Patent Description:
A circuit breaker with a semiconductor switching unit in at least one line and a mechanical bypass-switch connected in parallel to the semiconductor switching unit is also known as "hybrid circuit breaker". A circuit breaker according this concept is described in <CIT> by the applicant.

For a switch off operation the bypass switch opens, what causes the current to commutate to the semiconductor path. The current then would be switched off by the semiconductor switching unit. The arc voltage between the mechanical contacts of the mechanical switch is required for a current commutation from the mechanical switch to the semiconductor switching unit. After the current commutation, the contacts of the mechanical switch have to reach a distance great enough that an arc between them will not reignite when a surge voltage appears at a turn off of the semiconductor switching unit. After the opening of the contacts and the extinguishing of the arc, the temperature of the gas and/or plasma inside the mechanical switch decreases, and the dielectric strength of the air between the contacts will recover. The semiconductor switching unit has to conduct the commutated current until the mechanical switch reaches a minimum dielectric strength.

Switching off of the semiconductor switching unit causes a voltage rise in a metal-oxide-varistor (MOV) connected in parallel to the mechanical switch and the semiconductor switching unit. If the semiconductor switching unit switches off before the dielectric strength of the mechanical switch is high enough, an arc will reignite between the contacts of the mechanical switch.

As a drawback of the known concept, it is necessary to wait until the mechanical bypass switch reaches the required dielectric strength, before a current can be switches off by the semiconductor switching unit. During this time the value of a short current still rises, causing electrical and thermal stress. Therefore it is necessary to provide the semiconductor switching unit with semiconductors, which are able to switch high currents and which are suitable for high currents and high power losses. Usually the internal resistance and the physical dimensions of such semiconductors are higher compared to semiconductors with lower switching capabilities. Higher internal resistance additionally increases the heat generated by the semiconductors.

Further a Hybrid Circuit Breaker with two or more mechanical switches connected in series. All of these switches are operated to open at the same time. It turned out that this concept will not lower the necessary current conduction time for the semiconductor switching unit. The contacts of the separate serial switches will not operate at the exact same time. This results in a longer current commutation time.

The <CIT> discloses a DC circuit breaker device according to the preamble of claim <NUM> with a live line between a live supply connecting terminal and a live load connecting terminal, a first semiconductor switch and a second semiconductor switch, a first mechanical circuit breaker and a second mechanical circuit breaker, whereby the first semiconductor switch and the second semiconductor switch are connected in series in said live line.

The <CIT> discloses a circuit breaker device with a live line between a live supply connecting terminal and a live load connecting terminal, a first semiconductor switch and a second semiconductor switch, a first mechanical circuit breaker and a second mechanical circuit breaker.

The <CIT> discloses a circuit breaker device with two mechanical switches in series.

The <CIT> discloses a direct current circuit breaker comprising a positive supply line between a positive input terminal and a positive output terminal, and a negative supply line between a negative input terminal and a negative output terminal for connecting a direct current load to a supply.

It is an object of the present invention to overcome the drawbacks of the state of the art by providing a circuit breaker which can switch off a short circuit in short time, with low thermal and electrical stress.

According to the invention, this object is solved by the features of claim <NUM>.

As a reason the current conduction time of the solid state semiconductor switching unit, after current commutation from the first mechanical switch, is reduced. A shorter current conduction time reduces electrical and thermal stress on all electrical components of the circuit breaker and the electrical network protected by the circuit breaker.

As the second mechanical switch opens without current, no arc and no arc plasma will be created between the contacts of the second mechanical switch. Especially it is not necessary to wait until the switch, respective the gas or the plasma inside the switch cools down. Therefore the dielectric strength, which is necessary for switching off the current by the semiconductor unit, will be reached immediately after the contacts were opened. For instance the necessary air gab distances given in EN <NUM>-<NUM>:<NUM> table A. <NUM> can be considered.

As a result the necessary dielectric strength can be reached earlier compared to a single mechanical switch or multiple serial mechanical switches operated at the same time.

As a result it is possible to switch off the semiconductor switching unit just after the contacts of the second mechanical switch reached enough distance. A short current can be switched off as long as it is small compared to the described state of the art. It turned out that the current conduction time of the semiconductor switching unit can be reduced <NUM>% compared to a circuit breaker according <CIT>. As a further reason it is possible to use semiconductors with low maximum switching capability and low physical dimensions.

As a further result the second mechanical switch can act as a backup for the first mechanical switch.

Dependent claims describe further preferred embodiments of the invention.

The invention is described with reference to the drawing. The drawing shows a schematic of a preferred embodiment.

The Fig. shows a preferred embodiment of a circuit breaker <NUM> comprising a live line <NUM> between a live supply connecting terminal <NUM> and a live load connecting terminal <NUM>, a neutral line <NUM> between a neutral supply connecting terminal <NUM> and a neutral load connecting terminal <NUM>, and a semiconductor switching unit <NUM> located in the live line <NUM>, the circuit breaker <NUM> further comprises a bypass line <NUM>, which bypass line <NUM> is connected in parallel to the semiconductor switching unit <NUM>, with a first mechanical switch <NUM> and a second mechanical switch <NUM> located in the bypass line <NUM>, with the first mechanical switch <NUM> connected in series to the second mechanical switch <NUM>, whereby the semiconductor switching unit <NUM>, the first mechanical switch <NUM> and the second mechanical switch <NUM> are controlled by a processing unit <NUM> of the circuit breaker <NUM>, whereby the processing unit <NUM> is embodied to perform following steps in case of a short-circuit-detection or an overcurrent-detection:.

As a reason the current conduction time of the solid state semiconductor switching unit <NUM>, after current commutation from the first mechanical switch <NUM>, is reduced. A shorter current conduction time reduces electrical and thermal stress on all electrical components of the circuit breaker <NUM> and the electrical network protected by the circuit breaker <NUM>.

As the second mechanical <NUM> switch opens without current, no arc and no arc plasma will be created between the contacts of the second mechanical switch <NUM>. Especially it is not necessary to wait until the second mechanical switch <NUM>, respective the gas or the plasma inside the switch cools down. Therefore the dielectric strength, which is necessary for switching off the current by the semiconductor switching unit <NUM>, will be reached immediately after the contacts of the second mechanical switch <NUM> were opened. For instance the necessary air gab distances given in EN <NUM>-<NUM>:<NUM> table A. <NUM> can be considered.

As a result the necessary dielectric strength can be reached earlier compared to a single bypass-switch or multiple serial bypass-switches operated at the same time.

As a result it is possible to switch off the semiconductor switching unit <NUM> just after the contacts of the second mechanical switch <NUM> reached enough distance. A short current can be switched off as long as it is small compared to the described state of the art. It turned out that the current conduction time of the semiconductor switching unit <NUM> can be reduced <NUM>% compared to a circuit breaker according <CIT>. As a further reason it is possible to use semiconductors with low maximum switching capability and low physical dimensions.

As a further result the second mechanical switch <NUM> can act as a backup for the first mechanical switch <NUM>.

The actual circuit breaker <NUM> is a low voltage AC or DC circuit breaker <NUM>.

The circuit breaker <NUM> comprises at least two electric connections through the circuit breaker <NUM>. A first electric connection or live line <NUM> connects a live supply connecting terminal <NUM> of the circuit breaker <NUM> with a live load connecting terminal <NUM> of the circuit breaker <NUM>. A second electric connection or neutral line <NUM> connects a neutral supply connecting terminal <NUM> with a neutral load connecting terminal <NUM>. In case of direct current one of these two lines is a line for positive polarity and the other line is indented for negative polarity. The circuit breaker <NUM> can comprise further lines, especially for multi-phase applications.

The circuit breaker <NUM> comprises a semiconductor switching unit <NUM> located in the first or live line <NUM>. The semiconductor switching unit <NUM> is preferable embodied as 4Q-switching arrangement. Especially the semiconductor switching unit <NUM> comprises IGBTs, preferably Back-to-Back IGBTs with anti-parallel diodes, or MOSFETs.

A varistor <NUM> respective a metal-oxide-varistor (MOV) is connected in parallel to the semiconductor switching unit <NUM>.

A bypass line <NUM> is connected in parallel to the semiconductor switching unit <NUM>. The bypass line <NUM> contains a first mechanical switch <NUM> and a second mechanical switch <NUM>, with the first mechanical switch <NUM> connected in series to the second mechanical switch <NUM>.

According to a preferred embodiment both mechanical switches <NUM>, <NUM> are embodied essentially identical. The mechanical switches <NUM>, <NUM> are typically embodied as electric relays respective electro-mechanical switches with a very short opening time, also known as ultra-fast relays. A typical contact opening speed for a preferred embodiment for a first and/or second mechanical switch <NUM>, <NUM> is in the range of <NUM>/s to <NUM>/s (µm/µs). A typical reaction time for a first and/or second mechanical switch <NUM>, <NUM> is in the range of <NUM> to <NUM>. A typical contact distance for a first and/or second mechanical switch <NUM>, <NUM> is in the range of <NUM>. The opening time for a first and/or second mechanical switch <NUM>, <NUM> is typically.

The first mechanical switch <NUM> may also be called bypass-switch or arcing-switch.

The second mechanical switch <NUM> may also be called dielectric-switch.

The first mechanical switch <NUM> and the second mechanical switch <NUM> are controlled by a processing unit <NUM> of the circuit breaker <NUM>.

The circuit breaker <NUM> can comprise at least a third mechanical switch connected in series to the first mechanical switch <NUM> and the second mechanical switch <NUM>, and controlled by the processing unit <NUM>. The invention is further described with two mechanical switches <NUM>, <NUM>.

A circuit breaker <NUM> according to the described features, but only with one mechanical switch <NUM>, called bypass-switch, is known from the <CIT> of the applicant.

In normal operation both mechanical switches <NUM>, <NUM> are in closed state, and an electric current from the supply, as shown in the Fig. by the source <NUM> and the internal resistance <NUM> and internal inductance <NUM> of the source <NUM> respective an electric grid, to the load <NUM> passes the circuit breaker <NUM> via the first mechanical switch <NUM> and the second mechanical switch <NUM>.

According to the preferred embodiment the circuit breaker <NUM> further contains a first and a second galvanic separation relay <NUM>, <NUM>, which are also controlled by the processing unit <NUM>.

The circuit breaker <NUM> is embodied to detect a short circuit and/or an overcurrent.

Preferable the function of overcurrent-detection is embodied by using a shunt resistance <NUM> in the live line <NUM> for current measurement. According to the preferred embodiment the short circuit detection is embodied as a part of a - not shown - driver circuit of the semiconductor switching unit <NUM>. A short circuit would cause a desaturation of the semiconductors, which would be detected by the driver circuit, as further described in <CIT>.

The shunt resistance <NUM> and/or the driver circuit are connected to the processing unit <NUM>.

In case of a short-circuit-detection or an overcurrent-detection the processing unit <NUM> sends a first opening command to the first mechanical switch <NUM>. By opening of the first mechanical switch <NUM> the current commutates to the semiconductor switching unit <NUM>.

A time-delay after the sending of the first opening command, the processing unit <NUM> sends a second opening command to the second mechanical switch <NUM>. As already described, by opening of the second mechanical switch <NUM> the sufficient dielectric strength will be reached in a shorter time. Afterwards the processing unit <NUM> initiates the switching off of the semiconductor switching unit <NUM>.

In case that the circuit breaker <NUM> should switch off an operative or working current, the processing unit <NUM> initiates only the opening of the first mechanical switch <NUM>.

According to an example, which is not encompassed by the claims, the time-delay is a predefined constant time-delay. A constant time-delay is easy to implement, and further ensures a fail safe operation of the second mechanical switch <NUM>. In case the first mechanical switch <NUM> does not open, as a reason of a malfunction, the second mechanical switch <NUM> will open after the time-delay automatically.

The duration of this constant time-delay can be determined by the typical duration of the commutation time for a specific type of circuit breaker <NUM> with an additional tolerance.

According to the invention, the time-delay is a variable time-delay. According to this embodiment the second opening command is sent after a sufficient amount of commutation of the current to the semiconductor switching unit <NUM>.

According to the invention the circuit breaker <NUM> comprises a commutation detection arrangement <NUM> to detect at least the beginning of a current commutation from the bypass line <NUM> to the semiconductor switching unit <NUM>, with the commutation detection arrangement <NUM> being connected to the processing unit <NUM>. The commutation detection arrangement <NUM> can be implemented as a part of the driver circuit of the semiconductor switching unit <NUM> and/or as a separate unit. In the latter case the commutation detection arrangement <NUM> may not be a separate unit but it can be implemented by a combination of the driver circuit and the processing unit <NUM>.

The embodiment according to the only Fig. shows a current measurement unit <NUM> connected in series to the semiconductor switching unit <NUM> and in parallel to the bypass line <NUM> as a part of the commutation detection arrangement <NUM>.

According to the invention, the variable time-delay is defined as the period until the commutation detection arrangement <NUM> detects a predefined level of commutation of a current from the bypass line <NUM> to the semiconductor switching unit <NUM>. In this case the processing unit <NUM> waits until this level is reached and sends the second opening command afterwards.

According to the invention, the variable time-delay is defined as an expected commutation time minus a reaction time period of the second mechanical switch <NUM>. This variation takes the signal traveling time within the circuit breaker <NUM> as well as the inertia and inherent delays of the second bypass-switch <NUM> into consideration. The reaction time of the second mechanical switch <NUM> is usually well known for one special type of mechanical switch <NUM>.

In this context the expected commutation time will be estimated by the processing unit <NUM> under consideration of a variation in time of a current in the live line <NUM> and/or a current in the bypass line <NUM>. The signals describing the variation in time are delivered by the commutation detection arrangement <NUM>.

According to another embodiment of the invention, the processing unit <NUM> is embodied to send the second opening command after a further delay which is the constant time-delay in case, that the variable time-delay is longer than the constant time-delay. If the variable time-delay is shorter than the constant time-delay, the processing unit <NUM> sends the second opening command after the variable time-delay. This embodiment combines the advantages of the possibility of a short switch off time with safety.

Claim 1:
Circuit breaker (<NUM>) comprising a live line (<NUM>) between a live supply connecting terminal (<NUM>) and a live load connecting terminal (<NUM>), a neutral line (<NUM>) between a neutral supply connecting terminal (<NUM>) and a neutral load connecting terminal (<NUM>), and a semiconductor switching unit (<NUM>) located in the live line (<NUM>), the circuit breaker (<NUM>) further comprises a bypass line (<NUM>), which bypass line (<NUM>) is connected in parallel to the semiconductor switching unit (<NUM>), with a first mechanical switch (<NUM>) and a second mechanical switch (<NUM>) located in the bypass line (<NUM>), with the first mechanical switch (<NUM>) connected in series to the second mechanical switch (<NUM>), whereby the semiconductor switching unit (<NUM>), the first mechanical switch (<NUM>) and the second mechanical switch (<NUM>) are controlled by a processing unit (<NUM>) of the circuit breaker (<NUM>), whereby the processing unit (<NUM>) is embodied to perform following steps in case of a short-circuit-detection or an overcurrent-detection:
- sending a first opening command to the first mechanical switch (<NUM>),
- sending a second opening command to the second mechanical switch (<NUM>) a time-delay after sending of the first opening command,
characterized in that the circuit breaker (<NUM>) comprises a commutation detection arrangement (<NUM>) to detect at least the beginning of a current commutation from the bypass line (<NUM>) to the semiconductor switching unit (<NUM>), with the commutation detection arrangement (<NUM>) being connected to the processing unit (<NUM>), whereby the time-delay is a variable time-delay, whereby the variable time-delay is defined as the period until the commutation detection arrangement (<NUM>) detects a predefined level of commutation of a current from the bypass line (<NUM>) to the semiconductor switching unit (<NUM>) or the variable time-delay is defined as an expected commutation time minus a reaction time period of the second mechanical switch (<NUM>), whereby the processing unit (<NUM>) is embodied to estimate the expected commutation time under consideration of a variation in time of a current in the live line (<NUM>) and/or a current in the bypass line (<NUM>).