DE102005052956B3 - Arrangement for detecting and locating the positions of insulation faults in the heating rods of points heating systems, has means for applying an impulse voltage between the heating output lines and earth - Google Patents

Abstract

Arrangement comprises a resistance measurement arrangement with which it is detected if the measured resistance of rods falls below a minimum value. If this occurs an impulse voltage is applied between the heating output lines (4) and earth. A test current is if formed which varies between minimum and maximum values. An isolation resistance is formed for each heating rod and compared with a parameter minimum value.

Description

The The invention relates to a method and a device for detection and location of hot bar related insulation faults in electrical Point heating systems with power switching device for one or more heating outlets.

to Avoiding the freezing of points at low temperatures These are heated by point heating systems with electric heating elements. Such electrical point heating systems exist among others from a point heating distribution with electrical power switching device for switching of heating outlets. The heaters are attached to the rails and over heating rod connecting cables in remote terminal box, which are arranged next to the switch, and cables supplied by the point heating distribution.

In Electrical point heating systems can be damaged by faulty insulation due to aging of the heating elements for example fault currents over the Drain rail and earth. To protect damage be in the heating outlets Residual current circuit breaker arranged. When a limit is exceeded is, the shutdown of the faulty Heizabganges done.

to Avoidance of business interruptions By switching off faulty heating outlets, insulation monitoring devices are used in addition early a warning if the minimum insulation value is undercut give and thus serve needs-based maintenance.

to insulation monitoring electric point heating systems is known, according to the power switching device of the point heating distribution to arrange an insulation monitoring device that When the power switching device is switched off, the insulation resistance is measured via DC voltage measurement via the heating output conductor and earth captured. When falling below a minimum value of the Insulation resistance, a warning signal is generated as a message. A disadvantage of this method is that exclusively the Insulation resistance of the entire heating outlet is detected. There at each heating outlet over Remote connection box up to 12 heating elements are connected the detected insulation resistance only a total value and not unique. Furthermore is a localization of the faulty heating elements or not possible. The process is the less accurate, the larger or the more heating elements on one Heating outlet are connected.

Farther is a method and device for insulation fault location in isolated ungrounded AC network known, being in these for insulation monitoring an insulation monitoring device arranged is and in addition in case of an occurring insulation fault a test voltage generator a defined Test current generated between mains and earth and this by means of differential current is detected and the individual differential current measured values via test leads be transferred to an evaluation.

From the DE 10 2004 018 918 B3 For isolated networks, it is furthermore known that in such a method network disturbances are detected and the localization of the erroneous output is effected by simultaneous detection of all network outlets. The main disadvantage for point heating systems is that between test signal generator and differential current transformer, a communication line (bus) is required and which is divided in a plurality of outflows with simultaneous significant insulation errors of the test current to multiple outlets and a safe measurement of all outlets not possible.

method and to provide a device of the kind mentioned in the preamble, in which the insulation resistance of each heating element of an electric Point heating system by appropriate measures before occurrence of insulation faults is reliably detected and a quick and clear localization the faulty heating element (s) can be done.

Is solved the object by a method with the specified in claim 1 Characteristics or by a device according to claim 4.

The inventive method and the device for implementation the same is advantageous in electrical point heating systems with terminal box set off from the point heating distribution and several connected thereto heating rods used and allows the Detection of insulation resistance for each single heating element and a quick location of faulty electric heating elements.

The Invention will be explained in more detail with reference to the following embodiments and described and show it:

1 Overview of known devices for insulation monitoring

2 Timing of the method according to the present invention

3 Overview of a device according to the present invention

4 Top view of an inventive Design of a connection box

First, will to the well-known method for insulation monitoring in isolated networks discussed in more detail.

In 1 is a known arrangement of an electric point heater with transformer 1 , Power switching device 3 and a heating outlet formed by the same 32 shown. An unavoidable insulation resistance with ohmic leakage resistance Re 26 provides an insulation resistance between heating outlet lines 4 and earth. To monitor the ohmic portion of the bleeder resistors Re 26 is after the power switching device 3 an insulation monitoring device 28 with DC voltage measurement between heating output lines 4 and ground, so that thereby the leakage current of all ohmic bleeder resistors Re 26 with switched off power switching device 3 is detected by all at a heating outlet 4 connected heating elements 25 be formed.

If a significant insulation fault occurs in the heating outlet 32 the determination of the same is done with the insulation monitoring device 28 by DC voltage measurement method and there is a message via an evaluation unit, not shown.

The main disadvantage is that it only the insulation resistance of the entire Heizabganges 32 which is the sum of the conductivities of all bleeder resistors 26 results. As in point heating systems for a power switching device 3 up to approx. 200 heating elements 25 can be arranged, the minimum value of the insulation resistance in dependence on the number of connected heating elements 25 Specify project-specific and in particular with several significant simultaneous bleeder resistors 26 is a safe diagnosis on the basis of the warning message when falling below the insulation resistance is not possible. Another disadvantage is the high manual effort after the occurrence of the warning when falling below the insulation value for detecting the faulty heating elements, since all heating elements 25 Manual individually on site at the switch must be checked.

In isolated networks, such as hospital IT networks, in addition to the isolation monitoring device 28 the arrangement of test voltage generator 5 and differential current transformer 23 known for isolation fault location. In 1 this arrangement is after the power switching device 3 and insulation monitoring device 28 additionally shown. Falling below a detection value of the insulation resistance in an isolated network is done by the insulation monitoring device 28 an activation of the test voltage generator 5 that this a test current of fixed size between Heizabgangsleitung 4 and earth generated and this by means of differential current transformer 23 is detected and the detected individual differential currents to an evaluation unit, not shown, via bus line 33 be transmitted. After evaluating the measured values, an insulation fault location can be carried out.

The main disadvantage is that the test current of fixed size by different bleeder resistors Re 26 unevenly distributed and thereby measurement errors occur, which are particularly large in many arranged heating elements. Therefore, this method is only suitable for fault location in electrical IT network systems in which, for example, insulation faults occur concentratedly at a socket or a consumer and the remaining loads have no appreciable insulation resistance. In electric point heaters, this solution is disadvantageous because heating rods 25 subject to aging and thereby all have a significant insulation error and thus with this method, a reliable detection of the insulation resistance of the faulty heating elements 25 and an insulation fault location is not possible. It is also disadvantageous that between differential current transformers 23 and test signal generator 5 a bus line 33 for data exchange and for the measurement value activation of the differential current transformer 23 is required. This would mean a significant overhead in electrical point heating systems.

It Now follows the description of the peculiarity of the solution according to the invention.

In 2 is for an exemplary development of the insulation resistance Z _ges at time t0 to t5, the time course of the test current I _test and a detected differential current I _diff shown. In off-line operation of the electrical point _heater at the time t0, the activation of a test current I _test with the input of a minimum test current I _Prüf-min . From these, the total insulation resistance Z _{ges is} determined in a known manner. At time t1, for example, the minimum value of the insulation resistance Z _{message is} undershot. As a result, the differential current detection are activated at time t1 and initiated measuring cycles, starting with minimum test current I _test-min for each heating element 25 At the same time during each measurement cycle, the differential _current I _{diff is} detected. In 2 is an example of a differential current transformer 23 the time course of the differential current I _diff as a function of the test current I _test shown. By simultaneous comparison of the differential _currents I _{diff of} all differential current transformers 23 with a setpoint, an evaluation into valid and invalid measurement takes place in each case at time t1 + n. A valid measurement occurs when all differential _currents I _diff greater than or equal to a differential current setpoint I _{diff target} , this differential current setpoint I _{diff target is} about 10% of the measuring range of the differential current transformer.

In the case of a valid measurement, the test current is maintained. In the case of an invalid measurement, for example, an increase of the test current takes place from time t2 and the measuring cycle is repeated in the same way. At time t3, all the differential _currents I _diff are again compared in an analogous manner with the differential current setpoint I _diff-Soll . Exemplary is in 2 in the measuring cycle 2 the differential _current I _diff again smaller than the differential current setpoint I _{diff target} . Thus, the measurement is according to the measurement cycle 2 invalid and at time t3 will be in the new measurement cycle 3 the test current in turn increased by one step.

At time t4, for example, after completion of the measurement cycle 3 determined in comparison that the differential _current I _{diff is} greater than the differential current setpoint I _{diff target} . Assuming at least one measured value, the evaluation takes place at time t4 as a valid measurement and the detection of the insulation resistance of all heating elements 25 , The following will be in the next measurement cycle 4 the test current is reduced again by one stage from time t4.

In 3 is a device consisting of transformer 1 , Point heating distribution 2 with power switching device 3 , Heating outlet pipes 4 , Test voltage generator 5 and via relays (DC voltage) 15 switchable communication test voltage generator 11 and DC voltage source 16 as well as connection box 17 with differential current transformer 23 for each heating element 25 and insulation resistance with ohmic leakage resistance Re 26 shown. The devices are by cable 27 connected to the energy supply. Even before an insulation fault occurs when the power switching device is switched off 3 becomes a test current through a test voltage generator 5 between heating outlet pipes 9 and ground coupled with sensor test current 6 stabilized to a minimum value. In a known way, insulation resistance of the entire heating outlet 32 by detection of the test current via sensor test current 6 and sensor test voltage 7 determined and falls below a minimum value via relay DC voltage 15 the DC voltage source 16 and communication test voltage generator 11 to the heating outlet pipes 4 connected. Voltage sensor junction box 18 detects the DC voltage and activates terminal box via relay 19 the communication connection box 20 and the measuring electronics connection box 29 , Via differential current transformer 23 are leakage currents generated by test current via bleeder resistor 26 for each heating element 25 via analog-to-digital converter connection box 21 detected. In the CPU connection box 22 a comparison of all differential _currents I _{diff of} the differential _{current transformer} takes place 23 with a setpoint I _diff-soll and subsequent evaluation in valid and invalid measurement. A valid measurement is present if at least one differential current I _{diff is} equal to or greater than a setpoint I _diff-soll . An invalid measurement is present if all differential currents are smaller than the setpoint I _diff-soll . With a valid measurement, the transfer of all differential current values I _diff to the test voltage generator takes place 5 and in the case of an invalid measurement, the transmission of a control signal to the test voltage generator takes place 5 , Communication takes place via the cable 27 and communication terminal box 20 and communication test voltage generator 11 ,

In 4 is a plan view of a junction box 17 with terminal strip 30 for connecting the cables 27 and twelve heating rods 25 as well as the measuring electronics 29 shown. The differential current transformer 23 are on the printed circuit board of the measuring electronics 34 arranged so that these just above the gland 31 the cable entry for the heating element connecting cable 24 are arranged.

1

transformer

2

Points heating distribution

3

Power switching device

4

Heizabgangsleitung

5

test voltage

6

sensor Test current

7

sensor Test voltage

8th

power source test voltage

9

CPU test voltage

10

Analog-Digital Converter test voltage

11

communication test voltage

12

Sensor heating voltage

13

Sensor heating

14

sensor DC

15

relay (DC)

16

DC voltage source

17

junction box

18

voltage sensor junction box

19

relay junction box

20

communication junction box

21

Analog-Digital Converter junction box

22

CPU junction box

23

Differential current transformer

24

Heizstableitung

25

heater

26

bleeder

27

electric wire

28

Insulation monitoring device

29

measuring electronics junction box

30

terminal block

31

gland

32

Heizabgang

33

bus line

Claims (7)

Method for detecting and locating insulation defects of heating elements in electrical point heating systems with grounded network in off-line operation, in which a plurality of heating elements are connected to a terminal box via Heizstableitung and the power supply via a switched power line and via detection of the total insulation resistance one Warning message then takes place when it falls below a certain minimum value, characterized in that between Heizabgangsleitungen ( 4 ) and earth by pulse voltage with positive and / or negative polarity an amplitude constant periodic and switchable between a minimum and maximum test current is formed and on this the total insulation resistance is determined and falls below a reporting value a short-circuit proof DC voltage on the cable ( 27 ) of the connection box ( 17 ) and the differential currents for each heating element ( 25 ) are detected at the same time, the test current is then increased by one level up to a maximum value when all the differential currents are less than the setpoint, the insulation resistance for each heater is established across the differential current and the test current is then reduced by one level to a minimum value all differential currents are equal to or greater than a nominal value, and that the insulation resistance of all heating elements 25 is compared with a parameterisable minimum value and, if it falls below an insulation fault, a message is issued with the switch number, installation location and heating rod type. Method according to claim 1, characterized that a period of the test current from at least one positive and at least one negative pulse or one or more positive or negative pulses. Method according to claim 1 or 2, characterized that while of the heating operation, an insulation fault location by time-clock-related forced shutdown of the power switching device is guaranteed at maximum rail temperature. Device for carrying out the method according to one of claims 1 to 3, characterized in that the test voltage generator ( 5 ) with sensor test current 6 , Sensor test voltage ( 7 ), controllable current source test voltage generator ( 8th ), CPU test voltage generator ( 9 ) and communication test voltage generator ( 11 ) a switchable periodic test current between Heizabgangsleitung ( 4 ) and earth forms and falls below a reporting value of the total insulation resistance via a relay DC voltage ( 15 ) a short circuit proof DC voltage source ( 16 ) and that a measuring electronics connection box ( 29 ), consisting of voltage sensor terminal box ( 18 ), Relay connection box ( 19 ), Communication terminal box ( 20 ), Analog-to-digital converter terminal box ( 21 ), CPU connection box ( 22 ) and differential current transformer ( 23 ) for activation, power supply, acquisition, evaluation and communication of leakage currents per heating rod ( 25 ) via differential current detection is present and that in the CPU terminal box ( 22 ) a setpoint value is stored and the detected differential currents are cyclically compared with this setpoint in the CPU terminal box, so that if all differential currents are smaller than the setpoint, the detected differential current values are invalid and a control signal for increasing the test current by one stage via communication terminal box ( 20 ), Electric wire ( 27 ) and communication test voltage generator ( 11 ) and that when at least one differential current is greater than or equal to the setpoint, the detected differential current values and a control signal for reducing the test current by one stage via communication terminal box ( 20 ), Electric wire ( 27 ) and communication test voltage generator ( 11 ) and a forwarding of the differential currents via bus line ( 33 ) to a higher-level control and, after a comparison with minimum values, a message of the faulty heating element ( 25 ) with point specification, installation location and heating rod type. Device according to claim 4, characterized in that the voltage supply of the test voltage generator ( 5 ) takes place from the control voltage and thereby insulation resistance localization is also possible outside the heating operation. Device according to claim 5, characterized in that the communication between test voltage generator ( 5 ) and connection box ( 17 ) via data line or radio. Device according to claim 4, characterized in that the measuring electronics ( 29 ) as a printed circuit board with arrangement of differential current transformers ( 23 ) in the pitch of stuffing box glands ( 31 ) for Heizstableitungen ( 24 ) is executed and shed is and in the junction box ( 17 ), that congruence between the pitch of Stopfbuchsverschraubungen ( 31 ) of the heating stave ( 24 ) with the openings of the differential current transformer ( 23 ) consists.