Drilling motor DC contactor disconnection protection system and method based on current detection

Abstract

The present invention discloses a drilling motor DC contactor disconnection protection system and method based on current detection. The DC contactor is respectively connected in series with a thyristor rectifier and a motor, and the thyristor rectifier is respectively connected in series with an incoming line circuit breaker and a programmable DC speed regulator, and the programmable DC speed regulator is connected to the incoming line circuit breaker; the output end of the DC contactor is connected to the input end of a programmable PLC through a current detection device, and the programmable DC speed regulator and the stop conversion switch are also connected to the input end of the programmable PLC. The output end of the programmable PLC is respectively connected to the motor and the alarm device, and the programmable PLC is connected to a host computer. The present invention compares the external detection loop current Current1 and the internal acquisition current Current2 of the DC speed regulator in real time, and disconnects the DC contactor after the load current is reduced to a safe value through the control of the programmable PLC, which can effectively prevent the damage of the main contacts of the DC contactor, reduce equipment maintenance costs, reduce equipment accidents, and extend the life of the DC contactor.

Description

Technical Field

[0001] The invention belongs to the technical field of DC contactors for oil drilling platforms, and relates to a drilling motor DC contactor disconnection protection system and method based on current detection. Background Art

[0002] A DC contactor is a type of contactor used in DC circuits, primarily for controlling DC circuits (main circuit, control circuit, excitation circuit, etc.). The iron core of a DC contactor is eddy-free and is typically made of soft steel or industrial pure iron in a round shape. Because the attraction coil of a DC contactor is energized by DC, there is no inrush starting current and no violent core impact, resulting in a long lifespan and making it suitable for applications with frequent starts and stops.

[0003] When a DC contactor disconnects, the magnetic field energy stored in the inductive load is instantly released, generating a high-energy arc at the disconnection point. This arc typically bypasses the insulator and travels along its surface, damaging it through arcing or burning. Because the arc distance of a DC contactor is long, disconnecting while on load is more likely to cause arcing damage or burning of the coil, leading to damage to the DC contactor and serious equipment failures and production losses. Therefore, preventing DC contactors from disconnecting while on load is a pressing issue. Summary of the Invention

[0004] The purpose of the present invention is to prevent the DC contactor from disconnecting under load and to provide a drilling motor DC contactor disconnection protection system based on current detection.

[0005] Another object of the present invention is to provide a method for performing disconnection protection of a DC contactor using the above system.

[0006] The present invention adopts the following technical solutions:

[0007] An oil drilling motor DC contactor disconnection protection system based on current detection, wherein one end of the DC contactor KM is connected in series with a thyristor rectifier SCR, and the other end is connected in series with a motor M. The thyristor rectifier SCR is connected in series with an incoming line circuit breaker Q and a programmable DC speed regulator, respectively. The programmable DC speed regulator is connected to the incoming line circuit breaker Q through the auxiliary circuit UV of the incoming line circuit breaker Q; the output end of the DC contactor KM is connected to the input end of the programmable PLC through a current detection device, the programmable DC speed regulator is also connected to the input end of the programmable PLC, the input end of the programmable PLC is also connected to a stop transfer switch, the output end of the programmable PLC is respectively connected to the motor M and the alarm device, and the communication interface of the programmable PLC is also connected to the host computer through a system bus.

[0008] The method for performing DC contactor disconnection protection using the above system of the present invention comprises the following steps:

[0009] S1. The current detection device detects the current signal current1 on the output side of the DC contactor and inputs it to the programmable PLC. The programmable PLC collects the current signal current2 of the DC speed regulator. The programmable PLC sets the system error value current4 of the difference between current1 and current2 when the motor M stops, and sets the safety value current5 of the difference between current1 and current2 when the motor M stops, where current5>current4.

[0010] When S2 and the silicon controlled rectifier (SCR) are operating normally, if the operator or the system triggers the stop switch to send a signal to disconnect the DC contactor, the programmable PLC receives the signal and performs a difference operation on current1 and current2 to obtain current3;

[0011] S3. If current3 is greater than current5, the programmable PLC controls the alarm device to sound an alarm, and at the same time displays the abnormal working alarm information of the DC contactor KM on the host computer through the system bus, prompting the operator to check the DC contactor KM or the operator to reduce the SCR load by himself;

[0012] S4. If current4 < current3 < current5, the programmable PLC transmits a signal to the programmable DC speed regulator, which controls the trigger pulse of the silicon controlled rectifier (SCR) to reduce the speed setting of motor M until it reaches zero. At this time, current2 is 0. At the same time, the programmable PLC sends a reset enable command to motor M to reduce current1 until current3 is less than current4.

[0013] S5. If the programmable PLC displays that current1 and current2 are both 0, the motor M is controlled to stop and at the same time, the DC contactor KM is disconnected.

[0014] As a preferred embodiment of the technical solution of the present invention, the current detection device is a current sensor, and the alarm device is a buzzer.

[0015] The present invention has the following beneficial effects:

[0016] 1. The arcing damage to the coil of the DC contactor is mainly caused by the large current in the motor circuit, the current not completely returning to zero or not dropping below its safe current, and the main circuit current is the decisive factor. The present invention compares the external detection circuit current Current1 and the internal acquisition current Current2 of the DC speed regulator in real time, and through programmable PLC control, the DC contactor's on-load current is reduced to a safe value before disconnecting. This can effectively prevent the motor from not being completely shut down or the operator from making a mistake, causing the DC contactor to be disconnected when there is still current in the motor circuit, causing damage to the DC contactor's main contacts. It is an effective way to reduce equipment maintenance costs, reduce equipment accidents, and extend the life of DC contactors. The present invention is suitable for on-load disconnection protection of all DC contactors, especially on-load disconnection protection of large-capacity DC contactors.

[0017] 2. The present invention was tested on a mud pump motor of oil drilling equipment, and the test results were consistent with the expected effect. The present invention can be extended to other occasions using DC contactors, and can also be extended to occasions using AC contactors. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the connection relationship between various devices in the DC contactor disconnect protection system of the present invention;

[0019] Figure 2 This is a program flow chart of the DC contactor disconnection protection method of the present invention.

[0020] Description of the drawings: Q-incoming circuit breaker; UV-auxiliary circuit UV of incoming circuit breaker Q; PLC-programmable controller; SCR-silicon controlled rectifier; KM-DC contactor; M-motor. DETAILED DESCRIPTION

[0021] The present invention is described in detail below with reference to the accompanying drawings.

[0022] Reference Figure 1 and Figure 2 The present invention discloses a current detection-based DC contactor disconnection protection system for an oil drilling motor. In this system, a DC contactor KM is connected in series with a thyristor rectifier (SCR) at one end and a motor (M) at the other end. The thyristor rectifier (SCR) is connected in series with an incoming line circuit breaker (Q) and a programmable DC speed regulator (Siemens 6RA80). The programmable DC speed regulator (Siemens 6RA80) is connected to the incoming line circuit breaker (Q) via its auxiliary circuit (UV). The output of the DC contactor KM is connected to the input of a programmable programmable logic controller (Siemens S7-1500) via a current sensor. The programmable DC speed regulator is also connected to the input of the programmable PLC (Siemens S7-1500). The input of the programmable PLC is also connected to a stop transfer switch. The output of the programmable PLC is connected to the motor (M) and a buzzer. The communication interface of the programmable PLC is also connected to a host computer via a system bus.

[0023] Connect all devices as described above. The current sensor detects the current signal current1 on the output side of the DC contactor and inputs it to the programmable PLC. The programmable PLC collects the current signal current2 of the DC speed regulator. The programmable PLC sets the system error value current4 of the difference between current1 and current2 when the motor M stops, and sets the safety value current5 of the difference between current1 and current2 when the motor M stops. Current5 should be greater than current4.

[0024] During normal operation of the silicon controlled rectifier (SCR), if the operator operates the stop switch to signal the DC contactor to disconnect, or if the operator mistakenly operates the stop switch to signal the DC contactor to disconnect, or if the system is disturbed by external factors and the stop switch mistakenly signals the DC contactor to disconnect, the programmable PLC receives the signal and calculates the difference between current1 and current2 to obtain current3. Ignoring detection errors and data processing errors, current1 and current2 should be equal, and the difference current3 should be zero. The set value current4 is close to zero after accounting for these errors and can be set based on the actual situation of motor M.

[0025] If current3 is greater than current5, the programmable PLC controls the buzzer to sound an alarm and displays an abnormal DC contactor KM alarm on the host computer via the system bus, prompting the operator to check DC contactor KM. If current4 is less than current3 and less than current5, the programmable PLC transmits a signal to the programmable DC speed regulator, which controls the trigger pulse of the silicon-controlled rectifier (SCR), reducing the speed setting of motor M to zero. At this point, current2 is zero. Simultaneously, the programmable PLC issues a reset enable command to motor M, reducing current1 until current3 is less than current4. If current3 is less than current4, motor M cannot be completely shut down. Only by further reducing current1 through the aforementioned method until both current1 and current2 are simultaneously zero can motor M be shut down. Therefore, if the programmable PLC displays current1 and current2 as zero, motor M is shut down and DC contactor KM is disconnected.

Claims

1. A drilling motor DC contactor disconnect protection system based on current detection. One end of the DC contactor KM is connected in series with a silicon controlled rectifier (SCR), and the other end is connected in series with the motor M. The silicon controlled rectifier (SCR) is connected in series with the incoming line circuit breaker Q. This system is characterized by: The silicon controlled rectifier SCR is also connected in series with a programmable DC speed regulator, which controls the output of the silicon controlled rectifier SCR. The programmable DC speed regulator is connected to the incoming circuit breaker Q through the auxiliary circuit UV of the incoming circuit breaker Q. The output end of the DC contactor KM is connected to the input end of the programmable PLC through a current detection device. The programmable DC speed regulator is also connected to the input end of the programmable PLC. The input end of the programmable PLC is also connected to the stop transfer switch. The output end of the programmable PLC is respectively connected to the motor M and the alarm device. The communication interface of the programmable PLC is also connected to the host computer through the system bus. The method for performing DC contactor disconnection protection by the drilling motor DC contactor disconnection protection system based on current detection comprises the following steps: S1. The current detection device detects the current signal current1 on the output side of the DC contactor and inputs it to the programmable PLC. The programmable PLC collects the current signal current2 of the DC speed regulator. The programmable PLC sets the system error value current4 of the difference between current1 and current2 when the motor M stops, and sets the safety value current5 of the difference between current1 and current2 when the motor M stops, where current5>current4. When S2 and the silicon controlled rectifier (SCR) are operating normally, if the operator or the system triggers the stop switch to send a signal to disconnect the DC contactor, the programmable PLC receives the signal and performs a difference operation on current1 and current2 to obtain current3; S3. If current3 is greater than current5, the programmable PLC controls the alarm device to sound an alarm, and at the same time displays the abnormal working alarm information of the DC contactor KM on the host computer through the system bus, prompting the operator to check the DC contactor KM or the operator to reduce the SCR load by himself; S4. If current4 < current3 < current5, the programmable PLC transmits a signal to the programmable DC speed regulator, which controls the trigger pulse of the silicon controlled rectifier (SCR) to reduce the speed setting of motor M until it reaches zero. At this time, current2 is 0. At the same time, the programmable PLC sends a reset enable command to motor M to reduce current1 until current3 is less than current4. S5. If the programmable PLC displays that current1 and current2 are both 0, the motor M is controlled to stop and the DC contactor is disconnected at the same time.

2. The drilling motor DC contactor disconnection protection system based on current detection according to claim 1, characterized in that: The current detection device is a current sensor.

3. The drilling motor DC contactor disconnection protection system based on current detection according to claim 2, characterized in that: The alarm device is a buzzer.

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