating elements from a minimum to full load condition in a continuous manner; 4. An ability to be integrated with the customers other energy systems so as to reduce the peak demand requirement and to utilize the energy for heating purposes during periods of small demand by such other systems;

5. Optimum utilization of generating equipment obtained through heating with off peak power and subsequent use of stored heat energy during peak power periods.

Finally, other considerations require that a heating system have a good wave form to prevent radiation and interference with instrumentation and television reception, be of relatively low cost and simplicity of design.

SUMMARY OF THE INVENTION In order to obtain these desirable features, the instant invention includes a control, preheater tank and a transformer which, in combination, act as a modulator for a load tank. In the preferred embodiments, a three phase transformer is adapted to be connected to a power supply with the primary and secondary windings being connected in series to heating elements within a fluid conducting medium and then to return or neutral conductor. The heating elements may comprise pairs of electrode sets within fluidtanks. Means are provided for varying'the voltage and current flow between the electrode sets in series with the secondary winding so as to modulate power delivered to the load tank. Such means may include a motor which provides relative movement between the electrode sets to vary the distance and effective area between them. Alternatively,

a flow control system which increases or decreases the extent to which the conducting fluid medium surrounds the electrodes and establishes load resistance may be used.

Accordingly, it is a primary object of this invention to provide a most desirable system and apparatus for converting electrical energy to heat energy. An important object of this invention relates to the control of power utilization from a minimum core magnetizing requirement of the transformer to approximately four times its rated load in a continuous manner. Another object is to provide a heating system in which energy utilized for the heating of liquids can becorrelated with other power demands so as to minimize thepeak demand of the installation and the use of higher cost energy. Too, it is an object of this invention to provide a heating circuit which has an inherent current limiting feature and eliminates the need for switching devices. Another object of my invention is to obtain all of the other desirable features previously mentioned such as a good output wave form. Finally, it is an object of my invention to provide and electrical control circuit which can vary the voltage and current delivered to other loads in any circuit.

DESCRIPTION OF THE DRAWINGS The manner in which these and other objects of the invention can be obtained can be better understood with reference to the following specifications and drawings in which:

FIG. 1 is a circuit diagram of a preferred embodiment of my invention;

FIG. 2 is a side elevation view of a preferred embodiment of the heating apparatus of my invention; and

FIG. 3 is a side elevation view taken along the lines 3-3 of FIG. 2;

FIG. 4 is a graphical illustation of typical current, voltage, and power relations of my invention over its control range;

FIG. 5 is a circuit diagram of another preferred embodiment of my invention;

FIG. 6 is a circuit diagram of another preferred embodiment of my invention;

FIG. 7 is a schematic view of another preferred embodiment of my invention; and

FIG. 8 is a plan view taken along the lines 8-8 of FIG. 7.

DETAIL DESCRIPTION A preferred embodiment of the heating apparatus of my invention is illustrated in FIG. 1. Preferably, an electrical circuit is adapted for connection to a three phase supply through

lines

12, 13 and 14, which, in turn are connected in series to the

primary windings

16, 17 and 18 of three transformers or a single three phase transformer 15. Placed in series with each of these primary windings are, preferably, balanced

variable loads

24, 26 and 28 in a wye-wye connection, the center of which is grounded as indicated. The loads (referred to herein as the primary load) may take the form of heating elements within a liquid container 23 which will be discussed with reference to FIGS. 2 and 3 herein.

FIG. 1 also discloses that the

secondary windings

19, 20 and 21 are connected in series to, preferably, balanced

variable loads

30, 32 and 34; the secondary circuits being completed by the ground connections as indicated. These loads (herein referred to as control 3 loads) may also take the form of heating elements within a liquid container 29 which is similar in construction to the container 23 connected to the primary windings.

The variable loads 30, 32 and 34 of the secondary circuit and preferably those of the primary circuit '(24, 26 and 28) may be controlled through a motorM having mechanical linkages to each variable load or resistance as indicated by dotted lines. In turn, the motor M may be actuated by various control circuitry. Preferably, the user will correlate the loads attached to the heating apparatus with other loads which have a priority. For example, a users priority loads may comprise lighting, elevators, or manufacturing equipment while the loads related to my circuit comprise a water heater system. Accordingly, the power demand of the priority loads can be measured by a toroid which senses current flow in the priority load circuit. The magnitude of this power demand can be transmitted to a control panel 36 which may include a comparator to activate motor M to vary the impedance of the primary load in an inverse manner to those priority loads. Obviously, a temperature measuring device may also be connected to the control panel to limit or obtain control of the temperature of the fluid medium. As will be shown, the control load 29 in the form of a preheater tank in conjunction with the transformer comprises a modulator for the load tank 23.

This modulator and heating system provides excellent operating characteristics when utilized with a liquid heating apparatus depicted in FIGS. 2 and 3. Preferably, two water heater tanks 23 and 29 (FIG. 1) are utilized, one associated with the primary windings, and another associated with the secondary windings. Since the construction of these tanks can be identical, only the container 29 associated with the

secondary windings

19, and 21 will be discussed.

l The container 29 may comprise an annular upstanding cylinder 64 having a bottom closure 62 and a top closure 66 as indicated. A waterof liquid supply port 68 delivers a conducting liquid to the tank 29 so as to provide sufficient fluid pressure to outlet conduit 70 upon demand. Variable loads 30, 32 and 34 have movable components carriedby an upstanding center post 72 and fixed components which are supported by the side wall 64 of the tank 29.

Considering variable load or heating element 30, such comprises a set of electrodes 86, connected in parallel and carried by a fixed insulating unit 84 which is supported by the sidewall 64 through supports 82. As indicated, this electrode set is connected in series to the secondary winding through a conductor 90. The insulating unit 84 may comprise an are shaped upstanding wall with flanges 85 at its upper and lower ends for supporting the electrodes. Too, flanges 87 are provided at each end of the arc to minimize undesired current flow through the conducting liquid to one of the other variable loads which might otherwise occur due to the phase relation of the three loads.

Heating element 30 also comprises a second set of electrodes 79 connected in parallel and carried by an insulating unit 76 which is rotatably supported on the control post 72 through arms 74. The insulating unit 76 also has an are shaped upstanding wall with flanges 78 at the'top and bottom as indicated to support the electrodes 79 while each end has a flanges 77 adjacent flanges 87 of insulator 84 to minimize undesirable current flow to one of the other loads. The electrode set 79 is then connected in series to the center post 72 by conduit 93 which is grounded. The remaining

variable loads

32 and 34 are of similar construction.

Being supported above the center post 72 which is appropriately journaled at the top and bottom of the tank as indicated, the motor M can rotate the shaft 72 and the electrode sets 79 into and out of juxtaposition with the fixed electrode sets 86. Thus, if the shaft is rotated from the full line position to the dotted line position by the motor M, the electrode set 79 will be out of juxtaposition with electrode set 86 and adjacent insulators 88 which are similar to insulators 84, but have no electrodes therein.

The described arrangement of the

heating elements

30, 32 and 34 is one form of a modulator which permits the desired control of current flow and power usage in both the control tank or load and the primary tank or load. The current flow in the conducting medium is a function of voltage, the conductivity of the liquid, the length of the current path and its cross sectional area. Asshownby the full line position of FIG. 3, the length of the current path is a minimum while the area approaches that of the cross sectional area of the electrodes. Thus, maximum current flow is permitted. However, in the dotted line position, the distance of the current path is maximized. Too, the cross sectional area is a minimum since it only consists of the gaps between the top and side flanges of the insulating units. In this position, current flow is a minimum. The gap between the top and bottom flanges should be wide enough to permit circulation of the fluid and to preclude the development of steam due to a current flow in a narrow path. Too, the center post 72 might be insulated to preclude current flow from the electrodes 86 to the center post.

MODE OF OPERATION Assuming that the control circuit is connected to

water heater tanks

29 and 23 such as that depicted in FIGS. 2 and 3, the primary and secondary windings are connected to the heating elements which form the primary and control variable loads. If the electrode sets 79 mounted upon the rotational shaft 72 are in the dotted line position in which they are separated from the op-. posing set of electrodes 86 the largest possible distance and are further insulated by insulators 88, the loads of both the primary and secondary windings will have a large impedance and, depending upon the conductance of the water, little current is drawn from the power supply. In effect, the high impedance appears as an open circuit to the

secondary windings

19, 20, 21 and in view of this no-load condition, only magnetizing current can flow in the

primary windings

16, 17 and 18 due to their counter EMF. This condition can be visualized in FIG. 4 in which current, voltage and KVA is illustrated on the vertical axis with the control resistance being illustrated from maximum to minimum logarithmically on the horizontal axis. With the maximum impedance in the control circuit, the control voltage is high and control current is a minimum. Under these conditions, the voltage drop in the primary circuit occurs across the

primary coils

16, 17 and 18 with minimum voltage drop existing across the

variable loads

24, 26 and 28.

However, as the motor M rotates the electrode sets 79 to the full line position of FIG. 3, the impedance of the control loads 30, 32 and 34 is reduced and current is permitted to flow in the secondary. This current flow in the

secondary windings

19, and 21 tends to magnetize the transformer core in a direction opposing the magnetizing action of the primary current, and permits current to increase. Thus, if the control electrodes 79 are rotated to the full line position, the impedance in the secondary loads is a minimum as shown by FIG. 4. At this position, current of both the primary and secondary currents increases to a maximum while the voltage of the

loads

24, 26 and 28 of the primary tanks is a maximum. Under this condition, maximum KVA is drawn and converted to heat energy. Between the positions, the load KVA may be continuously increased or decreased as indicated by the load curve.

To control the position of the electrode sets, the control panel may be connected to a motor on each of the

tanks

23 and 29, or only a single motor might be utilized with a mechanical interconnection there between. Alternatively, both the control loads and the primary loads can be placed in the same tank with appropriate insulation. The control panel can be utilized only in conjunction with a thermostat so as to maintain a constant water temperature, but preferably it should be interconnected with the other circuits of the facility so as to correlate the use of power for heating in an inverse relation to the power requirements of the other circuits. A fluid connection between the control tank 29 and the primary tank 23 will permit the control tank to act as a pre-heater.

Considering the function of this heating apparatus, it is apparent that the transformer is utilized only to provide impedance for controlling the power drawn from the line, and the variable loads provide continuous current control from a minimum core magnetizing current to its maximum. The power control range can be 30:l or larger. With the embodiment of FIG. 1, the KVA of the secondary windings will not exceed A of the KVA of the sum of the loads connected to the primary winding. This permits the use of a transformer for control purposes which has a KVA rating of only A that of the load. Too, due to the smaller KVA rating of the transformer, the circuits short circuit protection is increased due to its higher impedance. Obviously, such protection is inherent in the proposed system since the coils are in series with the loads. Finally, the use of this control circuit and the control loads can be used in connection with other loads, such as machine tools, etc. to vary the current, voltage and power directed thereto.

ALTERNATIVE EMBODIMENTS An alternative embodiment which is within the scope of my invention includes the connection of both the primary and secondary windings to the power source as shown in FIG. 5. Under these circumstances, both the primary and secondary will form a phase shifting network such that the voltage across the windings can be varied from near zero to approximately twice the line voltage while load currents can be varied over a wide range. Additionally, a delta connection for the loads is included within my invention. Too, as shown in FIG. 6, the heating elements of the load tank 23 may be fixed loads or resistances 24', 26' and 28. Otherwise this embodiment has the structure similar to that of FIG. 2.

Another embodiment of my invention is depicted in FIGS. 7 and 8 in which the control and

load tanks

29 and 23 each have three heating elements and are connected to the primary and secondary windings of the circuit of FIGS. 1 or 5 as previously discussed. However, the heating elements of each tank comprise fixed

electrodes

104 and 106 supported by insulation 100. Instead of varying the voltage in the control tank by relative movement of the sets of electrodes, control is effected by a fluid control system. Here the effective current path between the

electrodes

104 and 106 of the control tank is varied by controlling the water level within tank 29. Such a fluid system may take various forms, but as depicted, it includes a pump Pl delivering fluid from a sump S through a conduit 120 to the load tank 23. A conduit 112 interconnects the load tank 23 with control tank 29, and flow to tank 29 is controlled by a thermostatic valve 114 which closes as the temperature of the fluid in the load tank 23 rises. A second pump P2 within a conduit also interconnects

tanks

23 and 29 and is utilized to remove fluid from tank 29. Preferably pump P2 has a smaller gallon per minute (GPM) flow capacity than the valve 114 when the latter is fully open. Thuse, when the fluid is below the desired temperature, valve 114 will open and the fluid level within tank 29 rises, increasing the effective cur rent path and current flow in the primary windings l6, l7 and 18 connected to the electrodes of the load tank 23. As temperature increases, the valve 114 closes, and the pump P2 will empty tank 29 decreasing the effective current path between the electrode and the current through the

primary windings

16, 17 and 18.

If the pump P2 is ofa fixed displacement, a restrictor 116 may be placed in parallel with valve 114 to insure some fluid flows through the pump for lubrication. Alternatively, the pump P2 may be of variable displacement and controlled by a control panel in accord with the desired parameters. A conduit 124 is used to deliver fluid from the load tank 23 and safety overload valves may be used to insure that tank 29 can be emptied without exceeding the volumetric capacity of tank 23.

Obviously, the flow control system between

tanks

23 and 29 of FIGS. 7 and 8 may take many forms, but one important aspect of this embodiment is the construction of a modulator comprising the secondary windings of the

transformer

19, 20 and 21 and a control tank 29 in which the control voltage and amperage is varied by changing the fluid level within the tank.

Other means of forming the modulator is to utilize heating elements in which one set of electrodes elements are moved in and out the tank or by inserting insulation between them.

Accordingly, applicant has disclosed a fluid heating system and a modulator thereof which has a very large turndown ratio, and provides the various desired characteristics previously described.

I claim:

1. An apparatus for heating fluids comprising:

A. Fluid container means adapted to receive electrically conductive fluid;

B. Transformer means adapted to be connected to a source of alternating current and having primary and secondary winding means;

C. A first pair of spaced electrode means carried by said container means and connected in series with said primary winding means and adapted to be immersed in said conductive fluid received in said container;

D. A second pair of spaced electrode means carried by said container means and connected in series with said secondary winding means and adapted to be immersed in said conductive fluid received in said container; and

- E. Means for varying the impedance between said second pair of electrode means for controlling the energy delivered to said fluid within the container means.

2. An apparatus as recited in claim 1 including:

A. Means for varying the impedance between said first pair of electrode means.

3. An apparatus as recited in claim 1 in which the means for varying the impedance between said second electrode means comprises:

A. Means for obtaining relative movement between the members of said second electrode means so as to vary the effective length and area of the current path.

4. An apparatus for heating fluids comprising:

A. Fluid container means;

B. Transformer means having primary and secondary windings, said primary windings adapted to be connected to a source of alternating current;

C. Heating means carried by said container means for heating an electrically conductive fluid received in the container means and connected in series with one of said windings;

D. Modulating means connected in series with said other winding and including variable impedance electrode means within said container means immersed in said conductive fluid for modulating the energy directed to the heating means.

5. An apparatus as recited in claim 4 in which:

A. Said modulating means includes control means for varying the impedance between said electrode means so as to modulate the energy directed to the electrode means and heating means connected to said windings.

6. An apparatus as recited in claim 5 in which:

A. Said container means comprises two separate containers, one carrying said electrode means and another carrying said heating means.

7. An apparatus as recited in claim 5 in which:

A. Said transformer means is a three phase transformer; and

B. Said variable electrode means and said heating means each include three pairs of electrode means.

8. A power control circuit comprising:

A. A transformer having a core with primary and secondary windings, said transformer adapted for connection to a power source;

B. Said primary windings being connected to heating elements within a fluid medium;

C. Said secondary windings being connected to other heating elements within a fluid medium;

D. Means for varying the impedance of said heating elements connected to said secondary windings whereby the power utilized by said load is continuously variable from a minimum core magnetizing power level to the maximum power loading of the source by varying the impedance of said variable load.

9. A modulating system for a fluid heater comprising:

A. Fluid container means having heating elements therein;

B. A transformer having a first set of windings adapted for connection to an alternating power source and in series with some of the heating elements in said fluid container. and a second set of windings connected in series with others of the heating elements in the fluid container means; means establishing an effective current path between the heating elements connected in series with said first set of windings and between the heating elements connected to the second set of windings;

C. Means for varying the impedance of the respective effective current paths between the heating elements within the fluid container means.

10. An apparatus as recited in claim 9 in which:

A. The means for establishing the current paths between the respective heating elements includes an electrically conductive fluid in which the heating elements are immersed;

' B. The means for varying the effective current path comprises fluid flow control system for regulating the quantity of fluid which forms a current path between the heating elements.

11. An apparatus as recited in claim 9 in which:

A. The means for varying the effective current path comprises means for obtaining relative movement between the heating elements connected to the respective winding sets.

Claims

1. An apparatus for heating fluids comprising: A. Fluid container means adapted to receive electrically conductive fluid; B. Transformer means adapted to be connected to a source of alternating current and having primary and secondary winding means; C. A first pair of spaced electrode means carried by said container means and connected in series with said primary winding means and adapted to be immersed in said conductive fluid received in said container; D. A second pair of spaced electrode means carried by said container means and connected in series with said secondary winding means and adapted to be immersed in said conductive fluid received in said container; and E. Means for varying the impedance between said second pair of electrode means for controlling the energy delivered to said fluid within the container means.

2. An apparatus as recited in claim 1 including: A. Means for varying the impedance between said first pair of electrode means.

3. An apparatus as recited in claim 1 in which the means for varying the impedance between said second electrode means comprises: A. Means for obtaining relative movement between the members of said second electrode means so as to vary the effective length and area of the current path.

4. An apparatus for heating fluids comprising: A. Fluid container means; B. Transformer means having primary and secondary windings, said primary windings adapted to be connected to a source of alternating current; C. Heating means carried by said container means for heating an electrically conductive fluid received in the container means and connected in series with one of said windings; D. Modulating means connected in series with said other winding and including variable impedance electrode means within said container means immersed in said conductive fluid for modulating the energy directed to the heating means.

5. An apparatus as recited in claim 4 in which: A. Said modulating means includes control means for varying the impedance between said electrode means so as to modulate the energy directed to the electrode means and heating means connected to said windings.

6. An apparatus as recited in claim 5 in which: A. Said container means comprises two separate containers, one carrying said electrode means and another carrying said heating means.

7. An apparatus as recited in claim 5 in which: A. Said transformer means is a three phase transformer; and B. Said variable electrode means and said heating means each include three pairs of electrode means.

8. A power control circuit comprising: A. A transformer having a core with primary and secondary windings, said transformer adapted for connection to a power source; B. Said primary windings being connected to heating elements within a fluiD medium; C. Said secondary windings being connected to other heating elements within a fluid medium; D. Means for varying the impedance of said heating elements connected to said secondary windings whereby the power utilized by said load is continuously variable from a minimum core magnetizing power level to the maximum power loading of the source by varying the impedance of said variable load.

9. A modulating system for a fluid heater comprising: A. Fluid container means having heating elements therein; B. A transformer having a first set of windings adapted for connection to an alternating power source and in series with some of the heating elements in said fluid container, and a second set of windings connected in series with others of the heating elements in the fluid container means; means establishing an effective current path between the heating elements connected in series with said first set of windings and between the heating elements connected to the second set of windings; C. Means for varying the impedance of the respective effective current paths between the heating elements within the fluid container means.

10. An apparatus as recited in claim 9 in which: A. The means for establishing the current paths between the respective heating elements includes an electrically conductive fluid in which the heating elements are immersed; B. The means for varying the effective current path comprises fluid flow control system for regulating the quantity of fluid which forms a current path between the heating elements.

11. An apparatus as recited in claim 9 in which: A. The means for varying the effective current path comprises means for obtaining relative movement between the heating elements connected to the respective winding sets.