Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2000-06-09
2003-09-23
Assouad, Patrick (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C361S097000
Reexamination Certificate
active
06625551
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a detection system that detects fault currents and differential currents that are supplied to an electric device and triggers a protection switch to prevent such currents from being supplied to the electric device. More particularly, the present invention relates to a detection system that triggers the protection switch when harmful fault currents and differential currents are detected and that does not erroneously trigger the protection switch when harmless transient interference pulses are detected. In addition, the present invention relates to a method performed by the detection system and a software program for implementing the method.
BACKGROUND OF THE INVENTION
In many applications, electrical currents are supplied to one or more electric devices to provide power for the devices. For example, electrical currents are supplied from a power company to one or more electrical outlets in a residential home, and a user can connect an electric device to an outlet to supply power to the device. If the electric device malfunctions or is mishandled by the user, a potentially dangerous situation may arise. For example, if the user contacts a portion of the electric device that receives electrical currents from the power company, the electrical current will pass through the user to the ground and may cause the user's heart to suffer from a cardiac arrest. Also, if the portion of the electric device that receives electrical currents is improperly grounded due to faulty insulation, a large amount of current will be supplied to the electric device and may start a fire in the user's home. The additional surge of current that is supplied to the user's home when the electric device malfunctions or is mishandled is known as a fault current.
In order to prevent fire in the user's home or to prevent the user from being harmed, a circuit breaker has been developed that detects fault currents and that blocks the supply of electrical current to the one or more electrical outlets in the user's home if the detected fault currents exceed certain levels.
FIG. 5
shows an example of such a circuit breaker
1
, which comprises a sum-current transformer
2
, a power supply
4
, triggering circuit
5
, a triggering relay
6
, a switching mechanism
7
, and a switch
8
.
The electric currents are supplied from the power company to the user's home via a conductor network LN, and the network LN includes three active conductors L
1
, L
2
, and L
3
and a neutral or ground conductor N. The conductor network LN is wrapped around a core
3
of the sum-current transformer
2
to form a primary winding N
1
of the transformer
2
. Also, a secondary winding N
2
is wrapped around the core
3
of the transformer
2
, and the triggering circuit
5
is connected to the winding N
2
. Specifically, the triggering circuit
5
is connected across the output terminals of the winding N
2
, and the triggering relay
6
is connected across the output terminals of the circuit
5
. The triggering relay
6
controls the switching mechanism
7
to selectively open the switch
8
, and the switch
8
is provided in the path of the conductor network LN between the power company and the electrical device.
When the electric device in the user's home is operating or being handled under normal conditions, no fault currents exist. As a result, the vector sum of the currents flowing through the core
3
via the conductor network LN is zero. However, if a fault current I
f
is generated, the vector sum of the currents is not zero, and a voltage U
e
is generated across the secondary winding N
2
. The characteristics of the voltage U
e
correspond to the characteristics of the fault current I
f
, and the triggering circuit
5
generates an output voltage U
a
based on the input voltage U
e
. The output voltage U
a
causes an operating current I
a
to flow through the triggering relay
6
. When the fault current If exceeds a triggering current I
trigger
, the triggering circuit
5
triggers the relay
6
. The triggering of the relay
6
causes the switching mechanism
7
to open the switch
8
to block the supply of current from the power company to at least one outlet in the user's home.
Since the value of residual operating current I
a
is based on the value of the fault current I
f
, the relay
6
triggers when the fault current I
f
increases to a point that causes the current I
a
to flow. Accordingly, when the user contacts a conductive portion of an electric device and causes a large fault current I
f
to be generated, the relay
6
triggers, and switching mechanism
7
opens the switch
8
. As a result, the dangerous fault current I
f
is no longer supplied to the user and will not harm the user. Similarly, if the insulation in the electric device is faulty and a large fault current I
f
is generated, the relay
6
triggers so that the switching mechanism
7
opens the switch
8
. Thus, the dangerous fault current I
f
is no longer supplied to the electric device, and any possibility of the electric device starting a fire is eliminated.
However, since the circuit breaker
1
shown in
FIG. 5
is implemented via hardware circuitry, the circuit breaker
1
is often activated when dangerous fault currents are not present, and thus, the circuit breaker
1
unnecessarily interrupts the operation of the electric device. For example, when one or more electric components connected to the conductor network LN are initially turned on, transient interference pulses are generated that have large amplitudes but last for only a short period of time. For example, as shown in
FIG. 1
, when the electric components are turned on, transient interference pulses typically occur from the time t=0 (i.e. t
0
) to the time t=10 (i.e. t
a, min
).
When such pulses (and similar pulses) are generated, the triggering circuit
5
outputs a current I
a
that triggers the relay
6
, and the switching mechanism
7
causes the switch to prevent power from being supplied to the electric device. However, by the time the relay
6
triggers, the transient interference pulses no longer exist, and thus, circuit breaker
1
unnecessarily blocks the supply of the electrical power to the electric device. As a result, the operation of the electric device is unnecessarily stopped.
In an attempt to overcome the above problem, the hardware of the circuit breaker
1
has been redesigned to try to prevent it from triggering between the times to and t
a, min
. However, the ability to successfully redesign the circuit breaker
1
to suppress the times at which it will trigger is limited because such hardware modification is expensive and complicated. For example, the additional circuitry needed to prevent the circuit breaker
1
from triggering at certain times adversely affects the values of the triggering times at which the circuit breaker
1
needs to trigger when a fault current is detected. In addition, the time periods during which the circuit breaker
1
should trigger (or not trigger) vary based on the specific applications under which the circuit breaker
1
is to operate and vary based on the different standards adopted by different countries. Since hardware circuitry is used to control the times when the circuit breaker
1
will trigger or not trigger, modifying the circuit breaker
1
so that it can operate under different applications and according to the standards of different countries is very time consuming and difficult.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a fault or differential current detection system that accurately triggers when harmful fault currents and differential currents are detected and that does not erroneously trigger when harmless transient interference pulses are detected.
Another object of the present invention is to provide a fault or differential current detection system that can be easily mass-produced and that can be easily modified to work in many different environments.
In order to achieve the
Gies Stefan
Schmid Reinhard
Assouad Patrick
Sughrue & Mion, PLLC
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