DE1093466B - Electrical safety circuit - Google Patents

Description

The invention relates to the known and most frequently used contact protection measures "zeroing" and "protective earthing" as well as the "residual current protection circuit", which is also well-known and has recently been used to an increasing extent.

All of these contact protection measures offer a perfect function principle Protection ■ when touching the housings of power consuming devices. Still, they are in the Practice not proven to the desired extent. The reason lies particularly in human failure. Either when applying a touch protection measure certain measures are forgotten, or they are carried out improperly so that they are ineffective or later become, or it is caused by connection mix-up or the thoughtless overlook of existing interruption devices (e.g. fuses) created the possibility that the system parts to be protected can come directly under tension. All such mistakes make the touch protection measure ineffective or even create a danger in the first place and thus put people at risk of accident or death the end. These disadvantages apply, partly in a modified form, to the other contact protection measures (Fault voltage protection circuit, protective line system, protective separation, low voltage, Protective insulation).

Two other serious disadvantages of all these known touch protection measures are that the Ineffectiveness of the contact protection measure created as a result of an error in the majority of cases remains undetected (the electrical system remains functional!), often until something has happened, and that protection is generally not guaranteed if a person is live with the Conductor (e.g. defective device cable, lamp sockets, open device connections and Cans, overhead lines, etc.) comes into direct contact.

The invention of the fault current protection circuit was based on the idea from the beginning, the same way to be interpreted that a shutdown occurs at a relatively low and non-fatal fault current strength he follows. This would eliminate practically all of the above-mentioned errors in the touch protection measures currently in use can only lead to minor accidents and fatal accidents are practically excluded be.

The economically viable manufacture of a residual current circuit breaker with such a low Tripping residual current does not present any problems anymore. Still it was until today

Electrical safety circuit

Applicant:

Dipl.-Ing. Friedrich Lauerer,
Electrotechnical auditor

Munich-Passau,
Munich 23, Ohmstr. 11

Dipl.-Ing. Friedrich Lauerer, Munich,
has been named as the inventor

not possible to implement this application in practice. The reason is that different Power consuming devices (especially heating and cooking devices) have leakage currents that are often larger

^a 5 as the tripping fault current strength considered here. These natural leakage currents, which are absolutely permissible in the context of the relevant VDE regulations, then cause the residual current circuit breaker to switch off and thus make operation impossible. Practice showed z. B. that a tripping fault current strength of 50 mA, which can already have a deadly effect, is far too low; therefore the series production of such a residual current circuit breaker was not started either. With regard to these natural leakage currents, the industry, in agreement with the other relevant authorities, does not manufacture or market a residual current circuit breaker with a nominal tripping fault current strength below 30OmA.

Despite the presence of leakage currents, the invention allows the use of a residual current circuit breaker with a low and non-fatal tripping fault current strength thanks to a special circuit arrangement. This circuit is characterized / that a residual current circuit breaker used with a relatively low and non-lethal tripping fault current and the protective conductor (neutral conductor, grounding conductor or the like) with the summation current transformer of the Residual current circuit breaker is performed. By this circuit arrangement, which is practically a combination of residual current circuit breaker and zeroing or modified protective earthing are the same

OM 508/328

1. The advantages of zeroing or protective earthing are given, in particular the device housing , Down £ r <ipcitisn | ial,

_: 2 * ! Sann ^ teum , failure of the zeroing or protective earthing or in the case of direct contact with a live conductor, the current flowing through the human being to earth will not have a lethal effect and

3. the device leakage current can assume any level, without causing the residual current circuit breaker ίο to switch off.

In order to achieve optimal security (also against electrical Injuries or for constant isolation control) an adaptation to the given circumstances (in particular Insulation resistances), the level of the tripping fault current will depend on made adjustable below.

So that there is not an excessively high leakage current to one caused by a device insulation fault The cause of the fire is also the leakage current generated around the protective conductor magnetic field used for signal triggering or for shutdown.

In order to enable an adaptation to the given circumstances in each individual application, the level of the tripping leakage current is also made adjustable.

The interruption of the power supply caused by a fault current or by an excessively high leakage current is associated with undesirable side effects in practically all cases:

1. The fault must be eliminated,

2. The residual current circuit breaker must be switched on again, and

3. There is a loss of time, which can have a particularly sensitive effect on companies.

Eliminating the disorder is an inevitable necessity. But since many disturbances are only briefly (e.g. the person through whom the current flows immediately frees himself; the defective device becomes immediately disconnected from the mains if this is recognized), the other two disadvantages can thereby be eliminated or largely reduce that after the fault current or the excessively high leakage current has ceased an automatic restart of the residual current circuit breaker takes place, similar to that of the »short interruption« in medium-voltage overhead line networks is known and used.

The drawing shows an application example of this safety circuit in which the neutral conductor is used as a protective conductor. The mode of operation of this circuit is assumed to be through the following status options explained:

1. Zeroing has been carried out in accordance with regulations. The device housing of the power consumer thus has it Earth potential, and a contact voltage worth mentioning cannot occur. Kick If a short-circuit to the body opens, the upstream fuse switches off in good time.

2. The neutral conductor is connected to the device housing, but the first zeroing condition is not fulfilled (ie the internal resistance of the system is too high). In the event of a shock to the body, the upstream fuse S cannot or cannot switch off in time. If a person comes into contact with the device housing G , a contact voltage against earth occurs, but the current flowing through the person to earth cannot assume a lethal size, since the residual current coil F (= summation current transformer) of the residual current circuit breaker interrupts the current beforehand Switch C causes.

3. The neutral conductor is not connected or the same is interrupted in the supply line. Now leads the neutral conductor (ζ. Β. through a body contact or through a switched on light conductor) voltage against earth, then a fatal one can also be fatal for the reasons listed under 2 Residual current to earth does not come about.

4. The same applies, of course, if the device housing is directly on the live conductor is connected or when the person is in direct contact with the live conductor comes.

5. Zeroing is OK and the leakage current is too high. Then through the Leakage current coil ^ i interrupted the power supply.

6. If the zeroing is not correct, a shutdown occurs even with normal leakage current strength triggered, which forces you to fix the zeroing.

Result: Regardless of whether the system is properly installed downstream of the circuit breaker is or not, can be fatal (for all ladder and system parts that are strongly drawn out in the drawing) effective fault current to earth and an excessively high leakage current do not occur. This becomes a achieved a high level of accident and fire safety.

Claims (5)

Patent claims: 1. Electrical safety circuit using the residual current circuit breaker and zeroing or protective earthing, characterized that the residual current circuit breaker has a low, non-lethal tripping residual current and that the protective conductor (neutral conductor, grounding conductor, etc.) with the summation converter of the residual current circuit breaker. 2. Safety circuit according to claim 1, characterized in that the tripping fault current strength can be regulated down to completely harmless values. 3. Safety circuit according to claim 1 or 2, characterized in that by the Protective conductor due to any leakage currents caused a signal or the magnetic field Power cutoff is triggered. 4. Safety circuit according to claim 1 or the following, characterized in that the height the tripping leakage current can be regulated. 5. Safety circuit according to claim 1 or the following, characterized in that after cessation the fault current or the excessively high leakage current causes an automatic restart he follows. Considered publications:
German Auslegeschrift No. 1,057,683;
German patent specification No. 971 476. 1 sheet of drawings © 0O9 508/328 4.60