US1760064A - Safety device for electric heaters - Google Patents

Description

May 27, 1930. L. P. HYNES ,7

SAFETY DEVICE FOR ELECTRIC HEATERS Filed May 9, 1923 4000 -OHMS Q gvvucutoz LEE P. HYNE5 9.51 1 1% lbtmm Patented May 27, 1930 warren sTATns PATENT err-ice LEE 2. 8, Oi ALBANY, NEW YORK, ASSIGNOR, BY MESNE ASSIGNMENTS, TO CON- SOLIDATBD CAB-HEATING COMPANY, INC., OF ALBANY, NEW YORK, A CORPORATION or nnwxonx ear-1m! nnvrcr. ron nrnc'rnrc rmArnns Application med May 9, 1923. Serial No. 37,843.

For a detailed description of the present form of my invention, reference may be had to the following specification and to the ac.- companying drawing forming a part thereof.

My invention relates to safety devices for electric heaters and is illustrated by the accompanying drawing.

It is customary in electric railway cars, because of the voltage used, to place the several heaters in the car in series and to rely on a fuse to protect the heater circuit. The most common accidents are the breaking of a heater coil, a loose connection, or the insertion of a foreign piece of metal or wire. These and other causes occasion a grounding of the heater circuit at some point along its length. This will short circuit one or more of the series of heaters and cause an abnormal How of current in those which are not short circuited. Even if it occurs near the ground, it may not seriously overload the heaters but is likely to cause flashing to the case with danger to passengers and the car. Hence it is uncertain whether, in the case of accident, there will or will not be a suiiicient amount of current in the heater circuit to blow the fuse, while it is also necessary to allow a considerable margin in fusing on' account of the high temperature coeflicient on some of the heater elements now used. For this reason fuses have become an inadequate means of protection for electric heaters, while other protective devices, dependent on the rise in current value, are sub ect to similar uncertainties. In addition, there is such a variety of amperage in difierent heater circuits that it would take careful figuring to get the right setting on such a device for different installations and for difierent circuits in any one installation,

and it is also quite possible that a broken wire near ,the ground would reduce an are which would even decrease rat er than increase the am erage.

o overcome these dilficulties, I have devised a protector dependent on the differential magnetic action of coils located at the respective nds of the heater circuit. By this means any difference in the amperage at the opposite ends of that circuit, regardless of what the total amperage may be, will serve to set in action some appropriate cut-out agency that will break the heater circuit. I prefer to utilize as such a cutting-out agency the automatic switch that is dominated by the car thermostat in maintaining a given temperature in the car.

Referring to the drawing, the members 1 to 8 indicate eight electric heaters connected in series in the heater circuit a which goes from trolley T by way of blow-out coil 14, switch M to ground at G. Before this circuit reaches the heaters, after passing through the usual fuse 18, it passes through a magnet coil X and after it leaves the heaters it passes through the magnet coil Y which is wound on the same core as coil X but in the opposite direction. Coils X and Y' are wound'of large wire that will carry the heater current continuously without heating. So long as the heatin circuit is intactthe same current will pass t rough both coils, which will neutralize each other and the magnet will remain inactive. If, however, there should be an accidental ground on the circuit-say at the point Z-a greater or less portion of the current-would be diverted from coil Y which would then be overpowered by coil X. The magnet would then be energized and attract its armature C. Also if an accidental connection should be established between the terminals of coil X it would cause coil Y to act, While an accidental short-circuiting of both coils wculd he certain to blow the fuse. In either event the heaters would be cut oil.

M is the main switch for the heater circuit and is operated automatically by the thermostat D. The switch is held open by a retracting spring H so long as the car is heated to the predetermined degree, but is automatically closed when the temperature falls below that de ree. From the trolley T a shunt circuit d of about 4000 ohms, assumin that the trolley voltage is about 550, to the ranchin point W. Thence a'branch da goes throug magnet K, of about 900 ohms resistance to ground at 9 and a second branch db goes through thermostat D to ground atlO. The ther mostat is preferably of the mercury type and when the temperature is up it closes branch circuit db and thereby short-circuits magnet K which allows that magnet to release'its armature and open switch M. When the temperature is down the thermostat breaks branch circuit db, thereby removing the short circuit from magnet K. The magnet is thereby energized and attracts its armature closing the heater switch M. To this arrangement, which is old and well known, I add a third branch circuit dc which is controlled by the aforesaid differential action of the coils X and Y in a way like to the control of the branch circuit db by the thermostat D. The core on which coils X and Y are wound is provided with an armature C, which projects under the lower end of a rod P which is pressed down by a spring Q. The upper end of P bears agalnst the outer end of a latch R which engages a shoulder on the indicator lever S and locks it against the rotating force of a spring J. The lever S is grounded, the ground connection being indicated at 8.-

Assumin that the equality of ma netizing effect of 001 s X and Y is disturbed y an accidental ground on the heater circuit as above described, one of the two coils will preponderate and energize the core. The armature C will then be attracted, lifting rod P, tripping latch R and allowin lever S to rotate into contact with a stop which constitutes the terminal of the aforesaid branch circuit dc. The result will be the short-circuiting of magnet K of the master switch M, just as it is short-circuited when the branch db is closed by thermostat D. Magnet K will then release its armature and break the heater circuit. The released position of lever S is shown in dotted lines. In this position the top plate of lever S, which is colored red, is brought into a vertical position in front of window 16. Thereby an observation of the apparatus, without openin the box, will show that it has acted, and lfmore than one such apparatus is contained in the same box, it will show which one has acted. In some cases there are two or more heater circuits in the same car and I .have indicated at b a second heater circuit in parallel with the circuit a. and controlled by the same master switch M.

This circuit b may have its own individual set of coils'X and Y with associated arts contained in the same box with those 0 circuit a. If either one of these two circuits is accidentally grounded, both circuits will be broken.

goes through a resistance F That will more quickly call attention, by a drop in temperature which the thermostat fails to correct, to the fact that the emergency cut-out has acted, provided that such action was not noticed at the time it occurred. The box will be locked, but an authorized ins ector will unlock it, after the action takes p ace, and will reset it by simply turning lever S back to its vertical position. That will break the short-circuit established by circuit dc of the master switch magnet K which will close and admit current to the heater circuit before lever S reaches its upright position. If the accidental ground on the heater circuit still remains, the latchR will not act and lever S will not stay in its lifted position. That will show that the heaters can not be used. But if the ground has disappeared the lever S will be atched and remain upright, the heaters being then in workable condition.

I also provide a grounding push-button 5, by which the circuit dc may be manually grounded. By this means the car conductor or other person can turn the heaters off or on at will merely by pushing in or drawing out the button 5 without resort to the large heavyduty switches ordinarily employed for that purpose. When he pushes in the button 5 he does not disturb in any way the cut-out apparatus, but grounds out ma et K just as the thermostat does when it c oses circuit db to ground and the heaters are thereby cut off. If later he wishes to cut them in again, he pulls the button out. So long as the button remains in neither the thermostat nor the cut-out can exercise control to cut in the heaters. Another merit of myarrangement is that there is no interference with the normal functioning of the thermostat control. So

long as the heater circuit is in its normal condition, the thermostat will continue to cause the cutting off of the heaters when the temperature of the car is too hi h and their cutting in when it is too low. nly in the event of an accidental ground will the cut-out act and then it will not affect the thermostat which will'resume its function as soon as the ground has been removed.

What I claim as new and desire to secure by Letters Patent is:

1. A safety device for electric heaters that are connected, in series, comprisinga main switch in the heater circuit, a switch-closingmagnetfor said switch, a circuit shunting said closing magnet, a thermostat controllin said shunting circuit, a branch from said shunting circuit, a spring-closed switch in said branch, and a releasing magnet therefor having differential coils contained in the heater circuit on o posite sides of the heaters.

2. A safety devlce for electric heaters that are connected in series, comprising a main switch in the heater circuit, a switch-closingmagnet for said switch, a circuit shunting said closing magnet, a thermostat controlling said shunting circuit, a branch from said shunting circuit, a spring-closed switch in said branch, a releasing magnet therefor having diiierential coils contained in the heater 5 circuit on opposite sides of the heaters, and means including a manually cperable switch for independently grounding said branch circuit, so as to shunt said spring-closed switch. Signed at Albany, county of Albany and 10 State of New York, this 7th day of May, 1923.

LEE P. HYNES.

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