Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-05-30
2003-04-15
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S071000, C361S022000, C361S104000, C439S620180
Reexamination Certificate
active
06548924
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to hermetically sealed, electromotively driven compressors for air conditioning and refrigeration applications and the like and more particularly to protective devices used with such compressors.
BACKGROUND OF THE INVENTION
Protective devices for de-energizing hermetically sealed, electromotively driven compressors which are mounted on a sealed terminal assembly inside the sealed casing of the compressors and which have a fuse function actuated by detecting an over-current generated by a faulty motor or the like are known.
FIG. 14
is a perspective view of the back side of a prior art protective device
101
for a hermetically sealed type electromotively driven compressor. Surface
103
of housing
102
of protective device
101
has holes
104
that correspond to electrically conductive pins of a sealed terminal assembly of the compressor casing (not shown in the drawing). The protective device has some electrically conductive parts that are exposed or openings which expose conductive parts. For example, the electrically conductive part of a protector
106
is exposed at opening
105
that was formed in connection with the forming of housing
102
. In addition, electrically conductive parts such as a current fuse
107
and that part to which the fuse is welded are also exposed.
It is known to maintain an insulation distance for these exposed parts as stipulated in an official standard for electrically conductive parts of the sealed terminal or other conductive parts in a hermetically sealed casing.
However, if a large electric current, generated at the time of a fault condition of the electric motor, is detected and the current fuse is melted, an extremely large reverse electromotive force is generated at that moment. This reverse electromotive force generates an electric discharge phenomenon. If an electrically conductive part is exposed on surface
103
that faces the sealed terminal in the casing and unless a sufficient insulation distance is provided, the electric discharge phenomenon between the electric current fuse can jump to the sealed terminal or conductive parts in the sealed casing, thereby forming an electric circuit which could develop into such problems as a sealed terminal jump or earth leakage due to internal short circuiting.
In the conventional protective device for a hermetically sealed electromotively driven compressor, it has been difficult to avoid exposing the electrically conductive parts due to restrictions on the techniques used for the preparation of the electrically conductive parts or for the preparation of the protector assembly. The fuse function that is actuated by detecting a large electric current generated at the time of a fault of the electric motor is a comparatively new technology and using the standard for insulation distances based on the official specifications that presently exist does not adequately deal with this new technology. The development of sealed terminal jumps due to internal short circuiting or an earth leakage have been reported in the past despite the fact that these standards were observed.
Leakage of a coolant gas in a hermetically sealed electromotively driven compressor and equipment provided therewith is an example of an abnormal condition to which such compressors can be subjected and a room air conditioner is a representative device employing such a hermetically sealed electromotively driven compressor. In the case of the normal room air conditioner, the condenser is usually referred to as outdoor equipment and the evaporator as indoor equipment and these are arranged at a distance from each other. If there is some fault in the installation work of the equipment, a crevice or cracking could occur in the cooling system which should be air-tight, with a result that coolant gas starts leaking and air starts entering the system. Even in the case of a refrigerator and the like for which no piping installation work is required, such a crevice or cracking could develop if there is damage during the course of transportation or usage, or if there is a defect in manufacturing, with a similar result of coolant gas leakage, thereby allowing air to enter into the cooling system.
Coolant gas leakage is one of the major causes for burning of electric motors in such systems. In view of the fact that the coolant gas also serves to cool the motor by removing heat produced by the motor when the gas circulates inside the hermetically sealed electromotively driven compressor, a leak of the coolant gas brings about a rise in the temperature of the motor. When this happens, the temperature of the motor increases but the operating current decreases. Therefore, protection cannot be provided by a protector of the type that detects an over-current for shutting off the electric current. As a consequence, the electric motor is easily damaged. If the electric motor in a hermetically sealed electromotively driven compressor is damaged, the insulation film on the windings is destroyed, thereby developing short-circuiting which will, in turn, bring about the generation of an extremely large electric current. If such a large electric current is allowed to continue, the sealed terminal pins of the hermetically sealed electromotively driven compressor can be blown out of the terminal assembly or a fire can result due to over-heating by the electric current. In order to solve such a problem, protector devices have been provided with an electric current fuse for the purpose of shutting off such a large electric current. On the other hand, however, there are cases where the sealed terminal jump or earth leakage of the hermetically sealed type electromotive compressor occurs through the use of the electric current fuse. That is, as stated above, when the large electric current generated upon burning of the electric motor is shut off, an extremely large reverse electromotive force is generated in the motor.
A rough schematic of the electric circuit of the normal operation of equipment provided with a hermetically sealed electromotively driven compressor is shown in FIG.
15
. As shown in the figure, an electric current fuse
118
d
is connected in series with the power source circuit of the electric motor having a main coil
118
a
, a start coil
118
b
and a capacitor
118
c
. Due to voltage from the power source, electric current flows driving the motor and the hermetically sealed compressor is operated normally and, in this state, electric current fuse
118
d
is not affected.
FIG. 16
is an electric circuit schematic at the moment when a fault develops in the equipment that is provided with a hermetically sealed electromotively driven compressor, causing a large electric current and actuation of the current fuse. In this state, fuse
118
d
is melted and the power source circuit is open as shown in the figure. At this instant, a reverse electromotive force
119
a
is generated in the direction of continued current flow in conformity with Lenz's law. This reverse electromotive force
119
a
, which is dependent upon the size of the motor and the kind of the electromotive system, sometimes reaches a range between approximately 6000 and 9000 volts because the electric current fuse cuts off the current in an extremely short period of time. This is clearly observed from the function of the electromagnetic induction:
Electromotive Force e=M(di/dt)
(M=mutual inductance, di=amount of a change in the electric current, and dt=changed time)
In the case of a commercial power source, one phase is usually grounded. Schematics of the electric circuit in equipment which is provided with a hermetically sealed electromotively driven compressor including its grounding is shown in
FIGS. 17 and 18
. In
FIG. 17
, the commercial power source is grounded at
120
a
on the side where the electrical current fuse
118
d
is connected. In addition, a dashed line indicates a sealed casing
120
b
grounded at
120
c
. In
FIG. 18
, the commercial power source is grounded at
121
a
on the
Furukawa Hideharu
Ishikawa Yoshihiko
Shimada Toshio
Sugawara Wataru
Baumann Russell E.
Telecky Frederick J.
Texas Instruments Incorporated
Waks Joseph
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