JP2008141823A - Motor protective relay - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make protection possible by detecting a failure without causing malfunction even while a starting current is flowing in a motor 21. <P>SOLUTION: A motor protective relay has a dependent time-lag element 1 and a definite-time element 2. It is configured to use the dependent time-lag element 1 during starting time based on a preset starting time of the motor 21 and to change over to the definite-time element 2 by a changeover switch 4 after the lapse of the starting time. The dependent time-lag element 1 is set in such a way that a trip command 9 is not outputted with the starting current during the starting time and that the trip command 9 is outputted if an overcurrent is caused to occur by a locking failure. After the lapse of the starting time, the definite-time element 2 performs protective operation reliably and speedily if an overload or the lock failure occurs. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a motor protection relay that protects a motor by detecting an overcurrent.

  In the conventional motor protection relay, a bypass circuit is provided in parallel with the motor protection relay, and the protection time can be arbitrarily set by arbitrarily operating the contact of the auxiliary relay (see, for example, Patent Document 1).

JP 2005-27362 A

  In the conventional motor protection relay (motor protection relay), while the starting current is flowing in the motor, the protection relay is deactivated by bypassing the current input to the protection relay. There is a problem that protection is not possible when a failure occurs. Moreover, it is necessary to provide an auxiliary relay and a timer outside the motor protection relay, and it is difficult to simplify the device configuration of the entire protection circuit.

  The present invention was made to solve the above-described problems, and has a structure of a motor protection relay that can detect and protect a failure even when a starting current flows through the motor. It is an object to provide a simple apparatus configuration.

  The motor protection relay according to the present invention includes a start detection means for detecting the start of the motor, and an indefinite time when the overcurrent is detected based on the motor current signal and the protection operation command is output after a short time as the current signal increases. A time limit element that outputs a protection operation command after elapse of a predetermined time when an overcurrent is detected based on the current signal of the motor, and a switching means. The switching means uses the inverse time element during the start time from the start time of the motor detected by the start detection means based on a preset start time of the motor, and after the start time has elapsed. Switch to the above fixed time element.

  The motor protection relay according to the present invention includes an infinite time element and a infinite time element, and uses the infinite time element during the starting time from the start of the motor, and switches to the infinite time element after the starting time has elapsed. During the start-up time, malfunction due to the start-up current can be prevented, and the failure detection and protection operation can be performed. After the start-up time elapses, the protection operation is reliably performed when an overload or a restraint failure occurs. In addition, since the start detection means is provided to detect the start of the motor in the motor protection relay and the time limit element is operated, the motor protection relay can be configured without requiring a special external circuit. The device configuration can be simplified.

Embodiment 1 FIG.
FIG. 1 is an internal block diagram of a motor protection relay according to Embodiment 1 of the present invention. As shown in the figure, two time limit elements, an inverse time limit element 1 and a fixed time limit element 2, are incorporated, and a switching means including a time limit element switching determination unit 3 and an input changeover switch 4 for switching between the two time limit elements is provided. . In addition, it includes a return control unit 5 arranged in the subsequent stage of the two time limit elements 1 and 2 and an LED 6 for operation display.

  The time limit element 1 includes a level determination unit 1a that detects an overcurrent and a time limit timer 1b. When the motor current signal 7 that is an analog signal is input and the level determination unit 1a detects an overcurrent, The inverse timer 1b outputs a trip command 9 that is a protection operation command after a short time has elapsed as the current signal 7 increases. The time limit element 2 includes a level determination unit 2a that detects an overcurrent and a time limit timer 2b. When the overcurrent is detected by the level determination unit 2a with the motor current signal 7 as an input, the time limit element 2 is set to a predetermined time. Trip command 11 is output after elapse. Further, when each level determination unit 1a, 1b detects an overcurrent, it outputs an overcurrent detection signal 8, 10 to blink the LED 6 and display an operation. Trip commands 9 and 11 are output to the outside via the return control unit 5 as operation signals, and the LED 6 is turned on to display a protection operation. 14 and 15 are OR circuits.

  The time limit element switching determination unit 3 includes a start detection unit 3a and a start time determination unit 3b as start detection means. The start detection unit 3a receives a D / I signal 12 interlocked with the contact of the circuit breaker and starts the motor. Is detected, the start time determination unit 3b outputs a switching signal 13 to the input changeover switch 4 when a preset start time of the motor has elapsed. The input changeover switch 4 is switched so that the current signal 7 is input to either the inverse time limit element 1 or the fixed time limit element 2.

  As shown in FIG. 2, when an overcurrent flows through the motor 21, the motor protection relay 20 outputs a trip command (operation signal) to the circuit breaker 23 that interrupts the motor feeder 22 that is an electric path to the motor 21. Further, the D / I signal 12 indicating the state of the pallet switch 24 interlocked with the contact of the circuit breaker 23 is input to the motor protection relay 20.

The operation of the motor protection relay configured as described above will be described below with reference to FIGS. FIG. 3 is a diagram showing an input D / I signal 12 and selection / non-selection by the change-over switch 4 of the time limit elements 1 and 2. FIG. 4 is a diagram showing a waveform of the motor current and a timed operation state.
First, when the motor feeder 22 is interrupted by the circuit breaker 23, the D / I signal 12 is OFF, the infinite time element 1 is in an operable state with the input of the current signal 7, and the fixed time element 2 is Since there is no input, it is in a return state.
Next, when the circuit breaker 23 is turned on and the D / I signal 12 is turned ON, the start detection unit 3a detects the start of the motor 21, and the start time determination unit 3b counts the time from the start point and is preset. When the starting time is reached, the change signal 13 is output to the input changeover switch 4.

As shown in FIG. 4, when the circuit breaker 23 is turned on and the motor 21 is started, a starting current several times the rated current flows through the motor 21 for several seconds to several tens of seconds. Although the time during which the starting current flows varies depending on the type of motor 21 and the nature of the load, the starting time is set in advance with a margin for the time during which the starting current flows and is held in the starting time determination unit 3b.
Further, when the motor 21 is started, the motor protection relay performs an infinite time operation, that is, the current signal 7 of the motor 21 is input to the infinite time element 1, and an overcurrent exceeding the overload level is detected by the level determination unit 1a. Then, the infinite time timer 1b outputs a trip command 9 which is a protection operation command after a short time has elapsed as the current value of the current signal 7 increases. Here, the counter-time timer 1b is after a time longer than the set start time in the current signal 7 of the start current level, and after a time shorter than the set start time in the current level when the restraint failure of the motor 21 occurs. It is assumed that the trip command 9 is set to be output.
While the overcurrent is detected and the counter-time timer 1b is counting, the LED 6 blinks by the overcurrent detection signal 8, and when the trip command 9 is output, the LED 6 is turned on. Is output as an operation signal of the motor protection relay to interrupt the circuit breaker 23.

Then, as described above, when the set start time has elapsed, the start time determination unit 3b outputs the change signal 13 to the input changeover switch 4, the input of the current signal 7 of the motor 21 is changed, and the fixed time element 2 The motor protection relay performs a fixed time operation. That is, when an overcurrent is detected by the level determination unit 2a, the trip command 11 is output after a predetermined time has elapsed. The inverse time element 1 is in a return state because there is no input.
Also in this case, while the overcurrent is detected and the fixed time timer 2b is counting, the LED 6 blinks by the overcurrent detection signal 10, and when the trip command 11 is output, the LED 6 is lit and this trip is detected. The command 11 is output as an operation signal for the motor protection relay to shut off the circuit breaker 23.

When the circuit breaker 23 is cut off, the start detection unit 3a detects that the D / I signal 12 is turned OFF, outputs the switching signal 13 to the input selector switch 4, and inputs the current signal 7 (current 0). To be connected to the inverse time element 1.
Note that it takes a certain amount of time for the trip command 9 to be output and the circuit breaker 23 to be cut off. If the input of the current signal 7 is switched from the counter-time element 1 to the fixed time element 2 during that time, the interruption operation is normal. Therefore, the return control unit 5 continues to output the trip command 9 for a predetermined time and normally shuts off the circuit breaker 23.

  As described above, in this embodiment, the motor protection relay is provided with the infinite time element 1 and the infinite time element 2, and the infinite time element 1 is set during the start time based on the preset start time of the motor 21. After the starting time has elapsed, switching to the fixed time element 2 was made. For this reason, using the inverse time element 1, the trip command 9 can be output and a protection operation can be performed if an overcurrent due to a restraint failure occurs without outputting a trip command due to the start current while the start current of the motor 21 flows. . Further, after the start time has elapsed, if an overload or a restraint failure occurs, a protective operation can be performed quickly and reliably. Further, since the starting time is set longer than the time until the starting current is generated and no longer decreases, it is possible to prevent the fixed time element 2 from malfunctioning immediately after the input is switched to the fixed time element 2. In this way, it is possible to detect the start without requiring a special circuit such as an auxiliary relay or a timer, and to perform an appropriate protection operation during and after the start time.

Embodiment 2. FIG.
In the first embodiment, the input switch 4 is used to switch the current signal 7 to either the inverse time element 1 or the fixed time element 2, but in the second embodiment, the inverse time element 1 shows switching between 1 and a fixed time element 2 on the output side.
FIG. 5 is an internal block diagram of a motor protection relay according to Embodiment 2 of the present invention. As shown in the figure, two time limit elements, an inverse time limit element 1 and a fixed time limit element 2, are incorporated, and a switching means including a time limit element switching determination unit 3 and an output changeover switch 16 for switching between the two time limit elements is provided. . Further, the OR circuits 14 and 15 provided on the output side are deleted. Other configurations are the same as those in the first embodiment.

When the motor feeder 22 is interrupted by the circuit breaker 23, the D / I signal 12 is OFF, but the anti-time element 1 and the time limit element 2 are in an operational state with the input of the current signal 7 connected thereto. At this time, the output changeover switch 16 connects the output of the infinite time element 1 to the external output.
When the circuit breaker 23 is turned on and the motor 21 is started, the current signal 7 of the motor 21 is input to both the time limit element 1 and the time limit element 2. Thereby, both the time limit elements 1 and 2 operate. When the D / I signal 12 is turned on and the start detection unit 3a detects the start of the motor, the start time determination unit 3b outputs the switch signal 17 when the preset motor start time has elapsed. 16 is output. The output changeover switch 16 switches from the infinite time element 1 to the fixed time element 2 and connects the output of the infinite time element 1 to the external output.

In this embodiment, when the motor 21 is started, both the infinite time element 1 and the fixed time element 2 operate, but one of the trip commands 9 and 11 to be output is switched and output to the outside. The During the set start time, the trip command 9 for the inverse time limit operation 1 is output, and after the start time has elapsed, the trip command 11 for the time limit element is output.
For this reason, as in the first embodiment, while the starting current of the motor 21 flows, an overcurrent due to a restraint failure or the like occurs without using the inverse time element 1 to output a trip command with the starting current. A trip command 9 can be output to perform protective operation. In addition, after the start-up time has elapsed, if the overload or restraint failure occurs using the time limit element 2, the protective operation can be performed quickly and reliably, and the same effect as in the first embodiment can be obtained. In addition, the time limit element 2 is already operating at the time of output switching, and there is an effect that the operation time related to the processing time of the time limit timer 2b does not occur.

  In the first and second embodiments, the D / I signal 12 interlocked with the contact of the circuit breaker 23 is input to detect the start of the motor 21. However, as shown in FIG. A voltage signal detected by providing a voltage detector 25 may be input. Since the voltage is applied to the motor 21 by turning on the circuit breaker 23, the turn-on of the circuit breaker 23, that is, the start of the motor 21 can be detected by acquiring the voltage signal. Thereby, the start of the motor 21 can be detected with high reliability.

  In addition, as shown in FIG. 7, the start of the motor 21 may be detected by inputting a current signal detected by a current detector 26 provided in the motor feeder 22. By turning on the circuit breaker 23, a current flows through the motor 21, and the start of the motor 21 can be detected by the current signal. This current detector 26 can be shared with the one installed for overcurrent protection, that is, the motor 21 can be started by inputting the current signal 7 input to the time limit elements 1 and 2 to the start detection unit 3a. It can be detected. Thereby, there is an effect that the start can be detected without installing an extra device for detecting the start of the motor 21.

It is an internal block diagram of the motor protection relay by Embodiment 1 of this invention. It is a figure explaining the starting detection of the motor in the motor protection relay by Embodiment 1 of this invention. It is a figure which shows the selection / non-selection by D / I signal interlock | cooperated with the contact of the circuit breaker by the switch of each time limit element by Embodiment 1 of this invention. It is a figure which shows the waveform of a motor current, and a time limit operation state by Embodiment 1 of this invention. It is an internal block diagram of the motor protection relay by Embodiment 2 of this invention. It is a figure explaining the starting detection of the motor in the motor protection relay by another example of Embodiment 2 of this invention. It is a figure explaining the starting detection of the motor in the motor protection relay by another example of Embodiment 2 of this invention.

Explanation of symbols

1 time limit element, 2 time limit element, 3 time limit element switching determination section, 3a start detection section,
3b Start time determination unit, 4 input selector switch, 7 current signal,
9, 11 Trip command, 12 D / I command, 20 Motor protection relay, 21 Motor, 22 Motor feeder, 23 Circuit breaker, 24 Pallet switch, 25 Voltage detector,
26 Current detector.

Claims (6)

Start detection means for detecting the start of the motor, an over-time element that outputs a protection operation command after a short period of time when the overcurrent is detected based on the current signal of the motor, and the current signal of the motor When the overcurrent is detected based on the time limit element that outputs a protection operation command after a lapse of a predetermined time, and the motor start time detected by the start detection means based on a preset motor start time And a switching means for switching to the fixed time element after the start time elapses after the start time elapses. The current signal of the motor is input to one of the time limit elements selected by the switching means among the inverse time limit element and the fixed time limit element, and the protection operation command output from the selected time limit element is used. The motor protection relay according to claim 1. The current signal of the motor is input to both the anti-time limit element and the fixed time element, and the protection operation command output from one time limit element selected by the switching means is used. The motor protection relay according to 1. The motor protection according to any one of claims 1 to 3, wherein the start detection means detects the start of the motor by a digital signal input interlocked with a contact of a circuit breaker that interrupts an electric path to the motor. relay. The start detection means detects the start of the motor by inputting a voltage signal detected on the motor side from a circuit breaker that interrupts an electric path to the motor. The motor protection relay described in Crab. The motor protection relay according to any one of claims 1 to 3, wherein the start detection means detects the start of the motor by inputting a current signal detected in an electric path to the motor.

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