U.S. patent application number 09/117585 was filed with the patent office on 2001-09-06 for method of establishing the residual useful life of contacts in switchgear and associated arrangement.
Invention is credited to ELSNER, NORBERT, POHL, FRITZ.
Application Number | 20010019268 09/117585 |
Document ID | / |
Family ID | 7784059 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019268 |
Kind Code |
A1 |
POHL, FRITZ ; et
al. |
September 6, 2001 |
METHOD OF ESTABLISHING THE RESIDUAL USEFUL LIFE OF CONTACTS IN
SWITCHGEAR AND ASSOCIATED ARRANGEMENT
Abstract
It has been suggested that to determine the remaining lifetime
of contactor contacts, the contact spring action at the clearance
gap can be determined as a substitute criterion for contact
erosion, and to determine the erosion of the contact points, the
change in spring action during the shutdown cycle can be measured
and converted to the remaining lifetime, for which purpose, the
time of the armature movement from the start of the armature
movement to the start of contact opening is measured with the
solenoid actuator having an armature with solenoids and associated
yoke. According to the present invention, the measured values of
the time signal t.sub.k of contact opening on the load side of the
switching device monitored and the time signal t.sub.A are
determined by voltageless signaling of the start of armature
movement. In particular for use in three-phase systems, the
switching voltage is measured as a voltage change at an artificial
neutral point. In the respective arrangement, a voltageless signal
line (20) is provided between the switching device (1) and analyzer
unit (100, 200, 300).
Inventors: |
POHL, FRITZ; (HEMHOFEN,
DE) ; ELSNER, NORBERT; (BUBENREUTH, DE) |
Correspondence
Address: |
BIRCH,STEWART,KOLASCH & BIRCH,LLP
8110 GATEHOUSE ROAD
SUITE 500 EAST
FALLS CHURCH
VA
22042
US
|
Family ID: |
7784059 |
Appl. No.: |
09/117585 |
Filed: |
July 30, 1998 |
PCT Filed: |
January 29, 1997 |
PCT NO: |
PCT/DE97/00173 |
Current U.S.
Class: |
324/423 |
Current CPC
Class: |
H01H 2071/044 20130101;
H01H 1/0015 20130101; H01H 9/167 20130101 |
Class at
Publication: |
324/423 |
International
Class: |
G01R 031/02; G01R
031/327 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 1996 |
DE |
196 03 310.1 |
Claims
1. Method of determining the remaining lifetime of contacts in
switchgear, in particular contactor contacts, the so-called contact
spring action at the contact gap being determined as a substitute
criterion for contact erosion, and the change in spring action
during the shutdown cycle being measured in each instance to
determine the erosion of the contact points and being converted to
the remaining lifetime, for which purpose the time of the armature
movement from the start of armature movement to the start of
contact opening is measured when the contactor is driven by an
armature with solenoid and associated yoke, characterized by a
measured value acquisition of contact opening on the load side of
the monitored switchgear and by a voltageless signaling of the
start of armature movement.
2. Method according to claim 1, characterized in that for use in
three-phase systems, the start of contact opening of the contact
points with the greatest erosion of one of the switching poles is
detected by measuring the switching voltage as voltage change at an
artificial neutral point on the load side of the switching device
monitored, from which the remaining lifetime of the main contacts
of the contactor can be determined.
3. Method according to claim 2, characterized in that for use in
three-phase systems with three external conductors (L1, L2, L3) and
a neutral conductor (N), the start of contact opening of the
contact points with the greatest erosion of one of the four
switching poles is detected by determining the switching voltage as
the voltage change between the artificial neutral point of the
external conductors (L1, L2, L3) and the neutral conductor (N) on
the load side of the monitored switchgear.
4. Method according to claim 1, characterized in that for use in
d.c. systems, the start of contact opening of the contact points
with the greatest erosion on one of the switching poles is
determined by measuring the switching voltage as a voltage change
between the phase conductors (L+, L-) on the load side of the
monitored switching device, from which the remaining lifetime of
the main contacts of the contactor can be determined.
5. Arrangement for carrying out the method according to claim 1 or
one of claims 2 through 4 with an analyzer unit for displaying the
remaining lifetime, characterized in that between the switching
device (1) and analyzer unit (100, 200, 300), a voltageless signal
line (8, 8', 38) is provided on the armature (3) and yoke (4) of
the solenoid (5) of the switching device (1).
6. Arrangement according to claim 5, characterized in that the
analyzer (100, 200, 300) is on the load side between the switching
device, in particular contactor (1), and the electric consumer
(20).
7. Arrangement according to claim 5, characterized by a first
monitoring module (101, 201) for detecting contact opening and a
second monitoring module (102, 202) for detecting armature
opening.
8. Arrangement according to claim 5, characterized by a
microprocessor (105, 205, 305) for determining the instantaneous
contact spring action from the time signals supplied by the two
monitoring modules (101, 201; 102, 202).
9. Arrangement according to one of claims 5 through 8 for use in
three-phase systems by the method according to claim 2,
characterized in that there is a circuit for generating a time
signal at the start of contact opening of the main contacts with
the greatest erosion, and the contact voltage (arc voltage) of the
three-pole switching device in the three-phase system is measured
at artificial neutral point (15) with this circuit.
10. Arrangement according to one of claims 5 through 8 for use in
three-phase systems by the method according to claim 2,
characterized in that there is a circuit for generating a time
signal at the start of contact opening of the main contacts with
the greatest erosion, and this circuit detects the contact voltage
(arc voltage) of the four-pole switching device with the three
external conductors (L1, L2, L3) and the neutral conductor (N) by
measuring the voltage between the artificial neutral point (15) and
the voltage of the neutral conductor (N) on the load side of the
switching device, in particular as a reference potential of a
resistor (17) at frame potential (M).
11. Arrangement according to claim 9 or claim 10, wherein for use
in three-phase motors, an overload relay is provided to protect the
motor load, characterized in that the overload relay (210) and the
analyzer unit (201, 202, 205) are integrated into a common control
device (200) for detecting the remaining lifetime.
12. Arrangement according to one of claims 5 through 8, for use in
contactors in d.c. systems by the method according to claim 1,
characterized in that a series connection of contact gaps is
provided for a single-pole or two-pole connection of the electric
system, and the measuring leads (30) are connected to the electric
load (20).
13. Arrangement according to claim 11, characterized in that the
analyzer unit (300) as a monitoring module for contact opening has
a blocking capacitor (32) for suppressing the d.c. component,
limiting resistors (34, 36), a Zener diode (33) for voltage
limiting and an optical coupler (35) for voltageless measurement of
the contact voltage.
14. Arrangement according to one of the preceding claims,
characterized by a system for data transmission, in particular a
bus system.
Description
[0001] The present invention relates to a method of determining the
remaining lifetime of contacts in switchgear, in particular
contactor contacts, wherein the contact spring action at the
contact gap is determined as a substitute criterion for contact
erosion, and the change in spring action during the shutdown cycle
is measured to determine the contact erosion of the contact points
and is converted to the remaining lifetime, for which purpose the
time of the armature movement from the start of the armature
movement to the start of contact opening is measured when the
contactor is driven by an armature with solenoid and associated
yoke. The invention also relates to the respective arrangement for
carrying out the method, with an analyzer unit for displaying the
remaining lifetime.
[0002] In the older German Patent No. 44 27 006 A0, which is not a
prior publication, the remaining lifetime of a contactor in the
shutdown cycle is derived from the difference in time between the
start of the armature opening movement and the start of contact
opening. Using an analysis algorithm, a microprocessor then
determines from the time difference value the present value of the
contact spring action, which decreases from its value when new
(=100% remaining lifetime) to its minimum value (=0% remaining
lifetime) due to contact erosion. The time signals required for
this are detected first by interrupting an auxiliary circuit over
the armature and yoke of the solenoid actuator and also by the
contact voltage at the main contacts and are converted to
well-defined voltage pulses, for which purpose measuring leads must
be attached.
[0003] Attaching measuring leads (six leads for three-phase
current) for analysis of contact voltages may be problematical
inasmuch as
[0004] a) the possibility of vagabond voltage forming from the
infeed side to the load side of the contactor cannot be ruled
out,
[0005] b) the required insulation voltage endurance (8 kV) results
in a higher cost for the analysis circuit, and
[0006] c) integrating the measuring leads into the contactor and
connecting them to a plug-in connector necessitates design and
safety-related changes.
[0007] Therefore, the object of the invention is to propose a
method and the respective arrangement, wherein the start of contact
opening need not be determined over measuring leads on both the
feed and load ends of the main circuit.
[0008] This object is achieved according to this invention by
measured value acquisition on the contact gap on the load side of
the monitored switching device and by voltageless signaling of the
start of armature movement. For use in three-phase systems, the
start of contact opening of the contact points with the greatest
erosion of one of the switching poles is preferably detected by
measuring the switching voltage as the change in voltage at an
artificial neutral point on the load side of the switching device
monitored, from which it is then possible to determine the
remaining lifetime of the main contacts of the contactor in
addition to the start of armature movement.
[0009] In the respective arrangement with an analyzer unit for
displaying the remaining lifetime, there is a voltageless signal
line on the armature and yoke of the solenoid actuator of the
switching device between the switching device and the analyzer
unit. The analyzer unit is thus located between the switching
device and the electric consumer on the load side.
[0010] To reduce the technical complexity, it is thus no longer
necessary to monitor each main circuit individually with regard to
contact erosion in three-phase systems in particular, but instead
only the spring action of the most eroded contacts of one of the
three switching poles is measured to determine the remaining
lifetime of the main contacts of the contactor. Furthermore, it is
possible to determine the remaining lifetime without a strict
spatial correlation with the contactor, the start of the armature
opening movement being signaled to the analyzer unit over a
voltageless signal line as contact interruption between armature
and yoke.
[0011] Voltageless signaling in the aforementioned context is
understood to refer to electric contacting between armature and
yoke, in contrast with a voltage signal, such as the contact
voltage on the main contacts.
[0012] Details and additional advantages of the present invention
are derived from the following description of the figures and
embodiments with reference to the drawing in combination with the
subclaims. They illustrate in block diagrams:
[0013] FIG. 1: determining the remaining lifetime of contactors in
the shutdown cycle,
[0014] FIG. 2: generating the time signal for the first main
circuit of contactors to clear in the shutdown cycle in a
three-phase system,
[0015] FIG. 3: the example of determining the remaining lifetime of
a reversing contactor circuit in particular, and
[0016] FIG. 4: determining the remaining lifetime of contactors in
the shutdown cycle in d.c. systems.
[0017] Parts with the same function are labeled with the same
notation in the figures. In some cases the figures are described
jointly.
[0018] FIG. 1 shows a schematic diagram of a device for determining
the remaining lifetime and associating it with a contactor 1.
Analyzer unit 100 is located between contactor 1 and electric
consumer 20, e.g., a motor, on load side 10, and it is contacted
with external conductors L1, L2, L3 over a first monitoring module
101 for detecting contact opening. A two-wire communication line 8
connects armature/yoke contact 7 of contactor 1 to a second
monitoring module 102 for detecting opening of the armature. A
microprocessor 105 determines the instantaneous contact spring
action from the time signals supplied by monitoring modules 101 and
102 and determines from this the remaining electrical lifetime of
the main contacts.
[0019] The value determined by analyzer unit 100 for the remaining
lifetime is displayed on an output unit 106 and can be output over
a bus system for further processing.
[0020] As shown by control measurements on a contactor with the
armature/yoke contact brought out, the time signals from which the
remaining lifetime is determined are subject to time fluctuations
due to mechanical tolerances and decay of the magnetic force. The
time difference between the time signals may therefore differ by a
few 1/10 ms between two successive analyses. To avoid a
corresponding fluctuation in the output quantity, the remaining
lifetime is determined on the basis of a sliding average, e.g., the
last ten measurements. Therefore, an accuracy of 1/10 mm is
considered realistic in determining the contact spring action.
Faulty analyses in determining the time difference can be prevented
by analyzing only those time signals within a predetermined time
window.
[0021] FIG. 2 shows an example of a circuit for generating a time
signal t.sub.k at the start of contact opening of the most eroded
main contacts. The essential characteristic of this circuit is that
it measures the contact voltages (arc voltage) of a triple-pole
switching device in a three-phase system at "artificial" neutral
point 15. For the contact voltages, i.e., the arc voltage at
interconnection point 15 of the output lines over fine-wire fuses
11 and resistors 12 (R=160 k.OMEGA.), the following equations
hold:
U.sub.1+U.sub.2+U.sub.3=O,
I.sub.1+I.sub.2+I.sub.3=O
U.sub.1-U.sub.STPR*I.sub.1+L*d/dt(I.sub.1)+UB.sub.1
[0022] U.sub.2-U.sub.STP=R*I.sub.2+L*d/dt(I.sub.2)+UB.sub.2
U.sub.3-U.sub.STP=R*I.sub.3+L*d/dt(I.sub.3)+UB.sub.3
Total:U.sub.STP=-(UB.sub.1+UB.sub.2+UB.sub.3)/3,
[0023] where the following symbology has been selected:
[0024] U.sub.i=phase voltages
[0025] I.sub.1=phase currents,
[0026] U.sub.Bi=arc voltages,
[0027] i=1, 2, 3
[0028] U.sub.STP=neutral point displacement voltage,
[0029] R=ohmic load,
[0030] L=inductive load.
[0031] With the main contacts of the contactor closed
(UB.sub.1=UB.sub.2=UB.sub.3=0), the neutral point displacement
voltage would have to be 0 volt. In fact, however, the real phase
voltages do not correspond to ideal sinusoidal voltages, so that
the total of the phase voltages differs from zero and the
neutral-to-ground voltage fluctuates around the voltage zero line.
This signal noise can be reduced by a high-pass filter 16 (e.g.,
where C=3 nF, R.sub.parallel=500 k.OMEGA.) so that a
signal-to-noise ratio of >10 is achieved. Electronic frame
potential M can be picked off over a measuring shunt (e.g.,
R.sub.Me.beta.=10 k.OMEGA.). Time signal t.sub.k, i.e. the voltage
signal at "artificial" neutral point 15, is processed according to
its polarity by one of two comparators 18 and 18' whose outputs are
coupled to the signal output of the monitoring module for contact
opening via an OR gate 19.
[0032] FIG. 3 shows a device for determining the remaining lifetime
on the example of a contactor reversing starter with two contactors
1 and 2; for application in three-phase motors, there are many
different terminal conditions for controlling the speeds and
direction of rotation.
[0033] The main circuits switched by contactors 1 and 2 correspond
in basic design to the main circuits according to FIG. 1 or 3.
There is usually an overload relay 210 on the load side of
contactor 1 or 2 to protect the motor load. It is therefore
expedient to integrate overload relays 210 and the device for
determining remaining lifetime into a common control unit. As
already described in the older German Patent No. 44 27 006 A0, this
control unit could have additional functions for monitoring the
circuit state, so that this would ultimately result in a "general"
control unit 200 for monitoring the entire electric system.
[0034] In the example in FIG. 3, only one second measuring channel
is needed on monitoring module 202 for armature opening to detect
the remaining lifetime of both contactors 1 and 2. Microprocessor
205 attributes the calculated lifetime to the contactor represented
by the signaling measuring channel.
[0035] In three-phase systems, not only three-pole consumers, but
also four-pole consumers, e.g., ohmic loads, are connected to the
system and disconnected from it by electric switchgear. The
electric switchgear have four switching poles, three of which are
connected to external conductors L1, L2, L3, while the fourth
switching pole is connected to the neutral conductor. Each of these
four switching poles is subject to contact erosion when the
four-pole consumer is connected and disconnected, so that wear on
all contact points must be monitored, and the remaining lifetime
must be determined according to the most eroded contact points.
[0036] The latter is achieved by measuring the switching voltage of
one of the three switching poles connected to external conductors
L1, L2, L3 at artificial neutral point 15 and measuring the
switching voltage of the fourth switching pole connected to neutral
conductor N on neutral conductor N. Both the voltage of artificial
neutral point 15 and the voltage of neutral conductor N are
detected on load side 10 of monitored switching device 1, and the
error voltage, the difference between the two voltage values, is
analyzed as the switching voltage of the first, most eroded contact
tips to clear.
[0037] FIG. 4 shows a device for detecting the remaining lifetime
of contactors in d.c. systems. Depending on the system d.c. voltage
and whether or not the d.c. system is grounded, the contact gaps
are usually connected in series, and the connection of the electric
system is designed with a single pole or two poles. To obtain a
uniform terminal condition for the test connectors for monitoring
contact opening and to rule out vagabond voltage from the infeed
side to the load side of contactor 1, the measuring leads are
connected to load side 10.
[0038] In the embodiment in FIG. 4, a monitoring module 300 has
individual circuit elements 31 through 38. Specifically, it shows a
contactor 1 with load side 10, a d.c. motor 20 and output lines 30
for connecting monitoring module 300. It contains two fine-wire
fuses 31, an RC combination 32 (C=0.22 MF, R.sub.1=1 k.OMEGA.), a
Zener diode 33, a resistor 34 (R.sub.2=330 .OMEGA.) and an optical
coupler 35, whose output is connected to voltage U across a
resistor 36 (R=106 k.OMEGA.).
[0039] Blocking capacitor C in monitoring module 300 for contact
opening serves to suppress the d.c. component; associated limiting
resistors R1 and R2 with the Zener diode serve to limit the
voltage, and optical coupler 35 in particular is for voltageless
measurement of the contact voltage. A microprocessor 305 determines
the contact spring action from time signal t.sub.k of contact
opening in the delay to the time signal of armature opening, and
from this it determines the remaining lifetime of the main contacts
of the contactor.
[0040] In all embodiments, the values determined by the
microprocessors can be displayed directly on associated output
units or sent to a system for data transmission, in particular a
bus system, for further analysis.
* * * * *