US3157820A

US3157820A - Gas-filled liquid cathode elongated rectifier having condenser chamber and automatictank cooling means therefor

Info

Publication number: US3157820A
Application number: US63375A
Authority: US
Inventors: Funke Birger; Samuelsson Rune
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1959-10-28
Filing date: 1960-10-18
Publication date: 1964-11-17
Anticipated expiration: 1981-11-17
Also published as: CH379650A; GB900894A; DE1221732B

Description

Nov. 17, 1964 FUNKE ETAL 3,157,820

GAS-FILLED LIQUID CATHODE ELONGATED RECTIFIER HAVING CONDENSER CHAMBER AND AUTOMATIC TANK COOLING MEANS THEREFOR Filed Oct. 18. 1960 2 Sheets-Sheet l QirBEr FWWZ Wan E yd muE/man/ NOV. 17, 1964 N E ETAL 3,157,820

GAS-FILLED LIQUID CATHODE ELONGATED RECTIFIER HAVING CONDENSER CHAMBER AND AUTOMATIC TANK COOLING MEANS THEREFOR Filed 00'6. 18, 1960 2 Sheets-Sheet 2 INVENTORS 5096-5? Pow/v5,

BY W

ATTORNEYS .than in the other.

United States Patent The present invention relates to a method for cooling the condensing chamber of a liquid cathode rectifier, said chamber forming a preferably horizontally placed, elongated tank.

A very important factor in the operation of gas filled rectifiers, particularly mercury rectifiers for higher power, is to obtain an effective and exact cooling of the rectifier owing to the power loss of the rectifier, as it is of great importance for the normal operation of the rectifier that the temperature in the discharge chamber is kept within certain very narrow temperature limits.

When a rectifier with a plurality of anodes for high voltage was formed as an elongated cylindrical, horizontally placed tank with the anodes arranged in one or more rows on the top of the tank, as mentioned in Patent No. 2,976,440, great advantages have been obtained with regard to the cooling of the tank, as it is very easy, owing to the small diameter of the tank, to get an efiective cooling of the whole tank. Thus suitably the most simple form of cooling, i.e. air cooling, could be used, generally by means of a casing surrounding the tank and a current of cooling air, which is led through this casing longitudinally of the tank.

This form of cooling has, however, the drawback that the cooling air is heated on its way along the tank, which causes cooling of the tank to be greater in the one end If it is for instance made certain that the power loss is equal all over the tank and that the cooling surface per unit of length is constant along the tank, the increase of the temperature along the tank will be the same as the increase of the temperature of the cooling air. As the anodes are arranged in a row longitudinally of the tank, this means that the different anodes will operate under different temperature conditions. If no special measures are taken, the difference of the temperatures of the two ends of the tank can be of the same magnitude as or greater than the range of temperature within which the tank must be kept it a normal undisturbed operation of all anodes is to be maintained. The object of the present invention is therefore to obtain an equal cooling of such a tank along its whole length.

The invention is characterised in that a current of cooling air is led through a casing surrounding the tank along the surface of the tank and longitudinally thereof in such quantities and with such velocity that the increase of the temperature of the air is kept below a fixed value and that the flow of air is completely interrupted by means of a temperature sensitive organ is when the temperature of the tank has decreased to a fixed value, while the flow of air is resumed when the temperature of the tank has increased to a certain other and higher value.

The invention is thus based on the principle that the increase of the temperature of the cooling air is inversely proportional to the quantity of cooling air per unit of time,

which quantity of air, with a fixed cross-sectional area of the cooling casing, is proportional to the velocity of the air. The volume of the cooling casing and the velocity of the cooling air are so chosen according to the invention that the increase of the temperature of the cooling air, at full load of the rectifier, is kept within the allowable limits with a substantial margin of error. With a continuous current of air such cooling, however, is too efiective so that the invention, as mentioned above, comprises means for interruption or" the air flow, when the temperature of the tank has decreased to a fixed low value and resuming the flow of air when the temperature has increased to a certain other and higher value. It is important that the fiow of air is alternatively completely interrupted and resumed with full velocity, as a regulation of the velocity of the air to a low value can cause the difference of the temperatures of the two ends of the tank to be unallowably high. In this connection it is also pointed out that, with too low velocity of the air and consequently too high temperature differences, the controlling of the cooling air may be dependent on where the temperature sensitive organ is placed, in relation to the longitudinal direction of the tank, while this is of less importance, when the velocity of the cooling air is sufficiently high.

The surface of the tank may suitably be provided with cooling ribs in order to make the cooling more effective. Independent of this, however, a certain quantity of cooling air is necessary to keep the increase of the temperature of the cooling air within the allowable limits. If a calculation shows that the necessary quantity of cooling air is excessively high, the allowable increase of the temperature of the cooling air could be increased and the quantity of air thus decreased when, according to the invention, the area of the cooling ribs is graduated in such a way that this area increases in the direction of the air current, so that the transmission of air is equal longitudinally of to the tank in spite of the increase of ternperature of the cooling air.

Owing to the necessary precision of the control of the cooling air and to the low specific heat of the cooling air, e.g.' in relation to a liquid cooling medium, the temperature sensitive organ must be very sensitive and stable and have very low heat capacity.

According to the invention these demands are fulfilled by using a thermistor inserted in the control circuit of an amplifier as the temperature sensitive organ. According to the invention this amplifier is made in two stages, one of which consists of a bridge with four branches, two opposite branches consisting of non-inductive resistances and the two other opposite branches consisting of two primary windings of an isolating transformer, the secondary winding of which is connected to said thermistor.

The exciting current of the transformer is compensated by a condenser. The supply voltage is connected to one diagonal of the bridge, while the output voltage of the amplifier is taken out from the other diagonal of the bridge and connected to the other stage of the amplifier, which could be of any known kind, e.g. a transductor amplifier. 7

By regulation of the two non-inductive resistances the bridge is adjusted to a certain output voltage, at which the other stage of the amplifier is balanced and which corresponds to a certain temperature of the rectifier tank. A change of this temperature causes a change of the resistance of the thermistor, which influences the resistance of the two primary windings, so that the potentials of the two output terminals of the bridge are changed in opposite directions and cause a change of the output voltage of the bridge.

The invention is described in the following with reference to the attached drawing which shows schematically a cooling system according to the invention for a rectifier with four anodes.

FIGURE 1 shows a complete condenser cooling system;

FIGURE 2 is a side elevation, particularly of the rectifier;

FIGURE 3 is an elevational view from the right hand end of FIGURE 2; and

FIGURE 4 is a cross section on the line 4-4 of FIG- URE 2.

FIGURE 1 shows a rectifier 1 with four anodes. The discharge tank is placed in a cooling casing 2, through which the cooling air is led by means of a fan 3 arranged at the one end of the tank. The cooling air through the cooling casing is controlled by means of a damper 4 arranged at the other end of the tank. The volume of the cooling casing and the effect of the fan is, as mentioned above, so dimensioned that the temperature difierence between the two ends of the tank is kept within certain limits with a continuous current of air and full load on the rectifier. The limitation of the cooling by interruption of the air current, is caused by means of the damper 4, which is controlled by means of a temperature sensitive organ, in this case a thermistor 5. The thermistor 5 is inserted in the control circuit of a two-stage-amplifier, in which the first stage consists of a bridge 6 with four branches. Two opposite branches in this bridge consist of two primary windings 7 and 8 of an isolating transformer 10. One of the primary windings 7 is connected in parallel with a capacitor 11. This capacitor compensates the reactive power of the transformer and could thus also have been connected over the secondary winding 9. The two other opposite branches in the bridge consist of two non-inductive resistances 13 and -14. The control circuit consists, as shown, of the secondary winding 9 of the isolating transformer 10 in series with the thermistor 5. The supply voltage of the bridge is connected over one diagonal of the bridge, namely at the points and 16. The supply voltage is an alternating voltage, which is taken from a secondary winding 21 on a transformer 20. The output voltage is taken from the other diagonal of the bridge 6, namely from the points 17 and 18. The setting of the damper 4 is produced by means of a two-phase motor 30. The supply current to the motor 30 is derived from a secondary winding 23 on the transformer via two equal transductors 25 and 25, which form the other stage of the amplifier, each of them being auto self-excited. Further the transductors are excited by two windings 26 and 27 by a direct current derived from a secondary winding 22 of the transformer 20 via a rectifier 24. The current of the two exciting windings 26 and 27 is controlled by means of

variable resistors

28 and 29. The transductors 25 and 25 and thus the motor 39 are controlled by means of the two

exciting windings

31 and 32, which are fed from the output voltage of the bridge 6 via the rectifier 33. The

exciting windings

31 and 32 are counter-acting in such a way that an increase of the current from the rectifier 33 through both the

exciting windings

31 and 32 will increase the inductance of one of the transductors and decrease the inductance of the other one, while a decrease of the current has the opposite result.

The thermistor 5 is placed at the middle of the discharge tank, the device operating in the following way:

At the desired temperature of the discharge tank the resistances 13 and 14 are adjusted in relation to each other in the same way and in relation to the resistances of the other branches of the bridge in such a way that they take up nearly half of the feeding voltage. This means that the bridge is biased to a certain degree, so that a certain output voltage is obtained from the terminals 17 and 18.

Owing to the fact that the bridge is fed with alternating current, the same output voltage is obtained at another adjustment, namely symmetrically .to the first adjustment in relation to the balancing point. The operation point for the bridge is therefore so chosen that this other point is not obtained at temperatures actually reached in operation.

The output voltage from the bridge 6 feeds the

exciting windings

31 and 32 of the transductors 25 and 25', via a rectifier 33. These windings are so connected that the two transductors are excited in opposite directions.

At the proper temperature of the rectifier tank the current in the

control windings

31 and 32 is compensated by the exciting current in the windings 26 and 27, respectively so that the two transductors are choked and take up practically all the voltage from the winding 23 of the transformer 20. The motor is then at a standstill.

If the temperature of the rectifier tank is changed, the resistance of the thermistor is also changed, so that the resistance of the windings 7 and 8 of the isolating transformer 10 is changed. Owing to this the biasing of the bridge 6 is changed, so that the potentials of the points 17 and 13 are changed in opposite directions.

The current in the

control windings

31 and 32 is then also changed so that the inductance of one of the transductors is increased, while the inductance of the other transductor is decreased, so that this transductor feeds the motor 39 in such a way that one of the motor windings is fed directly while the other winding is fed via the condenser 34, so that the current in said last mentioned winding is displaced in phase in relation to the current in the directly fed winding. The motor will thus have a torsion moment and open the damper if the temperature is too high. If the temperature of the tank is too low, the current in the

windings

31 and 32 is changed in the opposite directions and the transductors will operate in the opposite directions.

The winding of the motor, which was fed directly, is now fed by the condenser 34, while the other winding is directly fed. The motor will thus rotate in opposite direction and close the damper. Thus the damper will be fully opened or fully closed, when the temperature increases or decreases too much.

FIGURES 2 to 4 show the rectifier 1 comprising the cooling case 2 with the discharge tank 12 inside it. The rectifier is provided with four anodes and a cathode 36. The discharge tank is provided with cooling ribs 37. In FIGURE 2 these cooling ribs are shown graduated longitudinally of the rectifier tank so that the cooling area of the ribs increases in the direction of the cooling air. By this means the increase of the temperature of the cooling air may have a higher value so that the velocity of the air current can be lower and thus a smaller fan can be used.

\Ve claim as our invention:

1. In a liquid cathode rectifier having a condensing chamber, said chamber comprising a horizontally placed elongated tank; means for cooling said tank comprising a cooling casing surrounding said tank, a fan driving a current of cooling air through said cooling casing along the surface of the tank and longitudinally thereof in such quantities that the increase of the temperature of the air is kept below a fixed value; a damper controlling the current of air, and means operatively connected to said damper and responsive to the temperature of the tank to close the damper fully when the temperature of the tank increases to a certain other and higher value; cooling ribs arranged on the surface of said tank, the cooling area of said ribs increasing in the direction of the current of cooling air.

2. Means for cooling the condensing chamber of a liquid cathode rectifier, said chamber comprising a horizontally placed elongated tank, said means comprising a cooling casing surrounding said tank, a fan driving a current of cooling air through said cooling casing along the surface of the tank and longitudinally thereof in such quantities that the increase of the temperature of the air is kept below a fixed value, a damper controlling the current of air and means operatively connected to the damper and responsive to the temperature of the tank for closing the damper completely when the temperature of the tank decreases to a fixed value, and for fully opening the damper when the temperature of the tank increases to a certain other and higher value.

3. In a liquid cathode rectifier having a condenser chamber forming a horizontally placed elongated tank; means for cooling said tank comprising a cooling casing surrounding said tank, a fan driving cooling air through said cooling casing along the surface of the tank and longitudinally thereof in such quantities that the increase of the temperature of the air is kept below a fixed value; a damper controlling the current of air, means operatively connected to the damper and responsive to the temperature of said tank to close said damper completely when the temperature of the tank decreases to a fixed value and to open the damper fully when the temperature of the tank increases to a certain other and higher value; said temperature-dependent means including a device sensitive to the temperature of the tank, said device constituting an amplifier, a thermistor in the control circuit of said amplifier, said amplifier opening and closing said damper; said amplifier comprising an insulating transformer and a bridge having four branches, two opposite branches consisting of non-inductive resistances, the two other opposite branches consisting of two primary windings of said insulating transformer; the secondary winding of said transformer in series with said thermistor forming the control circuit of said amplifier, a capacitor compensating the reactance of said secondary winding, a supply voltage of said bridge being connected to the one diagonal of the bridge, the output voltage of the amplifier coming from the other diagonal of the bridge.

4. In a liquid cathode rectifier having a condensing chamber, said chamber comprising a horizontally placed elongated tank; means for cooling said tank comprising a cooling casing surrounding said tank, a fan driving a current of cooling air through said cooling casing along the surface of said tank and longitudinally thereof in such quantities that the increase of the temperature of the air is kept below a fixed value; a damper controlling the current of air operatively connected to said damper, an amplifier; said amplifier having a control circuit, a thermistor in said control circuit, said amplifier controlling said damper in such a way that the damper is fully closed when the temperature of the tank decreases to a fixed value, while the damper is fully opened when the temperature of the tank increases to a certain other and higher value.

References Cited by the Examiner UNITED STATES PATENTS 2,022,644 12/35 Ashcraft 3l324 X 2,171,930 9/39 Gerecke 3l324 X 2,873,954 2/59 Protze 3l324 X GEORGE N. WESTBY, Primary Examiner,

RALPH G. NILSON, DAVID J. GALVIN, Examiners.