DE19830016A1 - Electronic over-current release operating method for power switch - Google Patents

Abstract

The method involves calculating at least one characteristic size for a curve shape of the current within each period in the over-current release. The characteristic size is compared with a preset threshold value specific to the connected load, and the switching off of the power switch is triggered only at the overstepping of the measured characteristic size above the preset threshold value. A slope element of the current, calculated within each period as a ratio of a slope and an effective value of the current, is preferably evaluated as the characteristic size.

Description

The invention relates to a method for operating a electronic overcurrent release for a circuit breaker and a suitable one for carrying out the method electronic overcurrent release.

Circuit breakers with electronic overcurrent release should a consumer and the affected electrical systems protect against short circuits and thermal overload. she now have the conventional ones with bimetallic triggers and electromagnetic triggers working power switch replaced.

In circuit breakers with electronic overcurrent releases, when a certain threshold value of the monitored current, which is usually measured as an effective value, is exceeded, the square of the current over the current flow is summed up (I ² t measurement) and the switch-off is triggered when a limit value is exceeded. In addition, when a current value is exceeded, which is a certain and adjustable amount above the aforementioned threshold value of the current, there is an immediate switch-off, that is to say that such a current is interpreted as a short-circuit current.

For consumers with a non-sinusoidal current draw under certain circumstances, however, currents with high amplitudes which are not short-circuit currents. So can occur when operating electrical drives that have Converters are controlled, high current amplitudes occur due to the operation of the converter are conditional, and which are significantly above the effective value of the  Current. Here, for example, with a electronic switch (thyristor) an inductance in the DC link of the converter briefly "short-circuited". Such consumers with electronic overcurrent protected from solvers, this can lead to false triggers come, although the consumer uses a normal network RMS value charged.

The invention is therefore based on the object Specify the process by which also with consumers significant harmonic components in the current safe triggering criteria to differentiate between regular current peaks and short-circuit currents are used.

According to the invention the object is achieved in that Overcurrent release at least within each current period calculates a parameter for the curve shape of the current and with a preset, for the connected Consumer specific threshold value compared and only at Exceeding the measured parameters above the above set threshold the opening of the circuit breaker is triggered.

The crest factor and / or the form factor of an alternating variable is used.

The crest factor, based on the measured alternating current, is

ks = | I.

The form factor, based on the measured alternating current, is

kf = I / | i |

These parameters indirectly describe the curve shape of a Change size and so can be an evaluable reference to the Provide properties of electricity.

The overcurrent release is equipped with a digital evaluation circuit for the or at a certain consumer with non-sinusoidal current draw expected characteristic sizes and corresponding comparators. Such consumers are, for example, with converters interacting electric motors. The expected characteristics sizes of a connected consumer are operated field of the overcurrent release set. If necessary, must for setting the values beforehand by competent personnel a measurement of the expected parameters for the curve shape of the current can be carried out.

The overcurrent release then turns on in every current period Comparison between the parameters from the measured current and the preset values. In this way the overcurrent release can safely switch between a "normal" Peak value and a peak value caused by a Short circuit or overcurrent. Miss tripping can be safely avoided.

Modern overcurrent releases work with a micro anyway processor, so that in this case all calculations and Comparisons can be made in the microprocessor and no separate evaluation circuit and comparators are required. A current threshold value can also be defined in which a switch is triggered in any case. The invention is illustrated by the following figures are explained. Show it  

Fig. 1 shows the control panel of an electronic shutter overcurrent,

Fig. 2 is a affected by harmonics current with its characteristics,

Fig. 3 shows an equally harmonic current with a different amplitude and different parameters.

Fig. 1 shows the front panel 2 of an overcurrent release 1 , on the control panel 2 a 3 different triggering criteria can be set by means of rotary coding switches. Below this, rotary coding switches 3 a, 3 b are provided, with which the specific values of a consumer for the crest factor ks and for the form factor kf can be set, which are then processed by the overcurrent release 1 in accordance with the method of operation provided by the method.

Figs. 2 and 3 each show a period of two currents, whose effective values and harmonic components, the latter characterized by the distortion factor, in both cases are almost the same. However, the amplitude of the current in FIG. 3 is approximately 1.5 times the amplitude of the current in FIG. 2. A conventional overcurrent release 1 would evaluate both current curves according to the same criteria and, in the case of the current according to FIG. 3, assume a short circuit and tripping cause. If, on the other hand, the crest factor ks and the form factor kf are taken into account, the overcurrent release 1 also recognizes in the case of the current according to FIG. 3 that the values are within the range of the expected values and that there is therefore no short circuit. A trigger under therefore remains.

The invention is not limited to those shown here Embodiments. Rather, it is possible through Combination and modification of means and characteristics more Realize design variants without the scope of the Leaving invention.

Claims (5)

1. A method of operating an electronic overcurrent release for a circuit breaker, characterized in that the overcurrent release calculates at least one parameter for the curve shape of the current within each current period and compares it with a preset threshold value specific for the connected consumer and only when the measured parameters are exceeded the pre-set threshold is triggered when the circuit breaker is switched off. 2. The method according to claim 1, characterized in that as a parameter, the crest factor of the current, calculated as Relationship between peak value and effective value of the current one period at a time. 3. The method according to claim 1, characterized in that as a parameter, the form factor of the current, calculated as Relationship between effective value and rectifying value of the current one period at a time. 4. Electronic overcurrent release for a circuit breaker for performing the method according to one of the preceding claims, characterized in that the overcurrent release ( 1 ) is a digitally working evaluation circuit for at least one parameter for the curve shape of the current and at least one parameter with a preset threshold in each Contains comparator circuit comparing the current period, the output of which is connected to the overcurrent release ( 1 ). 5. Overcurrent release according to claim 4, characterized in that on the control panel ( 2 a) of the overcurrent release ( 1 ) adjustable rotary coding switches ( 3 , 3 a, 3 b) are arranged, which serve to set the threshold values.